Proceedings Volume 7591

Advanced Fabrication Technologies for Micro/Nano Optics and Photonics III

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Proceedings Volume 7591

Advanced Fabrication Technologies for Micro/Nano Optics and Photonics III

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Volume Details

Date Published: 16 February 2010
Contents: 10 Sessions, 30 Papers, 0 Presentations
Conference: SPIE MOEMS-MEMS 2010
Volume Number: 7591

Table of Contents

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Table of Contents

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  • Front Matter: Volume 7591
  • Non-Diffraction Limited 3D Laser Lithography
  • Nanofabrication I: Photonic Nanostructures
  • Advanced Lithography
  • New Materials
  • Laser-Based Fabrication
  • Nanofabrication II: Active and Passive Devices
  • Nanofabrication III: Growth and Deposition
  • Micro- and Nano-Optics
  • Poster Session
Front Matter: Volume 7591
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Front Matter: Volume 7591
This PDF file contains the front matter associated with SPIE Proceedings Volume 7591, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.
Non-Diffraction Limited 3D Laser Lithography
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Two-color photo-initiation/inhibition lithography
Robert R. McLeod, Benjamin A. Kowalski, Michael C. Cole
Traditional photolithography begins with single-photon absorption of patterned light by a photo-initiator to locally expose a resist. In two-color photo-initiation/inhibition (2PII) lithography, these exposed regions are confined by a surrounding pattern of inhibitors generated by one-photon absorption of a second color in a photo-inhibitor. Like a stencil used to confine spray-paint to a thin, sharp line, the inhibitory pattern acts as a remotely programmable, transient near-field mask to control the size and shape of the modified resist region. The inhibiting species rapidly recombine in the dark, allowing for fast sequential exposures and thus enabling fabrication of complex two- or threedimensional structures.
3D biomedical implants fabricated using direct laser writing
C. Schizas, V. Melissinaki, A. Gaidukeviciute, et al.
We present our investigations into the design and fabrication of a complex shape, readily assembled micro check-valve using the two-photon polymerization technique and a hybrid material. A computational fluid dynamics study has been carried out in order to evaluate the flow performance of the valve under blood pressures exhibited in healthy human veins. The fabricated micro-valves exhibit good dimensional accuracy when compared to the CAD-created valve design and the capability of an internal moving component to perform its intended function.
Nanofabrication I: Photonic Nanostructures
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Fabrication of vertical silicon nanowire photodetector arrays using nanoimprint lithography
Hongkwon Kim, Arthur Zhang, Yu-Hwa Lo
Nanoimprint lithography (NIL) is an attractive method for its ability to quickly and cheaply pattern nano-scaled dimensions, and is an enabling technology for patterning large area substrates. The benefits of NIL are demonstrated through its application towards large area nanowire image arrays. In this work, we have fabricated and characterized top down silicon nanowire detector arrays by using UV curing NIL and deep Reactive Ion Etching techniques. Fabricated devices show over 106 gain value at low incident light power, which is comparable to high sensitivity of an e-beam written lithography device. This technology is suitable for fabrication of high density, addressable imager arrays.
Critical nanofabrication parameters for the e-beam assisted design of a subwavelength aluminum mesh
Using finite difference time domain simulations and e-beam assisted lithography we designed and fabricated high transmission transparent contacts for UV nitride devices which consist in perpendicular sets of parallel aluminum lines with a period as low as 260 nm. Transmittance values as high as 100% were predicted for aluminum meshes with the optimized periods, metal line widths and thicknesses. Simulations were compared with optical transmittance measurements. The critical parameters -such as grain size, edge roughness and mesh coating- were determined. The large aluminum grain was decreased by performing a cold aluminum deposition. The aluminum oxide layer over the aluminum mesh was found to reduce the mesh transmittance. Several alternatives were studied to overcome this issue such as coating the mesh with a thin gold or silicon dioxide layer. While the second option appeared promising the addition of the gold layer required much more improvement.
Low-cost optical microstructures fabricated by imprinting porous silicon
Judson D. Ryckman, Marco Liscidini, J. E. Sipe, et al.
We present a direct-to-device method for stamping porous silicon to produce optical microstructures. The stamping technique utilizes a reusable silicon stamp fabricated by standard lithographic methods. Large area (9mm2) stamps are applied to single layer thin films of porous silicon with a force on the order of 1kN. The process affords precise control over both lateral and vertical dimensions of patterning while maintaining large area uniformity. We demonstrate tunable imprint depths in the 10nm-120nm range as well as lateral feature sizes down to 0.25μm. Imprinted structures are characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and optical diffraction experiments. By utilizing reusable stamps and a straightforward technique, the overall process can be performed at low-cost and high throughput. This enables a wide variety of optical microstructures to be readily fabricated. As an example, we present a porous diffraction grating and demonstrate proof-of-concept sensing capabilities, for exposure to water vapor as well as small molecules (3-aminopropyltriethoxysilane). Additional device structures enabled by this fabrication process are also discussed. The stamping process is expected to be applicable to other porous materials such as porous titania, porous alumina, and porous silica.
Hollow ARROW waveguides on self-aligned pedestals for high-sensitivity optical sensing
Evan J. Lunt, Brian S. Phillips, Jared M. Keeley, et al.
Antiresonant reflecting optical waveguides (ARROWs) provide a promising approach to realizing high-sensitivity sensing platforms on planar substrates. We have previously developed ARROW platforms that guide light in hollow cores filled with liquid and gas media. These platforms include integrated traditional solid waveguides to direct light into and out of sensing media. To improve the sensitivity of these platforms for optical sensing, hollow waveguide loss must be reduced. We are working towards this by using anisotropic plasma etching to create near-ideal hollow ARROW geometries. These structures rely on an etching mask that also serves as the sacrificial core for the waveguide. This self-aligned process creates a hollow waveguide on a pedestal which is surrounded by a terminal layer of air in three directions. We previously produced ARROWs by pre-etching the silicon substrate and aligning the sacrificial core to the pedestal. However, this necessitates using a pedestal which is wider than the core, leading to higher loss and poor reproducibility. We have also increased the hollow to solid waveguide transmission efficiency by using a design that coats the sides and top of the hollow core with a single layer of silicon dioxide. Using this design, we have demonstrated an interface transmission improvement of more than two times. A much improved optical sensor platform will incorporate both of these features, using the self-aligned pedestal process for most of the length of the hollow waveguides to decrease loss, and employing the single layer design only at the interfaces to improve hollow-solid waveguide coupling.
Inkjet printing techniques for the fabrication of polymer optical waveguides
Nicholas A. Vacirca, Timothy P. Kurzweg
A great deal of attention in recent years has been given to inkjet printing as an alternative to traditional lithographic techniques due to its potential for low cost and rapid turnaround fabrication. A Dimatix DMP-2831 materials printer is used to inkjet print polymer waveguides of SU-8 negative photoresist. Several obstacles must be overcome for the technology to be feasible on a large scale including the development of capable print devices, suitable materials for printing, and the ability to consistently and precisely print high-aspect-ratio geometries. We will discuss the inkjet printing fabrication process, explore some of the difficulties encountered through the method, present several of our first prototype waveguides, and report some preliminary results on waveguide characterization.
Advanced Lithography
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Design, fabrication, and control of scanning plasmonic probe for near-field photolithographic applications
Yu-Yen Huang, Yuyan Wang, Kazunori Hoshino, et al.
We report the design, fabrication and operation of a scanning plasmonic probe compatible with a fully customized Near-field Scanning Microscope system. The probe is a silicon cantilever with a hollow pyramidal probe tip. A silicon dioxide layer was thermally grown to form the probe. A 100 nm thick aluminum layer was then e-beam evaporated onto the released probe tip to form the metal-dielectric interface for surface plasmonic wave propagation. A 500 nm diameter aperture was subsequently milled with the Focus Ion Beam. The probe was controlled with a built-in scanning controller for the probe-sample distance using a force sensing tuning fork. A tapered optical fiber, connected to 405 nm wavelength laser source, was aligned to the backside of the probe tip to serve as the light source. The transmitted light through the aperture was used to expose the photoresist (AZ 5209E), on a piece of cover glass attached on the tuning fork. The probe was controlled for near-field photolithography, where a series of 15 exposures, varied from 0 to 8 minutes, were carried out on the photoresist stepwise at 6.5 μm separation with subsequent 60 seconds development time. The transmitted light beam spot was simulated with a Full Width Half Maximum of 227 nm. Atomic Force Microscope measurement showed a 200 nm lateral resolution for the photolithography. The depths and widths of the developed patterns were linearly correlated with increasing exposure time, showing slopes of 0.76 nm/second and 1.4 nm/second respectively.
Fabrication techniques of high aspect ratio vertical lightpipes using a dielectric photomask
Winnie N. Ye, Peter Duane, Munib Wober, et al.
We report the development of new fabrication techniques for creating high aspect ratio optical lightpipes in SiO2 layers of 10μm thickness and above. A dielectric photo mask was used for deep reactive ion etching. Our experiments show that CF4-based reaction gases were best for deep etching with high selectivity and etch rate. Trenches with diameters or width of 1.5μm were demonstrated, with an aspect ratio of 7.2:1 and a sidewall angle of 87.4 degrees. We also present the lift-off process of the etch masks and the via-filling procedures for the lightpipes. These structures are useful for image sensors, vertical interconnect and waveguiding applications.
New Materials
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Micro-patternable hybrid nanocomposites with tailorable mechanical and thermomechanical properties
Carsten Becker-Willinger, Pamela Kalmes, Petra Herbeck-Engel, et al.
A new type of cationically polymerizable organic-inorganic hybrid nanocomposite with micro-patternability and tailor able thermomechanical properties has been developed[1]. The material has been built by co-condensation of 3-glycidyloxypropyl-triethoxysilane and phenyltriethoxysilane followed by subsequent mixing with oligomeric cycloaliphatic epoxy resin as organic co-monomer. Nanocomposite mixtures have been formed by dispersing silica nanoparticles with 15 nm particle size into the performed matrix sol. To achieve an almost homogeneous distribution of the nanoparticles over the matrix different surface modifiers have been applied on the silica surface. The resulting transparent mixtures have been applied on silicon substrates and have been UV-polymerized using a cationic photoinitiator. The mechanical and thermomechanical properties as well as the resolution of photo patterns have been followed in dependence of the nanoparticulate filler content and the type of surface modification. Photo patterns could be created with high edge steepness even for highly filled systems. The universal hardness increased from 145 MPa for the unfilled hybrid resin to 244 MPa for the system containing 30 wt.-% silica. The same nanocomposite system showed an elastic modulus of about 5090 MPa compared to the unfilled hybrid resin of 3380 MPa which indicates the high potential of these materials forming mechanically stable patterns.
Laser-Based Fabrication
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Fabrication of micro- and nanostructures in thin metallic films by femtosecond laser ablation
We report maskless microfabrication of periodic structures in thin metallic films by femtosecond laser ablation. Two-dimensional (2D) triangular arrays of circular apertures with diameter of about 0.6-0.8 μm and a lattice period of 1.0 and 2.0 μm were fabricated by single- and multiple laser pulse ablation of 35 nm thick gold films sputtered on glass substrates. Optical transmission spectra of the fabricated samples exhibit transmission bands at infrared wavelengths. Theoretical modeling of the optical properties by Finite-Difference Time-Domain (FDTD) technique indicates that these bands are associated with localized and propagating surface plasmon (SP) modes. FDTD simulations also indicate substantial resonant enhancement of the near-field intensity at the metal's surface. Laser ablation of thin metallic films is therefore a promising route for fast prototyping of planar metallic micro- and nano-structures applicable as frequency-selective surfaces (FSS) and SP substrates.
Femtosecond laser photopolymerization of photonic and free-movable microstructures in sol-gel hybrid resist
We present the fabrication of microstructures for photonic and micro-/opto-fluidic applications using femtosecond laser 3D direct writing technique in zirconium-based sol-gel hybrid resist. The advantages and mechanism of photo-polymerization of this new material under fs-pulsed laser exposure are discussed. We suggest and achieve a novel method to fabricate free-standing and movable photonic microstructures, which exhibit much less distortion than the conventional structures attached to substrates, especially when made at close to the photopolymerization threshold. Fabrication of free-movable structures allows us to quantitatively study the shrinkage of photoresist and to improve the resolution. It also contributes to tuning the stop band position of photonic crystals to shorter wavelength. Furthermore, the demonstrated freely-movable property makes it possible to laser trap and manipulate photonic microstructures and have potential application in optofluidics and bio-applications.
Laser direct writing of submicron lines using micro- and nanofiber pens
Feng Tian, Guoguang Yang, Jian Bai, et al.
In this paper, a novel direct writing technique using micro- and nanofiber pens is presented. The micro- and nanofiber pen serves as a tightly confined point source and it adopts micro touch mode in the process of writing. The energy distribution of direct writing model is analyzed by Three-Dimension Finite-Difference Time-Domain method. The lines with feature sizes down to 100 nm are experimentally achieved by this technique. Experiments also demonstrate that direct writing using micro- and nanofiber pens has some advantages: simple process, large writing area, and controllable width of lines. In addition, by altering writing direction of lines, complex submicron patterns can be fabricated.
Nanofabrication II: Active and Passive Devices
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Challenges and opportunities of manufacturing the next generation of integrated photonics
R. Singh, N. Gupta, J. A. Sadie, et al.
Integrated photonics has the potential of fabricating a diverse set of photonic systems on a single substrate. At nanoscales (< 100 nm), the properties of material depend on quantum confinements. The challenge is to integrate these unique properties of nanostructures into low-cost manufacturing. For material deposition, a photo-assisted monolayer deposition technique can provide nanomaterials with an ultra-low defect density. Epitaxial dielectrics offer the possibility of growing defect-free optical materials including compound semiconductors on silicon substrates. In this paper, we have also provided manufacturing directions that must be incorporated for developing the next generation of integrated photonics.
Multiwavelength rolled-up InGaAs/GaAs quantum dot microtube lasers
We have studied the design, fabrication and characterization of free-standing rolled-up InGaAs/GaAs quantum dot microtube ring resonators, formed by the controlled release of coherently strained InGaAs/GaAs quantum dot heterostructures from the host substrate. The dependence of the 3-dimenionally confined optical modes on the tube wall thickness and surface geometry is investigated both theoretically and experimentally. We have further demonstrated optically pumped rolled-up microtube lasers at room temperature, which exhibit emission wavelengths in the range of 1.1 - 1.3 μm and a low threshold of ~ 4 μW. The design and fabrication of electrically injected rolled-up InGaAs/GaAs quantum dot microtube devices is also described.
Demonstration of thermal emission control
In this paper, we describe our efforts to control the thermal emission from a surface utilizing structured surfaces with metal/dielectric interfaces. The goal was not to eliminate the emission, but to control the output direction and spectrum. We focus on methods that lead to high emissivity at grazing angles, with low emission near normal. We describe the fabrication and measurement of large passive devices (15×15 mm) and arrays of smaller chips for thermal emission control in the longwave infrared (8 to 12 micron) spectral region. All the devices consist of a metal base layer covered with dielectric/metal posts or lines, 0.5 microns tall. The posts (0.9×0.9 micron) and lines (0.3 micron wide) are subwavelength. One-dimensional and two-dimensional devices with a 3 micron pitch will be shown. The devices are measured with both a hemispherical directional reflectometer and a variable angle directional emissometer. Both simulated and experimental results show the thermal emission effectively limited to a small spectral region and grazing angles from the surface (≥ 80°) in stark contrast to the typical Lambertian radiation seen from unstructured material. Finally, the effect of this thermal emission control is illustrated using an infrared camera.
Dry etching of TiO2/SiO2 DBR mirrors for tunable optical sensor arrays
O. Setyawati, M. Engenhorst, S. Wittzack, et al.
We have investigated the etching characteristics of high-index-contrast TiO2/SiO2 DBR mirrors by inductively coupled plasma reactive ion etching (ICP-RIE) with a focus on the etch rate and the etch selectivity by varying etch parameters (gas flow rate, RF and ICP power, pressure and temperature). Chrome, aluminum and ITO (indium tin oxide) were applied as etch masks. Various mixtures of SF6/Ar gas were used for the etch processes. An optimum etch profile was obtained with an etch rate of approximately 80 nm/min at a pressure of 6 mTorr and a temperature of 20 °C. The experimental results were applied to develop Fabry-Perot filters for tunable optical sensor arrays.
Nanofabrication III: Growth and Deposition
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Atomic layer deposition (ALD) for optical nanofabrication
ALD is currently one of the most rapidly developing fields of thin film technology. Presentation gives an overview of ALD technology for optical film deposition, highlighting benefits, drawbacks and peculiarities of the ALD, especially compared to PVD. Viewpoint is practical, based on experience gained from tens of different applications over the last few decades. ALD is not competing, but enabling technology to provide coatings, which are difficult for traditional technologies. Examples of such cases are films inside of tubes; double side deposition on the substrate; large area accurate coatings; decorative coating for 3D parts; conformal coatings on high aspect ratio surfaces or inside porous structures. Novel materials can be easily engineered by making modifications on molecular level. ALD coats large surfaces effectively and fast. Opposite to common view, it actually provides high throughput (coated area/time), when used properly with a batch and/or in-line tools. It is possible to use ALD for many micrometers thick films or even produce thin parts with competitive cost. Besides optical films ALD provides large variety of features for nanofabrication. For example pin hole free films for passivation and barrier applications and best available films for conformal coatings like planarization or to improve surface smoothness. High deposition repeatability even with subnanometer film structures helps fabrication. ALD enters to production mostly through new products, not yet existing on the market and so the application IP field is reasonably open. ALD is an enabling, mature technology to fabricate novel optical materials and to open pathways for new applications.
Modification of conformal-evaporated-film-by-rotation technique to improve uniformity of replicas of nonplanar biotemplates
We modified the conformal-evaporated-film-by-rotation (CEFR) technique to improve the uniformity of nominally ⪅ 1000-nm-thick films deposited on nonplanar biological templates to replicate surface features. The biotemplates selected are eyes harvested from Phormia regina, a common species of blow fly which has large compound eyes. Bulk chalcogenide glass with nominal composition Ge28Sb12Se60 was used as the source material for all coatings. The modified CEFR technique introduced a second degree of freedom in manipulating the biotemplate with respect to the average direction of the vapor flux. We were thus able to tailor the motion of the platform holding the biotemplate to improve the uniformity of the coatings. Cross-sectional images of the coated biotemplates obtained using microtomy and scanning electron microscopy confirmed the expected improvement.
Micro- and Nano-Optics
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Tolerancing and analysis of a diffractive beam shaper
This paper describes the design and analysis of a deep-UV diffractive beam shaper for converting a collimated Gaussian beam into a collimated flattop beam. Diffractive beam shapers can be manufactured in most common materials to provide good beam control with very low non-uniformity. Beam shapers, however, are generally very sensitive to beam parameters and alignment. Here we examine the sensitivity of the beam shaper to alignment and tilt of the input beam, phase surfaces, and various other fabrication errors. This device was successfully built and comparisons with laboratory measurements show excellent agreement with simulation predictions.
Precision glass molding: an integrative approach for the production of high precision micro-optics
Martin Hünten, Fritz Klocke, Olaf Dambon
Miniaturization and integration are the dominating factors for the success of numerous optical devices. Conventional manufacturing processes for the fabrication of precise glass optics by means of grinding and polishing cannot cope the increasing demands in terms of precision, volume and costs. Here, precision glass molding is the enabling technology to meet these demands of the future optical products and applications. Since the market requests further miniaturization and integration of the micro optical components the possession of the entire sequence of processes is absolutely essential. With the accomplished and ongoing developments at the Fraunhofer IPT, the replication of double-sided (a)spherical and (a)cylindrical glass lenses with form accuracies of < 150 nm as well as lens arrays and even freeform optics could be realized. Therefore, a sequence of processes needs to be passed. The FEM-simulation of the molding process which was driven to a point capable to simulate even the molding of freeform optics is the first process step. Further on, new mold design concepts were generated to enable the replication of free formed optics. The research works focusing on the mold manufacturing led to sophisticated grinding process strategies able to realized complex mold geometries such as lens arrays. With regard to the coating of the molds, proceedings were developed assuring a defect free and uniform coating which enables the longevity of the molds and therewith helps reducing the final costs per lens. Thus, the precision glass molding becomes more and more interesting even for highly complex mid volume lots, characteristic for European or US optics manufacturer.
Ion beam figuring (IBF) for high precision optics
Marcel Demmler, Michael Zeuner, Frank Allenstein, et al.
Recently and upcoming optical applications depend more and more on the precision of the optical elements used. The last is especially driven by shorter wavelength, higher flux densities and imaging close to the diffraction limit. Therefore a dramatically increasing demand on high precision and high quality optical components in leading edge equipment as well as common devices and instruments is observed. So far a few methods have been introduced to provide an adequate manufacturing performance using mechanical grinding and polishing techniques. Up to now the very sophisticated ion beam figuring (IBF) has not been used for common optics. The reasons for this might be the perception of higher costs and less knowledge about the technique in the industry. Now an affordable ion beam figuring technique has been developed to address precision aspherical optics applications. This paper introduces ion beam figuring technology based on equipment which is widely used in semiconductor mass production for ultra precise film thickness trimming. Ion beam figuring works by raster-scanning a focused broad ion beam across an optical surface with variable velocity and dwell time in order to precisely and locally trim away surface contour errors. As a new and cost effective approach the ion beam figuring system used in this presentation applies a 3 axis movement system only (compared to expensive 5-axis movements in other applications). X-and y-axes are used for the areal scan, and the z-axis is used for focus adjustment due to the surface contour of the optical element. The system was intentionally designed without the 2 additional tilt axes for incident angle adjustment and cleverly reduces the complexity and size of the system. It is shown that curved spherical or aspherical surfaces can be corrected down to λ/50 or better by using the state of the art 3-axes trimming system. Even with high spatial frequency parts final processing qualities better than λ/10 are achieved.
Multi-phase-level diffractive elements realized by binary effective medium patterns
Subwavelength structures open up the possibility to create an artificial index material which enables the realization of high-efficient diffractive structures. This can be used to generate optical elements with nearly arbitrary phase profiles. We demonstrate the realization of computer-generated holograms based on this effective medium approach. High diffraction efficiencies can be realized by multi-phase-level modulation based on two-dimensional binary nanostructures. The fabrication is performed by one lithographical step using a high-speed e-beam writer which allows high-resolution patterning even on large areas. A diffractive element in the visible range is experimentally demonstrated using the presented effective index approach.
Poster Session
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Fabrication of corrugated long-period fiber gratings by wet bulk micromachining
Chia-Chin Chiang, Liren Tsai, Hao-Jhen Chang, et al.
This study presents a novel fabrication method of corrugated long-period fiber gratings (CLPFG). The chemical wet etching process is used to fabricate the CLPFG, and the patterned SU-8 50 photoresist is used as etch mask. Since the CLPFG fabricated by the novel method reduces the complication and cost, it is suitable for mass production. In this study, the period of the CLPFG is 690 μm and the resonant-attenuation wavelength is 1558 nm. The maximum resonance-attenuation of the CLPFG is 23 dB. Eventually, the CLPFG in this study has demonstrated a high temperature sensitivity (60 pm/ °C), wavelength-shifting linearity (R2=0.99), and 1°C of resolution.
Dynamics of percolation phenomena in colloidal printing inks
Michael Angelo-Anthony Daniele, Alexandra L. Foguth, Parul Rungta, et al.
The conductivity of colloidal inks composed of poly(ethylene glycol) (PEG), 2-(4-tert-Butylphenyl)-5-(4-biphenylyl)- 1,3,4-oxadiazole (tPBD) or polystyrene-tPBD copolymerized colloids (PS-PBD) and carbon black (CB) were investigated to establish their percolation characteristics. The PS-PBD colloid supported inks (PEG/PS-PBD/CB) exhibited reduced percolation thresholds and enhanced conductivities above that of the individually carbon filled (PEG/CB) and small molecule blend (PEG/tPBD/CB) inks. Based on the DC conductivity analysis, the percolation threshold of the PEG/PS-PBD/CB composites was 3.6 vol%. The electrical resistivity of the PEG/PS-PBD/CB ink is lower than that of PEG/PBD/CB ink with the same CB content in the percolation region by 8 orders of magnitude. The percolation reduction was attributed to the heterogeneous dispersion of conductive filler aggregates "bridged" by PSPBD colloids. The aggregated dispersion of PS-PBD colloids in the ink matrix was characterized by photoluminescence spectroscopy (PL) which produced a red-shift at high concentrations, signaling the required proximity of PS-PBD colloids to form energy transfer complexes.
Antireflection on plastic substrates using ion etching with discontinuous metallic film
When a plastic substrate is under a highlight, the reflected light on the substrate always dazzles the observer. To prevent the effect, anti-reflected (AR) coating is applied. However AR-coating is difficult to be designed with wide wavelength range. In this research, the discontinuous metallic films were fabricated on the plastic substrates to reduce the reflection of the plastic substrates with wide wavelength range. To reduce more reflectance, the discontinuous metallic film can also be applied as the mask of selective ion etching to achieve rough surface. The results show the average reflectance of the AR-coating on the plastic substrates has been decreased 5%. The average transmittance has been increased 3%.
Quantum dots (QDs) immobilization on metal nanowire end-facets for single photon source application
J. Kim, B. C. Lee, C. Kang, et al.
We introduce a fabrication process to immobilize cadmium selenide (CdSe) Quantum Dots (QDs) on end-facets of metal nanowires, which can be possibly used as a cavity-free unidirectional single photon source with high coupling efficiency due to high Purcell factor. Nanowires were fabricated using E-beam lithography, E-beam evaporation, and lift-off process and finally covered with chemically deposited silicon dioxide (SiO2) layer. End-facets of metal nanowires were defined using wet etching process. QD immobilization was accomplished through surface modifications on both metal and QD surfaces. We immobilized thiol (-SH) functionalized 15 base pair (bp) ssDNA on Au nanowire surface to hybridize with its complimentary amine (- NH3) functionalized 15bp ssDNA and conjugated the amine functionalized 15bp ssDNA with QD. Presenting QD immobilization method showed high selectivity between metal nanowire and SiO2 surfaces.
Multi-photon polymerization of inorganic-organic hybrid polymers using visible or IR ultrafast laser pulses for optical or optoelectronic devices
Sönke Steenhusen, Thomas Stichel, Ruth Houbertz, et al.
Integrated passive and active devices are the key components in current and future information technology. In order to fulfill requirements in miniaturization for (integrated) optical or electronic devices, nano-scaled materials with a good compatibility to high-resolution processing techniques are needed. According to these requirements, multi-photon techniques attract much attention by providing a resolution far beyond the diffraction limit. The patterning of the inorganic-organic hybrid polymers, which are synthesized by catalytically controlled hydrolysis/polycondensation reactions, will be discussed with respect to the underlying photochemical processes. Emphasis will be on the direct writing of structures using femtosecond laser pulses, making use of two- and three-photon absorption (TPA/3PA) processes with visible or IR light, which also allows one to write arbitrary 3D structures. Due to the very sharp threshold fluence for these processes and its non-linear behavior, features down to 100 nm can be realized by choosing a suitable combination of material formulation and patterning parameters. Voxel arrays were written, whereas the resulting voxel sizes are compared to a growth model, and the influence of radical diffusion and chain propagation is discussed. In order to determine the TPA cross-section and to estimate the role of the photoinitiator, a z-scan experiment was realized. The initiators' cross-sections will be correlated to the resulting voxel sizes.
Device integration of Ti-catalyzed Si nanowires grown using APCVD
Mohammad A. U. Usman, Brady Smith
The integration of nanowires in photonic and photovoltaic devices have been discussed and studied by researchers for some time. Chemical vapor deposition (CVD) growth techniques has been one of the methods used for obtaining device quality nanowires that could potentially provide faster, and more efficient devices at smaller geometries. One dimensional metal catalyzed silicon nanowires grown using CVD techniques have been seen as a possible means to increasing electron transport and device speeds for silicon based electronics. In this experiment the possibility of integrating titanium catalyzed silicon nanowires grown using an atmospheric pressure based CVD method are investigated for possible use in silicon electronics. Growth experiments were conducted at various partial pressures of silicon tetrachloride, temperatures, and growth times to determine optimum growth rates and the window for oriented, straight silicon nanowires. Using linear regression analysis on a sample set of the grown nanowires we are left with the conclusion that nanowires grown using APCVD may possibly be growth limited due to diffusion through the solid catalyst interface and/or due to crystallization. Further experiments maybe needed to further validate titanium-catalyzed silicon nanowire growths and its optimum conditions. Overall, titanium-catalyzed silicon nanowires grown using an APCVD system provides a cost-effective method for growing silicon nanowires that could be used in future silicon based devices.