Proceedings Volume 5118

Nanotechnology

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Proceedings Volume 5118

Nanotechnology

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Volume Details

Date Published: 29 April 2003
Contents: 11 Sessions, 75 Papers, 0 Presentations
Conference: Microtechnologies for the New Millennium 2003 2003
Volume Number: 5118

Table of Contents

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Table of Contents

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  • Nanotechnology: Carbon Nanotubes and Beyond
  • Small is Different
  • Nano-Optics
  • Nanoelectronics: Single Molecules to Nanotubes
  • New Characterization Techniques for Nanotechnology
  • Nanotubes: their Networks and Characterization
  • Nanotechnology of Life
  • Power of Computation for Nanotechnology
  • Metal Interconnects on the Nanoscale
  • Limits(?) of Nanoscale Electronics
  • Poster Session
  • Nano-Optics
Nanotechnology: Carbon Nanotubes and Beyond
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Exploring the carbon nanocosmos: doped nanotubes, networks, and other novel forms of carbon
Mauricio Terrones, Pulickel M. Ajayan, Florian Banhart, et al.
Particular attention will be focused on efficient self-assembly pyrolytic routes to large arrays (<2.5 cm2) of aligned C, CNx and BxCyNz nanotubes (15-80 nm od and < 100 microns length). In general, these 'hollow' fibres do not easily break upon bending and may behave as shock absorbing fillers in the fabrication of robust composites. The electronic and field emission properties, as well as the density of states (DOS) of CNx and BCx nanotubes using scanning tunneling spectroscopy (STS) will be presented. We further demonstrate that the presence of N and B are responsible for introducing donor and acceptor states near the Fermi Level. Novel applications of these doped materials will also be discussed. Finally, it will be shown that high electron irradiation during annealing at 700 - 800 °C, is capable of coalescing and joining single-walled nanotubes (SWNTs). Vacancies induce the merge via a zipper-like mechanism, imposing a continuous reorganization of atoms on individual tube lattices within the adjacent tubes. Other topological defects induce the polymerization of tubes and creation of 'Y', 'T' and 'X' nanotube junctions. The latter results pave the way to the fabrication of nanotube contacts, nanocircuits and strong 3D composites using irradiation doses under annealing conditions.
Interaction of molecular and atomic hydrogen with single-wall carbon nanotubes
Julio A. Alonso, Juan S. Arellano, Luis M. Molina, et al.
Density functional theory is used to study the interaction of molecular and atomic hydrogen with (5,5) and (6,6) single wall carbon nanotubes. Molecular physisorption is predicted to be the most stable absorption state, with the molecule at a distance of 5-6 a.u. from the nanotube wall. The physisorption energies outside the nanutobes are about 0.07 eV, and twice as large inside. This means that uptake and release of molecular hydrogen from nanotubes is a relatively easy process, as many experiments have proved. A chemisorption state with the molecule dissociated has also been found, with the H atoms much closer to the nanotube wall. However, this dissociative state is separated from the physisorption state by an activation barrier of 2 eV or more. The dissociative chemisorption weakens C-C bonds, and the concerted effect of many incoming molecules with sufficient kinetic energies can lead to the scission of the nanotube.
Large-scale growth of aligned tungsten oxide nanorods
Tungsten oxide nanorods can be fabricated in large scale at low temperatures on planar substrates. The structure and the optical properties of the nanorods are investigated by SEM, TEM, X-ray diffraction and optical spectrometers, respectively. The dependence of the orientation preference of the nanorods on the growth conditions is also investigated.
Small is Different
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Polymer substrates as a medium for motion of nano objects
Svetlana A Prokhorova, Alexey Kopyshev, Ayothi Ramakrishnan, et al.
We discuss a novel pathway to move nano objects on or by a supporting polymer substrate. The idea is to use a periodically switchable topography of the underlying polymer surface, induced by two states: structured and flat. The polymer system we focus on are surface attached polymer chains ('polymer brushes') of two types: (i) diblock-copolymer chains densely grafted with one end to the solid substrate and (ii) a mixed brush composed of the mixture of A and B homopolymers, A-B blocks and random A-B chains. Recently, we have shown that both these brushes undergo reversible transitions between lateral and vertical microphase separation. Since the details of the switching process are crucial for understanding transport properties, we report here in-situ AFM observation of the switching process of a poly(methylmethacrylate-b-glycidylmethacrylate) p(MMA-b-GMA) diblock-copolymer brush and PMMA-PGMA mixed brush. The transition is induced by cyclically pumping chloroform and toluene vapours through the liquid cell: they represent a good (chloroform) and a bad solvent (toluene) to the brushes. We then report on results of motion and organization processes of silica particles induced by switching the polymer carpet in vapour and compare the results with the organization process of the same nano objects performed in liquids.
Deformations and thermal stability of carbon nanotube ropes
As it is well known, carbon nanotubes may be one fold (Single Wall Carbon Nanotubes, SWCNT) or contain several cylinders nested one inside another (Multi Wall Carbon Nanotubes, MWCNT). SWCNT's, in many cases, self-organize into crystalline bundles (set of a few to a few hundred aligned tubes arranged in a two-dimensional triangular lattice in the plane perpendicular to their common axes). A thorough understanding of carbon nanotubes (CNT's) includes the detailed and comprehensive characterization of their possible deformations due to interactions with a substrate or with other tubes, and their stability under thermal treatment or chemical agents. In this communication we concentrate on i) the structural characteristics and ii) the structural transformations under thermal treatment of bundles of SWCNT's. i) Deformations of the tubes away from their ideal circular cross sections may have non trivial effects in their properties such as conductivity or phonon spectrum. We have being able to synthesize novel crystalline bundles of 'polygonized' SWCNT's. Our finding opens up the question of what is the equilibrium configuration of a lattice of aligned tubes and the possibility of the existence of several metastable structures which could be obtained depending on the growth conditions. To shed some light on this problem we have performed extensive molecular dynamics simulations of lattices of monodisperse armchair and zigzag SWCNT's as a function of tube diameter. We find several metastable structures of the lattice characterized by different tube cross sections, hexagonal, rounded-hexagonal and circular, and increasing cell volume. The competition between different tube shapes is analyzed and compared to experiments. ii) On the other hand, CNT's are metastable; (the most stable form of carbon is graphite). Due to their metastable character CNT's may transform into more stable structures under the appropriate annealing conditions. We have found that bundles of SWCNT's coalesce forming MWCNT's, containing from two to six nested tubes, under thermal treatment at high temperatures. This structural transformation is confirmed by extensive Molecular Dynamics (MD) simulations. The simulations suggest a 'patching--and--tearing' mechanism for the SW-- to MWCNT's transformation underlying the 'concerted' coalescence of the tubes that begins with their polymerization. Tubes of different sizes and chiralities are considered.
Market Evolution from microsystems to nanosystems
A revision of 1998 report from the NEXUS task force MST market analysis results in a projected market growth form $ 30 billion in the year 2000 to $68 by the year 2005. With new emerging products and applications the market with rise 20% annually, which is 2% higher than previous predicated. The main fields of application are IT peripherals, bio-medical, automotive, household and telecommunications. The scope of products and application will be extended within the next decade with the beginning matureness of nanotechnology.
Nano-Optics
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Laser-induced nanoparticle formation
Peter Heszler, Lars Landstrom
General aspects, such as control of size-distribution, agglomeration/coagulation and material properties are discussed for laser-based generation of nanoparticles. Two model systems are presented, i) laser-assisted chemical vapor deposition (LCVD) of tungsten nanoparticles by H2 reduction of the excited tungsten fluoride precursor gas (WF6) and ii) laser ablation (LA) of tungsten and carbon targets at atmospheric pressure for W and C nanoparticle formation. Size-distributions of the nanoparticles are determined by electron microscopy (TEM) for the LCVD depositions and in-situ by a differential mobility analyzer and a particle counter for the LA experiments. The tungsten deposition rate is measured by X-ray fluorescence spectroscopy; materials characterization is performed by electron and X-ray diffraction techniques, Raman spectroscopy and X-ray photoelectron spectroscopy. The agglomeration/coagulation for LCVD is followed i) by the size-distribution measurements and ii) by optical emission spectroscopy of the emitted thermal (black-body) radiation of the laser-heated nanoparticles. Additionally, optical spectroscopy of the thermal radiation allows determining the temperature of the laser-heated nanoparticles. During laser ablation the size distributions and the amount of desorbed/ablated material are monitored for different ArF excimer laser parameters (fluence, rep. rate). The main and most important aspects of the presented techniques are compared and discussed.
Optical films with nanometer structures
Jing Zhu, Ding Rong Ou, Ruo Jian Zhu, et al.
The optical properties of random Sb-SiN films in which Sb nano-particles are randomly dispersed were studied. Results show that the random Sb-SiN films possess high transmittance and low optical absorption. Additionally, some optical nonlinear phenomena of the random Sb-SiN films have been observed. Based on the special optical properties of random Sb-SiN films, they can be applied in many fields, for example, optical storage and optical microscopy. When the random Sb-SiN film was prepared close to a phase-change-recording layer, it decreases the threshold of input power for recording and speeds up the phase transition of recording media, and also improves the resolving power of readout system. On the other hand, while the random Sb-SiN films were deposited on the slide glass used in far-field optical microscopy, it obviously improves the resolving power of optical microscope and reduces the value of resolution limit to less than half of the value calculated by the expression given by Lord Rayleigh.
Toward nanostructuring with femtosecond laser pulses
Frank Korte, Juergen Koch, Carsten Fallnich, et al.
The development of a simple laser-based technology for the fabrication of two-dimensional nanostructures with a structure size down to one hundred nanometers is reported. The ability to micro- and nano-structure is very important for the fabrication of new materials and multifunctional microdevices. Photolithographic technologies can be applied only for plane surfaces. Using femtosecond laser pulses one can fabricate 100 nm structures on arbitrary 3D-surfaces of metals and dielectrics. In principle, the minimum achievable structure size is determined by the diffraction limit of the optical system and is of the order of the radiation wavelength. However, this is different for material processing with ultrashort laser pulses. Due to a well-defined threshold character of material processing with femtosecond lasers one can beat the diffraction limit by using tightly focused femtosecond laser pulses and by adjusting laser parameters slightly above the processing threshold. In this case only the central part of the beam can modify the material and it becomes possible to produce sub-wavelength structures. In this presentation, sub-wavelength microstructuring of metals and fabrication of periodic nanostructures in transparent materials are demonstrated as promising femtosecond laser-based nanofabrication technologies.
Surface morphology and photoluminescence of InAs quantum dots grown on [110]-oriented streaked-islands under ultralow V/III ratio
Shiang Feng Tang, Shih Yen Lin, S. T. Yang, et al.
We present results concerning the influence of organometrallic vapro phase epitaxy (OMVPE) grwoth paramters under ultra low V/III ratio on the surface morphology and temperature-dependent photoluminescence. Due to Indium segregation inteh 2D InAs wetting layers and accumulation from multi-atomic step edge on (001) 2° off toward (111) n-type GaAs substrate, self-assembled InAs quatnum dot formation takes pace aroudn or above 2D InAs islands while ~ one monolayer of InAs is regularly grown on GaAs substrate. It is attributed that the desorbed Indium Recaptured and nucleated effect on edge along (110)-orientation of GaAs substrate.
Chemical etching effects in porous silicon layers
Daniel Navarro-Urrios, Cecilia Perez-Padron, Eduardo Lorenzo, et al.
We have studied the properties of p+-type doped porous silicon, formed by electrochemical etching, when is left in presence of the electrolyte for different post-etching times. Using an interferometric technique, we monitored the formation of the porous silicon layer during the electrochemical treatment as well as the change of its porosity during the post-etch process due to a chemical dissolution mechanism. These data are complemented with a study of the photoluminescence modification for different post-etching times.
Nanostructured holographic recording utilizing InOx photorefractive thin films
Photorefractive materials consistute a fast growing branch of nonlinear optics. The materials most commonly designated as photorefractive involve a charge-transport-induced non-linearity. Recent work on simple oxides such as InOx, prepared by dc sputtering, has demonstrated changes in their conductivity of more than six orders of magnitude after low power UV illumination and subsequent oxidation in and Ozon atmosphere. The structural changes on these films induced by growth parameters were studied by x-ray diffraction and Atomic Force Microscopy (AFM). Between Room Temperature (BRT) and 300°C it was found that there is a preferred growth along the (222) axis while AFM revealed a roughness increase as a function of film thickness and a tendency for nanoscale grains to be overgrown by larger neighbors. Based on these light induced charge-transport changes of InOx, ambient holographic recording process characteristics were obtained using a UV laser radiation at 325nm. It was realized that there exists a direct correlation of the recording efficiency with conductivity changes under ambient conditions. Evidence is provided for the presence of two coexisting processes in the recording regime.
Nanoelectronics: Single Molecules to Nanotubes
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Large-scale integration of carbon nanotubes into silicon-based microelectronics
Georg S. Duesberg, Andrew P. Graham, Maik Liebau, et al.
The integration of carbon nanotubes (CNTs) into conventional silicon-technology with potential applications as interconnects, transistors, memory-cells, and sensors is an promising goal. Theoretical and experimental results indicate that CNT-based devices can outperform conventional silicon microelectronics. Concepts for the creation of vertical interconnects and transistors made out of CNTs, which allow a large scale integration, are presented. A vital step for their realization is the synthesis of individual CNTs with controlled diameters at lithographically predefined locations. Employing catalyst mediated Chemical Vapor Deposition (CVD) isolated CNTs have been grown out of holes in silicon dioxide which have been created by optical lithography. This allows the precise placement of individual CNTs on silicon substrates. Furthermore, the diameter of each CNT adjusts to the hole size, which makes it possible to control this important property separately for individual CNTs. In combination with the vertical integration concept those findings constitute a milestone in the parallel manufacture of nanotube-based devices with scalable batch processes.
DNA-based biomolecular electronics: theoretical aspects of charge transmission through DNA
Inderpreet Kaur, Lalit M. Bharadwaj, Rakesh Dabas, et al.
Transmission properties of molecular bridges between conducting leads, especially DNA,as DNA can be synthesized in any sequence, orientation and length, trapped between the nanoeletrodes has drawn many researchers interest to understand how far and how freely charges can move along the stacks of base pairs in DNA. Considering Donor-Bridge-acceptor system, conduction properties of DNA are described in terms of attenuation parameter β and current density J(x), the β value ranges from 0.1-1.4 Å-1 for DNA and lower values of which corresponds to weak distance dependence of charge transfer and higher to strong distance dependence. Studying HOMO-LUMO distribution and energy gap, 'Critical' Bridge length Nx is determined, less than this many no. of molecules, means N < Nx, promotes super exchange tunneling transition and If N > Nx transition is through hopping. The paper also discusses the simulation of DNA based electronic components e.g. diode and transistors.
Electronic transport properties of incipient graphitic domain formation in PAN-derived carbon nanofibers
Wang Yu, Idalia Ramos, Rogerio Furlan, et al.
We have measured the electronic transport properties of PAN based nano-fibers obtained by electrostatic deposition from 1.9 K to room temperature and carefully fitted the temperature and magnetic field dependence of these measurements to pertinent theoretical models It is noteworthy that the anomalous temperature and magnetic field dependence of conductivity have been found in carbon fibers with diameter larger than 10 microns, and mostly, carbonized at heat treatment temperature (HTT) higher than 1000°C. It is interesting to evaluate the scaling of such effects that is, if similar effects exist after the diameter is reduced into the nano scale. This paper reports such an attempt after the authors obtained carbon nano-fibers by electro-spinning and measured their electronic transport properties. Single carbon nano-fibers were deposited on silicon oxide coated silicon wafer, and with a lithographed gold contact pattern array. The length and cross-section area of the fibers was measured using an optical microscope and a scanning probe microscope (SPM) operated in tapping mode. Four-probe resistance measurement was conducted continuously 300K down to 1.9K, without any applied magnetic field. Resistance was also measured at 1.9, 3, 5 and 10K when the applied magnetic field, perpendicular to the fiber, increasing and decreasing continuously between -9 and 9 Tesla twice. To suppress the possible heating effect, the total measuring power was limited to 5nW. At all the four investigated temperatures, MR is negative. Its magnitude increase with B and decrease with T. It is noteworthy that MR=-0.75 at T=1.9K and B=9T, the highest MR for such system as far as the authors knowledge.
Effect of substituted derivatives on carrier transport in organic polymers
This work examined the relationship between the zero field carrier mobility and the change in potential distribution caused by different subgroups within a conjugated polymer such as OC1C10 - PPV. It was observed that the potential profiles with different values of energy minimum could have a strong bearing on the trapping of carriers and a shallow profile involving a lesser number deep (trap) states also gave rise to short retention time for the trapped carriers. This had the effect of enhancing the zero field mobility. For the structures examined, it appeared that shorter subgroups attached to the polymer backbone (Structure D) would result in a shallower energy trough and the same effect was observed for a geometrically balanced structure with two subgroups attached to the opposite ends in the polymer backbone (Structure C).
Effect of molecular adsorbates on electron transport in carbon nanotube
Ranjit Pati, Laxmidhar Senapati, Yiming Zhang, et al.
Using first-principles gradient-corrected density functional theory, we have studied the adsorption of H2O molecule on a single-wall carbon nanotube and found that H2O molecules adsorbed on the nanotube surface with hydrogen forming a weak bond with the surface carbon atom. Subsequently, Green's function based Landauer-Buettiker multichannel formalism is used within tight-binding model to calculate the electron transport. Our calculations suggest that the conductivity of the nanotube is reduced with water adsorption is consistent with recent experimental measurements. We have also investigated the effect of endohedral doping in nanotube with C60 molecule on its electron transport property and ofund that encaging of C60 molecule in a semiconducting nanotube enhances the conductivity of the tube. We have compared our conductance results with available experimental results. The decrease of electronic conduction due to water adsorption and the increase in conductivity due to C60 encaging is explained on the basis of charge transfer between the host nanotube and guest molecules.
New Characterization Techniques for Nanotechnology
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Regularly coiled carbon nanotubes
Regularly coiled carbon nanotubes, their structure and formation mechanism are puzzling questions since many years. The first models were based on the very regular incorporation of a small fraction (of the order of 10%) of non-hexagonal (n-Hx) rings: (pentagons and heptagons) in a perfect hexagonal (Hx) lattice. It is difficult to understand by which mechanism takes place such a regular incorporation of isolated n-Hx rings. In the present work a new family of Haeckelite nanotubes is generated in a systematic way by rolling up a two-dimensional three-fold coordinated carbon network composed of pentagon-heptagon pairs and hexagons in proportion 2:3. In this model the n-Hx rings are treated like regular building blocks of the structure. Cohesion energy calculation shows that the stability of the generated 3D Haeckelite structures falls between that of straight carbon nanotubes and that of C60. Electronic density of states of the Haeckelite computed with a tight-binding Hamiltonian that includes the C-μ orbitals only shows that the structures are semiconductor. The relation of the structures with experimental observations is discussed.
New challenges in Rutherford backscattering spectrometric (RBS) analysis of nanostructured thin films
Aliz Simon, Zoltan Kantor
When determining exact quantitative elemental composition of thin films, the ultimate solution is often an application of ion beam analytical techniques, mostly Rutherford Backscattering Spectrometry (RBS). This technique is usually treated to be insensitive for the density of the layers, however, in some cases it became obvious that surface roughness, voids and precipitates may affect the shape of the spectral signature of a particular chemical element. In order to use RBS efficiently for nanostructured thin films, it is essential to know how the given surface topography (or above parameters) influences the relevance of the measurements. In this paper we present our contributions to the topic: the outline of a new simulation of RBS spectra of rough and nanostructured thin layers; and a brief discussion how the character and parameters of the geometrical structure (shapes, filling factors, etc.) can affect the interpretation of the measured data.
Nanopatterning by AFM nano-oxidation of thin aluminum layers as a tool for the prototyping of nanoelectromechanical systems
Cristina Martin, Zachary Davis, Esko Forsen, et al.
Nanolithography based on atomic force microscopy is a widely used techniques for the prototyping of nanostructures. This technique has attracted great attention due to its simplicity, versatility and precise control. Oxidation is performed at normal atmosphere where the meniscus connecting tip and surface plays a key role. The present study describes the electrical conductivity of this nanometer-size meniscus. By acquiring force vs distance curves, we determine the relationship between the tip-surface separation and electrical current. It is observed an increase of the electrical current at small finite separations (< 2 nm) due to a change in water meniscus properties, and a decrease of electrical current when the meniscus is elongated.
Nanomechanics for specific biological detection
Mar Alvarez, Laura G. Carrascosa, Javier Tamayo, et al.
Nanomechanical biosensors have emerged as a promising platform for specific biological. Among the advantages are direct detection without need of labelling with fluorescent or radioactive molecules, very high sensitivity, reduced sensor area, and suitability for integration using silicon technology. Here we have studied the immobilization of oligonucleotide monolayers by monitoring the microcantilever bending. Oligonucleotides were derivatized with thiol molecules for self-assembly on the gold-coated side of a microcantilever. The geometry of the binding and the surface density were studied by mixing derivatized oligonucleotides with spacer self-assembled monolayers and by controlling the oligonucleotide functional group form. These results are compared with fluoresencent and chemiluminescence techniques. Furthermore, we present the first results of direct pesticide detection with microcantilever-based biosensors. Herbicide DDT was detected by performing competitive assays, in which the cantilever was coated with a synthetic DDT hapten, and it was exposured to different rations between the monoclonal antibody and the DDT. A new technique is presented for the detection of the nanomechanical response for biosensing applications, in which the resonant frequency is measured with about two orders of magnitude higher sensitivity. The low quality factor of the microcantilever in liquid is increased up by using an active feedback control, in which the cantilever oscillation is amplified and delayed and it is used as a driving force. The technique has been applied for the detection of ethanol, proteins, and pathogens.
Laser-induced thermal characterization of nano Ag metal dispersed ceramic alumina matrix
Sajan D. George, Aji A. Anapara, K. G. K. Warrier, et al.
In this paper, we report the measurements of thermal diffusivity of nano Ag metal dispersed ceramic alumina matrix sintered at different temperatures using laser induced non-destructive photoacoustic technique. Measurements of thermal diffusivity also have been carried out on specimens with various concentration of nano metal. Analysis of the data is done on the basis of one-dimensional model of Rosencwaig and Gersho. The present measurements on the thermal diffusivity of nano metal dispersed ceramic alumina shows that porosity has a great influence on the heat transport and the thermal diffusivity value. The present analysis also shows that the inclusion of nano metal into ceramic matrix increases its interconnectivity and hence the thermal diffusivity value. The present study on the samples sintered at different temperature shows that the porosity of the ceramics varies considerably with the change in sintering temperature. The results are interpreted in terms of phonon assisted heat transfer mechanism and the exclusion of pores with the increase in sintering temperature.
High-voltage atomic force microscopy: a new technology for nanoscale optical devices
Yossi Rosenwaks, Michel Molotskii, Alex Agronin, et al.
Reversal of the spontaneous polarization direction under an applied electric field is a basic property of ferroelectrics. However the traditional techniques used for fabrication of domain gratings have been able to produce domains not smaller then 2 micrometers. Sub-micron and nanometer scale domains may be fabricated using atomic force microscopy based techniques; however, to date there was no success in fabricating stable domains that elongate without widening throughout thick ferroelectrics. A breakthrough in the field emerged with the recent development of the high voltage atomic force microscope that enabled to obtain sub-micrometer stable domain configurations in bulk ferroelectrics. Diverse stable domain configurations were fabricated in several ferroelectric crystals like LiNbO3 and RbTiOPO4. Studying the influence of the applied high voltage, and the tip velocity on the domain strips has allowed fabricating domain gratings (with a domain width of 590 micron) useful for backward propagating quasi-phase-matched frequency conversion. It is found that string-like domains are formed due to the super-high electric field of the high voltage atomic force microscope tip. The domains, which resemble channels of an electrical breakdown, nucleate under an electric field of around 10 in a power of seven Volts per centimeter at the ferroelectric surface, and grow throughout the crystal bulk where the external electric field is practically zero. A theory explaining the shape of the formed domains shows that the driving force for the domain breakdown is the decrease of the total free energy of the system with increasing domain length.
Scanning force microscopic investigations of the femtosecond pulse laser ablation of indium phosphide in air
Jorn Bonse, Martin Munz, Heinz Sturm
Laser ablation of single-crystalline indium phosphide (InP) was performed in air by means of linearly polarized Ti:sapphire femtosecond-pulses (800 nm, 130 fs, 10 Hz). As a result of the first laser pulses, several morphological changes (crater formation, rim formation, ripple structures and cones) were observed. These effects were explored using force modulation microscopy (FMM), a technique based on scanning force microscopy (SFM), allowing the simultaneous imaging of both topography and local stiffness at a high lateral resolution. The first laser pulse induces the formation of a protruding rim (height <20 nm, width ~300 nm) bordering the ablated crater. A Fourier-analysis of the multi-pulse generated topographies reveals the formation of wavelength-sized periodic ripples (modulation depth <100 nm) with an orientation perpendicular to that of the electric field vector of the laser radiation. Besides these morphological alterations, also material modifications were observed in the irradiated regions by means of the FFM technique. Within the ablated craters, local stiffness variations were found revealing an inhomogeneous material composition/structure as a consequence of the femtosecond pulse laser treatment.
Nanotubes: their Networks and Characterization
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Building and testing organized architectures of carbon nanotubes
Robert Vajtai, Bingqing Wei, Yung Joon Jung, et al.
This talk will focus on the directed assembly of multiwalled carbon nanotubes on various substrates into highly organized structures that include vertically and horizontally oriented arrays, ordered fibers and porous membranes. The concept of growing such architectures is based on growth selectivity on certain surfaces compared to others. Selective placement of ordered nanotube arrays is achieved on patterned templates prepared by lithography or oxide templates with well-defined pores. Growth of nanotubes is achieved by chemical vapor deposition (CVD) using hydrocarbon precursors and vapor phase catalyst delivery. The new technique developed in our laboratory allows enormous flexibility in building a large number of complex structures based on nanotube building units. The talk will provide an insight into the creation process of the longest (single walled) nanotube strands. We will also discuss some of our recent efforts in creating nanotube circuits selectively and controllably and on the spatially resolved electronic properties of nanotubes.
Determination of sorption properties, total heterogeneity, and fractal dimensions of carbon nanotubes
Piotr Staszczuk, Magdalena Matyjewicz, Ewa Kowalska, et al.
Using special thermogravimetry and sorptometry methods physicochemical properties of carbon nanotube surfaces were investigated. A numerical and analytical procedure for the evaluation of total heterogeneous properties on the basis of liquid thermodesorption from the sample surfaces under the quasi-equilibrium conditions are presented. The desorption energy distribution was derived from the mass loss Q-TG and the differential mass loss Q-DTG curves of thermodesorption of pre-adsorbed polar and apolar liquid films. It is shown that the samples are highly sensitive to benzene vapor because the mechanism of liquid adsorption depends largely on the active surface centers and molecular interactions. For the first time, the evaluation of the fractal dimensions of nanotubes using the sorptometry and thermogravimetry data is presented.
Conductance modulation of single-walled carbon nanotubes
Andrea Reale, Pietro Regoliosi, Luigino Tocca, et al.
We have performed studies on the correlation between mechanical deformation and conductivity on a set of carbon samples constituted by 70% of single-walled carbon nanotubes. The samples, in form of slabs (6 × 5 mm, thickness: 400 mm), were obtained by compacting the nanotube material at 200 and 600 bar. The changes of conductivity have been monitored by measuring the current variations induced by a modulated periodic elongation of the slabs via a coherent technique. The mechanical deformations were produced by forces applied vertically at the center of each slab, horizontally placed on a sample holder. A piezoelectric actuator controlled by a lock-in amplifier was fixed to the sample holder. The modulation of the current induced by the mechanical deformation of the nanotube slabs is huge, and the amplitude of the modulation is almost linearly proportional to the elongation induced by the piezoelectric actuator. Such change of conductivity is more than an order of magnitude higher than the change obtained by piezoelectrical deformation of Si. The behaviour of the nanotube samples has been compared to that of a reference sample made of graphite compressed at 200 bar to form a slab with similar dimensions. In this case the change of conductivity was below the sensitivity of the lock-in amplifier, which was unable to lock to the periodicity of the mechanical deformation. We are currently addressing the problem to interpret the strong response of the nanotube slabs, which could be attributed either to a piezoresistive response of the sample or to the direct effect of the deformation on the hopping transport processes.
Organic nanofibers: a new window to optics of ultrasmall aggregates
Nanoscaled photonic devices rely on a thorough understanding of the influence of microscopic morphological changes on the optoelectronic properties. Here, we investigate as a model system organic nanofibers from para-phenylene molecules, which provide high flexibility in terms of controlled growth manipulation, while on the other hand showing self assembled multiplication of individual entities. Examples on selective spectroscopy, scanning fluorescence optical microscopy and waveguiding of individual nanofibers as well as arrays of nanofibers are given. Both the linear optical properties as well as the waveguiding efficiency are strongly related to the nanofibers morphology, which turn out to be an interesting benchmark system for the investigation of the applicability of a variety of optical methods in the nanodomain.
Mechanical properties of hybrid polymer nanotube systems
In this work, mechanical properties of hybrid materials fabricated from nanotubes and commercially available polymers were investigated. It was found that, by adding various concentrations of arc discharge multiwall nanotubes, both Young’s modulus and hardness increased by factors of 1.8 and 1.6 at 1wt% in PVA and 2.8 and 2.0 at 8wt% in PVK, in reasonable agreement with the Halpin-Tsai theory. Furthermore, the presence of the nanotubes was found to nucleate crystallization of the PVA. This crystal growth is thought to enhance matrix-nanotube stress transfer. In addition, microscopy studies suggest extremely strong interfacial bonding in the PVA-based composite. This is manifested by the fracture of the polymer rather that the polymer-nanotube interface. The dependence of the polymer nanotube interfacial interaction on host polymer was studied by intercalating various polymers (PVA, PVP and PS) into single wall nanotube buckypaper. Even for short soak times, significant polymer intercalation into existing free volume was observed. Depending on the polymer and the level of intercalation tensile tests on intercalated sheets showed that the Young’s modulus, strength and toughness increased by factors of 3, 9 and 28, respectively. This indicates that the intercalated polymer enhances load transmission between nanotubes due the significant stress transfer. The level of stress transfer was observed to scale with polymer hydrophobicity as expected.
Synthesis procedures for production of carbon nanotube junctions
Imre Kiricsi, Zoltan Konya, Krisztian Niesz, et al.
A quite wide brunch of the carbon nanotube science, including the utilization of singlewall nanotube for production of nano-electronic devices has being continuously explored even nowadays. Tuning and modifying the synthesis procedures to obtain nanotube junctions of T, Y, H or X shapes lead to inappropriate results concerning the industrial or large scale production. However, the importance and the demand for these junctions are quite large, since these may be the secondary building units of carbon nanotubes based chips or even more complex nanoelectronic devices. Recently, some novel solutions of their preparation have been published. A Taiwanese group described a method to prepare multi-junctioned carbon nanotubes on mechanically pretreated silicon surface applying chemical vapor deposition (CVD) technology using decomposition of methane at 1373 K. The nanotubes were nucleated following the lines prepared by scratching the surface with 600-grit sand paper. Contrary to the physical pretreatment of a substrate surface, chemical reactions can also be used for the preparation of carbon nanotube junctions. P.W. Chu et al. reported interconnecting reactions between functionalized carbon nanotubes . By the described method, the carboxyl groups on the wall of singlewall carbon nanotubes are converted to carbonyl chloride groups by reaction with SOCl2 at room temperature. The formed COCl groups are very reactive on the outer surface and can be reacted easily with various amines, particularly diamines resulting in the formation of amide bonding. When two functionalized carbon nanotubes react with such an amine molecule interconnection of tubes is generated. The resulted carbon nanotube junctions have been investigated by AFM. In this presentation, we report on the results obtained on the preparation of carbon nanotube junctions applying two different procedures. The first method is similar to Chu’s one, which was mentioned above, i.e. we used functionalized multiwall carbon nanotubes and the successful interconnection of them by propylene diamine has been proven by TEM and AFM. The second method demonstrates a novel principle: catalyst material has been deposited on the outer surface of carbon nanotubes and branches of nanotubes were produced at this contact point by catalytic chemical vapor deposition (CCVD) of acetylene. The product has been characterized by TEM.
Nanotechnology of Life
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Spontaneously generated radioactive nanoparticles in the environment
William H. Marlow, Yung-Sung Cheng
For almost 100 years, and perhaps longer, observers have detected spontaneous dispersal of radioactivity from macroscopic quantities of radioactive materials with the first published observations reported in 1910. In the 1960’s and later, radioactivity was observed to migrate through HEPA filters de-spite their well-established filtration characteristics. In measurements of ground water, radioactivity has been found to disperse from its original location of deposition in soil, despite the size, insolubility, and resistance to chemical reactions of the radioactive particles originally deposited. Similarly, measurements of the uptake of these materials in lung tissue and studies of their solubility in simulated biological fluids showed the solubility to be related to the radioactivity of the materials. In numerous practical examples, the migration and deposition of radioactivity affects work and operational practices. Despite this long and varied history indicating the importance of self-dispersal of radioactive materials, no measurements had ever been reported of the materials which were actually dispersed until recently and the results are quite surprising, suggesting a well-defined process creating discrete nanoparticle fractions. This paper will review the history of the observations of spontaneous dispersal of radioactivity and close with a description of the first measure-ments of the dispersed nanoparticles and suggestions of the physical processes involved in their formation.
Comparison of Fe/Al2O3 and Fe,Co/Al2O3 catalysts used for production of carbon nanotubes from acetylene by CCVD
Zoltan Konya, Istvan Vesselenyi, Karoly Lazar, et al.
Investigation of the properties of nanometer sized particles is in the focus of material and chemical science. Several questions about the synthesis and application of carbon nanotubes have been addressed the researchers working in nanoscience and nanotechnology. The catalytic chemical vapor deposition (CCVD) method proved to be one of the most prosperous technologies for large scale production of both single and multiwall carbon nanotubes. It has been proven that supported transition metals are the most productive catalysts for CCVD. The bimetallic catalysts showed excellent catalytic activity in conversion of acetylene to multi wall carbon nanotubes (MWNT) . In our previous papers, we dealt with the cobalt-iron bimetallic catalytic system. We showed that the best quality MWNTs with high yield was observed on Co-Fe catalyst. From the in situ XPS results we concluded that Co-Fe alloy phase should be formed on the catalyst treated at high temperature in acetylene atmosphere, furthermore, we attributed the effectiveness of this catalyst to the presence of alloy phase. However, we have also indicated the importance of Mössbauer spectroscopic studies. In this contribution we report on the results of Mössbauer spectroscopy supplementing our previous conclusions drawn by chemical and XPS techniques.
Porous silicon optical sensors for vapors, liquids, and biological molecules
Recently, an increasing interest has been devoted to the use of porous silicon (p-Si) in photonics and in sensing fields. In particular, the great reactivity, mainly due to its large surface to volume ratio, has demonstrated to be promising in sensing applications for the detection of gases, vapors, and biochemical molecules. In this work, we present experimental and numerical results on p-Si optical microcavities as sensing transducers in biological and chemical fields. The measures are based on the change of the cavity reflectivity spectrum induced by the exposition to the bio-chemical specimen under test. The p-Si microcavity has a Fabry-Pèrot structure confined between two Distributed Bragg Reflectors (DBRs) with high reflectivity in the wavelength range of interest. The DBRs have been obtained modulating the porosity, therefore the refractive index, of p-Si layers during the silicon electro-chemical etching process. The optical thickness (nd) of each single-layer forming the DBR is l/4, where d is the layer physical thickness, n its refractive index and l is the Bragg wavelength. A l/2-thick layer placed between the top and bottom DBRs works as a microcavity resonating at the Bragg wavelength l. The realized sensors operate at the fiber optic communication wavelength of 1.55 mm. A complete experimental characterization of the devices as vapor and liquid sensor is reported. An analytical model, allowing the correct interpretation of the sensing dynamics, is also reported and discussed. Finally, preliminary results concerning DNA-probe immobilization in p-Si pores and consequent recognition of complementary DNA strands are presented.
Physics of drug delivery: dielectric spectroscopy to probe mucoadhesion
This work presents how dielectric spectroscopy can be used as a tool to obtain insight about properties on the nano-scale of interfaces of pharmaceutical interest. An outline for studying the adhesion in terms of a compatibility factor between pharmaceutical gels and biological tissue is put forward. The proposed compatibility factor is calculated from the high frequency response (kHz region) of the gel and porcine nasal mucosa separately, and from that of the combined system. It gives an assessment of the possibilities of intimate surface contact, which is generally considered to be the first step in the mucoadhesion process. The results from dielectric spectroscopy were compared to measurements using a tensile strength method and it was found that the gels with the highest compatibility factors were the same as those pointed out as having the highest mucoadhesion using the tensile strength method.
Power of Computation for Nanotechnology
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Experimental observation and quantum modeling of electron irradiation on single-wall carbon nanotubes
Jean-Christophe Charlier, Mauricio Terrones, Florian Banhart, et al.
In situ experiments, based on electron irradiation at high temperature in a transmission electron microscope, are used to investigate isolated, packed and crossing single-wall nanotubes. During continuous, uniform atom removal, surfaces of isolated single-wall nanotubes heavily reconstruct leading to drastic dimensional changes. In bundles, coalescence of single-wall nanotubes is observed and induced by vacancies via a zipper-like mechanism. 'X', 'Y', and 'T' carbon nano-structures are also fabricated by covalently connecting crossed single-wall nanotubes in order to pave the way towards controlled fabrication of nanotube based molecular junctions and network architectures exhibiting exciting electronic and mechanical behavior. Each experiment is followed by quantum modeling in order to investigate the effect of the irradiation process at the atomic level.
Molecular clusters of hydrogen, deuterium, and tritium: especially cationic species H+3 (H2)m: m=2, 5 and 14
I. A. Howard, Frederik E. Leys, N. H. March, et al.
Two recent experimental studies by Zweiback et al. and by Gobet et al. have motivated us to study the ground-state geometry and the consequent electronic structure of the singly-charged cationic hydrogen cluster H3+(H2)m for m=2,5 and 14, using at first the Hartree-Fock approximation. For the H+7 cluster the fully optimized ground-state geometry yeilds an isosceles triangle H3, with charge ~ 0.85(e), and sides 0.852 and 0.884 Å flanked by two H2 molecules lying parallel to each other, wiht bond lengths of 0.740 Å. In contrast, for the H+13 cluster, the central 'building block' is equilateral H3 with bond length 0.861 Å, and with charge ~0.815(e). This configuration of H3 is flanked by three almost-parallel H2 molecules with bond length 0.739 A. MP2 refinements of geometry, charge distribution and normal mode vibrational frequencies of the cationic tritium cluster T+7 and the corresponding deuterium cluster D+13 are also reported. Finally, Hartree-Fock and MP2 results are recorded for H+13.
Terahertz photomixing using plasma oscillations in a two-dimensional heterostructure
Mixing of two optical beams with close frequencies in photoconductive structures or their response to ultrashort optical pulses are widely used for the generation of terahertz (THz) electromagnetic radiation. The THz radiation produced by optically excited plasma oscillations in p-i-n structures has been observed by some teams. In this communication, we consider a heterostructure akin to a field-effect transistor with high electron mobility in its two-dimensional channel and report on the modeling of THz oscillations caused by optical signals in this heterostructure. The features of such a heterostructure are associated with the existence of weakly damped electron plasma oscillations and possibility of their resonant excitation, so that the two-dimensional electron channel serves as a resonant cavity with rather high quality factor. A conception of THz photomixing using the excitation of standing plasma waves (plasma oscillations) in the heterostructure under consideration has recently been proposed by the authors. We demostrate that due to the excitation of the electron plasma oscillations in the channel by the photogenerated electrons and holes, the heterostructure in question exhibits a pronounced resonant response leading to high amplitudes of the ac photocurrent oscillations. As shown, this can result in substantially higher efficiency of the THz radiation generation by optical signals than that in p-i-n structures.
First-principles simulation of scanning tunneling microscopy images of individual molecules in alkanethiol self-assembled monolayers on Au(111)
Bin Li, Changgan Zeng, Qunxiang Li, et al.
The density functional theory calculations with local density approximation have been performed to simulate scanning tunneling microscopy (STM) images of individual molecules in close-packed upright alkanthiol self-assembled monolayers (SAMs) on Au(111) surface. The internal patterns in the simulated STM images are dependent on bias voltage and alkanethiol chain length, and have characteristic of the topographic effect modulated by the electronic effect. The electronic structure of the adsorption system is analyzed for discussing STM imaging mechanism of alkanethiol SAMs. Besides enhancing the intermixing between alkyl part and Au substrate states, sulfur atom in alkanethiol obviously influences the pattern in STM image by its chemisorption mode on Au(111) surface. Simulated images qualitatively reproduce STM experimental results.
Vibrational properties of boron nitride nanotubes: Effects of finite length and bundling
We present ab initio calculations of phonons in single-wall boron nitride nanotubes. Raman and infrared active modes of isolated and infinitely long tubes are evaluated according to the non-symmorphic rod groups of BN nanotubes. For tubes of finite length, the selection rules are less restrictive and give rise to additional modes which may be observed in Raman and IR spectroscopy with an intensity depending on the tube length. Bundling of tubes is shown to have little effect on the phonon frequencies. However, arranging tubes in a large periodic array (larger than the wave-length of incoming light) gives rise to a strong frequency shift (LO-TO splitting) of some modes due to the establishing of a macroscopic electric field. Modes of A1 symmetry experience a shift for laser light along the tube axis and E1 modes are split for light incidence in the perpendicular direction.
Lattice dynamics of the h-BN monolayer and single-walled BN nanotubes using a tight-binding model
Eduardo Hernandez, Daniell Sanchez-Portal
Vibrational spectroscopy, and in particular, Raman spectroscopy, has been frequently used to characterise carbon nanotube samples, and has even been used recently on individual single-walled carbon nanotubes, where it has demonstrated its capability for providing a full structural determination. Single-walled nanotubes of BN can now also be readily synthesised, and in this context it is interesting to consider the application of vibrational spectroscopy for the characterisation of BN nanotube samples. In this talk I will present results from a theoretical study of the vibrational properties of a BN mono-layer and of a series of single-walled BN nanotubes. These results have been obtained using a non-orthogonal tight-binding model, which is complemented with an electrostatic model in order to take into account the polar nature of the material. I will discuss a number of properties derived from this study, such as phonon band structure and density of states, elastic constants, sound velocities, etc. I will also establish a comparison between the predictions derived from the zone-folding approach, frequently used in the analysis of Raman spectra of carbon nanotubes, and the direct calculation for BN nanotubes.
Metal Interconnects on the Nanoscale
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Development of microstructure in nanostructures and thin films
Max O Bloomfield, Yeon Ho Im, Jian Wang, et al.
We have created a finite-element based, multiple-material, levelset-based code to implicitly represent and track evolving islands and grains. With this method, the code can track island growth in three dimensions through nucleation to coalescence into a grain structure. We discuss the numerical methods, capabilities, and limitations of the code, and then examine the microstructures that result from different models of growth based on starting structures derived from atomistic Monte Carlo simulations. We show simulation results from a kinetically limited process (electroless deposition), a transport-limited process (physical vapor deposition), and a process neither transport nor kinetically limited (physical vapor deposition with orientation dependent sticking factors).
Laser-induced surface modification on LTCC materials for chemical metallization
Krisztian Kordas, Andrea Edit Pap, Jussi Saavalainen, et al.
Low temperature co-fired ceramics (LTCCs) are mainly applied in hybride microelectronics packaging technology, whereas the fabrication of metallic conductors on LTCC materials is done by various printing technologies. The conventional process is fast and cost-effective in the case of mass-production but too slow and difficult when repair and/or some modifications in circuitry are needed. Printing also fails when deposition of thin metal films on LTCC is demanded. Here, a simple laser-assisted process is presented by which the surface of LTCCs can be activated for consecutive electroless chemical metal plating. The method enables the realization of thick high-conductance metallic Cu micro-patterns and thin seed layers of Ag and Au, with a lateral resolution of a few tens of micrometers. The process is also suitable for 3D-MEMS applications. Morphological, structural and composition aspects of LTCC surfaces treated by a Nd:YAG pulses are carried out using FESEM, SEM, XRD and Raman measurements.
Novel organometallic nanomaterials exhibiting high nonlinearities including photorefraction at telecommunication wavelengths
Novel unique organometallic nanomaterials with high nonlinearities of various types (nonresonant, resonant, photorefractive) have been prepared. Two main kinds of nanomaterials actualizing the different nonlinear-optical processes have been created: 1) polymeric photorefractive nanocomposites with very low glass transition temperatures (ca. 8 deg C) based on poly[ethynediyl-arylene-ethynediyl-silylene]s and sensitive in the visible (633 nm) and near-infrared region (1000-1500 nm) have been developed. The TEM investigations of the composite thin films have revealed self-oganized lamellar structures. The red shift of the absorption spectra and the appearance of a long absorption tail in the near IR region in the case of the films (unlike the solutions) confirm the essentially pi-stacking mechanism in the formation of the supramolecular assembly. The mechanism of self-organization into lamellar phases is discussed. 2) chromium-containing polymeric nanocomposites of high optical and mechanical quality have been prepared. They contain bis-arenechromium complexes covalently bonded to polyacrylonitrile macrochains. The conditions of film-casting give rise to the formation of conjugated polynaphthyridine-type structures inside the polymeric matrix as a result of cyclization of the acrylonitrile units. In addition, the TEM investigations of the films showed that nanosize particles (20-30 nm), containing chromium are formed in the material. These materials exhibit record Kerr-type cubic nonlinearities (chi3 = -2.5×10-10 esu) suggesting a pi-stacking mechanism giving rise to self-organized supramolecular structures. Our theoretical calculations show that the level of nonresonant optical nonlinearity should in principle allow actualizion of fast optical switching with speeds suitable for modern optical connection systems (100 Gbit/s).
Formation of electrically conducting mesoscale wires through self-assembly of atomic clusters
Jim G Partridge, Shelley Scott, Alan D F Dunbar, et al.
Atomic clusters can be produced in a size range (100nm to 0.5nm) that bridges the gap between the limits of current lithographic fabrication technologies for integrated circuits and the atomic/molecular regime. The work presented here aims to combine established top-down device processing with bottom-up engineered cluster assembly. Conducting cluster deposition and standard optical fabrication techniques have been used to produce wires on a textured (V-grooved) substrate. The lengths of the wires (ranging from 2μm to 1mm) are defined simply by the separation of NiCr/Au contacts. The deposited nanoparticles range in size from 20-100nm and in principle define the width of the nanowire. In-situ conductance measurement allows precise control of the deposition process and the onset of conduction in the wire is readily monitored as a function of deposition time. The effectiveness of the surface templating technique is demonstrated by SEM and AFM imaging carried out after deposition. The surface coverage is seen to vary from <20% on the unpatterned (normal-to-beam) surface (which is required to be non-conducting) to >100% at the apexes of the V-grooves used to promote growth of the wire. Self assembly of the nanoparticles leads to completion of a wire between the pre-formed contacts with no possibility of a parasitic conduction path. Wires formed through this technique currently have minimum widths of ~1μm but straightforward extensions of the technique should soon allow nanowire formation.
Electric-field-mediated fabrication of nano/microstructures
Yong J. Yuan, Mike K. Andrews, W. Mike Arnold, et al.
Notable recent developments toward the realization of electronic nanocomputers have assembled logic circuits from semiconductor nanowires and individual carbon nanotube molecules. In spite of the broadly based and encouraging recent progress, a set of technical challenges still must be overcome to make a robust, commercially viable computer integrated on the molecular scale. The assembly of colloidal particles under an electric field offers many opportunities for the fabrication of ordered arrays, nanostructured films and microwires. We describe a method for the fabrication of gold nano/microstructures such as wires and dendrites on a lithographically patterned aluminium electrode with electric-field-induced assembly. The simple fabrication process will make these structures suitable for the miniaturisation of electronic circuits that can find application in sensors, actuators, and lab-on-a-chip devices. Our approach to electric-field-mediated fabrication exposes colloidal gold particles to the high electric field that can be generated between electrodes only 200 mm apart. We introduce an electric field of 100 Hz to 10 MHz by application of an alternating voltage of 5 to 10 V to the lithographically patterned microelectrodes. A suspension of gold nanoparticles of diameter 2.5 nm is added. We observe three types of fabrication, represented by three zones due to the different dielectophoretic force and convection effects. Some fibres grow through the liquid from one electrode toward the other, as could be seen in-situ by inverse optical microscopy. Dielectrophoretic-force-mediated fabrication, which is very flexible depending on the magnitudes of electric-field strength and frequency applied, has produced a notable advance in making mechanically flexible nano/microelectronic devices and led to a new understanding of the factors controlling the growth of nano/microstructures. When drops of suspension are patterned on the faces of components, three-dimensional structures can be generated. This type of system indicates how functional, self-assembling nano/microelectronic systems may be made. It provides a faster way of making devices, and the process can be very economical.
Electronic transport properties of single fullerene molecules
Jin Zhao, Bin Miao, Liang Zhao, et al.
C60 molecule have become increasingly important during the last decade concerning both their basic physical and chemical properties as well as potential applications. Explorations of C60 based nano-devices have been performed recently based on the unique properties of C60 molecules. In this paper, the transport properties of C60 single molecules in different tunneling junction configurations are reported and a summary of the theoretical and experimental development of C60 based molecular device is presented and discussed.
Metal and semiconductor nanoparticles stabilized in ultrathin nanofilms and layer-structured materials
Imre Dekany, Tamas Szabo, Laszlo Korosi
The interlamellar space of layer structured materials, such as montmorillonite, kaolinite, graphite oxide can be regarded as a nanophase reactor, in which size-quantized semiconductor and noble metal particles can be prepared. Particle growth is sterically hindered in the interlamellar space between neighboring lamellae which favors the formation of 2-10 nm particles. These synthesis strategies were successfully applied for the preparation and incorporation of Pd and Ag metal and CdS, ZnO, SnO2 semiconductor nanoparticles. Layer-by-layer self-assembled nanofilms were prepared from aqueous suspensions of semiconductor nanoparticles and various clay mineral suspensions onto glass surface. The nanoparticles adsorb on the surface of the support wiht their protecting layers allwoing the preparation of semiconductor and noble metal nanocomposites by this method. The properties of these nanocomposites have been investigated by optical measurements, x-ray diffraction, small angle x-ray scattering, atomic force and transmission electron microscopy.
Limits(?) of Nanoscale Electronics
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Are we there yet? Looking beyond the end of scaling in the Nanometer Era
Sandip Tiwari, Uygar Evren Avci, C. C. Liu, et al.
The major electronic applications of the coming decades and the technology that would make those applications possible are an important subject of discussion for industry and academia. Usefully employing gigantic scale of integration and working around the end of scaling underlie this subject, and in practice, the biggest challenge this faces is in control of power, designability, efficient interconnectivity, and reproducibility in a general purpose technology with provides a useful function. In this talk, I will use speculative examples, establish the practical issues in pursuing the examples, and then discuss from group’s work devices (back-plane and nano-scale), circuits (configurable and power-aware), technologies (three-dimensional), and architectures (configurable) that offer a fruitful direction.
Nanometer-scale analysis of current limited stresses impact on SiO2 gate oxide reliability using C-AFM
Marc Porti, Montserrat Nafria, Xavier Aymerich
The effect of current limited stresses (CLS) on the breakdown (BD) SiO2 gate oxides has been analyzed at a nanometric scale with a Conductive Atomic Force Microscope (C-AFM). Bare oxide regions have been stresed and broken down using the tip of the C-AFM as the metal electrode of a metal-oxide-semiconductor (MOS) structure. Afterwards, post-BD I-V characteristics and topographical and current images of the affected areas have been obtained to analyze the post-BD conduction, the structural damage induced in the oxide and the BD propagation. The results shwo that BD phenomenon, although triggered at one point, is electrically propagated to neighbor regions. Moreover, the area affected by BD, the structural damage and the post-BD conduction depend on the breakdown hardness. In particular, it is shown that these magnitudes are smaller when the current through the structure is limited during BD transient.
Transfer of single-crystalline silicon nanolayer onto an alien substrate
Alexander Y. Usenko, William N. Carr, Bo Chen
Starting from 60 nanometer node, next generations of mainstream semiconductor devices (i.e.,CMOS) will be mostly manufactured from silicon-on-insulator (SOI) initial substrates with the top silicon layer having a thickness 50 nm or less. We describe a process that is capable for transfer of nanoscale thick layers. The layer is delaminated from a single crystalline silicon substrate and laminated onto another substrate thus resulting in SOI. The process includes: (1) forming a trap layer for hydrogen in an initial substrate (2) delivery of hydrogen to the traps by diffusion of monatomic hydrogen (3) evolving the trapped hydrogen into a layer of hydrogen platelets (4) stiffening of the surface of the initial substrate by laminating to another substrate (5) delaminating a layer from the initial substrate along the hydrogen platelet layer. Details of the new layer transfer process is described. A depth where the buried trap layer locates is critical for the process. An implantation of heavy ions is used to form the trap layer. A trap capacity for hydrogen is evaluated as a function of implantation conditions. Plasma hydrogenation is used to deliver an atomic hydrogen to the traps. ECR, microwave, rf, and DC plasma are compared as the hydrogenation sources. Dependence of a thickness of a transferred layer as a function of the mass of implanted ions and implantation energy is described. Types of layer transfer faults are described. Mechanisms of the layer transfer faults are suggested. We discuss limits of scaling down of thickness of the layer that is transferred from one substrate to another one. Scaling limit of our process is compared to the limits of other (SIMOX, Smart-cut, and ELTRAN) processes.
Low-frequency noise in GaN-based two-dimensional structures
We will discuss results of the experimental and theoretical study of the low-frequency noise in GaN/AlGaN 2D structures and examine possible sources of noise, including contacts, surface and 2D channel itself. 2D GaN/AlGaN heterostructures exhibit a much smaller level of 1/f noise than bulk GaN films. In the frame of model linking noise to the tail states, this might be explained by a high degeneracy of the 2D electrons in this structures. Due to the electron degeneracy, the tail states mechanism of the 1/f noise is suppressed in GaN-based 2D structures. Our measurements show that contacts do not contribute much to overall low frequency noise. Concentration dependence of the Hooge parameter points out to the tunneling mechanism of noise in these structures.
Poster Session
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Dynamics of formation of nanoparticles by UV laser ablation
Qihong Lou, Jun Zhen
We will discuss reults of the experimental and theoretical study of the low-frequency noise in GaN/AlGaN 2D structures and examine possible sources of noise, including contacts, surface and 2D channel itself. 2D GaN/AlGaN heterostructures exhibit a much small level of 1/f noise than bulk GaN films. In the frame of model linking noise to the tail states, this might be explained by a high degeneracy of the 2D electrons in this structures. Due to the electron degeneracy, the tail states mechanism of the 1/f noise is suppresed in GaN-based 2D structures. Our measurements show that contacts does not contribute much to overall low frequency niose. Concentration dependence of the Hooge parameter points out to the tunneling mechanism of noise in these structures.
Comparative study of the growth curves of B. Subtilis, K. Pneumoniae, C. Xerosis, and E. Coli bacteria using nanometric silicon particles as a bacteriological sensor
Lilyanna Perez, Marjorie Flores, Javier Avalos, et al.
In this research nanometric particles from luminescent porous silicon film were synthesized. This particles were later inoculated in bacterial strains of B. subtilis (BSi) and K. pneumoniae (KSi). A comparison of the behavior of their growth curve and the ones reported for C. xerosis (XSi) and E. coli (ESi) in presence of silicon nanoparticles is presented. The growth curve of BSi, as well as the KSi, present changes compared to their standard curves. The BSi growth curve grows below the standard curve after teh fifth hor, while in the KSi this happens after the eighth hour. Based on our preliminary findings we can sepculate that at this point in time a critical population is present, and this may give rise to the possible incorporation of the silicon particles by the bacteria, or a possible pleomorphism inhibits reproduction. The stationary region, in both case, takes place sooner than in the standard curve. No significant oscillations are observed in any case, which differs from the XSi curve, were oscillations of intervals of almost 1 hour were reported. In addition, these curves have a different behavior when compared to the ESi growth curve, in which no significant differences between the standard and teh particle containing sample were reported.
Photoelectric characteristics of contacts In-semiconductor A3B5
Tinatin Laperashvili, Ilia Imerlishvili, Manana Khachidze, et al.
The effect of annealing structures on the electrical and photoelectric properties of metal-semiconductor contacts was investigated. Metal/semiconductor structures have been fabricated by method of electrochemically deposition of In on the electrochemically cleaned surface of the semiconductors A3B5 (GaP, GaAs). The dark capacitance and current -voltage characteristics and the hotoelectric spectra of zero bias for front-illuminated contact show near-ideal Schottky barrier diode properties for annealing temperature up to 250-3000C. Was found that the spectra of zero bias photocurrent of In/GaP beside the region photoconductivity resulting from band to band excitation, contains, also, separated of them the region photoconductivity in a long wavelength of spectra, which is related to the interaction between the metal and semiconductor. Samples used for the fabrication of In/GaP diodes were growing by Chochralski method especially un doped n-type GaP into (III) oriented wafers. The thickness and carrier concentration was 200-250 mimic and (2-4). 10 exp17 atom/cm3 respectively. At first ohmical contact to the one side of wafer was formed by alloying of indium at the temperature 5000C for GaAs and 600°C for GaP during 5 min in hydrogen. Then the sample with ohmic contact and wire for preceding the power was coaled with chemical stable polystyrene solution except the area where the metal will be deposited. The wafers were then ached chemically, rinsed in distilled water and were transferred immediately into electrolyte for deposition of In.
MOS-based nanocapacitor using C-AFM
Daniel Hill, Sascha Sadewasser, Xavier Aymerich
This report details the attempts made to realise nanocapacitors for nanoscale MOS based integrated circuits by AFM anodic oxidation, and therefore isolation, of nano-sized squares of poly-silicon, titanium and aluminium on Si/SiO2. Conductive AFM (C-AFM) was used to perform topographical and electrical characterisation. The experiments were performed with contact mode C-AFM, in ambient air, using Pt-Ir, Co-Cr and Ti coated (20nm) n-type silicon cantilevers. Each sample consisted of a 3-5nm thick conductor deposited on 6nm of SiO2, which was thermally grown on Phosphorus doped (1019 cm-3) n-type Si(100) substrates. Standard cleaning and passivation processes were used. Poly-silicon was immediately found to be too rough to oxidise. Initial current-voltage measurements inside of the titanium-oxide squares suggest initial isolation followed by degradation through Fowler-Nordheim tunnelling. Measurement inconsistencies seen suggest charge storage on the surface or tip with the barrier height of the native titanium oxide thought to be responsible. Al has a thicker natural oxide. To overcome this we designed a series of structures consisting of a Ti finger on SiO2, that is connected to a Ti bond pad, allowing direct probing by a semiconductor parameter analyser. AFM anodic oxidation was performed upon these Ti fingers to reduce their in-plane dimensions towards the nanoscale. To confirm the existence of a nanocapacitor topographical and electrical measurements were then done on and around them.
Near-field microscopy of light propagation in photonic crystal waveguides
A collection scanning near-field optical microscope (SNOM) is used to image the propagation of light at telecommunication wavelengths along straight and bent regions of silicon-on-insulator photonic crystal waveguides (PCWs) formed by removing a single row of holes in the triangular 410-nm-period lattice along GM direction of the irreducible Brillouin zone. High quality SNOM images of PCWs and access ridge waveguides excited in the wavelength range of 1520-1570 nm are obtained, demonstrating multimode behavior of ridge waveguides and good PCW (fundamental) mode confinement along with its low propagation loss. We analyze light intensity variations along the ridge and PCW waveguides measured with the SNOM at different distances from the sample surface. Considering the interference between a quasi-homogeneous background field and propagating mode fields and taking into account Bloch harmonics of the PCW modes, we account for spatial frequency spectra of the intensity variations and determine the dispersion of the PCW mode propagation constant. The possibilities and limitations of SNOM imaging for the characterization of PCWs as well as conventional waveguides are discussed.
New magnetic semiconductors CuCr1.5Sb0.5S4 with Co
We studied magnetic and electric properties new magenetic semicondcutors CuCr1.5Sb0.5S4 with Co. All compounds are characteristic for antiferromagnetics. A giant negative magnetoresistance has been found in the new magnetic semiconductors xCoCr2S4 - (1-x)CuCr1.5Sb0.5>S4, (x=0.25;0.5). Magnetoresistance is practically absent in CuCr1.5Sb0.5S4 and does not exceed 2% in CoCr2S4. The giant magnetoresistance and the postivie value of e are evidence for the existence of afmons in compounds with Ni.
Second-harmonic far-field microscopy of random metal nanostructures
Using a scanning far-field second harmonic (SH) microscope we have excited surface plasmon polaritons (SPPs) on a 70 nm thick gold film surface covered with randomly distributed 80 nm wide gold particles. Multiple scattering of the SPPs by these gold particles leads to localization of the electromagnetic fields causing strongly enhanced and spatially localized SH generation. We investigate wavelength and polarization dependencies of both position and intensity of these SH bright spots for two different densities of random scatterers. Comparing SH and fundamental harmonic (FH) images, we conclude that the localized SH enhancement occurs due to overlap of FH and SH eigenmodes. Furthermore we confirm that for incident laser powers in the range 3-40mW, the bright spots exhibit quadratic intensity dependence. For the higher incident laser powers however, the strong heating of the surface seems to change the material properties causing some bright spots to disappear and others to emerge.
Near-field imaging of out-of-plane light scattering in photonic crystal slabs
A collection scanning near-field optical microscope (SNOM) is used to image the propagating of light at telecommunication wavelengths (1520-1570 nm) along photonic crystal (PC) slabs, which combine slab waveguides with in-plane PCs consisting of one- and two-dimensional gratings. The efficient out-of-plane light scattering is directly observed for both 1D and 2D gratings (period 590 nm) fabricated on silicon-on-insulator wafers and the corresponding SNOM images are presented. Using the obtained SNOM images, we analyze light intensity distributions along PC gratings measured at different wavelengths and/or distances from the sample surface.
Fabrication of smooth thin diamond-like carbon microstructures by photolithography together with dry and wet etching techniques
Liujiang Yu, BengKong Tay, Divakaran Sheeja
Diamond-like carbon (DLC) films produced by the filtered cathodic vacuum arc (FCVA) technique have attracted considerable interest over the last few years, due to their excellent mechanical, electronic, optical and tribological properties in addition to the smooth surface morphology. However the utilization of DLC films in MEMS application has so far been limited due to the high compressive stress induced during growth. The large intrinsic compressive stress in the films causes the structure to curl up. By making use of substrate pulse bias of 1kV, the stress in the film has been lowered to 1.3GPa. Thin (~150nm) diamond-like carbon cantilever microstructures were fabricated in this film by photolithography together with dry (reactive ion etching (RIE)) and anisotropic wet etching techniques. The problems associated with lithography, etching and processing of the microstructures are discussed in detail, in addition to the characterization of the films such as stress, surface morphology and microstructure.
Electrical characterization of atomic-force-microscopy grown SiO2
Xavier Blasco, Montserrat Nafria, Xavier Aymerich
Atomic Force Microscopy (AFM) has been demonstrated to be one of the most powerful tools for nanoelectronic fabrication and characterization. However, AFM grown SiO2 has not been yet used as the gate dielectric, and its electrical behavior remains still unknown. After a topographic characterization, in this paper the conduction modes of AFM grown gate oxide (AFM-GOX) MOS structures are studied from measurements of their current-voltage (IV) characteristics. The results are compared to those obtained for thermally grown SiO2 (T-GOX), which is used as quality reference. Two types of structures have been used to study the conduction through AFM-GOX: a) MOS capacitors with polysilicon deposited gate, for standard electrical characterization and b) MOS structures without deposited gate, because the conductive AFM tip acts as gate terminal, for Conductive-AFM (C-AFM) measurements. Qualitatively, the fabrication process of the poly-Si gated structures consisted of: a field oxidation of the Si wafers, opening of windows in the field oxide to reach the substrate, then AFM oxidation was performed (4nm thick oxide), and as a last step a polysilicon gate was deposited. For the reference structures, AFM gate oxidation process was replaced by thermal oxidation with thickness of 3.5 and 4.5nm. The substrate was n-type Si. The standard electrical characterization, reveals that the dielectric breakdown of T-GOX happens at higher voltage than for AFM-GOX. Moreover, the current level through AFM GOX at voltages below the breakdown value is several orders of magnitude larger than that measured at same voltages for thermal oxides. These differences could be caused by defects introduced during the AFM oxidation, performed in ambient air. However, a comparison between the IV curves of AFM-GOX and T-GOX measured by C-AFM shows that at a nanometer scale both oxides behave similarly.
STM investigation of carbon nanotubes completely covered with functional groups
Antal Adolf Koos, Zsolt Endre Horvath, Zoltan Osvath, et al.
The functionalization of carbon nanotubes (CNTs) is important both for composite - to improve load transfer between CNTs and matrix - and nanoelectronic applications - to interlink individual nanotubes in a network. Oposite to earlier results, complete coverage of CNT surface with functional groups was achieved. The distribution of functional groups on the nanotube surface was investigated using STM and TEM. The influence of functional groups on the electron density of states of the nanotubes was studied with scanning tunneling spectroscopy (STS).
Three-dimensional nanostructuring by two-photon polymerization of hybrid materials
Two-photon polymerization (2PP) of photosensitive inorganic-organic hybrid polymers (ORMOCERs, developed at the Frauenhofer Institut fur Silicatforschung) is demonstrated as a very promising approach for the fabrication of complicated three-dimensional micro- and nanostructures. These materials are produced by sol-gel synthesis with molecular level mixing of different components. It is remarkable that properties of the hybrid polymers can be tuned from those that are characteristic for organic polymers to those that are similar to inorganic glasses. They have negative resist behaviour and can be used as storage-stable, liquid photo-polymerizable resins. When Ti:sapphire femtosecond laser pulses are tightly focused into the volume of this resin (which is transparent in the infrared) they can initiate two-photon polymerization process transferring liquid into solid state. This process is confined to a highly localized area at the focal point due to the quadratic dependence of the two-photon absorption rate on the laser intensity. When the laser focus is moved through the resin in three dimensions, the polymerization occurs along the trace of the focus. This allows to fabricate any computer-generated 3D structure by direct laser 'recording' into the volume of the ORMOCER. The non-irradiated liquid resin can be dissolved in alcohol leaving the polymerized copy of the computer model. Compared to conventional photo-lithography which is a planar processing, two-photon polymerization is a real three-dimensional volume microfabrication technique. These technologies can be used for rapid prototyping and low-cost fabrication of artificial micro- and nanostructured components which are required for different applications in optics, medicine, and biology. Numerous examples such as photonic crystals, micromechanical and microoptical devices will be demonstrated in this presentation.
Modeling of experimental reflectance for porous silicon multilayers
Cecilio Hernandez-Rodriguez, Ventura M. Hernandez, Nestor E. Capuj, et al.
This work exposes a computational simulation method to describe the infrared reflectance on periodical and effective media. We use this method in order to improve the parameters to design porous silicon multilayers (PSM). The procedure of the computer program takes into account the complex refractive index of each layer by using the effective dielectric constant for different porosities. The lateral inhomogeneity of the thickness for the successive layers are simulated using the thickness as a random function around one mean value. Averaging all the reflectance values and iterating the computational process for different random parameters gives the reflectance results of the model. We also show in this work the experimental reflectance spectrum for a PSM dielectric Bragg reflector. The comparison of the experimental spectrum and the simulations shows a good agreement in bandwidth and position of the maximum reflectance band.
STM and STS investigation of few-wall carbon nanotubes containing non-hexagonal carbon rings
Zoltan Osvath, Laurent Fulcheri, Geza István Mark, et al.
We performed scanning tunneling microscopy (STM) measurements on few wall carbon nanotubes that exhibited changing diameter. Such change in the diameter may occur if non-hexagonal carbon ring configurations are introduced in the nanotube walls. A few-walled nanotube knee of 4 degrees, with different diameter values on the two sides of the knee was imaged by STM. Theoretical model structures [1] of single-wall carbon nanotubes show that a bend of 4 degrees may occur when a pentagonal and a heptagonal carbon ring is incorporated side by side in the hexagonal nanotube structure. Scanning tunneling spectroscopic (STS) measurements show that additional electronic states are present in the energy gap in the region where the bend occurs. We also performed STS measurements on a single-wall nanotube with conical tip. In agreement with theory, the results show that the energy gap in the tapered end is larger than in the nanotube.
Single-molecule magnets on a polymeric thin film as magnetic quantum bits
Daniel Ruiz-Molina, Jordi Gomez, Marta Mas-Torrent, et al.
Single-molecule magnets (SMM) have a large-spin ground state with appreciable magnetic anisotropy, resulting in a barrier for the spin reversal As a consequence, interesting magnetic properties such as out-of-phase ac magnetic susceptibility signals and stepwise magnetization hysteresis loops are observed. In addition to resonant magnetization tunnelling, during the last few years several other interesting phenomena have also been reported. The origin of the slow magnetization relaxation rates as well as of other phenomena are due to individual molecules rather than to long-range ordering; as confirmed by magnetization relaxation and heat capacity studies. Therefore, SMM represent nanoscale magnetic particles of a sharply defined size that offer the potential access to the ultimate high-density information storage devices as well as for quantum computing applications. However, if a truly molecular computational device based on SMM is to be achieved, new systematic studies that allow us to find a proper way to address properly oriented individual molecules or molecular aggregates onto the surface of a thin film, where each molecule or molecular aggregate can be used as a bit of information, are highly required. Here we report a new soft, reliable and simple methodology to address individual Mn12 molecules onto a film surface, as revealed by Atomic Force Microscopy (AFM) and Magnetic Force Microscopy (MFM) images. Moreover, the advantageous properties of polymeric matrices, such as flexibility, transparency and low density, make this type of materials very interesting for potential applications.
Imaging of magnetic domain structures using optical techniques
Wayne Dickson, Satoshi Takahashi, Robert Pollard, et al.
High-resolution optical techniques for the imaging of magnetic domains in ferromagnetic materials such as confocal microscopy and scanning near-field optical microscopy are discussed. The imaging capabilities of different techniques and image formation are investigated in the case of in-plane as well as out-of-plane magnetic anisotropy in different polarisation configurations. It is shown that the magneto-optical resolution of near-field measurements depends on the film thickness and is limited by the diffraction on magnetic domains throughout the film. For thin magnetic films, sub-wavelength resolution can be achieved. High-resolution optical imaging is required for characterisation of the micro-magnetic and magneto-optical properties of novel magnetic materials in order to adopt a bottom-up approach in the search for new materials with improved characteristics.
Nanodistribution of the dissolved hydrogen and deuterium in near-surface area of metals
Eugeney A. Deulin, Ekaterina A. Rodina
Results of experiment shows, that concentration of the hydrogen dissolved in the stainless steel type 304 after keeping in normal atmosphere is CH2 = 2*1019 at/sm3, instead of theoretically expected CH2 = 2*1019 at/sm3, similarly, for deuterium, dissolved at CD2 = 7*10-6Pa, its concentration, instead of theoretically expected C theorD2 = 8*1015 at/sm3 is CD2 = 1*1018 at/sm3. As for hydrogen also as for deuterium it is possible to explain their increased concentration by the relay dissociation of sorbed water The results show that the residual atmosphere of hydrogen or deuterium influences on ions exchange processes of deuterium and hydrogen in layers of sorbed water. So, in the submitted results it is enough 0,002% dissociation of sorbed water to ensure the pointed mentioned concentration. Experiment with the sample keeping (during 76 days) in the atmosphere of deuterium at pressure PD2 = 5*10-4Pa shows, that the maximal concentration of the dissolved deuterium is CD2 = 1*1018 at/sm3, that is about eight times less than expected theoretically. Concentration of the dissolved gases grows up to C maxH2 = 2*1021 at/sm3 and C maxD2 = 3*1019 at/sm3 as a result of mechanical action influence that corresponds to the 8,5% dissociation of H2O, and corresponds to 0,1% dissociation of HDO. So it was shown that the friction processes stimulates the process of sorbed water dissociation.
Stress-induced leakage currents of silicon oxides in flash EEPROM transistor
In this paper, The stress induced leakage currents of thin silicon oxides is investigated in the ULSI implementation of FLash EEPROM transistor. The stress and transient currents associated with the on and off time of applied voltage were used to measure the distribution of high voltage stress induced traps in thin silicon oxide films. The stress and transient currents were due to the charging and discharging of traps generated by high stress voltage in the silicon oxides. The channel current for the thickness dependence of stress current, transient current, and stress induced leakage currents has been measured in oxides with thicknesses between 113.4A and 814A, which have the channel width x length 10-3cm2. The stress induced leakage currents will affect data retention and the stress current, transient current is used to estimate to fundamental limitations on oxide thicknesses.
Infrared emission from silicon and metallic lamellar grating
The infrared normal spectral emissions from degenerate (metallic-like) silicon and metallic (nickel) lamellar grating structures were investigated. The gratings were micromachined on (110) silicon wafer was with differing periods, groove widths and groove depths, where the dimensions of all samples were with feature sizes comparable to the measurement wavelengths (2.5 - 25 μm). The measurement temperatures for all samples were in the range 27 to 740 °C. Infrared normal transmission through diffraction was also measured. In general, it was found that the spectral emission of the metallic gratings was different from the degenerate silicon grating. This because the bulk absorption in the silicon samples was affecting the emission.
Electrical characterization of single-wall carbon nanotubes
Marco Berliocchi, Francesca Brunetti, Aldo Di Carlo, et al.
Single Wall Carbon Nanotubes (SWCNTs) based nanotechnology appears to be promising for future nanoelectronics. The SWCNT may be either metallic or semiconducting and both metallic and semiconducting types of SWCNTs have been observed experimentally. This gives rise to intriguing possibilities to put together semiconductor-semiconductor and semiconductor-metal junctions for diodes and transistors. The potential for nanotubes in nanoelectronics devices, displays and nanosensors is enormous. However, in order to realize the potential of SWCNTs, it is critical to understand the properties of charge transport and to control phase purity, elicity and arrangement according to specific architectures. We have investigated the electrical properties of various SWCNTs samples whit different organization: bundles of SWCNTs, SWCNT fibres and different membranes and tablets obtained using SWCNTs purified and characterized. Electrical characterizations were carried out by a 4155B Agilent Semiconductor Parameter Analyser. In order to give a mechanical stability to SWCNTs fibres and bundles we have used a nafion matrix coating, so an electrical characterization has been performed on samples with and without this layer. I-V measurements were performed in vacuum and in air using aluminium interdigitated coplanar-electrodes (width=20mm or 40mm) on glass substrates. The behaviour observed is generally supralinear with currents of the order of mA in vacuum and lower values in air with the exception of the tablet samples where the behaviour is ohmic, the currents are higher and similar values of current are detected in air and vacuum.
Quantum heterostructure antennas: an efficient and effective means for a future wireless scenario
Rangaswany Nakkeeran, K. SivaSathivel
For the past few decades, the world observes a tremendous growth in the fundamental concepts based on higher dimensional quantum structures. Several reports and results have been reported in the leading journals consistently on optical sources like light emitting diodes and laser diodes, modulators/switches and detectors by deploying the concepts of periodical structures like quantum wells, quantum dots and porous silica. Certainly in the world of ultra high-speed communication, the above said devices will pave way to get the best performance out of it. In general, antenna is the most inevitable part of wireless communication systems, particularly, desirable bandwidth with demanded directivity, compactness, high efficient antennas are expected to materialize in the future generation (4G) cellular mobile communication, mobile computing and personal communication services. In this paper an attempt has been made to study the radiation characteristics of quantum structures (QW, QWR, and QD). These radiation characteristics are compared with that of the conventional current carrying element. It is found that the radiation properties are much better than the conventional current carrying elements. Hence, radiators based on these structures can be made with high efficiency, directivity and low power consumption. Thus, this work paves a way to develop novel radiators to meet the demands of the future communication systems.
Stabilization of rhodium nanoparticles in an aqueous medium by polymer and layered silicates
Szilvia Papp, Jozsef Szel, Imre Dékány
The synthesis of rhodium nanoparticles was studied in aqueous polymer solution and on layerd montmorillonite and kaolinite minerals. The effect of the concentration of the rhodium precursor and polymer on the size of the particles formed was studied using neutral polivinylpyrrolidone. Reduction was done by sodium borohydride. Expansion of the interlayer space in kaolinite was effected by intercalation of dimethyl sulfoxide at 65°C. Interlamellar incorporation of nanoparticles was monitored by x-ray diffraction and small angle x-ray scattering, the size and the size distribution function were determined by transmission electron microscopy. Average particle size fell in the range of 1-3 nm, depending on the stabilization method used and the concentration of precursor rhodium ions. The valence of the rhodium particles on the support surface was examined by XPS analysis.
Incorporation of silver nanoparticles in kaolinite clays
Rita Patakfalvi, Imre Dekany
Silver nanoparticles were synthesized in the interlamellar space of alayered kaolinite clay m ineral. Disaggregation of the lamellae of non-swelling kaolinite was achieved by intercalation of dimethylsulfoxide. The Ag+ ions after adsorption in the interlamellar space were reduced by NaBH4 or by UV irradation. The changing of the structure of kaolinite and the intercalation of silver nanoparticles were monitored by x-ray diffraction. We compared the effects of the two reduciont methods on the size and the size distribution of Ag nanoparticles by TEM investigation and SAXS experiments how clay mineral structure is altered as a consequence of particle formation. It was established that the size of Ag nanoparticles depends on both silver content and the reduction method. The chemical reduction showed Ag nanoparticles with 7.1-10.5 nm and photoreduciont of silver led to the formation of relatively large Ag nanoparticles with 8.3-11.2 nm.
Nano-Optics
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Er3+-doped ultratransparent oxyfluoride glass-ceramics for application in the 1.54 micron telecommunication window
Victor K. Tikhomirov, David Furniss, Angela B. Seddon, et al.
We have fabricated ultra-transparent glass-ceramics in the system (SiO2)(Al2O3)(CdF2)(PbF2)(ZnF2):x(ErF3). Intensity, width and Stark-splitting of emission and absorption spectra of Er3+-dopants at 1.5 micron (4I13/24I15/2 transitions) change with the size of PbF2 nano-crystals hosting Er3+ dopants. We report the broadest and flattest emission spectrum of Er3+ and largest wavelength divergence of emission and absorption spectra for 4I13/24I15/2 transitions to date. Er3+ dopants are efficient nucleation centres in (SiO2)(Al2O3)(CdF2)(PbF2)(ZnF2):x(ErF3) oxy-fluoride glasses when heat-treated at 20 to 80°C above glass transition temperature Tg. The emission spectrum of Er3+ at 1.54 micron for the resulting glass-ceramics (GC) is the broadest (75 nm at the half-height-width in developed GC and up to 90 nm in quasi GC) and flattest (especially between 1530 to 1560 nm in quasi GC) to date to our knowledge. The broadness is of benefit for Erbium Doped Fibre Amplifier (EDFA) operating in the 1.54 micron fibre optic telecommunication window. The flatness is of benefit in the most often employed C-band of EDFA. We have achieved the largest reported wavelength divergence to date in the maximum of absorption (1505 nm) and emission (1544 nm) spectra of Er3+ in developed GC, which again is of benefit for reduction of noise in the EDFA caused by overlap of emission and absorption bands at about 1.54 μm (i.e. self-absorption).