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- Semiconductor Films
- Metal Films
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- Magnetic Films
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- Insulator Films
- Ferroelectric and Piezoelectric Films
- Organic and Polymer Films
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- Micromechanics and Other
- Ferroelectric and Piezoelectric Films
General
Optical properties of some organic and inorganic thin films in abnormal dispersion region and their applications
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In this paper the optical properties of some organic and inorganic optical storage thin films have been studied. The organic thin films include cyanine, phthalocyanine and azo- dye, which were prepared by spin-coating or LB methods. The inorganic thin films were GeSbTe phase-change materials, which were synthesized by sputtering method. The complex refractive indices were measured by spectroscopic ellipsometry technique. The optical properties are analyzed by using of different dispersion models that are based on Kramers-Kronig transformation. Finally, the application in optical storage with these thin films are discussed and demonstrated.
Characterization of thin films by surface mass spectrometry
Hubert Gnaser
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Secondary-ion mass spectrometry and secondary-neutral mass spectrometry use the atoms and molecules sputtered from the surface of a solid by energetic-ion impact to derive information on the elemental composition at the surface and, in conjunction with continuous sample erosion, in thin films. This contribution summarizes the basic principles of these techniques. Selected examples for the characterization of thin films and surfaces from various technologically important areas are presented, emphasizing aspects of quantification, detection sensitivity, and spatially resolved analyses. Specifically, reliable quantification schemes utilizing either post-ionized neutral species or specific molecular ions are highlighted; furthermore, it is shown that these mass spectrometric techniques enable the sensitive detection of essentially all elements at very low concentration levels, reaching even into the sub-parts-per- billion range in favorable cases. Finally, aspects of spatially resolved analyses are discussed, covering depth profiling, surface imaging and a fully 3D characterization of solids. It is exemplified that by using suitable primary- ion bombardment conditions, a lateral resolution of less than 100 nm and an in-depth resolution of a few nm can be achieved in thin-film analyses.
Refractive index measurement for planar photonic crystal using a microscopy-spectrometry method
Mike Xu Ouyang,
Emmanuel C. Onyiriuka,
L. D. Kinney
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We report a unique technique to measure the refractive index (n), extinction coefficient (k), and thickness of thin films based on either the reflection or transmission spectra. The method combines a spectrometer, an optical microscope and a video camera. It is inexpensive, versatile and fast (< a few sec). Using this technology, n&k of 1.68 and 0.376, respectively, at 1500 nm was measured on a planar photonic crystal. The photonic crystal with a dimension of 117 X 90 micrometers 2 mm has a periodic cermet structure on Si substrate made by Deutsch Telekom using the electron induced deposition.
Characterization of optical storage media films by time-of-flight-energy elastic recoil detection analysis
Yanwen Zhang,
Goran Possnert,
Lars Jonsson,
et al.
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The challenge of meeting the ever increasing demands for low-cost information storage media with greater information storage density and rapid access has prompted development of sophisticated optical technologies, e.g. CD (Compact Disc) and DVD (Digital Video Disc) in Read Only (ROM), Recordable (R), Re-writable (RW) and Random Access Memory (RAM). Here the suitability of Time of Flight-Energy Elastic Recoil Detection Analysis (ToF-E ERDA) to characterize optical storage media has been investigated. High-energy heavy ions (48 MeV 81Br8+ and 60 MeV 127I10+) from an accelerator were used to analyze CD-ROM, CD-R and CD-RW structures. Simultaneous characterization of H, C, O, Al, P, Co, Cr, Ge, Sb/Te could be made. The results demonstrate the unique power of the technique for characterizing the structure and depth profile of the optical multi-layers as well as the ingress and influence of foreign species.
Kinetic scaling of fractal growth of thin films
Fengmin Wu,
Yunzhang Fang,
Qiaowen Li,
et al.
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The fractal growth of 2D thin films on metal surface is studied by means of kinetic Monte Carlo simulation, using realistic growth model and physical parameters. Emphasis is given to time dependence of the size S(t) and branch width b(t) of the island. It is found that the island size S(t) grows with time t as tk, where growth-exponent k is slightly less than one when averaged from all islands. Similar results for the branch width of islands are also obtained from the simulations are not very low coverage, i.e., b(t) (infinity) t(alpha ). The kinetic scaling values k and (alpha) of fractal growth of thin films may be helpful to understand the growth mechanism of thin films.
Semiconductor Films
Optical and electrical properties of type III HgTe/Hg1-xCdxTe heterostructures
Charles R. Becker,
X. C. Zhang,
K. Ortner,
et al.
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By means of an optical investigation involving the envelope function approximation using the full 8 X 8 Kane Hamiltonian, it has been demonstrated that the valence band is primarily responsible for the separation between the H1- E1 and L1-E1 intersubband transition energies of semiconducting HgTe/Hg1-xCdxTe superlattices with a normal band structure. This results in an unequivocal determination of the valence band offset between HgTe and CdTe, (Lambda) , which is 570 +/- 60 meV at 5 K for both the (001) and the (112)B orientations. In order to correctly predict the temperature dependence of both intersubband transition energies, the following is required: (Lambda) is also temperature dependent according to d(Lambda) /dT equals -0.40 +/- 0.04 meV/K; the heavy hole effective mass has a significant temperature dependence; and the energy gap Eg(HgTe, 300 K)equals -160 +/- meV which is appreciably lower than the extrapolated values found in the literature.
Excitons in InSb quantum wells: a multiuse tool
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We use exciton signatures in optical absorption spectra to probe material and structural properties of InSb/AlxIn1-xSb multiple quantum wells. Excitonic transition lines have been observed up to room temperature for the system in which exciton binding energy is only 1 meV largely due to very weak LO-phonon-electron coupling. Parabolically graded quantum wells were grown and used to study the band offset ratio at the InSb/AlxIn1-xSb heterointerface. A 0.62 +/- 0.04 offset ratio is extracted from the exciton transitions measured on samples with Al concentrations in the range 2% to 12%. Furthermore, deformation potentials in the system have been studied. The hydrostatic and the shear deformation potentials are determined simultaneously to be around -6.5 +/- 0.3 and -1.5 +/- 0.2, respectively.
Optically detected magnetic resonance of semiconductor thin films and layered structures
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The principle, capabilities, advantages and limitations of the optically detected magnetic resonance (ODMR) technique will be briefly described. The ability of the ODMR technique to provide important information on physical properties of semiconductor thin films and layered structures will be highlighted. These include chemical identification, electronic and geometric structures of defects, carrier recombinations, etc. The important role in providing valuable feedback for improvement of growth process and in engineering material properties for device applications will be demonstrated. Representative cases from Si/SiGe- and InP- based structures grown by molecular beam epitaxy will be discussed as examples. The most recent progress, on-going efforts and prospects in achieving unprecedently high spectral, time and spatial resolution of the ODMR technique, meeting the demands and challenges raised by the increasing miniaturization of future electronic and optoelectronic devices, will also be outlined.
Infrared applications of quantum well structures
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The invention and the investigation of the semiconductor quantum well structures have influenced and changed the condensed matter physics, microelectronics, opto-electronics as well as other related scientific and technological fields tremendously in last three decades. The quantum well, superlattice and their new development or new generation, that is quantum wires and quantum dots and many other microstructures provide us furthermore really new challenge for the infrared application and technology. The cascade infrared laser, the multi-color and tunable infrared detectors, as well as the focus plane array based on the intersubband or interband transitions in usual multi quantum well or type-II superlattice structures are some of the examples. We report here mainly a comprehensive investigation on the application of GaAs/AlGaAs multi- quantum well structures as the long wavelength infrared detectors and their focus plane arrays based on the intersubband transitions of the quantum wells. The fundamental parameters of the devices, the performance of the detectors and the arrays, the modulation and tuning of detection wavelength via atom intermixing between wells and barriers, the coupling of the radiation with the electronic transitions and the demonstration of the imaging will be reviewed and discussed together with the comparison to the traditional infrared detectors.
Spontaneous and stimulated emission in ZnCdSe/ZnSe asymmetrical double quantum wells
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The spontaneous and stimulated emission in ZnCdSe/ZnSe asymmetric double quantum wells have been studied. The exciton photoluminescence both in the narrow well and in the wide well is influenced by two factors, the exciton tunneling and the thermal dissociation processes. The change of the emission intensity is determined by the stronger one. The carrier tunneling through the thin barrier is conductive to the stimulated emission from the wide well, and the threshold can be lowered by optimizing the structure.
Magneto-optical properties of diluted magnetic semiconductor nanostructures
Yasuo Oka,
Kazumasa Takabayashi,
Nobuhiro Takahashi,
et al.
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Low-dimensional diluted magnetic semiconductors have been made by epitaxy and microfabrication techniques. Multiple quantum wells of the Cd1-xMnxTe/ZnTe (x equals 0.1) system were grown by molecular beam epitaxy. Quantum wires of Cd1-xMnxSe (x equals 0.08) were fabricated from the quantum well of Cd1-xMnxSe/ZnSe by the electron beam lithography. Quantum dots of Cd1-xMnxSe (x equals 0.03) were grown by the self-organization mode on a ZnSe layer. Magneto-optical properties of these low dimensional structures were studied by time-resolved photoluminescence. The transient photoluminescence in the Cd1-xMnxTe/ZnTe multiple quantum wells shows the formation processes of magnetic polarons of excitons. The exciton luminescence from the quantum wires of Cd1-xMnxSe displays the influence of the 1D quantum confinement effect for the exciton states with the effective g-value of 100 - 150. The exciton luminescence from the wires is linearly polarized parallel to the wire direction. The exciton luminescence in the quantum dots shows the strong confinement effect of the exciton energy corresponding to the dot size of 4 - 6 nm as well as large effective g-value of 89. The quantum dot excitons also exhibit marked increase of the luminescence lifetime with increasing the magnetic field, which is caused by suppression of the non-radiative process due to the shrinkage of the exciton wavefunction.
Deposition of GaN Films on (111)GaAs substrates
Qixin Guo,
Akira Okada,
Mitsuhiro Nishio,
et al.
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GaN films were grown on (111)GaAs substrates by radio frequency magnetron sputtering in an ambient of argon and nitrogen, using gallium target. The structural properties of the GaN films were investigated by conventional (theta) - 2(theta) x-ray diffraction, high-resolution (omega) rocking curve and rotary phi scan. Crystalline wurtzite GaN films were obtained on (111)GaAs at substrate temperatures between 600 and 700 degree(s)C. The crystal quality of the GaN films was examined as a function of nitrogen content in sputtering gas and the best value of full width at half-maximum of rocking curve for the (0002)GaN was obtained at 880% nitrogen content in the investigated regions.
Influence of oxygen incorporation on beryllium- and silicon-doped InP grown by solid source molecular beam epitaxy
Ning Xiang,
Jari Likonen,
Jani Turpeinen,
et al.
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The effect of oxygen incorporation on electrical and optical properties of Be- and Si-doped InP grown by solid source molecular beam epitaxy has been studied. Oxygen was observed to reduce both the Be and Si doping efficiencies in InP and to introduce recombination centers that degrade the photoluminescence property. The compensation in Be-InP was more pronounced than in Si-InP. With high oxygen impurity concentration, Be-InP was found to be n-type in Hall measurements. Electrical inactivity of Be is likely due to the formation of Be-O complexes in InP. Oxygen was originated from the phosphorous source and could be reduced by employing lowered phosphorous cracker temperature.
Thickness and composition determination of MBE-grown strained multiple quantum well structures by x-ray diffraction
Brian F. Usher,
D. Zhou
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We present a new approach to determine the thickness and composition of individual layers in molecular beam epitaxy (MBE) grown multiple quantum well (MQW) structures by double crystal X-ray diffraction. The mean perpendicular lattice constant (d(perpendicular)SL0) and the period (P) of the MQW structures are calculated from the zeroth satellite peak position and the satellite peak spacings respectively. The thickness and composition of the individual layers are found by combining the growth times of the individual layers with d(perpendicular)SL0 and P. MQW structures of the form GaAs/XGaAs (X equals group III elements) grown on GaAs substrates are used to derive the theory for this approach and two MQW samples in the GaAs/InxGa1-xAs system are studied as an example of this approach. The results for both samples are checked by dynamical simulation. The simulated x-ray rocking curves for both samples have excellent agreement with the corresponding experimental x-ray rocking curves. This approach may be applied to other MQWs structures with two layers where one is a binary and the other is a ternary which includes the binary, such as AlAs/AlxGa1-xAs. It is therefore a technique not only for characterizing device structures containing MQW's but also for calibrating group III fluxes in MBE systems.
Electronic and structural properties of InN thin films grown by MOMBE on sapphire substrates
Jochen Aderhold,
V. Yu. Davydov,
F. Fedler,
et al.
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The development of high quality semiconductor thin films for different applications is a demanding problem in material science. InN has not been an intensively studied as AlN and GaN. There is relatively little information on the fundamental optical properties, charge carrier transport, and the properties and behavior of electrically active defects in the material. The absence of good-quality material lead even to conflicting data reported in the literature concerning the optical gap and band structure. In this publication it will be shown that InN thin films can be successfully grown using the MO MBE method. For the first time the proper choice of growth conditions allows to obtain good quality InN thin films with a charge carrier concentration as low as 8.8 X 1018 cm-3.
P-type polycrystalline Si films prepared by aluminum-induced crystallization
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p-type poly-Si thin films were prepared by aluminum induced crystallization (AlC) and doping of a-Si:H. The a-Si:H precursors were deposited by plasma enhanced chemical vapor deposition on glass substrates and then covered with thin Al layers of different thickness. The crystallization was performed by conventional thermal annealing. X-ray diffraction and secondary ion mass spectroscopy measurements were carried out to study the structure change and the Al profile in the annealed films. Resistivity, Hall mobility and carrier concentration were also measured. Results showed that poly-Si films could be obtained by annealing a-Si:H in contact with a thin Al layer at 450 - 550 degree(s)C for 5 - 60 minutes. The crystallized films are p-type and have low resistivity, high Hall mobility and carrier concentration of 0.06 (Omega) cm, 20 cm2/Vs and approximately 1018 cm-3, respectively, largely improved compared with the reported results.
Electrodeposition of CuInSe2 thin films for their use in photoelectrochemical solar cells
R. K. Pandey,
Archana Mishra,
B. P. Chandra
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Polycrystalline thin films of CuInSe2 were electrodeposited on to titanium substrates from acidic baths. For polysulphide electrolyte containing NaOH, Na2S and S (each 1 m) these films show best photoresponse, when electrodeposited with 60 m mole sodium citrate concentration. Due to surface treatment these films show good photoelectrochemical behavior with high conversion efficiencies and stability. Chemical etching is found to improve short circuit current and fill factor, whereas photoelectrochemical etching technique improves the stability of photo-anode in polysulphide solution. The efficiency is 4.04% and 3.5 and fill factor is 0.57 and 0.49 for chemically etched and unetched CuInSe2 thin films, respectively.
LPE-grown high-quality InGaAsP/GaAs semiconductor lasers
Jinhua Yang,
Xiaohua Wang,
Zhonghui Li,
et al.
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High power InGaAsP/GaAs separate confinement heterostructure single quantum well lasers have been grown by liquid phase epitaxy (LPE). The maximum output power as high as 4 W has been obtained with the threshold current density 300 A/cm2 and the external differential quantum efficiency 80%. Measurements and theoretical analysis showed that the wafers grown by LPE are in good agreement with design and can be comparable to that grown by MBE and MOCVD.
Comparison of surface morphologies of HgCdTe films grown by MBE and LPE
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The surface morphologies of both MBE and LPE HgCdTe films were observed by optical microscope and atom force microscope. Both HgCdTe films were grown on CdZnTe substrates. It was found that the surface morphology of LPE film is very sensitive to the orientation of CdZnTe substrate, while MBE film surface morphology is mainly dependent on the surface morphology of the substrate. The characteristic of the surface morphologies and the non- flatness of HgCdTe LPE and MBE films in different scales are studied.
Properties of gallium phosphide films prepared by rf magnetron sputtering
Jianquan Song,
Zhengtang Liu,
Dagang Guo,
et al.
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As a coating material with excellent durability in 8 - 12 micrometers waveband, GaP films can be used as anti-reflective and protective layers on the windows and domes of ZnS, ZnSe and Ge. In this paper GaP films have been deposited by radio frequency magnetron sputtering of single crystalline gallium phosphide. The deposition rate, composition, structure, hardness and optical properties of GaP films have been investigated, and it's application used as anti-reflective and protective films on ZnS substrate has also been studied.
Strains in Si substrate induced by formation of Ge islands
Weirong Jiang,
Zuimin Jiang,
Bin Shi,
et al.
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Grazing incidence x-ray diffraction measurements at different grazing angles for self-organized Ge dots grown on Si(001) are carried out by using synchrotron radiation as a light source. Deformation strains in the substrate underneath or surrounding the dots induced by formation of Ge quantum dots are investigated. Besides a tensile strain existing underneath the dots, a peak located at the higher angle side of Si(220) or Si(400) is observed for the first time, the origin of this peak is attributed to the near surface compressive strain in the peripheral substrate regions surrounding the Ge dots. This compressive strain corresponds to a -0.8% lattice constant change parallel to the interface.
Si growth on the Si(III)-B surface phase depending on the type of surface phase formation and initial boron coverage
A. P. Shaporenko,
V. V. Korobtsov,
V. V. Balashev
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Reflection high energy electron diffusion (RHEED) is used to study the Si growth on a Si(111)(root)3X(root)3-B surface, prepared by various procedures. The analysis of RHEED patterns, specular beam intensity oscillations and dependencies of specular beam intensity on incidence angle (rocking curves), shows that the Si growth mode and epilayers quality depend on both an initial boron coverage and the way of (root)3X(root)3-B surface phase formation. Increase of transition temperature, at which Si growth mode converts from layer-by-layer to step-flow growth mode, is discussed in terms of the theory of surfactant-mediated growth on semiconductor surfaces.
Surface texturing of crystalline silicon and effective area measurement
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In this paper, the surface area of solar cell is determined by the capacitance measurements of MOS structure. The texture etching technology can be controlled according to the change of silicon surface area, furthermore, the textured silicon surface and interface characteristic of solar cell can be studied by measuring the relationship of capacitance and voltage for MOS structure.
Dislocation evaluation of GaN etched by photoenhanced KOH solution by atomic force microscopy
Zhibiao Zhao,
Ming Qi,
Aizhen Li
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Atomic force microscopy (AFM) was used to investigate the surface topography of GaN grown by radio frequency plasma assisted molecule beam epitaxy and etched with a 1.0 M KOH solution in a photoenhanced process. Whiskers were observed in AFM photo and correlated with dislocations. Dislocations density was evaluated from whiskers density, and confirmed by x-ray 2D triple axis mapping estimated results.
Core structures of the edge dislocations in GaN epilayers
Junyong Kang
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Threading dislocations with edge components were investigated by a high-resolution transmission electron microscopy in undoped GaN epilayers grown on Al2O3 substrates. Two types of core images were observed. One is a fully filled core with regular contraction and expansion of diffraction bright dots and the other is incompletely filled with one bright dot less and irregular contraction and expansion of bright dots. The impurities around the cores were detected to contain oxygen and carbon elements by energy-dispersive x-ray spectrometer. This suggests that both types of dislocations be decorated with impurities.
Novel Si homojunction far-infrared detectors
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A novel concept to develop far-infrared (FIR) Si detectors is proposed based on homojunction internal photoemission. As the first approach, a 48 micrometers (lambda) c Si FIR detector is demonstrated on molecular beam epitaxy grown homojunction multilayers consisting of highly doped emitter layers and undoped intrinsic layers. The detector shows high responsivity over a wide wavelength range with a peak responsivity of 12.3 +/- 0.1 A/W at 27.5 micrometers and detectivity D* of 6.6 X 1010 cmHz1/2/W at 4.2 K. The (lambda) c and bias dependent quantum efficiency agree well with theory. Based on the experimental results and the model, Si FIR detectors (40 approximately 200 micrometers ) with high performance and tailorable (lambda) c can be realized using higher emitter layer doping concentrations.
High-power single quantum well array semiconductor lasers
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In this paper, through the analysis and in consideration of the facts which influence on the ultimate output power of semiconductor laser, we have designed a laser structure with gradient refraction index separate confinement single quantum well (GRIN-SCH-SQW) and have grown the laser structure by MBE. Moreover we have also fabricated array lasers by broad area structure. The lasers are cleaved into cm bars and coated with high- and low-reflectivity films (approx. 95% and 5%). The QCW output power of the array laser has reached 60 W (100 microsecond(s) , 500 Hz), the peak wavelength of the device is 806 approximately 810 nm.
Co-diffusion thin layer of phosphorus and boron for preparation of silicon BSF solar cell
Wan-Tao Yu,
Guang-Pu Wei
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Co-diffusion processing is emerging as a promising simplified process for manufacture of terrestrial back surface field (BSF) solar cells. In this work, we present results about co-diffusion of two dopant elements (phosphorus and boron) in a single thermal cycle in order to form emitter and BSF thin layer simultaneously. According to the measured sheet resistance, it was found that uniform, stable and controllable diffusion layers on front and back surface of silicon wafer can be obtained with co-diffusion method. Using the co-diffusion method, some silicon BSF solar cells with an efficient of more than 12% (at AM1) were prepared. The measurement results of minority carrier lifetime show that boron diffusion in back side of silicon wafer has a gettering effect on the p-n junction area and can improve the characteristics of solar cells.
Properties of the film electroluminescence of ZnS:TbF3
Dawei He,
Qingguo Yuan,
Guanghui Yu,
et al.
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The electroluminescence is reported from ZnS doped with terbium (Tb) thin films prepared by radio frequency magnetron sputtering method. We have systematically investigated the characteristics of the ZnS:TbF3 thin film electroluminescence devices, such as film characteristics of the ZnS/Tb active layer, substrate temperatures during magnetron sputtering and Tb concentration of the active layer, etc. From the results obtained, the mechanism of electroluminescence of thin film EL devices is discussed, and then the relationships between the EL characteristics and the device parameters are considered.
Tunable MQW-DBR lasers using selective area growth
Guoli Liu,
Wei Wang,
Jingyuan Zhang,
et al.
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The tunable ridge waveguide distributed Bragg reflector (DBR) lasers designed for wavelength-division-multiplex (WDM) communication systems at 1.55 micrometers by using selective area growth is reported. The threshold current of the DBR laser is 62 mA and the output power is more than 8 mW. The isolation resistance between the active region and the Bragg region is 30 K(Omega) . The total tuning range is 6.5 nm and this DBR laser can provide 6 continuous standard WDM channels with 100 GHz channel spacing; in the tuning range, the single mode suppression ratio is maintained more than 32 dB and the maximum output power variation is less than 3 dB.
Planar photonic device using surface thin film stressors
W.-X. Chen,
Q. J. Xing,
L. S. Yu,
et al.
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Employing photoelastic effect with thermally stable and controllable metal stressor stripes for low propagation loss (on the order of 1 dB/cm) optical waveguide has been achieved in both InP and GaAs based planar waveguides. The study of stressors is based on Ni and WNi stripes. Planar processes, involving both photoelastic WNi stressor and He- implantation, have been used in the fabrication of single- quantum-well photoelastic GaAs/AlGaAs lasers and of the InGaAsP/InP Franz-Keldysh effect electroabsorption waveguide modulators. Get high performance photoelastic semiconductor laser and electroabsorption modulator.
Wavelength tuning of GaAs/AlGaAs quantum well infrared photodetectors by rapid thermal annealing and proton implantation
Ning Li,
Xingquan Liu,
Na Li,
et al.
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Due to the mature material growth and device fabrication technology, GaAs/AlxGa1-xAs quantum-well infrared photodetector (QWIP) has been extensively studied and used in remote sensing, particularly in long wavelength range, e.g. the atmospheric window region of 8 approximately 14 micrometers . This paper reports the using of intermixing techniques to modify GaAs/AlGaAs multiple quantum well photodetectors (QWIPs). A red shift in response wavelength of QWIP has been obtained both by rapid thermal annealing (RTA) and proton implantation. The peak response wavelengths has been shifted into the atmospheric window (8.3 micrometers ) from the originally 7.7 micrometers . The response spectra have been measured as the function of the different temperature of the RTA and the ion doses in the range from 4 X 1014 to 5 X 1015 cm-3, respectively. The device performance such as dark current and blackbody response are also measured at different conditions. The effect of RTA and ion implantation on the device performance has been interpreted theoretically by the interdiffusion of Al atoms across the GaAs/AlxGa1-xAs heterointerfaces.
RFTIR measurement on backside-thinned detector film of InSb infrared focal plane arrays
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Reflection Fourier transform infrared (RFTIR) measurements were performed on backside-illuminated InSb infrared focal plane arrays for thinning process monitoring. InSb detector film thickness and its variation across the film can be measured from the RFTIR spectra taken by this contactless and non-destructive technique.
Recent studies on ZnTe homoepitaxial films deposited by synchrotron-radiation-excited growth
Mitsuhiro Nishio,
Kazuki Hayashida,
Hiroki Harada,
et al.
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Results of our recent experiments relating to the synchrotron-radiation (SR)-excited growth of ZnTe on the (100) ZnTe substrate using metalorganic sources are described. We have clarified the growth characteristics and quality of ZnTe films. The shape of deposited film suggests that surface excitation process, i.e., the excitation of the adsorbed species or sample surface, will be the dominant mechanism. The quantum yield for forming ZnTe molecules was estimated to be as high as 0.3% in the room temperature growth. ZnTe epitaxial film without carbon and oxygen contamination is attainable even at room temperature using SR as a light source. Near band gap luminescence can be observed even in the films grown at room temperature. It seems that a use of N2 carrier gas is promising for the inclusion of nitrogen as shallow acceptors and the suppression of defects. Through these experiments, we propose that the SR-excited growth is a powerful technique for a novel low temperature growth of compounds.
Properties of betaFeSi2 by first principles calculations
Akira Yoshida,
Kenji Tsuchiya,
Akihiro Wakahara
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Strain dependence of the band structure of (beta) -FeSi2 has been investigated using first principles calculations based on the density functional theory. Indirect transition in the band structure is predicted, when the crystal is strain-free. On the other hand, the band structure changes to the direct transition, when the a-axis is expanded or c- axis is compressed. In (beta) -FeSi2 pseudomorphic layer grown on Si(100) substrate, the direct band structure is expected.
Poisson's ratio of AIAs
D. Zhou,
Brian F. Usher,
T. Warminski,
et al.
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In this work, we present a new approach to determining Poisson's ratio of AlAs. This approach requires the growth of a particular structure with a multiple quantum well (MQW) - 10X[500 angstroms GaAs/800 angstroms AlxGa1-xAs] followed by two single layers - 0.5 (mu) AlAs and 0.5 (mu) AlxGa1-xAs on a GaAs substrate. The x-ray rocking curves of the as-grown sample give the perpendicular lattice constants in the two single epilayers, and following chemical etching to remove the two single layers, x-ray diffraction measurement of the MQW is used to determine the Al fraction x. With this data, we obtain a value for Poisson's ratio of AlAs which is VAlAs equals 0.255 +/- 0.003 assuming Vegard's law and a linear variation of the AlxGa1-xAs lattice constant with x. However we obtain VAlAs equals 0.328 +/- 0.003 if, as proposed by Z. R. Wasilewski, a nonlinear relationship with the bowing parameter c equals 1.245 X 10-3 is assumed. The value of 0.328 is in good agreement with most recent results obtained which do not assume Vegard's law. Our results therefore support the violation of Vegard's law in describing the relationship between the lattice constant of AlGaAs and its composition.
Mechanism of formation and photoluminescence of Si quantum dots embedded in amorphous SiO2 matrix
Yu Liang,
Yan Jia,
Yichun Liu,
et al.
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Films of a-SiOx with different oxygen content were deposited by electron cyclotron resonance microwave plasma technique at room temperature, where the films were annealed in an Ar ambient for 30 minutes at temperatures range from 250 to 1050 degree(s)C. The system of nc-Si quantum dots dispersed in SiO2 matrix was obtained for the films annealed at 1050 degree(s)C. The structural change induced from annealing was characterized by infrared and Raman spectra, which was correlated with the identification of luminescence centers. A broad photoluminescence band centered at 750 and 770 nm is attributed to the quantum confinement effect of the Si clusters. Another PL band between 560 - 620 nm is attributed to the defects in the interfacial regions: self- trapped excitons.
Influence of Cd diffusion on the structure and photoluminescence of CdSe/ZnSe multiple quantum wells
Yuxue Liu,
De Zen Shen,
Yichun Liu,
et al.
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In this paper, we have fabricated a 20 period CdSe/ZnSe MQW's on (001) orientated GaAs grown by metalorganic chemical vapor deposition under se-rich condition at the growth temperature of 500 degree(s)C. CdSe/ZnSe MQW's structure was characterized by means of x-ray diffraction and Raman scattering. These experimental results indicated the formation of new Cd1-xZnxSe layers and the existence of Cd and Zn vacancies in CdSe/ZnSe MQW's. The photoluminescence spectra of CdSe/ZnSe MQW's at low temperature was composed of a very strong and narrow band A at 2.4 eV and a weak and broadened band B at 2 eV. In order to understand the influence of Cd diffusion on the structure and photoluminescence (PL) of CdSe/ZnSe multiple quantum wells (MQW's), a new model of Cd diffusion in CdSe/ZnSe MQW's was given. Based on the simulation of Cd diffusion in CdSe/ZnSe MQW's and the calculation of the envelop-function approximation, the origin of PL of CdSe/ZnSe MQW's was discussed.
Infrared photoluminescence characterization of HgCdTe film
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The Fourier transform and double modulation Fourier transform photoluminescence measurements were performed on HgCdTe films from liquid helium temperature to room temperature in the infrared band to 10 micrometers where the influence from room temperature background blackbody emission is very strong. From the band to band transition photoluminescence peak, which dominated in HgCdTe films with the small cadmium composition, the cadmium composition, crystal-quality-related band tail energy, and the active energy of the non-radiative Shockly-Read center, are obtained. The photoluminescence characterization method is also used to investigate the intentionally doped impurity behavior in HgCdTe. The amphoteric impurity behavior of As implanted in HgCdTe is discovered with the donor and acceptor energy level of 8.5 meV and 31.5 meV, respectively. The Ag impurity level of 70 meV in MBE HgCdTe is also found.
Enhance action by introducing cesium on surface inversion layer of P-silicon
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This paper presents the carrier distribution of MIS/IL solar cell in the strong inversion condition. The variation of the surface potential Vs with the fixed positive charge density Qs/q, energy structure and the sheet resistance have been calculated using Fermi statistics distribution. Based that, the MIS/IL solar cells are fabricated with the solar grade silicon material. Consequently, the difference of the solar cell performance before and after doping cesium is compared.
Optical and electronic characteristics for of thin film
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CdTe thin films are obtained by on glass substrates by vacuum vapor deposition. This work mainly presents the optical and electrical characteristics of the CdTe films by varying stoichiometry of Cd and Te, doping-In and thermal treatment with N2. The variation of band gap and absorption coefficient is studied as well as the resistivity. The results show that the undoped-In samples have very high resistivity on which thermal treatment has little effect, which proves that the undoped CdTe thin film is high resistivity semiconductor. On the other hand, the resistivity of the doped-In samples decreases after thermal treatment. In general, the optical and electrical characteristics of the prepared CdTe thin film can be improved by proper doping and thermal treatment.
Scanning photoluminescence microscopy on GaAs/AlGaAs single quantum wire at room temperature
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The micro-photoluminescence ((mu) -PL) scanning has been performed on a GaAs/AlGaAs single V-grooved quantum wire (QWR) along the direction perpendicular to the wire. The variation of (mu) -PL spectra in different spatial positions with different quantum structures have been observed. In the region of QWR the PL spectra contain the peaks from QWR, necking quantum well and vertical quantum well while in that of about 1 micrometers leaving away from the QWR the PL spectra show only the peaks from side-wall quantum well and top quantum well. All the acquired spectra have been fitted by Gaussian line shape and the different PL components are decomposed. The intensity variation with the spatial position directly demonstrates the origin of the PL correlated to the different quantum structures. The PL energy for the each quantum structures has been precisely determined.
Numerical simulation of continuous Nd:YAG laser annealing of InP
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The semiconductor solid phase epitaxial model of continuous laser-annealing is used to simulate the laser-annealing process of different doping concentration of InP at the continuous Nd:YAG laser. Specially, quasi-static model is used to simulate the radial heat dissipation from radiant region to radiationless region. At the same time, thermal conductivity and optical absorption coefficient varied with temperature is also considered. The method of hidden-form different is used in solving 1D, non-homogeneous, nonlinear partial differential equation of heat conduction. At the room temperature T0 equals 300 K and the power intensity of laser I0 equals 800 W/cm2, the result is that the temperature of surface reaches about 1290 K after 3.8 sec.
Magneto-optical studies of ZnSe/Zn1-xMnxSe quantum wires
Z. H. Chen,
T. Saitou,
K. Shibata,
et al.
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ZnSe/Zn1-xMnxSe quantum wires were fabricated on mesa-patterned GaAs substrate. The light hole-heavy hole excitonic level crossing, which occurs at certain magnetic field Bc, is observed in the time-resolved magneto- photoluminescence measurements carried out on the samples. The shift of Bc for the quantum wire samples is well interpreted by taking into account of both the strain effect and the 1D quantum confinement effect.
Characteristics of reactive ion etching of indium nitride
Qixin Guo,
Motoatsu Matsuse,
Mitsuhiro Nishio,
et al.
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We have studied the characteristics of reactive ion etching of indium nitride, using CH4 and H2 gases. The effects of CH4/H2 gas composition and total gas pressure on the etching rates were investigated. It was found that variation of CH4 concentration in gas mixtures leads to changes in both the etching rate and the surface morphology. Smooth etched InN surface with the rate of around 610 approximately 710 angstroms/min was obtained in the range of 5 approximately 15% CH4 concentration and 25 approximately 55 Pa pressure.
Composition and structure of CdTe thin films
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CdTe film can be prepared on the glass by vacuum vapor deposition. We change the stoichiometry of Cd:Te, dope In, and thermally treat the samples in N2. Then, the compositions, structure, and grain size are studied by XRD, SEM and AES. The results reveal that the surface morphology and microstructures of the samples are improved after thermal treatment, In is incorporated into CdTe, and forms CdTe:In. Moreover, the preferential growth orientation along <111> appears.
Influence of annealing conditions on the chemical states of InP/SiO2 nanocomposite films deposited by rf magnetron co-sputtering
Ruiqin Ding,
Guorong Zhou,
Hao Wang,
et al.
Show abstract
Indium phosphide/silica composite thin films have been fabricated on water-cooled substrates and heated substrates respectively by radio frequency magnetron cosputtering technique. X ray diffraction patterns and optical absorption and photoluminescence spectra at room temperature strongly suggest that InP nanocrystals exist in the SiO2 matrices of the films deposited on water-cooled substrates after annealing and of the films deposited on heated substrates. X-ray photoelectron spectra show that there are quite a log of oxides of In and P and quite many oxygen deficiencies of SiO2 in the films deposited on water-cooled substrates, but there are few deficiencies of SiO2 and much less oxides of In and P in the films deposited on heated substrates. The component of InP increases and the oxides of In and P and oxygen deficiencies in SiO2 diminish at a large extent under suitable annealing temperature and time in a high vacuum system, but the role of annealing is limited because of the escape of P. The problem can be solved quite well by coating a SiO2 layer on the surfaces of the films before annealing and then annealing the films in H2 of 103 Pa.
Preparation of CuInSe2 film with electrodeposition
Wenyi Li,
Jian Yu,
Xuebin Yu,
et al.
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CuInSe2(CIS) films directly electrodeposited on sputtered Mo-glass, sprayed SnO2-glass substrates had been accomplished at room temperature in the potentiostatic mode from a bath containing CuCl, InCl3(DOT)4H2O and SeO2. The acidity of bath was adjusted to 1PH. Energy dispersive spectrometry, atomic force microscopy (AFM), x- ray diffraction and hot-probe method was utilized to characterize the CIS films. The key factor for preparing single-phase CuInSe2 is the proportion of CuCl, InCl3(DOT)4H2O and SeO2. The CIS films are nearly stoichiometry of CuInSe2 and polycrystalline on Mo- glass. The Cu excess films are p-type semiconductor, and the In excess films n-type. The deposition potential obviously affects the surface morphology of CIS films. AFM results had indicated that the CIS films on Mo-glass grow in layer and on SnO2 glass in island.
Preparation and characterization of silicon carbide thin films synthesized by rf reactive sputtering
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Carbon-rich SiC thin films were synthesized by rf-reactive sputtering at different anodic voltages, 1.2 kV, 1.6 kV and 2.0 kV respectively. XPS, FTIR, Raman spectra and Nano Indentor microhardness were used to characterize as- deposited thin films. The results showed that higher anodic voltage enabled to increase Si-C bond and sp3-bonded carbon atoms in the films. The sample grown at 2.0 kV exhibited Si/C ratio of nearly 1 from XPS results, a pronounced Si-C peak in the FTIR spectra, only a weak peak at 1420 cm-1 and no other graphite peak in the Raman spectra, the microhardness of 25.2 GPa.
Erbium-induced reconstructions on silicon (100) substrate
G. R. Chen,
D. W. Gong,
Jianhua Liu,
et al.
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Ultra-thin erbium layers are formed on Si(100) substrate by depositing 0.5 approximately 3 ML Er atoms in an ultra-high vacuum system. The films deposited at room temperature are in the amorphous form. After annealing at low temperatures, ordered structures form on the surface. The surface reconstruction is studied by in situ reflection high energy electron diffraction (RHEED). The transition of the RHEED patterns from (2X1) to (4X2) is observed with the increase of Er coverage up to 1 monolayers after low temperature annealing. Several cluster models are adopted for simulating Er adatoms located at different sites on Si(100) substrate to determine the favorable surface geometry. The first principle discrete variational cluster method based on ab initio local density approximation is used to calculate the total energies of different surface configurations.
Silicon solar cells with Shottky barrier based on metal films with different crystal state
Sh. S. Aslanov,
H. R. Nuriyev,
F. B. Dadasheva
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By forming platinum siliside of on n-type silicon plates are created Solar Elements with a Shottky barrier. Siliside of platinum with mono and polycrystalline structure are received. The crystalline condition of the siliside was determined by electron-graphical method. The influence of background temperature to parameters of preparing elements have been investigated in the temperature range of (100 - 300)D'Alembertian. It was obtained that ideality factor (n) and open circuit voltage (U D'Alembertian D'Alembertian) are increased, but short circuit current (Isc) is not changed with decreasing of temperature. It was established that the temperature dependence of solar elements parameters are strongly display in polycrystalline siliside.
High-power InGaAsP/GaAs SCH SQW lasers
Zhonghui Li,
Jinhua Yang,
Genzhu Wu,
et al.
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InGaAsP/GaAs SCH SQW lasers have been prepared by LP-MOCVD. The dependence of threshold current density (Jth) on cavity length (L) was explained by threshold current condition and gain characteristics diodes samples with output power of 1 to 2 W, threshold current density (Jth) of 330 to 450 A/cm2 and external differential quantum efficiency ((eta) d) 35% to 75%, are in good agreement with the designed requirement.
Development of SiGe/Si film heterojunction bipolar transistors
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In the paper, development on MBE-based SiGe/Si heterojunction bipolar transistors (HBT) is described. The SiGe/Si film used in the present work was grown by SIVA32 molecular beam epitaxy system made in Riber, France. 3 micrometers process technology with poly-silicon emitter was used to develop SiGe HBT devices. The experimental results indicated that both the direct current characteristics and the cutoff frequency of SiGe HBT are satisfactory. The current gain (beta) of HBT devices is 50, when the collector voltage Vc equals 2V and the collector current Ic equals 5 mA. The cutoff frequency fT equals 5.1 GHz. And the uniformity of the cutoff frequency of HBT is quite good.
Characteristics of CdSe thin film transistor
Yumei Jing,
Ruhua Ye,
Zhiming Li,
et al.
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Cadmium selenide thin film transistors were fabricated using normal evaporation and sputtering technique in multiple pumpdown of vacuum systems. The device structure, materials of each layer and deposition conditions are depicted. Characteristics of CdSe TFTs were studied. The results indicate that stable CdSe TFTs with good characteristics can be obtained by use of simple vacuum deposition processes and adding indium thin layer in the insulator/semiconductor interface.
Single-mode lasing of InGaAs/InGaAsP MQWs microdisk lasers with low threshold
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The lasing modes and the spontaneous emission factors of microdisk lasers are analyzed simply, in this paper, InGaAs/InGaAsP multiple quantum wells (MQW) microdisk lasers are fabricated by using the methods of active ion etching and selective chemical etching. The diameter of the microdisk lasers was 3 micrometers . InGaAs/InGaAsP MQW microdisk lasers was optically pumped when cooled with liquid nitrogen. We obtained the single-mode lasing at 1.5 micrometers wavelength, with threshold pump power 18 (mu) w.
Growth of n-type ZnTe films and formation of ohmic contacts
Kazuki Hayashida,
Mitsuhiro Nishio,
Yoshiaki Mitsuishi,
et al.
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N-type ZnTe films with resistivities of 2 and 13 (Omega) cm have been grown by metalorganic vapor phase epitaxial technique using triethylaluminum. The photoluminescence spectra from these films exhibit strong excitonic emission and donor-acceptor-pair emission associated with Al donor and very weak deep emission band due to the Zn vacancy and Al donor complex. We have examined various metals (Al, Mg and W) and an alloy (In-Hg) for ohmic contacts to n-type ZnTe. From the current-voltage characteristics between two contacts at room temperature for above-mentioned metals and alloy, it has been found that acceptable contacts are formed using W and In-Hg alloy. The best contact among the investigated electrodes is achievable by using W electrode.
Degradation of Isc and the pattern of degradation of a-Si:H
Yeshitila G. Michael,
Ilia M. Kachirski
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The pattern of light induced degradation, i.e. the degree of degradation of a-Si:H pinpin solar cell parameters were studied on different i-layer thickness using high intensity (approximately 10 AM 1.5) illumination. It was found that stacked cells do not show a uniform degradation pattern as in the case of single junction solar cells. In particular, the degradation in short-circuit current Isc of stacked cells shows a big difference for thick (approximately 500 nm) and thin (approximately 400 nm) pinpin cells. It was found that degradation of the stacked cells with thick bottom layers exhibit a degradation pattern similar to that of single junction cells, i.e. the degradation in efficiency comes from the fill factor and the short circuit current, while open circuit voltage being degraded slightly. The degradation in short circuit current of cells with thin bottom layers is negligibly small.
Light ray theory of semiconductor microdisk lasers
Genzhu Wu,
Jinhua Yang,
Zhonghui Li,
et al.
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The paper has analyzed the light waveguide characteristics of microdisk lasers with the light ray theory for the first time, obtained the same result derived by Helmholtz wave equation theory and it is in good agreement with experimental results.
Raman scattering and infrared absorption of silicon nanocrystals in silicon oxide matrix
Zhixun Ma,
Xianbo Liao,
Weimin Zheng,
et al.
Show abstract
Structural dependence on annealing of a-SiOx:H was studied by using infrared absorption and Raman scattering. The appearance of Raman peaks in the range of 513 - 519 cm-1 after 1170 degree(s)C annealing was interpreted as the formation nanocrystalline silicon with the sizes from 3 - 10 nm. The Raman spectra also show the existence of amorphous-like silicon phase, which is associated with Si-Si bond re-construction at boundaries of silicon nanocrystallites. The presence of the shoulder at 980 cm-1 of Si-O-Si stretching vibration at 1085 cm-1 in infrared spectra imply that except that SiO2 phase, there is silicon sub-oxide phase in the films annealed at 1170 degree(s)C. This sub-oxide phase is located at the interface between Si Crystallites and SiO2, and thus support the shell model for the mixed structures of Si grains and SiO2 matrix.
MBE growth and temperature-dependent PL of ZnSe:Cl epilayers
Shanzhong Wang,
Shengwu Xie,
Qianjun Pang,
et al.
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Some newly obtained photoluminescence (PL) data from the ZnSe:Cl epilayers grown by molecular beam epitaxy are reported here. The PL spectrum at 10 K is dominated by a strong and narrow Cl0X peak at 2.797 eV with the FWHM of about 13 meV. The quenching tendency of Cl0X peak with the increasing temperature is clearly characterized by two temperature regimes, corresponding to two thermal activated nonradiative mechanisms with activation energies of about 16 meV and 90 meV respectively. The weak emission at 2.713 eV is thermally quenched by the presence of nonradiative center with the same activation energy of about 90 meV as the Cl0X. The similar quenching tendency of the 2.713 eV emission and the Cl0X peak implies that they are quenched by the same physical mechanisms.
In-situ photomodulated reflectance study on GaAs/AlxGa1-xAs single surface quantum well
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We have studied the energy band transitions between confined sub-bands in 10 nm surface quantum well based on in-situ Photo-modulated Reflectance (PR) Spectrum in Molecular Beam Epitaxy system. The single surface quantum well (SQW) is confined by the vacuum on one side and by AlxGa1-xAs barrier on the other side. The structure parameters of the SQW are monitored by the Reflective High- Energy Electron Diffraction (RHEED) during growing procedure. In PR spectrum, we have observed clearly the transitions from the hole sub-bands to the electronic sub- bands. The transition of excitation states is first observed in single surface quantum well. The results are well explained by the effective mass approximation with parameters provided by RHEED.
Study of interdiffusion in HgCdTe/CdZnTe structures by infrared transmission spectroscopy
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Based on empirical rules for the intrinsic absorption coefficient and refractive index of Hg1-xCdxTe in Hougen's model, a novel calculation method determining the composition profile of epitaxy layer from room- temperature infrared transmittance spectroscopy is presented. The composition depth profile of Hg1-xCdxTe film samples grown by liquid-phase epitaxy and after annealing is determined using this method. The expression of the composition interdiffusion coefficient for Hg1-xCdxTe was deduced.
Capture barrier of Sn-related DX centers in AlGaAs epilayers
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Thermal capture and emission processes of Sn-related DX centers in AlxGa1-xAs (x equals 0.26) were measured by a constant capacitance voltage transient in various temperatures. By employing a Laplace defect spectroscopic method, the non-exponential transients were decomposed into several discrete exponential components. The results shown that more exponential components appeared int he small emission rate region as capture period increased. This indicates that electrons preferentially fill shallow energy levels due to their lower capture barriers. Discrete exponential components of the capture process were identified and four of their barriers were preliminarily measured to be about 0.14, 0.15, 0.16, and 0.17 eV, respectively.
Photoluminescence properties of ultrathin CdSe layer depositions in ZnSe matrix
Yu Yang,
De Zen Shen,
Jiying Zhang,
et al.
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The photoluminescence properties of ultrathin CdSe layer were reported in this paper. Several monolayers of CdSe well layer were deposited in ZnSe matrix by lower-pressure metalorganic chemical vapor deposition. Two peaks were observed in the ultrathin structure. It was considered that the high-energy peak came from the exciton combination in the ultrathin CdSe well layer and the low-energy peak might come from the interface or impurity. The decrease of growth periods could lead the peak value of exciton peak red shift and the full-width at half-maximum become narrow. This was codetermined by the effect of interdiffusion and interface roughness or well width fluctuation.
D-A emission in photoluminescence spectrum of GaN grown by rf plasma-assisted MBE
Zhibiao Zhao,
Wei Li,
Ming Qi,
et al.
Show abstract
Donor-acceptor pair (DAP) in wurtzite GaN films grown by radio frequency plasma assisted molecule beam epitaxy on sapphire substrates using low temperature GaN buffer layers have been studied using photoluminescence. The energy levels of N vacancy, as donors, were calculated using an approximate formula, and good agreement with DA emission results. Native defects related to DAP and their formation energies were discussed.
Photothermal ionization spectroscopy of Be acceptor in GaAs
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The photothermal ionization spectroscopy (PTIS) has been employed to study Be shallow acceptor states in GaAs grown by MBE. We have observed the G line, D line and C line transitions which are from the ground state 1s3/2((Gamma) 8+) of Be acceptor to the first three excited odd-parity states 2p3/2(Gamma) 8-), 2p5/2((Gamma) 8-) and 2p5/2((Gamma) 7-), respectively. The transition from the ground state 1s3/2((Gamma) 8-) to the excited state 2p1/2((Gamma) 6-) is identified as well. According to the PTIS, we deduce the binding energy of Be ground state in GaAs is 28.6 mev.
Longitudinal optical phonon-plasmon-coupled modes in epitaxial GaN films on sapphire substrate
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We have studied the longitudinal optical phonon-plasmon coupled (LPP) modes in device quality GaN epitaxy thin films deposited on sapphire substrate using infrared reflection spectroscopy. By theoretical calculation and fitting with the experimental IR reflection spectra for a series of Si doped GaN epilayers we obtain the phonon vibration parameters and the plasmon frequency and damping constant in GaN. The LPP modes have been deduced by the imaginary parts of the reciprocal dielectric function in IR reflection measurement. Both high and low branches of the LO phonon- plasmon coupling mode (LPP+ and LPP-) are well resolved. With the increase of doping level, the frequency of the LPP+ mode shifts to higher while that of the LPP- mode trends toward TO phonon of GaN. The carrier concentration and mobility in GaN have also been deduced. The IR measured concentration of carriers coincides with the Hall measurement. The mobility ratio of Hall to IR is about 1.75 approximately 1.96, implying a dominating mechanism of ionized impurity scattering. Raman measurement has also been performed on the same series of samples. The spectral reveal the similar behavior of the LPP modes to that in IR measurement. Our results show that both IR reflection and Raman scattering are powerful and nondestructive tools to investigate the carrier properties in GaN thin films.
Photoluminescence characterization in GaAs/AlGaAs quantum well infrared photodetectors
W. Y. Cai,
Z.F. Li,
Na Li,
et al.
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Micro-photoluminescence ((mu) -PL) experiments have been carried out on the cleaved facet of quantum well infrared photodetector to extract multiple quantum well signal. Some structures and peak response wavelength have been estimated by a numerical calculation based on the square well model. Thus, a relationship between PL spectrum and parameters was built.
Optical investigations on pseudomorphic delta-doped AlGaAs/InGaAs/GaAs quantum wells
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In this paper, photoluminescence (PL) measurements were performed on several series of single-side Si doped MBE pseudomorphic high electron mobility transistors (p-HEMTs) quantum well samples, with different spacer layer widths, well widths and Si (delta) -doped concentrations, under different temperatures and excitation power densities. PL signals from the transitions of the second electron subband to the first heavy-hole subband (e2-hh1) and the first electron subband to the first heavy-hole subband (e1-hh1) have been observed with good symmetry and narrow full with at half maximum indicating high sample quality compared with previous reported results. The dynamic competitive luminescence mechanism between the radiations of e2-hh1 and e1-hh1 was discussed in detail. The confining potential, subband energies, corresponding envelope functions, subband occupations and transferring efficiency have been calculated by self-consistent definite differential method at different temperatures in comparison with our experiment results. The relative variation of the integrated luminescence intensity of the two transitions (e1-hh1 and e2-hh1) was found to be dependent on the temperature and the structure's properties, e.g. spacer layer width, dopant concentration and well width, which is an efficient characterization method before p-HEMTs device fabrication.
Theoretical analysis of InGaAsP multiple-quantum-well electroabsorption modulators with both polarization insensitivity and negative chirp
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Polarization-sensitivity of electroabsorption (EA) modulators is analyzed by fractional-dimensional approach. Chirping parameter (alpha) is then calculated using Kramers- Kronig relations. It is found that polarization insensitive and negative chirp operation can be realized simultaneously for InGaAsP multiple-quantum-well EA modulators with optimized well width and amount of strain. We propose a polarization insensitive InGaAsP EA modulator with 9 nm wide 0.38% tensile-strained quantum wells. The modulation characteristics remains polarization independent up to 80 kV/cm, corresponding to an extinction ratio of over 15 dB, and the chirping parameter (alpha) is estimated to be around -0.25.
Growth and Si-doping of GaN on GaAs(001) by MBE
Q. Huang,
Hong Chen,
Zhiqiang Li,
et al.
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The GaN growth and Si-doped GaN are studied in this work. By means of x-ray diffraction and photoluminescence (PL) measurements we found that the GaN sample directly grown on GaAs substrate is pure cubic phase and that grown on AlAs buffer is pure hexagonal phase. The present study shows that the phase of GaN samples grown on GaAs substrates can be controlled using different buffer layers. The PL properties of Si-doped cubic GaN with different carrier concentrations were investigated at room temperature. It was found that when the carrier concentration is increased from 5 X 1015 to 2 X 1018cm-3, the PL peak shifted towards low energy, from 3.246 to 3.227 eV, and the PL linewidth increased from 77.1 to 121 meV. The PL peak shift is explained by the bandgap narrowing effect due to the high doping concentration. The PL linewidth includes two parts: one is doping concentration-independent, which is caused by the imperfection of samples and phonon scattering; the other is doping concentration-dependent. We assign the second part to the broadening by the microscopic fluctuation of the doping concentration. The experimental measurements are in good agreement with the model.
MBE growth of HgCdTe and device applications
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The recent progress in MBE growth of HgCdTe at the Research Center for Advanced Materials and Devices, and the National Laboratory for Infrared Physics is reported. It is found that the excellent compositional uniformity and reproducibility of HgCdTe can be archived by MBE technique. The results of surface morphology, dislocation density, electrical properties and focal plane array detectors are described in the paper.
Metal Films
Room-temperature operation of Nb-based single-electron transistors
Jun-ichi Shirakashi
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Room temperature operation of Nb/Nb oxide-based single- electron transistors (SETs) was successfully achieved and was reported in detail. First, the SETs were fabricated by a scanning probe microscope (SPM)-based anodic oxidation technique, and then the junction area was further reduced by thermal oxidation. Ultra-small tunnel junctions were easily obtained by utilizing these two kinds of oxidation processes, and clear single-electron charging effects were observed through the Nb/Nb oxide-based SETs at room temperature.
Influence of hydrogen plasma processing on gas-sensitive tin dioxied thin film properties
Igor A. Karapatnitski,
Konstantin A. Mit',
Daniya M. Mukhamedshina,
et al.
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The influence of glow discharge hydrogen plasma processing on undoped tin dioxide (SnO2) thin film structure and properties have been investigated. The films of 150 - 200 nm thickness were deposited by a method of magnetron sputtering on Al2O3 substrate at the temperature of this one 250 degree(s)C with a rate of 1.5 - 2.0 nm/min in argon-oxygen mixture atmosphere. It was shown these films are amorphous just after fabrication, theirs polycrystalline structure appears after annealing and disappears after processing in the hydrogen plasma. Such a processing expands a temperature range of film sensitivity to ethanol and heptane vapors, increases the sensitivity to low concentration of those.
Surface emitter in near UV: study on metallic film
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The photoemission characteristics of aluminum (Al) and gold (Au) thin film photoelectric cathodes were studied. The metallic cathode stability after exposed to air was investigated. The results of the experiments and study on its photoemission were given, and the application prospect of surface emitter in near UV region was proposed.
Simulation of nucleation and initial growth of thin films on metal surface
Fengmin Wu,
Yuanchun Liu,
Xiongwei Wang,
et al.
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The atomic processes of nucleation and initial growth of thin films on metal surfaces are simulated by Monte Carlo method, using realistic growth model and physical parameters. The effects of adatoms evaporation from the substrate and diffusion along the edge of the islands are included in the simulation model. It is shown that the compact structure of Fe island grows on Fe(001) surface over the wide range of temperatures from 250 to 2000 K, which is consistent with the nucleation theory. The simulation results not only nicely reproduce the experiments of thin film growth at intermediate temperature, but also predict the growth situations of thin films at high temperature.
Behavior of current under dc field and switching, and current-controlled negative resistance and oscillation on MOM device of Bi2O3 film
Kazunori Komorita
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By using the MOM device of Bi2O3 films, some electrical properties on these films or the device are studied as follows: (1) The behavior of the electric current across the thick Bi2O3 films under DC field, is elucidated by the formula Ivaries direct asVn for the regions of low (n equals 1), ohmic (n equals 1), high (n > 2) conductivities and SCLC (n >= 1.5 approximately 2). A hysteresis of the I-V curve results from the residual space charge and polarization in the device. (2) The memory switching and oscillation (in CCNR) phenomena on the device of thin Bi2O3 films are observed under the AC applied voltage in the room temperature and 77 K. These rest upon a thermal effect due to the current injection to the device.
Gratings in resonant multilayer structures
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Enhancement of the free-space diffraction efficiency of titanium-ion implanted gratings by inserting them into multilayer dielectric Fabry-Perot cavities has been demonstrated theoretically in previous works. In this paper, we discuss the sensitivity of the diffraction efficiency to the optogeometrical parameters of the structures obtained using titanium-ion implantation. A process to perform a phase grating in a seven-layer mirror Fabry-Perot cavity is described and experimental results pertaining to efficiency measurements on this structure are compared to numerical simulations.
Tunneling-type giant magnetoresistance of Fe-SiO2 granular thin films prepared by rf magnetron sputtering
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A tunneling magnetoresistance of Fe-SiO2 granular films was studied. The samples were prepared similarly by the preparation of multilayer films using two disks of Fe and SiO2 sputtering targets. The superparamagnetic feature and tunneling magnetoresistance were observed for the samples with Fe composition rate of lower than 0.45. Small Fe granules isolated by SiO2 matrix were observed by the transmission electron microscope. The magnetoresistance curves of these samples exhibited `two step' resistivity change, which was not observed from the annealed sample. This unique feature of tunneling magnetoresistance at a low magnetic field was presumably attributed to the existence of 2D structure of granules.
Effects of seedlayers on magnetic properties and microstructure in CoCr(Ta)/Cr thin films
Huizhong Jia,
Joeri Veldeman,
Marc Burgelman
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In order to improve the magnetic properties of Co-based thin films, different seedlayers (SiO, ITO, SiO2, Ag and Al) have been applied on a PET substrate. The thickness of Cr underlayers and of magnetic layers is varied to obtain thin films with optimal magnetic properties. The magnetic properties of CoCrTa and CoCrPt thin films are improved clearly when the magnetic layer is thin. Specifically, the coercive force of CoCrPt thin films reaches 100 kA/m sputtered with a sputter pressure 50 mTorr on pure argon at room temperature. AFM topographies indicate that the average grain size and the grain shape of thin films vary with thickness of Cr underlayer and of magnetic layer. This influences the magnetic interactions inside thin films and subsequently adjusts the magnetic properties. The crystal structure of each thin film with a seedlayer is improved as well.
Direct evidence of magneto-optical and optical size effects in Fe-Ag granular films
Song-You Wang,
H. Y. Li,
Shi-Ming Zhou,
et al.
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For prepared FexAg100-x granular films, the Kerr rotation and ellipticity change monotonically with the photon energy and after annealing have two peaks near 2.0 and 3.8 eV, respectively. The peak value increases with annealing temperature TA. Numerical calculations show that the peak at low energy is induced by the change in the off-diagonal element of dielectric tensor of Fe particles and the peak at high energy results from the changes in optical properties of Ag particles near its plasma absorption edge. These results clearly show the simultaneous existence of both the magneto-optical size effect of Fe particles and optical size effects of Ag particles in metallic granular films.
Tungsten thin films deposition on tool steel substrates
Qixin Guo,
Mitsuhiro Nishio,
Hiroshi Ogawa
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Thin films of tungsten used as buffer layers for diamond coating on tool steels have been prepared by rf magnetron sputtering. The tungsten deposition rates as functions of argon pressure and rf input power are reported. The effects of argon pressure and rf input power on the film structures have also been studied. Finally, it has been demonstrated that continuous diamond films can be grown on tool steels by using tungsten films as buffer layers.
Characterization of surface oxidation on rare-earth Er film x-ray laser target
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Oxide growth on rare-earth erbium film at room temperature was quantitatively followed by means of quartz oscillation technique. Structure and chemistry of the oxide layer were characterized by x-ray diffraction and x-ray photoelectron spectroscopy. The humidity in oxidizing environment is found to be the key factor leading to the increase of oxidation rate of the erbium film. The oxide layer is composed of crystallites of erbium and erbium oxide. The O 1s photoelectron spectra are characterized by two components that are assigned to oxide and hydroxide species respectively. The oxide layer shows a layered structure with an oxide layer covered by a hydroxide overlayer.
AFM study on silver/HOPG interface sputtered by low-energy argon ions
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The effect of argon ion bombardment on interface of silver and high oriented pyrogenic graphite (HOPG) was investigated by atomic force microscopy. The Ag/HOPG interface morphology has been explored as a function of irradiation time. It can be seen that the size of crystal particle on HOPG is almost unchanged with increase of irradiation time, while the size of Ag crystal particle in part of the terrace increased and became highly ordered. There is no obvious mixing between Ag and HOPG, and Ag particles in nanoscale are isolated on HOPG surface. This will result in the reduction of depth resolution of the surface analysis by ion sputtering technique.
Research on the structure of Ag-TCNQ thin films for information storage
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The structure and the electrical bistable properties of vacuum deposited thin films of Ag-TCNQ (7,7,8,8- Tetracyanoquinodimethane) complex have been investigated. The characteristics of obtained films under different preparation conditions have been compared. The optical transmission spectra and the x-ray diffraction measurements were conducted to analyze the structure and the thermal stability of the films. The atomic force microscope was used to examine the morphology and grain size of the films. The corresponding electrical switching property was measured upon the Ag-TCNQ films with different combined sandwich- shaped electrodes. The results how that the films can have very stable switching properties. The switching time between high and low impedance states is about 10 ns, and the switching voltage is around 4.0 V. The film preparation parameters and different layered structure have an important influence on the characteristic of the films. The switching mechanism was discussed.
Preparation and optical property of island silver films embedded in silica
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Island silver films (nanoclusters, quantum dots) embedded in silica are prepared on silicon wafers and glasses by sputtering. Atomic force microscope is used to characterize the morphology and distribution of silver nanoclusters, the size of nanoclusters varies from several ten to several hundred nanometers. Linear optical absorption spectra of annealed samples have a blue-shift compare to that of as- prepared samples, it suggests thermal treatment decomposes large clusters to small clusters. Z-scan technique is applied to study the third-order non-linear optical properties. It is found that the embedded silver nanoclusters present remarkable third order nonlinear effect even if the size of silver nanoclusters are as large as several tens to several hundreds nanometers. Thermal treatment leads to a slight reduction in NRIC, indicating annealing also dissolve tiny nanoclusters. The size distribution of silver nanoclusters therefore becomes centralized after thermal treatment.
Metal Oxide Films
Microwave-assisted reactive sputtering of aluminum oxynitrides
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Aluminium oxynitride thin films have been produced by using a reactive dc magnetron sputtering system incorporating a microwave plasma to improve the ionization of the reactive gases. This allows films of high optical quality to be deposited at commercially acceptable deposition rates. A series of homogeneous films of aluminium oxynitride films covering the range of compositions from aluminium oxide to aluminium nitride have been prepared and their optical constants characterized over the wavelength range 300 nm to 1500 nm. As a demonstration of the stability and reproducibility of the system, some complex graded-index optical filters have been designed and fabricated using a simple control program based only on setting the gas flows and times for each layer. The experimental results are shown to agree very well with theoretical results based on the dispersive optical constants of the individual layers.
Epitaxial growth and characterization of oxide thin films
Guozhen Yang,
Huibin Lu,
T. Zhao,
et al.
Show abstract
More than ten kinds of oxide thin films and their heterostructure have been successfully fabricated on SrTiO3 (001) substrates by laser molecular beam epitaxy. Measurements of atomic force microscopy, high-resolution transmission electron microscope and x-ray small-angle reflectivity reveal that the surfaces and interfaces are atom-level-smooth. The unit cell layers and the lattice structure are perfect. The enhancement of second-harmonic generation in BaTiO3/SrTiO3 (BTO/STO) superlattices and the thickness dependent structural characteristics of BaTiO3 (BTO) thin films were observed.
Evaluation of ZnO films produced by a single-step deposition on optical fibers
E. Y.M. Lee,
Leong Mar,
Robert N. Lamb
Show abstract
The effectiveness of Single Source Chemical Vapor Deposition as a one step process for producing zinc oxide films on silica fibers was evaluated. The physical and chemical properties of films grown on optical fibers and films grown on planar silica substrates under identical conditions were probed for differences using X-Ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The XPS analysis of the film surface and bulk found no significant variation in the chemical composition between films grown on planar substrates and films grown on optical fibers. The XRD of films grown on planar silica substrates showed these films to be composed of crystallites roughly 30 - 40 nm in size and oriented in the c-axis direction. SEM revealed some differences in the morphology between standard grown on planar silica substrates and growth on silica fibers although films in both cases were composed of columns of crystallites. Although it was found that film thickness varied around the circumference of the silica fiber relative to the position of the precursor source, the films were nevertheless continuous and consistent in chemical composition.
Deposition of TiO2 thin films by plasma-enhanced chemical vapor deposition
Wenjun Li,
Junfu Zhao,
Xiaolin Zhao,
et al.
Show abstract
Titanium dioxide films were deposited onto Si(100) substrate by plasma enhanced chemical vapor deposition. Titanium isopropoxide (Ti(OC3H7)4 was used as precursor. Argon was used as a carrier gas for the precursor and the reactant for the plasma process. The deposition rate was studied as functions of deposition parameters such as r.f. power, substrate temperature, carrier gas flow rate. The structures of the films were characterized by x-ray diffraction and by Raman scattering. The thickness and refractive index of the films were characterized by ellipsometry. It was found that the refractive index of the films increased from 1.8 to 2.5 with substrate temperature range from 150 degree(s)C to 700 degree(s)C. And it increased monotonically with annealing temperature range from 400 degree(s)C to 900 degree(s)C. Films deposited onto Si(100) substrates were amorphous at substrate temperatures between 80 degree(s)C and 200 degree(s)C, a mixture of anatase and amorphous at 230 degree(s)C - 450 degree(s)C, anatase between 500 degree(s)C and 600 degree(s)C, and only rutile above 650 degree(s)C.
Influence of preparation parameters of protecting film on discharge characteristics in ac PDP
Hongxia Ren,
Yue Hao
Show abstract
With MgO film as an example, the effect of different technical parameters in preparation of protecting film overcoating the dielectric layer in AC PDP (Plasma Display Panel) by electron-beam evaporation method on the performance of AC PDP are thoroughly studied and discussed in this paper. These parameters explored include the substrate temperature, the deposition rate, etc. The relation between the composition, the crystal structure, the appearance of protecting film and emissive properties is researched, and their influence on the properties of AC PDP is also studied, the optimal process of preparing film is examined. And also this observed dependence of the discharge characteristics on the various parameters of the panel fabrication process is explained in terms of a postulated effect of oxygen on the surface properties of MgO films and the changes in the surface properties of the MgO films produced by ion bombardment during the discharge.
Preparation of zirconia thin films via sol-gel process from inorganic precursor
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ZrO2 thin films were prepared by sol-gel technology from suitable zirconia aqueous colloidal suspensions containing nano-crystalline ZrO2 at room temperature synthesized by hydrothermal process from inorganic precursor (ZrOCl2 (DOT) 8 H2O). By adding a soluble organic binder PVP to the suspension prior to application, it substantially increased the coating refractive index and the abrasion- resistance as well as the laser damage threshold. The features of the coatings and the colloidal suspensions were investigated. Multilayer highly reflective dielectric coatings were also elaborated by laying down quarterwave- thick alternating coatings of the binder-aided zirconia and silica, which was prepared with the sol-gel process from TEOS. Laser damage thresholds of 20 and 18 J/cm2 (1064 nm, 1 ns) were achieved for single ZrO2-PVP coating and ZrO2-PVP/SiO2 multilayers respectively.
Analysis of characteristics of films with TiOx-TiO2 structure
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Ti was prepared on substrates by sputtering methods, then followed by an oxidization step to form TiOx. TiO2 films with dopents (In, Ta and Nb ions etc.) or without, could be directly coated on the surface by TiOx by a sol-gel process to obtain the films with TiOx-TiO2 structure. TiOx films in the oxidation process of Ti were calculated by diffusion equations and analyzed by x-ray diffraction. Crystalline phases, grain size and morphology of TiOx,-TiO2 cross section have been observed by transmission electronic microscopy and scanning electron microscopy, respectively. Raman spectra of the films with the dopants demonstrated existence of anatase phase even in nigher temperature. The electrical properties of the films were analyzed and compared with each other. The results have been explained by transferring theory of the excitons with the structure.
Annealing studies of solution-deposited ZrO2 thin films on self-assembled monolayers
K. A. Ritley,
F. Schreiber,
K.-P. Just,
et al.
Show abstract
Thin films of ZrO2 were deposited from aqueous solution on Si(100) substrates precovered by alkyltrichlorosilane self-assembled monolayers. The interface structure, thermal stability and densification of these films in the temperature range from room temperature to 750 degree(s)C in vacuum were measured using in situ x-ray reflectivity. The growth rate is a nonlinear function of time in solution. Decreasing film thickness and increasing density is found upon annealing up to 750 degree(s)C. A 25 nm film revealed the appearance of a mixed-phase crystalline structure at 800 degree(s)C which disappeared upon cooling. There is no visible evidence of stress-induced microstructural changes, such as peeling or cracking.
Structural, infrared, x-ray photoelectron, and Raman spectral characterization of electrochromic nickel oxide films
Yonggang Wu,
Guangming Wu,
Xingyuan Ni,
et al.
Show abstract
Nickel oxide films were deposited onto indium-tin oxide coated substrates by electron-beam evaporation and were electrochemically colored and bleached in KOH electrolyte. X-ray diffraction, infrared, x-ray photoelectronic and Raman spectroscopy were used to characterize the films. Results show that the as-deposited films are composed of crystallites with preferential orientation of cubic NiO(111), and retain their original structure after electrochromic redox reaction. The boundary and surface of the NiO crystallites play a critical role in the electrochromic reaction, the sites of the injection and ejection of OH- ions and relevant electrochromic reaction are at the interface of NiO crystallites, the major composition at the interfaces of the crystallites are NiO for the as-deposited films, NiOOH for the colored films and Ni(OH)2 for the bleached films.
Study of thin film gas sensors using optical methods
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The optical sensitive characteristic of SnO2 and V2O5 thin films to the gas SO2 was investigated with photometric and ellipsometric methods. It is found that thin films of the Pd-doped SnO2 and pure-V2O5 have good optical sensitive characteristics to SO2 in the visible range, and the Zr-doped SnO2 film in the near-infrared area. The results show that the change of the optical characteristic is directly related to the variation of optical gap and the concentration of free carrier in thin films.
Effect of structure development on self-trapped exciton emission of TiO2 thin films
Ilmo Sildos,
A. Suisalu,
V. Kiisk,
et al.
Show abstract
Photoluminescence of thin crystalline TiO2 films was studied. The films contained an anatase phase and were grown by the atomic layer deposition method on different single crystal substrates. A polarized re-combination emission of self-trapped excitons was observed in the films at 5 K. A comparison of the obtained spectra with those of the single crystal anatase allowed determining crystallite orientations in the films. Results were consistent with the x-ray diffraction and reflection high-energy electron diffraction data.
Optical and electrochemical properties of sol-gel-deposited tantalum pentoxide thin films
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Sol-gel spin-coating technique was applied to produce tantalum pentoxide thin films. Pseudo-ternary phase diagrams were used to outline the sol-solution stability and the optimal Ta2O5 thin films formation regions of Ta(OC2H5)5-C2H5OH- CH3COOH-H2O system. Forbidden band gap of Ta2O5 thin film was calculated and found to be Eg equals 3.7 ev. Room temperature cyclic voltammetric measurements clearly revealed a protonic conductor behavior for Ta2O5 thin films.
Optical and structural properties of sol-gel-made WO3 and Zr-doped WO3 thin films
Esra Ozkan,
Fatma Tepehan
Show abstract
The aim of this study was to determine the optical properties of WO3 and Zr doped tungsten oxide films deposited by the sol-gel process. The optical properties of WO3 and Zr doped tungsten oxide films deposited by the sol-gel process depend on the number of coating layers. The refractive index and absorption coefficient of WO3 thin films increases with an increasing number of deposited layers. Transmittance of Zr doped tungsten oxide thin films are greater than tungsten oxide thin film. A scanning electron microscope was used for the analysis of surface structure. Optical constants of tungsten oxide and zirconium tungsten oxides were determined by using spectrophotometric transmissivity in the UV-Visible region.
Wetability of sol-gel-derived TiO2 films
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TiO2 thin films were deposited on glass substrates by the sol-gel process using spin-coating technique. Three kinds of sol systems were used to produce the films which were then baked at various temperatures. Water contact angles of the films were measured using the tilting plate method. The initial water contact angle of an as-prepared film was < 5 degree(s), and after a certain period of placement it started to increase gradually up to a maximum of 72 degree(s). Water adsorption was found to accelerate the increase of the contact angle. Appropriate UV light irradiation could make the high (72 degree(s)) water contact angle of the film return to the initial value, i.e., < 5 degree(s). Films prepared with DEA-chelated precursors have higher speed of increase in the water contact angle than those prepared with AcAc-chelated precursors or without any chelating agent. AFM images showed that the surface roughness of these films were different, suggesting that the surface roughness is another factor affecting the wettability of the films.
New way of preparing ion barrier ultrathin film without pollution
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A new technology and method preparing ions barrier film on the input face of multi-hole substratum, MCP, without carbon pollution were studied and introduced in this paper. The composition of the film and the performance of MCP coated with ion barrier film were tested by XPS and UV photoelectric emission method. The new process made the carbon content largely decrease in the film, and the characteristics of MCP unmodified.
Effect of protecting film materials on discharge characteristics in ac plasma display panel
Hongxia Ren,
Yue Hao
Show abstract
In order to decrease the cost of AC PDP by using low voltage driving system, using an measuring system which can imitating AC PDP operating, the influence of protecting film prepared by different materials on discharge characteristics in AC PDP are explored. The studied materials include MgO which commonly used in AC PDP, new materials--compound alkaline earth oxides with different proportion, such as (CaSr)O and (MgSr)O. In this paper, the study direction of new film materials id determined, and the problems must be dissolved in using the high emissive materials film are investigated.
Effect of heat treatment condition for protecting film on discharge characteristics of ac PDP
Hongxia Ren,
Yue Hao
Show abstract
With MgO film as an example, the effect of different heat treatment conditions in preparation of protecting film overcoating the dielectric layer in AC PDP (Plasma Display Panel) prepared by electron-beam evaporation method on the performance of AC PDP are thoroughly studied and discussed. The studied baking condition mainly focuses on treating atmosphere, air, vacuum, and inert gases atmosphere are considered. And also this observed dependence of the discharge characteristics on heat treatment condition of panel fabrication process is explained in terms of a postulated effect of oxygen on the surface properties of MgO films and the changes in the surface properties of MgO films produced by ion bombardment during discharge.
Preparation and properties of IrO2 thin films grown by dc magnetron reactive sputtering method
Shijun Wang,
Aili Ding,
Pingsun Qiu,
et al.
Show abstract
Iridium oxide (IrO2) thin films were successfully grown on SiO2/Si(100) substrate by DC magnetron reactive sputtering method with an Ir target (99.99% purity). The effects of sputtering parameters and annealing conditions on the crystalline nature and morphology of IrO2 thin films were discussed. High orientation at (110) or (200) of IrO2 thin films were occurred by annealed films. For fatigue properties, PZT thin films using an IrO2 electrode have largely improved than that using a Pt/Ti electrode.
Computer simulation of Nb2O5/SiO2 sputtering process for narrow-band optical filter
Mike Xu Ouyang,
L. D. Kinney,
Emmanuel C. Onyiriuka
Show abstract
Sputter deposition process conditions for dielectric metal oxide films was simulated by SIMSPUDTM (Simulation of Sputtered Distributions). Collision cross-sections of Nb and Si were found to be 50 angstroms2 and 55 angstroms2 respectively by pinhole experiment and simulation. Film thickness distributions of Nb and Si films vs their oxide counterparts (Nb2O5 vs SiO2) showed that the deposition rate ratio of SiO2 to Si is 2.03 - 2.05:1 while Nb to Nb2O5 is 1.76 - 1.77:1. It was determined that the current density distribution and oxygen flow for reactive sputtering had great influence on film stoichiometry and thickness. It was also found that the ion source flattened the oxide film thickness. SIMSPUD was shown to be a desirable tool for new product development and as such could be beneficial in the design of the next generation PVD system.
Influence of ZnFe2O4 doping on the structural and optical properties of TiO2 films
Guanghai Li,
Lin Yang,
Lide Zhang
Show abstract
Amorphous TiO2 thin films with and without the doping of ZnFe2O4 were prepared by radio frequency magnetron sputtering. The influence of post-deposition annealing on the structural and optical properties was studied. It was established that the anatase single phase exists between 250 degree(s)C and 800 degree(s)C in the TiO2 thin films, and between 450 degree(s)C and 650 degree(s)C in the TiO2 thin films with 2 wt% doping of ZnFe2O4. The absorption edge of TiO2 thin films with and without doping exhibits a blue shift with decreasing annealing temperature and the absorption edge of TiO2 doped with ZnFe2O4 has moved to visible spectrum range. The enhanced photoluminescence of the TiO2 films doped with ZnFe2O4 was found in comparison with pure TiO2 thin films at room temperature.
Magnetic Films
Magnetic properties of amorphous TbFeCo films
Yong Zhou,
Chunsheng Yang,
Di Zhou,
et al.
Show abstract
The effects of sputtering conditions on magnetic properties of amorphous TbFeCo films were investigated. By fixing the current set, the sputtering power reduces with the increase of sputtering Ar pressure, and the coercivity increases with the decrease of sputtering power, in contrast to the magnetization decreases. Film deposited at an Ar pressure of 0.42 Pa and a sputtering power of 7 W develops very good magnetization loops and high perpendicular anisotropy at room and low temperature. Magnetization measurements show that the in-plane magnetization loop at 10 K becomes larger with the increase of saturation magnetic field. This may be caused by the disorder of Tb atoms. At fixed Ar pressure, the coercivity decreases with the increasing sputtering power an the magnetization loop becomes narrow at high sputtering power. The effect of film thickness on magnetization loops is also studied.
Influence of film size on giant magneto-impedance effect
Jinqiang Yu,
Yong Zhou,
Bingchu Cai,
et al.
Show abstract
The relationship between the magneto-impedance (MI) effect and the size of amorphous FeSiB film is reported in this paper. The MI change ratio of FeSiB film is different for the three samples with different widths, and increases with the increasing of sample length when the width is fixed. Experimental results can be explained in terms of stress anisotropy and different external inductance of the sample.
Crystallization of Ni-Fe-P amorphous films prepared by electroless plating
Lingling Wang,
Lihua Zhao,
Guifang Huang,
et al.
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The structure, crystallization processes and products of electroless Ni-Fe-P alloy deposits at various heat treatment temperature were studied, with prepared and composition. The deposits were amorphous structure with NaH2PO2 concentration from 18 g/L to 48 g/L. The surface of the deposited specimens was smooth, bright and homogeneous. Heating these deposits from 200 to 700 degree(s)C produces structural changes. A two-step process of crystallization was observed for the amorphous alloys. At first, the crystallization phases were (gamma) -(Fe,Ni) solid solution phases and Ni3Fe, then Ni3P, Fe3P and (Ni,Fe) solid solution phases for high temperature in the films.
Doping caused great magnetoresistance change in Co-based sandwiches
H. Wang,
Q. Y. Jin,
Jiaju Ma,
et al.
Show abstract
Some results in sandwiched Co/spacer/Co structures have been achieved. With doping Mn and NiO in the Cu spacer, the GMR curve as a function of the magnetic field changes a lot, and the saturation/switching field for GMR can be reduced greatly compare with that in Co/Cu/Co systems. The most important characteristic of the MR change for Co/CuMn/Co system was its two peaks became narrow and sharp, but for Co/NiO-Cu/Cu system, was its two peaks became wide and flat. These results may indicate some new ways in consideration of candidates for novel magnetic devices.
Magnetic and magneto-optical properties of Mn/Sb multilayer films on GaAs substrate
Ming Cai,
Chenjia Chen,
Xuezhong Wang,
et al.
Show abstract
Mn/Sb multilayer films were grown on GaAs (100) by ultrahigh vacuum evaporation technique and subsequent thermal annealing for short duration. Structural, magnetic properties and magneto-optical Kerr effect were investigated. Magnetization measurements reveal strong room- temperature ferromagnetism even for unannealed films. X-ray diffraction patterns show high-quality crystal structure of MnSb is formed. The film annealed at 350 degree(s)C also shows the lowest coercivity and the largest saturation magnetization. Both the polar and longitudinal magneto- optical Kerr rotations are observable for annealed films and the dependence of the Kerr rotation angles on the magnetic field is nearly the same as that of magnetization.
Magnetoresistance behavior of Co/CuMn/Co sandwich structures
R. Cao,
H. Wang,
Q. Y. Jin
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The Giant magnetoresistance behavior of Co/CuMn/Co sandwich structures has been investigated, combined with the surface magneto-optical Kerr effect (SMOKE) method in air. Very low saturation/switching field was achieved by diluting Mn atoms into the Cu metal, but GMR value has no much change, which may imply a way to get high sensitive GMR material. The SMOKE measurements showed steps in Kerr loop, indicating the antiparallel alignment of magnetizations between two neighbored Co layers due to their different switching fields.
Influence of magnetron sputtering CoZrNb stochiometric relation in deposition film
Jiliang Zhang,
Sanming Xiang,
Chunsheng Yang
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The experiments of Co89Zr4Nb67 magnetron sputtering showed that the stoichiometric relation in deposited film is obviously different from that in target. The fact that Zr and Nb contents, which have larger atomic mass, in deposited film were more than that in target showed there were different virtual sources of Co, Zr and Nb between target and substrate.
Hooklike domain transition of MR magnetic head in the process of reversal magnetization
Jun Zhu,
Jinyue Yu,
Chunsheng Yang,
et al.
Show abstract
The requirement to recording density is always increasing with the rapid development of information technology. MR magnetic head was developed under the situation. The main problem met in the application of MR read head is the Barkhausen noise due to the magnetic domain activities in sensor element. There are reports indicated that magnetic domain will tend to single domain structure when the ratio of length and height of rectangle sensor is over 20 and the problem of Barkhausen noise can be resolved. The element which length, width and height is 300 micrometers , 3 approximately 6 micrometers and 40 nm respectively with the ratio of length and height over 50 is studied by bitter powder method. We found that multi-domain activities exist in sensor resulting from the irregular shape of lead line.
Indirect transition process of Neel domain wall polarity during magnetization reversal in magnetic thin film element
Jianguo Qian,
Jinyue Yu,
Jun Zhu,
et al.
Show abstract
There are two patterns of the transition process of Neel domain wall in magnetic thin film elements. One is the direct transition from positive polarity (N+) to negative one (N-). And the other pattern of N+ yields Nct yields N- is indirect transition process recurring to cross-tie wall (Nct). The latter pattern is observed and analyze in this paper.
Influence of nitrogen defects in AIN coverlayers on thermal stability of DyFeCo MO films
Rui Xiong,
Wufeng Tang,
Jing Shi,
et al.
Show abstract
Thermal stability of amorphous DyFeCo films covered with non-stoichiometric AlN layer has been investigated. When RE- dominated films were annealed in air for 10 hours at 200 degree(s)C, the Kerr loops showed the characteristic of magnetic double-layered films. This behavior can be interpreted as follows: the reaction of diffusing N with Dy leads to a reduction of the magnetic active Dy content at the interface and created a very thin TM dominated DyFeCo layer between AlN and DyFeCo layer. This interpretation was demonstrated by XPS measurements.
Magneto-optical Kerr properties of Co-Ag-annealed granular films
Weimin Zheng,
H. Wang,
Song-You Wang,
et al.
Show abstract
A series of CoxAg100-x granular films was prepared by ion beam sputtering and annealed at 100 degree(s)C, 250 degree(s)C, 400 degree(s)C, 500 degree(s)C, respectively. The optical constants, the complex dielectric function and magneto- optical Kerr parameters were measured at room temperature. It was found that Kerr rotation and ellipticity with increasing of the Co content. For the samples Co17Ag83, the strong Kerr effect enhancement is observed around the Ag plasma edge. With the annealing temperature increasing, the enhancement peak shifted toward the low photon energy region. From the analysis of the numerical calculations, it is concluded that the magneto-optical Kerr effect enhancement is due to the presence of the steep plasma edge.
Annealing effects on magnetic properties of amorphous TbFeCo films
Yong Zhou,
Chunsheng Yang,
Di Zhou,
et al.
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Annealing effects on magnetization behaviors of amorphous TbFeCo films have been investigated by vibrating sample magnetometer. Thermal annealing at 100 degree(s)C shows that large perpendicular anisotropy and coercivity still remain after annealing, and inverse magnetostrictive anisotropy is responsible for the decrease of coercivity. It is shown that the coercivity and anisotropy decrease greatly after annealing at temperature over 130 degree(s)C, however, long time annealing does not affect the magnetic properties of TbFeCo films evidently. Annealing at 180 degree(s)C shows that the room temperature magnetization loop in perpendicular direction is similar to that for films annealed at 130 degree(s)C, but the in- plane magnetization loop becomes strong. The remains of perpendicular anisotropy may be attributed to the pair ordering anisotropy and can not be eliminated by low temperature annealing.
Giant magneto-impedance in sandwiched FeSiB/Cu/FeSiB films
Yong Zhou,
Chunsheng Yang,
Jinqiang Yu,
et al.
Show abstract
Giant magneto-impedance (GMI) effect has been studied in the sandwiched FeSiB/Cu/FeSiB films in the frequency range of 1 - 40 MHz. With magnetic field, Ha and AC current applied along the longitudinal direction, the field dependence of the GMI ratio shows that the GMI ratio increase with magnetic field, reaching a positive maximum value at a certain field, and then gradually decreases to the negative GMI ratio. At a frequency of 5 MHz the positive maximum GMI ratio is 1.6% at Ha equals 15Oe, and is smaller than the negative GMI ratio, -7.4% at Ha equals 50Oe. With a transverse field applied, at a frequency of 5 MHz a large negative GMI ratio, -12.2% and -15.4% are obtained for Ha equals 70Oe, respectively. The larger negative GMI ratios at relatively large fields may be associated with the dispersion of easy axis and the related domain structures.
Effect of easy axis orientation and bias field on MI effect in FeSiB amorphous film
Show abstract
The influence of easy axis orientation and bias field on magneto-impedance (MI) effect has been investigated in FeSiB amorphous films. The magnetic field corresponding to the maximum MI ratio shifts to a low value with the increase of the easy axis angle deviated from the transverse direction, and the sensitivity of MI change ratio to longitudinal field can be enhanced by applying a proper bias field along transverse direction.
Superconductor Films
Laser irradiation effects in crystalline and amorphous YBaCuO thin films
S. J. Lewandowski,
G. Jung,
V. D. Okunev,
et al.
Show abstract
We have conducted a systematic study of the effects of laser irradiation on the properties of crystalline and amorphous YBaCuO thin films obtained by laser deposition. The irradiation experiments were mainly performed with a KrF and XeCl pulsed (25 ns) excimer lasers producing energy densities of the order of 0.1 J/cm2, but we used also Cu vapor green and Ar ion blue lasers with medium power output. In all cases the irradiation produced irreversible changes in the investigated samples. We measured structural, optical and transport properties of the irradiated films. After high dose laser treatment of crystalline (orthorombic) films their superconducting properties as a rule deteriorated, but even small dose was sufficient for a marked improvement of surface smoothness. The response of amorphous films was more complex, dependent on the substrate and relied on the presence of crystalline clusters embedded in the amorphous matrix. X-ray diffraction studies of amorphous films revealed structural transformations caused by the interaction with laser light, and the results of optical spectroscopic measurements lead to interesting conclusions concerning the band structure in the investigated materials. Photon assisted structural transformations are suggested as the possible explanation of the observed effects.
I-V properties of heterostructures of superconductor ferroelectric junction
Show abstract
We have grown a heterostructure of YBCO/STO/YBCO on (100) MgO substrate for fabrication of SXS junction. The epitaxial YBCO films were grown by MOCVD method, and the STO layer was deposited by unbalanced magnetron sputtering method. All of films are dominated by a-axis oriented phases. The individual YBCO films revealed critical-current densities around 2.5 X 105 A/cm2 at 77 K. The resistive transition observed in the vertical transport devices is dominated by the X layer properties. These devices display RSJ-type I-V characteristics and the values of IcRn significantly depend on the X layer thickness. The SXS junction with STO layer of 0.1, 0.2 and 0.3 micrometers have IcRn of 115, 90 and 42 (mu) V, respectively.
Growth of HgBa2CaCu2Ox thin films on yttria-stabilized ZrO2 substrates with a buffer layer
J. D. Guo,
Yunxi Sun,
X. L. Xu,
et al.
Show abstract
High quality HgBa2CaCu2Ox (Hg-1212) films have been synthesized on yttria-stabilized ZrO2 substrates by using YBa2Cu3O7 (YBCO) as a buffer layer. These films with Hg-1212 as the major phase were found to possess Tc (R equals 0) > 115 K and Jc approximately 106 A/cm2 (at 77 K). The X-ray diffraction patterns indicated that the obtained films have an in-plane epitaxial structure with the c-axis perpendicular to the film surface. The morphological investigations on the film surfaces have revealed the occurrence of layered spiral-like growth features. The influence of the YBCO buffer layer on the growing of Hg-1212 films is discussed.
Fabrication of multielement arrays based on high-Tc superconducting microbolometers
Show abstract
The 4 X 4 element arrays based on high Tc superconducting infrared microbolometers have been fabricated using the micromachining technology. The detectivities D* for various bolometric elements are ranged from 1.2 X 108 to 7.2 X 108 cmHz1/2w-1 at the operating temperature approximately 88 K.
Insulator Films
Optical characterization of synthetic diamond films
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Synthetic diamond films grown by vapor-phase growth have attracted much interest because of promising applications in electronic devices. Improvement of film quality by reducing the number of crystal defects and impurities is the most important prerequisite for successful device applications. Defects and impurities produce deep states in the wide band gap of diamond. These mid-gap states decrease the efficiency of edge emission and exhibit `visible' luminescence. Recently, it has become possible to obtain high-quality diamond films that show phonon-assisted exciton recombination radiation from the indirect edge. The analysis of edge emission spectra can be used to characterize crystallinity and purity of synthetic diamond films. We have studied band edge structure of synthetic diamond films of differential reflectance spectroscopy as well as cathodoluminescence. The differential reflectance spectrum obtained from a high-pressure-high-temperature synthetic diamond shows interband transitions assisted by phonon emission. On the other hand, chemical vapor deposited diamond films show a zero-phonon exciton transition together with the phase-assisted transitions. This indicates light absorption by bound excitons due to crystal defects. Furthermore, we have investigated higher interband transitions localized in the Brillouin zone by a newly developed electron-beam electroreflectance spectroscopy.
Influence of rf power on carbon nitride films prepared by rf magnetron sputtering
Liudi Jiang,
A. G. Fitzgerald,
M. J. Rose
Show abstract
Since (beta) -C3N4 has been predicted to be a superhard material with a higher hardness than diamond, many research groups have attempted to synthesize carbon nitride materials. We have prepared amorphous carbon nitride (a-C:N) films by rf magnetron sputtering of graphite with N2 as the sputter gas. In this investigation, a series of film samples have been deposited at different rf power. AFM images have shown that the higher the rf power, the bigger the cluster size on the films and the rougher the surface of the films. By analyzing the results of our XPS experiments, we have found that with the decrease of the rf power, not only the incorporated nitrogen but also the concentration of sp3-bonded nitrogen in the films increased. We believe this is because f lower rf power results in smaller carbon clusters on the surface of the films, leading to larger carbon surface area. A larger film surface area makes it easier for the nitrogen to bond with carbon.
Nitrogen-doped plasma-enhanced CVD amorphous carbon: processes and properties
Steven A. Voight,
Steven M. Smith,
Harland G. Tompkins,
et al.
Show abstract
In this work we discuss thin film amorphous carbon which is deposited in a dual frequency plasma enhanced CVD system with a nitrogen-containing ambient. Unlike most carbon films deposited using PECVD, the films in this study were deposited on the grounded electrode and therefore subject to little energetic bombardment during growth. Methane was used as the carbon-containing precursor. We illustrate some potential applications for this type of film and discuss the effect of various process parameters on resulting film properties, such as optical constants, stoichiometry, and chemical bonding and structure.
Sputtering deposition and optical properties of SiCxNy films
Xingcheng Xiao,
Lixin Song,
Weihui Jiang,
et al.
Show abstract
In this paper, the SiCxNy films were prepared by RF magnetron sputtering with SiC target. The influences of the basic process parameters on the deposition rate and optical properties were studied. The results revealed the formation of a complex network among Si, C and N. The deposition rate decreased with increasing partial pressure of nitrogen. The increase of N2 flux resulted in the wider optical gap. The greater the sputtering power, the higher the deposition rate and the narrower the optical band gap.
Diamond film: a promising passivation film of porous silicon
Show abstract
In this paper homogeneous and dense diamond films with good crystalline quality are successfully deposited on porous silicon surfaces by the microwave plasma assisted chemical vapor deposition method. Photoluminescence measurements show that the CVD diamond film-coated porous silicon has a weak shift of emission wavelength as compared with the stored porous silicon without a diamond film, and its PL intensity almost doesn't change with time. It means the diamond film can efficiently stabilize the PL wavelength and intensity of porous silicon and provide a better passivation effect. In addition, due to its well-known high hardness, the CVD diamond film can improve the mechanical strength of PS surface, and is therefore a promising candidate for passivation of porous silicon in the future.
Defects eliminated by hydrogen and boron ion bombardment in polycrystalline diamond films
Yiben Xia,
Takashi Sekiguchi,
Weimin Shi,
et al.
Show abstract
Bombardments of hydrogen and boron ions are performed by applying a negative bias voltage to the substrate during microwave plasma chemical vapor deposition process. The size of (001) faces increases after hydrogen ion etching, while other grains are etched off. The surfaces of [001]- oriented films after boron dying are investigated by scanning electron microscope and cathodoluminescent (CL) spectra. The absence of the band-A emission in the CL spectra means a low density of dislocations in the films. It is the first time to indicate that the peak at 741.5 nm and the broad peak at around 575 and 625 nm in the CL spectra are reduced efficiently after boron doping in (001) polycrystalline diamond films. We propose that these phenomena could be explained in simple terms by a penetration or adsorption model through the lattice nets of the [001]-oriented surfaces.
Spectroellipsometric study of buried SiC layers formed by carbon implantation with a metal vapor vacuum arc ion source
Wensheng Guo,
Dan Zhu,
Zhihong Liu
Show abstract
SiC material is of intense interest because of its unique properties. Two samples were prepared by carbon ion implantation into silicon substrates with a metal vapor vacuum arc ion source at an energy of 65 keV and a dose of 1.0 X 1018 cm-2. Following implantation, one sample was annealed in nitrogen ambient at 1250 degree(s)C for 10 hours. Spectroscopic ellipsometry (SE) was performed on these two samples (as-implanted and annealed) over a spectral range of 400 - 2000 nm at a fixed incidence angle. In order to lessen the parameter correlation existing in the regression analysis, a multiple sample analysis method was employed. From the interpretation of SE spectra, structural and optical properties of the annealed and the as-implanted samples were derived. SE results confirmed the formation of a thick buried SiC layer for the annealed sample, but the optical properties of this buried layer were found to be different from those of bulk SiC material. For the as- implanted sample, the gradual carbon atom profile was simplified homogeneous composition layers with varying carbon concentrations. The carbon-rich region was treated as a single layer whose optical properties can be represented by one term of Lorentz oscillator, useful information could be obtained.
Microstructure and infrared optical properties of hydrogenated carbon nitride film
Jianhua Ju,
Yiben Xia,
Weli Zhang,
et al.
Show abstract
Microstructure and optical properties of nitrogen doped hydrogenated carbon (a-C:H:N) film deposited by rf plasma enhanced chemical vapor deposition method were studied by AFM, Raman, FTIR and IRE spectrometer. Absorption intensities of the peaks CNH (1600 cm-1), CN (2200 cm-1) and NH (3250 cm-1) in the IR spectra increase with the ratio of flux N2/CH4. Raman spectra show the shape of D and G band of a-C:H:N film varies slightly with the increase of N content, which means the main structures of N doped films are still diamondlike carbon films. However Gaussian fit results show that G band widens and the peak shifts to the low wavenumber in Raman spectra is that amorphous C3N4 structure formed in the film. AFM topographies and LFM images of a-C:H:N film confirm the amorphous C3N4 exists as several ten nanometers particles in the film. IRE spectra analysis results show that refractive index of the film in infrared band (2 - 14 um) slightly decreases from 1.8 to 1.6 with increased nitrogen content in the films.
New type of low-loss SiO2 Y-branch waveguide
Baoxue Chen,
Yifang Yuan,
Mamoru Iso
Show abstract
A novel Y-branch waveguide structure, in which a transitional guide is embedded between an incident channel and output branches, is presented. The transitional guide is used to improve the mode field matching between both waves supported by the incident and output waveguides. Numerical simulations show that this geometry can minimize the junction loss to 0.041 dB at 1310 nm and 0.052 dB at 1550 nm wavelength, respectively. Silica samples based on the design are fabricated by PECVD. Determination shows that the samples exhibit very low junction loss of about 0.08 dB and 0.09 dB at the two wavelengths.
Cubic boron nitride films prepared with different deposition times
Liudi Jiang,
A. G. Fitzgerald,
M. J. Rose,
et al.
Show abstract
Since the physicochemical properties of cubic BN (c-BN) makes it a very useful material for various industrial and technological applications, cubic boron nitride films have aroused much attention in recent years. In this paper, c-BN films have been prepared by tuned substrate rf magnetron sputtering with different deposition time, which correspond to different growth stages of the BN films. Fourier Transform Infrared Absorption spectroscopy, X-ray Photoelectron Spectroscopy and Atomic Force Microscopy (AFM) have been used to characterize the films. We have found a change of composition and microstructure of the films with different deposition times. AFM images of thicker films showed that there are two BN layers on the substrate and nucleation lines were observed on the lower BN layer of the film. We believe that the thickness difference between the edge and the center of the c-BN sheets of the film, which was also observed in the AFM profile, gives some information about the growth mechanism of c-BN films.
Heteroepitaxial film of silicon carbide grown on sapphire with a nitride buffer layer
Jianping Wang,
Yue Hao,
Jun Peng
Show abstract
Heteroepitaxial growth of single crystal Silicon Carbide (SiC) films on a novel compound substrate is discussed. Sapphire has successfully been used as substrate material for SOS structure. It shows good isolating properties. Comparing with silicon, its higher melt temperature makes this heteroepitaxial structure more sustainable for later high temperature device fabricate process. GaN and AlN are both wide band semiconductor, they are deposited on sapphire as buffer layer by the means of metal organic chemical vapor deposition to decrease the lattice mismatch between the substrate and the epitaxial layer, and SiC films was grown on buffer layer using APCVD. X-ray diffraction and scanning electron microscope are used to study the polytypes and morphology of the film. Some hexangular etching pits with size of 1 - 5 micrometers are found on the films.
Simulation study of multiple acceptable models existing in the interpretation of ellipsometric data
Wensheng Guo
Show abstract
Ellipsometry has been widely used in the measurements of thin film thickness and optical properties. The existence of multiple acceptable models has been confirmed in the interpretation of the measured ellipsometric data, which can degrade the measurement accuracy. How to eliminate this ambiguity is very important. In the present paper, we apply a simulation method to study the existence of multiple acceptable models and to seek the methods to alleviate such kinds of ambiguity. In the simulation study, a simple structure model (silicon dioxide film coated on silicon substrate) is used.
Bias voltage dependence of sp3 fractions of amorphous carbon films prepared by magnetically filtered carbon ion deposition studied by spectroscopic ellipsometry
Wensheng Guo
Show abstract
Amorphous carbon films (a-C) attract much attention for years because of its unique properties. However, its properties strongly depend on the preparation conditions. The determination of the sp3-bonded carbon fractions is very crucial. In this paper, a series of a-C films have been prepared on silicon substrates with different bias voltages using magnetic filtered carbon ion deposition. Spectroscopic ellipsometry (SE) has been applied to study these samples over the VIS-NIR spectral range. during the analysis of the measured ellipsometry data, Forouhi and Bloomer model, which was shown to be appropriate for amorphous diamond-like carbon films, is firstly applied to describe a-C films. The thickness and optical constants of a-C films can be obtained. Because our object is to directly determine the sp3-bonded carbon fractions, ia mixed composition film including sp3, sp2 components is assumed to represent the a-C films. Comparison of deduced values from these two models will be given. In order to verify the SE results, results obtained from optical absorption measurements have also been given and compared.
Textured growth of [100] diamond on Al2O3 ceramic substrate by microwave plasma chemical vapor deposition
Show abstract
[100]-textured diamond thin film on a rough and randomly oriented Al2O3 substrate has been achieved by MPCVD. The cyclic technique--the cyclic modulation of the H2 plasma (etching process) and CH4+H2 plasma (growing process)--has been applied during the growth stage with various etching/growth time ratios. The dependencies of properties and morphologies of the films on the etching time interval were well explained by the selective etching of hydrogen ions to non-[100]- oriented grains. The strong effects of different methane concentrations and substrate temperatures on the [100]-textured growth were also concluded. Growth mechanisms of [100]-textured diamond thin films on Al2O3 substrates were discussed based on the detailed results of Scanning Electron Microscopy, Raman Spectrum and X-ray Diffraction Spectrum.
Large-power piezoelectric ceramic transformer for providing computer CRT display high voltage
Liying Chai,
Donglin Xia,
Xianghong Zhang,
et al.
Show abstract
The working principle and characteristics of a large-power piezoelectric-ceramic-transformer (PCT) high voltage power supply are introduced for computer cathode-ray-tube monochromatic display application at first. The experimental results show that such a PCT high voltage power supply can completely meet the technological demands of computer monochromatic display. Moreover, the substitute of the conventional flying back transform with the piezoelectric ceramic transformer can improve the reliability of computer display, lower the cost, and decrease greatly the volume of high voltage winding.
Ferroelectric and Piezoelectric Films
Low-temperature preparation of SrBi2Ta2O9 ferroelectric thin film by pulsed laser deposition and its application to metal-ferroelectric-insulator-semiconductor structure with nitride buffer layers
Masanori Okuyama,
Hideki Sugiyama,
Toshiyuki Nakaiso,
et al.
Show abstract
SrBi2Ta2O9 (SBT) ferroelectric thin films have been deposited at temperatures as low as 500 degree(s)C by Pulsed Laser Deposition method on silicon nitride (SiNx) and silicon oxynitride (SiON), being insulating barrier against inter-diffusion. Metal-Ferroelectric-Insulator-Semiconductor (MFIS) structures has been fabricated using SiNx/SiO2/Si and SiON/Si and shows good C-V hystereses. It is confirmed by RBS analysis and C-V characteristics that the SiNx layer shows good barrier effect compared with SiO2 layer. It is also clarified from the direction and voltage-scanning speed of in the C-V curve that their MFIS structures show hysteresis induced by ferroelectric polarization. An Al/SBT/SiO2/Si structure shows a large memory window in C-V curve and a smaller shift than those in the Al/SBT/SiO2/Si structure. An Al/SBT/SiON/Si structure also shows good C-V characteristics whose gradient corresponding to the SiO2/Si interface trap is very small. Moreover, retention characteristics of the memorized states of the capacitance have been measured and analyzed, taking into account leakage current through ferroelectric and insulator films.
Preparation of PZT thick films by 0-3 composite method
Show abstract
PbZr0.40Ti0.60O3 (PZT) thick films are prepared on Pt/Ti/SiO2/Si substrate by a sol gel based 0 - 3 composite method. The influence of processing variable including powder characteristics, solvents feature and annealing condition is investigated. Microstructure and electric property of PZT thick films are examined and analyzed. Optimum parameters of process are suggested. PZT thick film of 10 micrometers thickness with excellent ferroelectric and dielectric properties has been obtained (Pr 24 (mu) C/cm2, (epsilon) r 680 at 1 kHz.
Effects of annealing temperature and time on the structure and ferroelectricity of sol-gel-derived Ba0.8Sr0.2TiO3 thin films from highly diluted precursor solutions
Jian-Gong Cheng,
Jun Tang,
Shaoling Guo,
et al.
Show abstract
Ba0.8Sr0.2TiO3 thin films were prepared from a high dilute precursor solution by a sol-gel process using a layer-by-layer heat treatment method. The annealing temperature ranged from 600 to 700 degree(s)C and the annealing time ranged from 5 to 15 min. Analysis by X-ray diffraction, Raman spectroscopy and field emission scanning electron microscopy showed that the annealing temperature and time strongly affected the structure of the films. The crystallinity and grain size of the films increased with the annealing temperature increasing. The grain size of the films annealed at 700 degree(s)C increased from 80 to 200 nm when the annealing time increasing from 5 to 15 min, and the film annealed at 700 degree(s)C for 15 min showed a pure columnar structure. Electrical measurements showed the ferroelectricity of the films annealed at 700 degree(s)C became better with the annealing time increasing. The film annealed at 700 degree(s)C for 15 min showed a remnant polarization of 3.5 (mu) C/cm2 and a coercive field of 83 kV/cm.
Characterization of PZT thick films derived from sol-gel techniques
Jinrong Cheng,
Laiqing Luo,
Zhongyan Meng
Show abstract
Crack free and preferred orientation Pb(ZrxTi1-x)O3 (x equals 0.45) thick films were prepared onto Pt(111)/Ti/TiO2/Si substrates by sol-gel and RTA techniques. Dielectric constants of PZT films increase with increasing the thickness. The as-prepared PZT films exhibited self-poling phenomenon and intrinsic piezoelectric responses. The PZT thick and thin films have different self- poling and poling effects. The internal bias field contributed to the intrinsic piezoelectric responses.
(Ba0.5Sr0.5)TiO3 thin films prepared by excimer laser method for dynamic random access memory
Hao-shuang Gu,
Guang Yang,
Jie Zhu,
et al.
Show abstract
(Ba0.5Sr0.5)TiO3 (BST) thin films have been deposited on Si(100) substrates by excimer laser (308 nm) ablation at 600 degree(s)C, the thickness of BST films is 400 nm. The capacitance-voltage characteristics and current-voltage characteristics of the BST films were studied. The dielectric constant of BST films is 300, and the dissipation factor is 0.015 at 1 MHz. The leakage current density is 2 X 10-9 A/cm2 at 2 V. The charge storage density is 35 fC/micrometers 2 at an applied electric field of 0.125 MV/cm.
Synthesis, dielectric characteristic, and microstructure of acetate-based (Ba,Sr)TiO3 thin films
Huyong Tian,
Weigen Luo,
Xinghua Pu,
et al.
Show abstract
A modified sol-gel process with acetate based precursor solutions for Sr-doped barium titanate thin films is presented. A four-step heating procedure was employed to prepare the Ba0.8Sr0.2TiO3 thin films. The thermal decomposition and crystallization temperatures of the precursors were determined by means of FTIR, TGA/DTA, and XRD measurements. The nonlinear C-V characteristics are due to strong depletion that can not originate from the BST/electrode interface, but must come internally from the BST films.
Sol-gel-derived PLZT (7/60/40) thin films on ITO/glass and LNO/glass substrates
Show abstract
The PLZT (7/60/40) thin films were prepared on ITO/Glass and LNO/Glass substrates by sol-gel process. The crack-free, uniform and dense films were obtained by post-annealing at the temperature between 450 degree(s)C and 600 degree(s)C. Pyrochlore phase was completely changed to perovskite phase above 570 degree(s)C with the increase of annealing temperature. The crystal buffer layer of ITO or LNO can promote the growth of perovskite. Films deposited on LNO/Glass substrates possesses good ferroelectric characteristics, Pr equals 18 (mu) C/cm2, Ec equals 55 kV/cm. The asymmetrical switching characteristics can be observed for the films deposited on LNO/Glass substrates, which is mainly due to the difference between top electrode Au and bottom electrode LNO.
Effects of Pt/RuO2 hybrid bottom electrodes on the electrical properties of BST thin films
Tianjin Zhang,
Hong Ni
Show abstract
The effects of the different bottom electrodes on the electrical properties of BST thin films have been investigated. The electrical properties of BST films spin- coated on Pt/RuO2 hybrid electrodes were improved compared to the films on RuO2 electrodes. The dielectric constant and dissipation factor of the 0.1 micrometers BST thin films on Pt/RuO2 bottom electrodes were 582 and 0.035 at zero bias voltage. The leakage current density of this film was 7.2 X 10-8 A/cm2 at 1.5 V which was about one order of magnitude lower than leakage current density (5.2 X 10-7 A/cm2 at 1.5 V) of BST capacitor with RuO2 films.
Applications of GGF method in analysis of ferromagnets
Bratislav S. Tosic,
Ljiljana D. Maskovic,
Radojica Maksimovic,
et al.
Show abstract
We apply the GGF (Generalized Green Function) method on a ferromagnet with magnetic impurities. In order to minimize the numerical calculations, we use Ising ferromagnet model. We are interested in temperatures around the phase transition in a ferromagnet, were Ising model gives real results which are often used in the literature. Investigations of a domain around the phase transition of a ferromagnet with impurities with the GGF method show that the phase transition is made on lower temperatures than in the case of ideal ferromagnet. In the point of phase transition, the derivative with respect to temperature of the ordering parameter is infinite as in ideal ferromagnet, bat this parameter does not vanish, it has a turning point.
Low-temperature preparation of BaTiO3 thin film by MOD and hydrothermal treatment
Zhiqiang Wei,
Huaping Xu,
Kaoru Yamashita,
et al.
Show abstract
BaTiO3 (BTO) thin films with perovskite structure have been prepared on Ti/Pt/Ti/SiO2/Si substrate using a combined process of conventional MOD process and hydrothermal method. BTO thin films with polycrystalline structure are obtained on silicon at low processing temperatures lower than 200 degree(s)C. The film thickness ranged from 0.20 to 0.84 micrometers . The structural and ferroelectric properties were investigated as a function of film thickness by x-ray diffraction, scanning electron microscopy, Raman spectroscopy and ferroelectric test system. The film retains the tetragonal perovskite structure with the (100) preferred orientation perpendicular to the film surface independent of film thickness. With increasing of thickness, polarization and coercive field of BaTiO3 thin films increased and shown the same trends.
Microstructure and optical properties of PbTiO3 film deposited on transparent sapphire by rf sputtering
Show abstract
PbTiO3 (PT) thin film with perovskite-type microstructure was synthesized directly on transparent sapphire using a rf-magnetron sputtering system with a composite target. The results show that the film is completely [111] oriented, and the lattice constant is larger than that of bulk PT material. The optical properties were calculated from the transmittance spectrum alone, and the dispersion was found to fit the single-term Sellmeier relation well. The minimum refractive index of the film is found to be 2.51, and the direct band-gap energy is estimated to be 3.65 eV from the linear fitting of the absorption coefficient to the Tauc plot of ((alpha) hv)2 vs hv.
Internal stress model for abnormal p-e hysteresis behavior of inhomogeneous Ba0.7Sr0.3TiO3 thin films
Yongping Ding,
Zhongyan Meng
Show abstract
The inhomogeneous Ba0.7Sr0.3TiO2 thin films characterized by Ba/Sr ratio fluctuation in micro-region hold the P-E hysteresis loop from low temperature to 150 degree(s)C, which is higher than the upper limited Curie temperature of Ba1-xSrxTiO3 (BST) solid solutions. The fluctuation of Ba/Sr ratio in sub-micron scope results in abnormal ferroelectric behavior for BST thin films. We suggest that this phenomenon can be explained by the internal stress effect caused by lattice mismatch in the inhomogeneous BST thin films. The inhomogeneity of the thin film was simulated according to the Gaussian distribution and the internal stress was calculated. The simulated results show that three kinds of typical stressed micro-regions exist in the inhomogeneous film. Especially, the Ba-rich micro-regions are compressed biaxially in film plane, which tends to promote the polarization normal to the film plane and so ferroelectricity of the Ba-rich micro- regions keeps to higher temperature. The internal stress model is reasonable to explain the ferroelectric abnormality of the thin films.
Infrared optical properties of PbZrxTi1-xO3 thin films
Zhiming Huang,
Chunping Jiang,
Pingxiong Yang,
et al.
Show abstract
Lead zirconate titanate PbZrxTi1-xO3 (PZT) thin films grown on Pt/Ti/SiO2/Si substrates with x equals 0.3 and 0.5 have been measured by infrared spectroscopic ellipsometry (IRSE). The IRSE data measured at an angle of incidence 75 degree(s) for x equals 0.3 and 70 degree(s) for x equals 0.5 are fitted by a proposed dielectric function formula. The refractive index and extinction coefficient of PZT with x equals 0.3 and 0.5 are determined in the spectral range of 2.5 - 12.5 micrometers . As the wavelength increases, the refractive index decreases, on the contrary, the extinction coefficient increases. The absorption coefficient for x equals 0.5 is greater about 1.5 times than that for x equals 0.3. The effective static charges of PZT is also derived by fitting the IRSE data. The values obtained are 1.792 +/- 0.031 and 1.838 +/- 0.0465 for PZT with x equals 0.3 and 0.5, respectively. The results reveal that charge transfer is not complete in PbZrxTi1-xO3 thin films.
Optical properties and the mechanism of BaxSr1-xTiO3 ferroelectric thin films prepared by sol-gel method
Chengyu Jin,
Zhongyan Meng
Show abstract
Ultraviolet-visible spectrophotometer was used to study optical properties of BaxSr1-xTiO3 (BST) system ferroelectric thin films derived by sol-gel process. Transmission spectrum show that the thickness, refractive index and the optical band gap of films on fused silica are changed with annealing conditions due to the densification with pore collapse and the phase transformation. The refractive index n of BaTiO3, Ba0.7Sr0.3TiO3, SrTiO3, and Ba0.7Sr0.3TiO3+1at%Mn thin films annealed at 800 degree(s)C are about 1.987, 1.902, 1.8 and 2.044 at 450 nm, 550 nm, 650 nm, and 550 nm, respectively. The bandgap of well-crystallized BST thin films is about 3.63 eV.
Optical properties of MBE GaAs films on SrTiO3 (100) substrates
Show abstract
This paper reports the molecular beam epitaxy growth of the GaAs films on the SrTiO3 (100) substrates. The microstructures of the films are characterized by XRD and SEM. SEM results show the different shapes of islands at different thickness. Micro-Raman studies show that the crystal lattice vibrations of the GaAs films are similar to that of GaAs bulk material. Using the photo modulated reflectance spectroscopy and photoluminescence measurement techniques, optical transitions close to GaAs band gap energy are observed, and large blue shifts are observed.
Characterization of smart PZT/NiTi heterostructure and membrane actuators
Show abstract
Combining sol-gel and Rf magnetron sputtering techniques, the smart PZT/NiTi/Ti/SiO2/Si and PZT/Pt/Ti/SiO2/Si heterostructures were prepared. Based on these material systems, two types of membrane actuators were designed and fabricated by using semiconductor micro-fabrication techniques. The 0.4 micrometers thick PZT thin films were used as actuator components, which were driven by sinusoidal or triangular wave current with different frequency. A single laser interference system was used to examine dynamic displacements. Compared with the PZT/Pt/Ti/SiO2/Si, the PZT/NiTi/Ti/SiO2/Si membrane actuators revealed more complexes and larger dynamic displacement. The highest deflect displacement of PZT/NiTi/Ti/SiO2/Si and PZT/Pt/Ti/SiO2/Si actuators occurred at the resonance frequency of 21.11 and 33.6 kHz respectively.
Properties of oriented (Ba,Sr)TiO3 thin films
Wen Ding,
Zhongyan Meng
Show abstract
Ba0.7Sr0.3TiO3 thin film/Ba0.5Sr0.5TiO3 buffer layer/Pt/Ti/SiO2/Si(100) multilayer structures were investigated. The buffer layer was obtained from a highly dilute solution (0.1 M) by sol-gel technique through rapid thermal process. X-ray diffraction patterns show that the upper main BST film is preferential oriented and good in-plane relationship of BST(111)//Pt(111). After using the buffer layer, the leakage current was reduced two orders of magnitude. The dielectric properties are much better than those of the thin films without buffer layer at the same thickness of 150 nm.
(Ta2O5)0.92(TiO2)0.08 thin films prepared by pulsed laser deposition
Show abstract
(formula available in paper)thin films have been deposited on Si substrate by 248 nm pulsed laser deposition in O2 gas environment. The structure and properties of (formula available in paper)polycrystalline thin film were investigated as a function of the deposition temperature, oxygen pressure and the substrate-target distance. The film with the thickness of 190 nm showed a dielectric constant (epsilon) r equals 56.
Comparison of PbTiO3 and BaTiO3 buffer layers for sol-gel-derived PZT thin films
Laiqing Luo,
Jinrong Cheng,
Zhongyan Meng
Show abstract
Pb(Zr,Ti)O3 (PZT) thin films with different thickness of PbTiO3 (PT) and BaTiO3 (BT) buffer layers were prepared by using a sol-gel spin-coating process respectively, followed by rapid thermal annealing. The experimental results indicated that both PT and BT could offer nucleation sites to lower the activation energy for the crystallization of PZT thin films, leading to a low annealing temperature and that PZT thin films with PT buffer layer annealed at 600 degree(s)C for 30 min are highly oriented. The ferroelectric properties of the films are strongly affected by the buffer layer. The different microstructures and dielectric properties of PZT films with PT and BT buffer layers are discussed.
Effect of PbO-coated layer on the microstructure and electrical properties of sol-gel-derived PZT thin films
Show abstract
Highly (100)-oriented lead zirconate titanate Pb(Zr0.52Ti0.48)O3 thin films with and without a PbO- coated layer were prepared on LaNiO3 (LNO)-coated silicon substrates by a simple sol-gel process. X-ray diffraction and atomic force microscope were applied to study the microstructure of the films. The ferroelectric and fatigue properties were measured by a RT66A system. An infrared spectroscopic ellipsometer was used to determine the thickness of the thin films. The leakage current density (J-t) was carried out with a Keithley 617 programmable electrometer. All measurements were conducted on a Pt-PZT- LNO capacitor structure. It was observed that the PbO-coated layer has no effect on the texture of the PZT thin films while it leads to a great improvement in the surface morphology. The results indicated that samples with a PbO- coated layer show higher remnant polarization and lower coercive field (18.6 (mu) C/cm2 and 58.5 kV/cm) than that of samples without PbO-coated layer. After 108 switching cycles, the net-switched polarization for the film with a PbO-coated layer does not show any drop.
Influence of top electrode of PZT capacitor on ferroelectric properties
Show abstract
PZT thin films were prepared by a modified sol-gel technique. Au was used as a top electrode of PZT capacitor. An influence of the process of the top electrode on the PZT ferroelectric capacitor was investigated. The relationship between remnant polarization, coercive electric field and the conditions of thermal treatment for the top Au electrode was discussed. The diffusion of Au and the interface between PZT and Au were analyzed by Auger spectra too. The proper heat treatment condition for optimal ferroelectric performance in the PZT capacitor was suggested.
Theoretical study of monolithic pyroelectric sensor arrays by thermal diffusion equation
Show abstract
Distributed parameter model is used for computation of the performances of single pixel of PZT ferroelectric thin film infrared uncooled focal plane array (IR-UFPA) with two kinds of thermal isolation structures. The detector performances are found to be related closely to the thermal isolation structure. The preferred thickness of pyroelectric thin film is in the region of 0.3 - 2 micrometers for pixel dimensions 50 X 50 and 100 X 100 micrometers 2. And the preamplifier current noise is the dominant noise when it more than 10-16 A(DOT)Hz-1/2 in PZT-UFPA device.
High dielectric tunability of Ba0.7Sr0.3TiO3 thin films by compositional fluctuation of Ba/Sr ratio in microregion
Yongping Ding,
Jianshen Wu,
Zhongyan Meng
Show abstract
The perovskite Ba0.7Sr0.3TiO3 thin films were fabricated by a sol-gel method with two kinds of microstructures, which are characterized were by fluctuant and homogeneous distribution of Ba/Sr ratio in micro-region respectively. It is found that the films with compositional inhomogeneity have higher dielectric tunability than that of the films with compositional homogeneity, 32% and 13% respectively at the bias field of 100 kv/cm. From the TEM observation, we found the micro-domain clusters with domain- width of 2 - 5 nm. We proposed that the compositional heterogeneity of Ba and Sr in `A' sites of (Ba1-xSrx)TiO3 induces the lattice-metastability and promotes the sensitivity of phase transition to electric field, which gives rise to higher dielectric tunability.
Theoretical investigation of the lattice vibration of GaAs/SrTiO3
Show abstract
The 1D atom chain with the multi-neighbor interactions is studied as a simplified model for the lattice vibration of ferroelectric with the long-range Coulomb interaction. The real space method to investigate the lattice dynamic of the non-perfect lattice is introduced. The combined 1D chain model to simulate GaAs/SrTiO3 system is proposed and the Raman spectrum is analyzed.
Substrate stress effect on phase transition properties of ferroelectric films from Landau theory
C. L. Wang,
X. S. Wang,
Y. Xin,
et al.
Show abstract
The influence of film/substrate stress on the phase transition property of ferroelectric thin films has been investigated from Landau theory. The stress is introduced through a coupling term of stress and polarization in the expression of free energy. The stress is assumed decreasing exponentially away from the substrate. Profiles and temperature dependence of polarization have been obtained for films with different strength of stress. The extensive stress reduces the polarization and shifts the Curie temperature to a low temperature; whilst the tensile stress enhances the polarization and shifts the Curie temperature to a high temperature, even higher than that of corresponding bulk Curie temperature if the tensile stress is strong enough.
Frequency characteristics of microwaves in gyromagnetic waveguides
Qi Wang,
Zhong Wu,
Songmao Li,
et al.
Show abstract
Systems involving nonlinear media and their interaction with electromagnetic waves are potentially useful in various important practical applications. In the last decade or so, the availability of high-quality gyromagnetic crystal has led to a growing interest in nonlinear magnetic waves14. The interactions of gyromagnetic crystals with infrared waves or microwaves have drawn much attention. And many distinguishing features have been discovered in gyromagnetic waveguides. Recently. we have studied the frequency characteristics of magnetic spatial solitons on the surface of two-sublattice uniaxia! antiferrornagnetic crystal241. The striking feature of the soliton is the existence of the frequency passband(s) and stopband(s) that can be switched into each other by varying the power. In this article we studied the TE (transverse electric) surface waves, in the region of microwave frequency, on the interface between a linear ferromagnet and a two sublattice Un iaxial nonlinear antiferromagnet.
Organic and Polymer Films
Photoinduced phenomena in polysilane films
Yoshikazu Nakayama,
Hiroyuki Inagi,
Tatsuo Fujii,
et al.
Show abstract
The photoinduced phenomena involving the photoscission of (sigma) bonds and photocreation of electronic defects have been studied systematically in films of (MeSiPh)n, (n- Hex2Si)n, (c-HeSiMe)n and (n-pentyl2Si)n as different polysilanes with and without phenyl substituents. The results have revealed the followings. A photoscission model established for (MeSiPh)n, where the photoscission cross-section is larger for longer segments and the reaction is thermally activated with the activation energies being distributed in a shape given by a combination with two exponential functions, is consistent with the processes in other polysilanes. The photoscission of (sigma) bonds creates defects to decrease the photoluminescence for polysilanes with phenyl substituents and some centers to enhance the photoluminescence for (c-HexSiMe)n and (n- pentyl2Si)n. The photoscission of (sigma) bonds occurs preferably at edges of the segments in (c-Hex2Si)n and at the inside of the segments for other three polysilanes. The orientation of (MeSiPh)n is effective to decrease the photoscission cross-section.
Fabrication and structure characterization of molecular deposition films
Qiangbin Wang,
Hongchen Gu,
Manglai Gao,
et al.
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Molecular Deposition (MD) is a new kind of nanometer ultrathin film, which is made by electrostatic attraction between opposite charges from cationic and anionic compounds. The fabrication and structure characterization of four different molecular deposition films, monolayer MD film, bilayer MD film, trilayer MD film and tetralayer MD film, were reported in this paper. According to the topography analysis of the clear Au substrate and monolayer MD film by atomic force microscope and to the element content results of the four different MD films by X-ray Photoelectron Spectroscopy, the depositing process of MD film is illustrated to be deposited by monolayer. The authors first put forward to calculate the charge distribution in the molecular of the MD film with ab initial calculation, and the results first theoretically explain why the depositing process of MD film is deposited by monolayer.
Sol-gel processing of inorganic-organic transparent nanocomposite hard coating
Haoying Li,
Yunfa Chen,
Guocheng Zhang,
et al.
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Inorganic-organic nanocomposite hard coatings were prepared on the PMMA surface using spinning technique with attempts of incorporating homogeneously nanosized AlOOH particles into the organic-inorganic hybrid matrices. The hybrid matrices were derived from 3-glycidoxypropyltrimethoxysilane and tetraethoxysilane. The AlOOH particles with different shapes (plate and needle-like) were prepared from aluminum isopropoxide and introduced into the hybrid sols directly. The coatings obtained are dense, transparent and their scratch-resistance is greatly improved, especially the contribution of needle-like particle is remarkable in comparison with the hybrid coatings without particle addition.
Electronic transport in amorphous 2,4,7-trinitro-9-fluorenone thin films
Ilia M. Kachirski
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The effect of trapping centers on the conductivity of amorphous 2,4,7-Trinitro-Nine-Fluorenone (a-TNF) is investigated by Space Charge Limited Current, Thermally Stimulated Current and Transient photoconductivity methods. It is found that electron traps in a-TNF have a smoothly varying distribution centered at about Et equals 0.29 +/- 0.04 eV with a dispersion parameter (sigma) equals 0.11 +/- 0.02 eV. The true activation energy at room temperature is Ea equals 0.45 +/- 0.03 eV. The zero-field extrapolated activation energy is Eao equals 0.65 +/- 0.02 eV. It was suggested that the transport of charge carriers in a-TNF is controlled by traps. Concentration of traps and drift mobility of electrons were evaluated.
Optical properties of thin solid films of J-aggregated dyes with long alkyl substituents
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Thin solid films of low-dimensional J-aggregates of amphyphylic cyanine dyes with various lengths of the N-alkyl substituents were obtained. It was shown that the chemical modification of dye helps obtaining the stable thin films of J-aggregates by spin-coating method without any stabilization polymer. The optical properties of the thin films are described.
Photoinduced polarization inversion of excitons in conjugated polymer films
Rouli Fu,
Junhao Chu,
Weimin Zheng,
et al.
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The study shows that, in a conjugated polymer, there exists a novel photo-induced phenomenon: a photo-induced polarization inversion, when a single-exciton is photoexcited and becomes a bi-exciton. The reason is that, in a conjugated polymer, a single-exciton displays normal polarization, whereas a bi-exciton exhibits negative polarization. The physical significance of negative polarization is explored. Photo-induced polarization inversion is an ultrafast switching process, which could be used to make photo-induced ultrafast switch devices.
Optical nonlinearity of MEH-PPV thin film
Yongping Bai,
Zonghao Huang,
Yuxiao Wang,
et al.
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The Z-scan technique was used to investigate the third-order optical nonlinearity of MEH-PPV and PPV thin-films. The measured magnitude of every x(3) of the two polymers was the order of 10-9 esu and the x(3) of MEH-PPV was larger than that of PPV's. At the same time, the crystal orbital program was used to calculate the electronic structure of two polymers. According to our discussion, the p-(pi) conjugation between the oxygen atom and the PPV main chain in the MEH-PPV should be one of the main reasons for MEH-PPV having the larger x(3) value.
Narrowing and enhancing effect of PL in PPV-film microcavity vessel
Zonghao Huang,
Xingyuan Liu,
Jiamin Zhao,
et al.
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The photoluminescent properties of an optical microcavity formed by a single layer of PPV film sandwiched between a quarter-wavelength distributed Bragg reflector and a metal Ag reflector was studied. The significant microcavity effect was observed. (1) The PL emission spectrum of PPV film is a wide band spectrum with two peaks at 510 nm and 550 nm, respectively. The PL emission spectrum of the microcavity shows 2 peaks, which is at 564 nm and 599 nm, respectively. The FWHM of the narrowed emission spectrum is 7 nm. The PL emission intensity of the microcavity at the resonant mode of 564 nm is enhanced by 19 times. (2) It was found that the peak of the microcavity is blue-shifted with the decreasing of emission intensity obviously when the detection angle is increased. We consider that this is a novel phenomenon and worth investigating further.
Synthesis and characteristics of metal-phthalocyanine-polymer composite films
Jianming Chen,
Jiancheng Zhang,
Yue Shen,
et al.
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Fe(III)-2,9,16,23-tertracarboxy-phthalocyanine (Fe (III)- taPc) was synthesized, and was bonded to polystyrene (PS) with covalence by Friedel-Crafts reaction to form a new polymer [Fe (111)-taPc-PS] [polymer (II)]. Uv-Vis and Infrared spectra indicated that Fe (III)-taPc was successfully bonded to PS. A photoreceptor device of sandwich structure consisting of alternate layers of polymer (II) and fullerene (C60) was prepared. The experiment results show that the photoconductivity of the photoreceptor is higher than that of the single-layer film of polymer (II) or C60, because of the charge-transfer effect between the layers.
Mass-statistical analysis of the properties of concrete
Ljiljana D. Maskovic,
Ratko Vujovic,
Bratislav S. Tosic
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Characteristics of several types of concrete were analyzed by the application of statistical methods, where the mass was the basic parameter determining the energy levels. Such method is mathematically simple yet leads to the results which agree satisfactorily with the experiments. The method was applied to the standard concrete and four types of polymerized concretes. It was concluded that only the polymer concrete (sand + india - rubber + water) has thermal isolation properties much better than the standard concrete. In all other cases, it was not possible to conclude that polymerization leads to any special advantages over the standard concrete.
Application of sol-gel thin films on the transparent hologram
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The application of sol-gel thin films on the transparent hologram is introduced in this paper. The plastic films coated with titanium dioxide using sol-gel process were embossed to form special patterns in micrometer scales and thus the transparent holographic thin films were made. AFM, SEM, ellipsometer and electrophotometer were used to characterize the TiO2 coating and the transparent hologram. The results show that the titania coating has nano-porous structure and the refractive index of the titanium dioxide coating is about 1.9. The diffraction efficiency of the titanium dioxide derived transparent holographic thin film is about 2.0%.
Phosphorescent emission from organic electroluminescent device
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A novel organic electroluminescent device with EuGd complex (Eu0.1Gd0.9)(TTA)3(TPPO)2 as an emitter is presented, and the characteristics of the device are investigated. The phosphorescence emission from the device are observed, which are discussed in terms of yields of phosphorescence from the triplet excited state of the Gd and Eu chelates due to the strong protuberance to the spin-orbit levels of the ligands by the paramagnetic Gd3+ ions. Both the photoluminescent and electroluminescent efficiencies at different temperature between 77 K and 300 K are measured by integrating sphere method. Our results show that the phosphorescent emission from the triplets excited sate might be useful to improve the quantum efficiency of organic electroluminescent devices.
White light organic electroluminescent device using a naphthalimide derivative as the emitter layer
Guoqiang Chu,
Xingyuan Liu,
Yun Liu,
et al.
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The electroluminescent (EL) device was fabricated using a naphthalimide derivative, N-Propyl-4-acetylamino-1,8- naphthalimide (PAAN), as the emitter layer, N,N'-diphenyl- N,N'-bis(3-methyl-phenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD) as the hole transport layer, ITO and Al as the anode and cathode, respectively. The EL emission of the device showed a white light. There are two peaks located at 491 nm and 669 nm in the EL spectrum. The emission peak at 491 nm comes from PAAN, while the emission peak at 669 nm results from neither the emission of PAAN molecule nor that of TPD molecule. It showed that the showing up of the new emission peak in the EL spectrum of the device is due to the exciplex formation at the PAAN and TPD bilayer interface.
White light emission from organic microcavity electroluminescent device
Guoqiang Chu,
Xingyuan Liu,
Dongjiang Wu,
et al.
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White light emission from an Organic light emitting device (OLED) with a microcavity was demonstrated. The structure of the microcavity OLED is Glass/DBR/ITO/TPD/Alq/Al. The microcavity is sandwiched between a distributed Bragg reflector and a metal Al reflective mirror. The ITO and Al were used as the anode and cathode, respectively. The TPD was used as the hole transport layer, and the Alq was used as the light-emitting layer, which has a typical broad bandwidth. A white light emission was achieved due to the multimode emission of the microcavity. The emission peaks of the microcavity were located at 462 nm, 555 nm and 615 nm, respectively.
Polarization properties of AlN single crystalline film
Yifang Yuan,
Baoxue Chen,
Shaofeng Qiu,
et al.
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An aluminum nitride single crystalline film on sapphire substrate was prepared by metal-organic chemical-vapor deposition. The method of waveguide measurement was employed for studying polarization properties of the single crystalline film. The theoretical analysis of polarization properties of the film and the optical properties of the TE and TM modes obtained from experimental results are given. It is first time to study on polarization properties of AlN single crystalline film.
Improved and enhanced thermal stable second harmonic generation of poled polymer films
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Melamine formaldehyde resin films with good optical quality could be fabricated easily by controlling the initial molecular weight. It was used as a matrix of nonlinear molecules. The optical properties of nonlinear molecules guest-host and covalent-bonded type of poled polymer systems were investigated. The optical propagation losses are around 1 dB/cm at 1072 nm for two kinds of films studied. The in situ corona poling second harmonic generation method and UV- visible absorption measurement were used. The experiment results showed that the materials we fabricated have improved second-order susceptibilities and higher thermal stability.
Design and fabrication of large single-mode rib polymer waveguides
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Mode-matching and effective-index methods have been used to analyze single-mode operation of optical polymer rib waveguides. The single-mode conditions have been obtained for rib waveguides fabricated from guest-host polyetherketone. The propagation loss of straight rib- waveguides is about 0.7 dB/cm at 1.3 micrometers wavelength.
Optics Films
Refractive index modifications and thermal properties of optical thin films with the prism coupler
Francois Flory,
Pascal Huguet-Chantome,
Ludovic Escoubas,
et al.
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The prism coupler can be used with a single beam to measure the refractive indices of isotropic or anisotropic single layers and of layers in multilayer stacks with an accuracy of 1. X 10-3. The refractive index modification with temperature can also be measured easily. The refractive index of a thin film can also change under illumination. A two-beam set-up has been developed to achieve a very high sensitivity of 1. X 10-6 on the refractive index changes. The nonlinear response of the layer's materials is mainly due to thermal effects. As well the diffusion length of the effect as the frequency response are measured even for low absorbing thin films. Examples of measurements are given. The heat equations permit to calculate the temperature distribution in the whole system so that both theoretical and experimental means can now be used to determine thermal properties of materials in thin film form.
Aluminum oxynitride rugate filters grown by reactive rf sputtering
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Aluminium oxynitride of graded-index films in which the refractive index changes continuously with thickness over the range 1.56 - 1.97 have been produced by reactive RF sputtering. Optical properties and other characteristics with deposition parameters have been investigated by Fractional Factorial Designs. We showed that the optical density of laser rejection filters can be made close to 5 and rejection wavelength can be chosen from 300 nm to infrared, coupled with good optical properties, hardness and adherence of these films. This work also showed that Factorial Design is a very efficient way to investigate or optimize the sputtering conditions.
Thickness monitoring method of infrared optical thin film irregular coatings
Minfeng Hu,
Furong Zhu,
Fengshan Zhang
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A kind of method proposed in dealing with irregular coatings during optical thickness automatic monitoring of coating process in this paper, and accordingly appropriate program algorithm is also listed here, comparison results between theoretical calculation and this application indicates its efficiency and utility.
Laser-induced damage of 1064-nm ZnS/MgF2 narrow-band interference filter
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The laser-induced damage thresholds, weak absorption and damage morphology of ZnS/MgF2 interference filters, which were designed to pass radiation around a wavelength of 1064 nm, have been examined. The theory about the electric field and the temperature rise in the multilayer was presented to explain the phenomena, which were observed in the experiments.
Preparation and structure investigation of AgI thin films in the silica capillary with a liquid phase deposition technique
Tianfa Wen,
Jianping Gao,
Jiuming Zhang,
et al.
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A metal (Ag)/dielectric (AgI) hollow glass waveguide is an attractive and flexible for easy handling mid-IR fiber used in the systems of Er:YAG lasers and high-power CO2 lasers radiation transmission. The quality of AgI thin films is one of the key factors, which greatly influence on the attenuation of waveguides. In this paper, with a liquid- phase deposition technique AgI thin films were successfully fabricated in the silica capillary, whose inner diameter was 0.53 mm. By means of XRD, AFM and AES, the process of iodination and the structure of AgI thin films were firstly investigated. It can be concluded that the AgI phase in the AgI films was a mixture of (beta) -AgI and (gamma) -AgI which converts slowly to (beta) -AgI in the iodination process. And the interface of AgI film, Ag film, and substrate is obviously distinguished and the thickness of AgI films can be measured directly about 0.625 micrometers .
Nanometer Films
Preparation and properties of scratch-resistant nanoporous broadband AR silica films derived by a two-step catalytic sol-gel process
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A new method to strengthen nano porous broadband anti- reflectance silica films is described. Silica sols were made from TEOS with a base/acid two-step catalytic process. Properties of silica films deposited with a dip-coat method are characterized with AFM, SEM, spectrophotometer and abrasion test. Experimental results show that an average reflectance of a glass coated with the nano porous silica films is less than 1% in the visible region; and that the two-step catalysis obviously strengthens the films. Finally, the strengthening mechanism of the films is discussed.
Resorcinol-formaldehyde-derived carbon aerogel films
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Carbon aerogels derived from organic sol-gel process and supercritical drying are novel porous materials with interconnect structures and higher electrical conductivity, which are considered to be ideal electrode materials for supercapacitors and rechargeable batteries. The objective of the research was to synthesize carbon aerogel films at ambient conditions. Resorcinol formaldehyde (RF) and carbon aerogel films have been produced with extremely high RC ratio (molar ratio of resorcinol to catalyst) followed by subcritical drying. The structure of the porous films was investigated using electron scanning microscope. The specific surface area was measured by using nitrogen adsorption and electrical conductivity was measured with four-probe method. It was found that with extremely high RC ratio, the porous structure of RF and carbon aerogel films can be controlled from micro to macro porous at ambient conditions. With respect to the application as electrodes for full cells, carbon aerogel films with different porous structures on the two surfaces have been also obtained through optimizing the sol-gel process.
Influence of some physical parameters on sol-gel-derived TiO2 thin films
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We present some physical parameters that affect the deposition of TiO2 films by the sol-gel method. A set of solutions with different TiO2 concentrations has been prepared. After synthesis of a set of TiO2 films by spin coating at different spinning speeds, the films were annealed at different temperatures. The viscosities of the start solutions were measured by a viscometer. The thickness of the films and their refractive index were measured by a monochromatic ellipsometer. The results showed that the thickness is decreasing exponentially with increasing spinning speed and decreasing linearly with temperature according to the relation d(nm) equals 104 - 0.125 T( degree(s)C) + 322e-S/900. The thickness of the films ranges from 56 to 129 nm. The refractive index is decreasing with the spinning speed and increasing with the temperature according to the relation n equals 1.791 + 6.107X10-4T( degree(s)C) + 1.733e-S/600. The refractive index of the prepared films ranges from 1.89 to 2.125 depending on annealing temperature and spinning speed. The viscosity of the start solutions increased with increasing the TiO2 concentration and the aging time. One week, after preparing the solutions the viscosity was found to be in the range of 1.4 to 4.4 mPa.s depending on the concentrations.
Formation and photoluminescence of self-assembled CdSe quantum dots
Yi Yang,
De Zen Shen,
Jiying Zhang,
et al.
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Self-assembled CdSe quantum dots (SAQDs) were fabricated by lower pressure metal organic chemical vapor deposition. 2MLs of CdSe coverage were deposited directly on GaAs(100) substrates. The formation process of CdSe SAQDs was monitored by atomic force microscopy. The formation of SAQDs below critical thickness was contributed to the effect of surface diffusion and releasing strain. The SAQDs PL spectrum was studied primitively.
Platinum silicide formation during pulsed laser annealing prepared by pulsed laser deposition
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The formation of PtSi ultra-thin film prepared by pulsed laser deposition during pulsed laser annealing has been studied. The growth sequence of the Pt2Si and the PtSi phases that evolved as the result of the diffusion reaction in the bilayers was monitored by X-ray photoelectron spectrum (XPS). The structure characteristics of PtSi thin films prepared by different preparing conditions were investigated by X-ray diffraction and XPS. Compared to conventional furnace anneal, we got superior uniformity, lower continuous film thickness of the resulting PtSi layers and smoother PtSi/Si interfaces.
Optical absorption properties of Ag nanoparticles embedded in partially oxidized amorphous silicon matrices
Lin Yang,
Guanghai Li,
Lide Zhang
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Nanocomposite films consisting of nanosized Ag particles embedded in partially oxidized amorphous Si matrices were prepared by the radio frequency magnetron co-sputtering method. Effects of the subsequent heat treatments at different temperatures ranging from 200 degree(s)C to 500 degree(s)C on the optical absorption properties of the films were investigated by spectrometry. The analysis shows that the blue shift of the plasmon resonance absorption peak position of Ag nanoparticles does not originate from the different oxidation degrees of Si matrices. A deviation from the (1/R) dependence of peak width on the particle size is probably due to the activity of the interface of the Ag nanoparticles and the Si matrix. The concept of a `surface resonance state' is introduced to discuss the blue shift of the peak position, the decrease of the peak intensity and the broadening of the peak width with decreasing size of the Ag particles together with `quantum size effect'.
Improvement of nucleation and growth of CVD diamond films by using explosive detonation nanodiamond
Lexi Shao,
Xiaoping Liu,
Shuwen Xue,
et al.
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Ultradispersed nanodiamond powder, which was synthesized by explosive detonation, was used as the coating material on the substrate for the purpose of enhancing nucleation density and promoting growth of diamond thin films. The experiment show that in comparison with the scratching pretreatment with diamond particles of approximately micrometers in diameter, the pretreatment with the nanodiamond powder can not only enhances nucleation density and film growth rate, but also improves the quality of the grown-up films significantly. The films by this pretreatment possess a lot of outstanding properties, such as compact structure, low surface roughness, fine facets and high crystalline quality. In contrast, the films on the scratched substrate exhibit significant second nucleation. As an important result, present experiment confirms that the pretreatment with the explosive detonation nanodiamond powder is very cost- effective economically; reproducible and non-damaging to the substrates of diamond film growth as well.
Nanocomposite multilayer optically variable coatings
Junxia Lu,
Zhenquan Lai,
Jiandong Wei,
et al.
Show abstract
The optically variable coatings can prevent counterfeiting of value documents. The cost of these coatings deposited by physical technology is very high. The sol-gel technology has the feature of a relatively lower cost and can be used to produce thin films with low refractive. We studied the optically variable coatings by the nano-composite technology (i.e., compound method of sol-gel technology and physical technology). The degree of color shift of some film structures with the viewing angle, including PET (substrate)/Cr/SiO2/Al and PET(sub.)/Cr/resin/Al etc., was calculated according to the color perception of human eyes. And the coatings produced were measured with the spectrometer.
Photoconducting properties of C60-toluene derivative films
Yue Shen,
Jiancheng Zhang,
Jianming Chen,
et al.
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This paper reports a study of fluorescence spectra and photoconducting properties of C60-toluene derivative. The fluorescence spectra show that C60-toluene derivative exhibits photoluminescence (PL) near 460 nm at room temperature in contrast to pure C60. But the PL intensity decreases after doping with I2. The photoconductivity of the films doped with I2 increases by one order of magnitude. The fluorescence analysis indicates that a charge-transfer complex of C60-toluene and I2 is formed.
Excited-state enhancement of third-order optical nonlinearity in a PPV derivative
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By using two-color femtosecond optically heterodyned optical Kerr effect experiment, we studied the real components of third-order nonlinearity of 2,5-dioctyloxy poly(p-phenylene vinylene) (DO-PPV). As pump wavelength was set near the absorption region of the material, the value of x(3) of DO-PPV was improved by one order of the magnitude comparing with that of nonresonant condition. We suggest that this enhancement result from the contribution of the excited state.
Photoconductivity property in composite films of poly (p-phenylene vinylene) derivatives and C60
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In this paper, we report the photoconductivity property of different poly (p-phenylene vinylene) (PPV)/C60 composite films fabricated by physical jet deposition technique. The results indicate that the photoconductive enhancement effect in PPV/C60 composite films depends on the different charge transfer efficiency at the interface between PPV derivatives and C60. The wavelength dependence and temporal evolution of photoconductivity of composite films were also measured in our experiments, and it was found that some PPV/C60 composite films showed quite better photoresponse and stability. It can be expected that the conjugated polymer/fullerene composite film optimized by an appropriate configuration have the potential application in thin-film photoelectric devices.
Micromechanics and Other
PMMA deep etching by O2RIE
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The microstructures that have relatively large height, high aspect ratio are very important for improving micro-devices' characteristics. In this paper reactive ion etching (RIE) of PMMA to create high aspect ratio micro-structures was described. We use Ni film as mask, which was patterned by usual photochemical etching, then use O2RIE technology to etch PMMA thick film (100 micrometers ). During the etching process, O2 pressure, etching power are very important for the etching results. There are grass-like residues remained on the etched surface until the PMMA was over etched, this phenomena is caused by the micro-mask effect. With over etched, the grass-like residues can be eliminated. The etched surface is very smooth and the side wall is vertical. The etching depth can get up to higher than 100 (mu) M and the aspect ratio is 5.
Microfabrication process study for stator winding of electromagnetic micromotor
Xiaolin Zhao,
Bingchu Cai,
Chunsheng Yang,
et al.
Show abstract
The micro-fabrication process for electromagnetic micro- motor stator winding, including adopting of new insulating material such as polyimide, is discussed in present study. A diameter of 2 mm electromagnetic micro-motor after adopting the new micro-fabrication process improves its performance. The motor output torque is 25% higher than before, and the operating temperature can reach 180 degree(s)C. Two examples of practical usage of micro-motor made by new process are given.
Measuring rotating substrate temperature by laser
Siyuan Lu,
Xiufang Ma,
Yuanhua Shen
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Temperature measurement by laser, which has the advantage of accuracy, rapidity and non-touching is suitable for measuring the temperature of substrate in vacuum coating plant. But till now this method was limited to measuring the stationary substrate, which couldn't meet the need of practical coating process because substrate rotating is essential for the uniformity of heating and coating. Since the thickness of the laser incident point changes with the rotating of the substrate, the interference fringe movement either caused by this reason or by temperature increment can't be distinguished. Recently we developed an automatic measuring system being able to measure the temperature of a rotating substrate. The installment of a micro-switch on the stationary frame and a projection on the turntable enables the computer to count the movement of interference fringes when and only when the substrate turns to an identical position. This development makes the method more useful in practical coating process. The design for the system is outlined, the measuring process is detailed, and an example of temperature measurement is presented.
Electroabsorption modulator integrated distributed feedback lasers for trunk line fiber communication
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Electroabsorption modulator integrated distributed feedback lasers have been fabricated using identical epitaxial layer approach. The influence of wavelength detuning on device characteristics is investigated to achieve optimum device performance. Gain coupling is introduced into the device to improve single mode yield and wavelength stability. Integrated light source modules have also been fabricated for 2.5 Gb/s trunk line applications.
InP and InGaAsP materials grown by solid-source molecular beam epitaxy
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We report all-solid-source molecular beam epitaxy growth of InP and InGaAsP semiconductor materials using a three- temperature-zone valved cracker cell based upon a homemade MBE system. High quality InP film was grown with surface defect density of 65 cmMIN2 and unintentional doping concentration of 1 X 1016 cm-3. Substrate temperature is found to play an important role on surface morphology, growth rate and p-doping characteristic of the InP epitaxial layer. For InAsyP1-y, incorporation of As with In seems to increase linearly for As fraction less than 0.6, and independent of As flux when As fraction is greater than 0.9. In0.56Ga0.44As0.94P0.06 lattice matched to InP has been grown with low temperature PL spectrum peak at 1507 nm and FWHM of 9.8 meV.
Characterization of the critical behavior of Ising thin films
Manuel I. Marques,
Julio A. Gonzalo,
Juan Romero,
et al.
Show abstract
Monte Carlo calculations of Ising thin films with equal area (LXL) and different thickness (D) have been performed for D<<L. The thickness dependence of the transition temperature has been determined by the Binder Cumulant method for free and periodic boundary conditions. We find that, in the case of very small thicknesses, the expected critical temperature finite size scaling dependence holds just for the case of periodic boundary conditions. The effective critical exponents for Ising thin films have been determined all through the crossover region and before it. We determine explicitly the dimensional crossover to the 2D behavior for all exponents and for both boundary conditions. A marked under-swing effect is found for the susceptibility effective critical exponent at values of the thickness around D equals 10. Scaling relationships are checked all trough the crossover region. They seem to hold better in a zone inside the crossover region with maximum extent for values of the thicknesses around D equals 5 and become more undefined below and above this D value.
Ferroelectric and Piezoelectric Films
Low-temperature preparation of highly (001)-oriented PZT thin films on Pt/Ti/SiO2/Si using LaNiO3 as a buffer layer
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LaNiO3 (LNO) thin films on Pt/Ti/SiO2/Si substrates were prepared by a simple chemical solution technique using lanthanum nitrate and nickel acetate as the start materials. A subsequent Pb(Zr0.50Ti0.50)O3 thin film annealed at 550 degree(s)C on the LNO-coated Pt/Ti/SiO2/Si substrate was prepared with a modified sol-gel process. The techniques of x-ray diffraction and scanning electron microscopy were used to characterize the structure of the films. All the electrical measurements were carried out in a Pt-ferroelectric-LNO/Pt configuration. Pt was sputter deposited into the sample using a mask and the bottom electrode (LNO/Pt) was etched to be exposed by ion etching technique. The resistivity of the LNO film and the ferroelectric and fatigue properties of the Pt/PZT/LNO/Pt/Ti/SiO2/Si capacitor were measured by the four-point probe method and RT66A system, respectively. The LNO film shows good metallic property, which is comparable with the LNO films derived from physical techniques. It is found that the PZT thin film annealed at 550 degree(s)C is pure perovskite phase with highly (001) orientation, even though the LNO layer is randomly oriented polycrystalline. The ferroelectric capacitor derived from these films displayed a good P-E hysteresis loop at an electric field of 200 kV/cm with Pr and Ec of 16.6 (mu) C/cm2 and 46 kV/cm. The PZT thin film capacitor does not show obvious drop in polarization up to 109 switching cycles.