bluuebunny/crossref_metadata_2025 huggingface dataset:
Voc Saturation Effect in High-temperature Hydrogenated Polycrystalline Silicon Thin-film Solar Cells
Authors: Hidayat Hidayat , Widenborg Per I. , Aberle Armin G.
Published: September 2011

Hydrogenation of polycrystalline silicon thin-film solar cells is performed to improve the one-sun open-circuit voltage (Voc) of the device. Voc is found to increase linearly with increasing hydrogenation temperature and then saturates. For planar and textured samples, the Voc saturates at about 340 ºC and 307 ºC respectively. The low hydrogenation temperature helps to lower thermal budget during industrial process. Arrhenius plot of Voc prior to the saturation shows that the textured samples have lower activation energies than the planar sample. The activation energies of samples 188 (planar), 788 (textured) and 888 (textured) are 1.31 eV, 0.86 eV and 0.92 eV, respectively. The lower activation energies of the textured samples could be due to the shorter diffusion thickness and the increased surface area that is exposed to the hydrogen plasma.
11.0% Stable Efficiency on Large Area, Encapsulated a-Si:H and a-SiGe:H based Multijunction Solar Cells Using HF Technology
Authors: Banerjee A. , Beglau D. , Su T. , Pietka G. , Yue G. , Yan B. , Yang J. , Guha S.
Published: September 2011

We report on the investigation of large area a-Si:H/a-SiGe:H double-junction and a-Si:H/a-SiGe:H/a-SiGe:H triple-junction solar cells prepared by our proprietary High Frequency (HF) glow discharge technique. For investigative purposes, we initially used the simpler double-junction structure. We studied the effect of: (1) Ge content, (2) cell thickness, and (3) SiH4 and GeH4 gas flow on the light-induced degradation of the solar cells. Our results show that the double-junction cells with different Ge concentration have open-circuit voltage (Voc) in the range of 1.62-1.75 V. Voc exhibits a flat plateau in the range of 1.65-1.72 V for both initial and stabilized states. The light-induced degradation for cells in this range of Voc is insensitive to the Ge content. In terms of thickness dependence of the intrinsic layers, we found that the initial efficiency increases with cell thickness in the thickness range 2000-4000 Å. However, light-induced degradation increases with increasing thickness. Consequently, the stabilized efficiency is invariant with cell thickness in the thickness range studied. The results of SiH4 and GeH4 gas flow on cell characteristics demonstrate that the deposition rate decreases by only 20% when the active gas flow is reduced to 0.25 times standard flow. The initial and stabilized efficiencies are similar. The information gleaned from the study was used to fabricate high efficiency, large area (~464 cm2) double- and triple-junction solar cells. The highest stable efficiency, as measured by NREL, was 9.8% and 11.0% for the double- and triple-junction structures, respectively.
Sliver Solar Cell Technology: Pushing the Material Boundaries
Authors: Franklin Evan , Blakers Andrew , Weber Klaus , Everet Vernie
Published: September 2011

One of the primary objectives of the global photovoltaic research community is to effect significant manufacturing cost reductions, either by reducing material and processing costs or by increasing solar cell efficiency. One very promising technology for achieving both of these goals is Sliver technology, which offers potential for a 10- to 20-fold reduction in the consumption of purified silicon, while at the same time achieving very high cell efficiencies by fully exploiting the advantages of mono-crystalline silicon.

Sliver solar cells are thin, mono-crystalline silicon solar cells fabricated using a combination of micro-machining techniques and standard silicon device fabrication technologies. Rather than fabricating a single solar cell on the surface of a wafer, many hundreds to several thousand individual Sliver solar cells are fabricated within a single wafer. The dimensions of a Sliver cell depend upon wafer size, wafer thickness, and the micro-machining method employed.Cells typically have a length of 5 – 12cm, a width of 0.5 – 2mm, and a thickness of 20 – 60 micron. 20% efficient Sliver solar cells using standard cell processing methods and a robust processing sequence, have been fabricated at ANU. Current research efforts are directed towards developing and establishing new fabrication techniques to further simplify the fabrication sequence and to improve cell efficiency.

This paper presents an overview of Sliver technology. The fabrication method and some key challenges in producing Sliver cells is presented along with the measured performance of cells fabricated in the ANU solar research laboratory.
Band energy structure arrangement for organic solar cells with metalized deoxyribonucleic acid strands on anode electrode
Authors: Guvenc Ali Bilge , Guo Shirui , Ozkan Cengiz , Ozkan Mihrimah
Published: September 2011

Deoxyribonucleic acids provide exciting opportunities as templates in self assembled architectures and functionality in terms of optical and electronic properties. In this study, we investigate the effects of metalized DNA sequences in organic bulk-heterojunction solar cells. These effects are characterized via optical, quantum efficiency and current-voltage measurements. We demonstrated that by arranging the band energy structure of the devices via placing metalized deoxyribonucleic acid sequences on the hole collection side of the active layer lead to a 20% increase in the power conversion efficiency.
The two origins of p-type conduction in transparent conducting Ga-doped SnO2 thin films
Authors: Wang Huan-hua , Yang Tieying , Wang Baoyi , Ibrahim Kurash , Jiang Xiaoming
Published: September 2011

The p-type conduction in transparent Ga-doped SnO2 thin films was realized and its two origins were discerned through comparison experiments associated with growth conditions, Rutherford backscattering spectroscopy and x-ray photoelectron spectroscopy analysis. All the experiment results suggest that the adsorbed oxygen both in the grain boundaries and at the surfaces is another origin of the net hole conduction in the polycrystalline thin films. This mechanism provides a fairy well explanation for the growth temperature dependence of the p-type conductivities of the films. It also offers a useful guide to better the properties of p-type conducting oxide thin films.
Identification of Impurity Phases in Cu2ZnSnS4 Thin-film Solar Cell Absorber Material by Soft X-ray Absorption Spectroscopy
Authors: Bär M. , Schubert B.-A. , Wilks R.G. , Marsen B. , Zhang Y. , Blum M. , Krause S. , Yang W. , Unold T. , Weinhardt L. , Heske C. , Schock H.-W.
Published: September 2011

The composition of Cu2ZnSnS4 thin-film solar cell absorbers was varied to induce the.formation of secondary impurity phases. For their identification, the samples have been investigated by Cu L3 and S L2,3 soft x-ray absorption (XAS) spectroscopy. We find that Cu L3 XAS is especially sensitive to the presence of copper sulfides as well as copper oxides and/or changes in the electron configuration, suggesting a basis for future studies of the surface, defect, and interface characterization of similar samples. Additionally, it is shown that the S L2,3 absorption data can be used as a very sensitive probe of the variations in the prevalence of S-Zn bonds in the near-surface region of the investigated samples.
Structure and photocatalytic properties of Bi25FeO40 crystallites derived from the PEG assisted sol-gel methods
Authors: Bu Shundong , Cai Dengrong , Li Jianmin , Yu Shengwen , Jin Dengren , Cheng Jinrong
Published: September 2011

Sillenite Bi25FeO40 crystallites have been fabricated via a sol-gel approach. X-ray diffraction results show that single-phase Bi25FeO40 can be synthesized at the annealing temperature of 600 oC with the help of PEG additive. The amount of additives and the annealing temperature has great effects on the formation of phase pure Bi25FeO40 crystallites. The morphologies of Bi25FeO40 crystallites were observed by SEM techniques. UV-vis diffuse reflectance spectroscopy indicated the good visible light absorption of Bi25FeO40 crystallites. The photo-catalytic activity of Bi25FeO40 powders was evaluated by the degradation of methyl orange solution assisted by H2O2 under UV-Vis light and Vis-only light irradiation, which suggested that Bi25FeO40 crystallites are potential photocatalytic materials.
New designs of hydrophobic and mesostructured Ultra Low k materials with isolated mesopores
Authors: Grunenwald Anthony , Ayral André , Albouy Pierre Antoine , Rouessac Vincent , Jauffres David , Verdier Marc , Gergaud Patrice , Licitra Christophe , Zenasni Aziz , Jousseaume Vincent , Simon Jean-Paul
Published: September 2011

In this work, hydrophobic mesostructured organosilica thin films, exhibiting isolated mesopores (~ 7 nm), have been successfully deposited by spin-coating using different polystyrene-block-polyethylene oxide copolymers (PS-b-PEO) as structure-directing agents and methyltriethoxysilane (MTES) as organosilica precursor. Different ordered mesostructures (Face Centered Cubic, 2D or 3D Hexagonal and Body Centered Cubic) can be achieved by controlling different synthesis parameters. X-Ray Diffraction (XRD) and Grazing Incidence Small Angle X-Ray Scattering (GISAXS) techniques were used to investigate the mesostructure evolution through thermal and UV treatments. Swelling and shrinkage were evidenced by in-situ XRD and X-Ray Reflectivity measurements during the thermal removal of the meso-templates. Infrared spectroscopy and 29Si NMR were additionally used to investigate the microstructure evolution. The film porosity was estimated thanks to Ellipsometry Porosimetry (EP). Correlation between mechanical properties through nanoindentation measurements and the mesostructure ordering is discussed as well as assessments of the dielectric constant k by mercury contact probe.
Patterning Organic Fluorescent Molecules with SAM Patterns
Authors: Wu Qiong , Hao Juanyuan , Shi Shoulei , Wang Weifeng , Lu Nan
Published: September 2011

We report a low-cost and high-throughput method to fabricate large-area light emitting pattern via thermal evaporation of organic molecules on the patterned self-assembled monolayer of homogenous 3-aminopropyltrimethoxysilane. This method is based on the selective deposition of the organic light emitting molecules on the template of self-assembled monolayer (SAM), which is patterned with nanoimprinting lithography. The selectivity can be controlled by adjusting the design of the pattern, the storage duration and the substrate temperature. The deposition selectivity of the molecules may be caused by the different binding energy of the molecules with the SAM and the substrate surface.
Microstructure of sputter-deposited noble metal-incorporated oxide thin films patterned by means of laser interference
Authors: Catrin Rodolphe , Gries Thomas , Horwat David , Migot Sylvie , Muecklich Frank
Published: September 2011

Laser interference patterning-induced microstructural modifications have been investigated in two noble metal-incorporated oxide thin film systems: Pd0.25Pt0.75Ox and gold-incorporated yttria-stabilized zirconia - Au-YSZ. Transmission electron microscopy was used to investigate the influence of the laser treatment on the microstructure of the samples. In the case of Pd0.25Pt0.75Ox, the formation of a nanocomposite arrangement resulted from the precipitation of metal nanograins in the oxide matrix triggered by laser irradiation. In Au-YSZ, the starting microstructure consisted of gold nanograins embedded in a YSZ matrix. A noticeable growth and coalescence of gold nanograins occurred near the surface in the region of maximum interference. Simultaneously, a foamy morphology, mostly consisting of gold crystals, was formed at the film surface. In contrast to thermal annealing, the laser treatment proposed here is a fast procedure to partially relocate gold at the film surface and provide a local solid lubrication.
Experimental Demonstration of Hopfield Neural Network using DNA molecules
Authors: Akin Hayri E. , Karabay Dundar , Mills Allen P. , Ozkan Cengiz S. , Ozkan Mihrimah
Published: September 2011

DNA Computing is a rapidly-developing interdisciplinary area which could benefit from more experimental results to solve problems with the current biological tools. In this study, we have integrated microelectronics and molecular biology techniques for showing the feasibility of Hopfield Neural Network using DNA molecules. Adleman’s seminal paper in 1994 showed that DNA strands using specific molecular reactions can be used to solve the Hamiltonian Path Problem. This accomplishment opened the way for possibilities of massively parallel processing power, remarkable energy efficiency and compact data storage ability with DNA. However, in various studies, small departures from the ideal selectivity of DNA hybridization lead to significant undesired pairings of strands and that leads to difficulties in schemes for implementing large Boolean functions using DNA. Therefore, these error prone reactions in the Boolean architecture of the first DNA computers will benefit from fault tolerance or error correction methods and these methods would be essential for large scale applications. In this study, we demonstrate the operation of six dimensional Hopfield associative memory storing various memories as an archetype fault tolerant neural network implemented using DNA molecular reactions. The response of the network suggests that the protocols could be scaled to a network of significantly larger dimensions. In addition the results are read on a Silicon CMOS platform exploiting the semiconductor processing knowledge for fast and accurate hybridization rates.
Improvement of solubility and biocompatibility of MnO based nanoparticles in aqueous solutions
Authors: Koll Kerstin , Schladt Thomas D. , Weber Stefan , Jochum Florian D. , Theato Patrick , Schreiber Laura M. , Tremel Wolfgang
Published: September 2011

MnO nanoparticles were surface modified using two different multifunctional polymers. By introducing a PEG group, the long term stability, MRI applicability and sterile filtration could be greatly improved. Furthermore, PEGylated MnO NPs were less toxic compared to non-PEGylated NPs. The results suggest that these nanoparticles are suitable for in vivo applications.
Rational Designs on TiO2-based Nanocomposites for Solar Photocatalytic Purification
Authors: Gao Shanmin , Xu Tao
Published: September 2011

We report an template-free process to fabricate S-C-codoped and (I2)n-C-codoped meso/nanoporous TiO2 nanocrystallites. Methylene blue solutions are used as a model pollute to evaluate the sorption and photocatalytic activity of the samples under visible light radiation. The high photocatalytic activity in visible light region of our samples is attributed to numerous oxygen vacancies, large specific surface area and the continuous states in the band gap of TiO2 introduced by I2 or S doping.
Anodically Fabricated Sr-doped TiO2 Nanotube Arrays for Photoelectrochemical Water Splitting Applications
Authors: Hamedani Hoda A. , Allam Nageh K. , Garmestani Hamid , El-Sayed Mostafa A.
Published: September 2011

The present work reports the synthesis of self-organized strontium-doped titania nanotubes arrays as a potential material for photocatalytic water splitting. Electrochemical anodization process was used to grow such material under various electrochemical conditions. The effect of dopant concentration on the morphology and photoelectrochemical properties of the material was investigated. The microstructure, morphology and composition of as-prepared and heat treated nanotubes were characterized by field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS). The results showed that increasing the dopant concentration up to its solubility limit results in higher photoelectrochemical activity. A preliminary proof of concept of the photocatalytic activity of the fabricated material was estimated in terms of the use of such material as a photoanode for photoelectrochemical water splitting.
Morphology and Electronic Structures of Calcium Phosphate Coated Titanium Dioxide Nanotubes
Authors: Liu Lijia , Kim Sun , Chan Jeffrey , Sham Tsun-Kong
Published: September 2011

Titanium dioxide nanotubes (TiO2-NT) have been synthesized via an electrochemical anodization strategy followed by calcination under different temperatures to form TiO2 nanostructures of anatase and rutile crystal phases. The nanotube-on-Ti structure is further used as a substrate for calcium hydroxyapatite (HAp) coating. The effect of TiO2 morphology and crystal phases (i.e. amorphous, anatase and rutile) on the coating efficiency of HAp has been investigated in comparison with HAp coating on bare Ti metal. The HAp coated TiO2-NT have been studied using X-ray absorption near-edge structure (XANES) at the Ti K- and Ca K-edge. The results show that TiO2 of amorphous and anatase phases are of comparably good performance for HAp crystallization, and both are better than rutile TiO2, while HAp is hardly found on bare Ti. The implications of the findings are discussed.
Microcapsule-based materials for electrophoretic displays
Authors: Dai Runying , Wu Gang , Yin Peipei , Chen Hongzheng
Published: September 2011

Electrophoretic displays, the rewritable non-light-emitting display technology based on the movement of colored pigments inside a low dielectric liquid as a voltage is applied, have attracted a great deal of academic and commercial interests due to the combination of the advantages of both electronic displays and conventional paper, including paper-like high contrast appearance, ultra-low power consumption, thinness, flexibility etc. Fabrication of electrophoretic ink by microencapsulating the electrophoretic suspension into individual microcapsules is one way to realize such application. However, there are still some limitations for its commercial application, such as the dispersion and the electrophoretic mobility of charged particles due to the nano-particles aggregation, the barrier property and stability of microcapsule wall due to the suspension releasing, etc. In this presentation, systematic studies on the preparation of electrophoretic particles and microencapsulation by complex coacervation method were carried out to solve the mentioned problems. The obtained microcapsules can be quasi-monolayer coated on ITO/PET substrate and driven by static mode to obtain a matrix character display prototype.
Hybrid Aerogel-MLI Insulation System Performance Studies for Cryogenic Storage in Space Applications
Authors: Begag R. , White S. , Fesmire J.E. , Johnson W.L.
Published: September 2011

Long duration storage of large quantities of cryogenic fluids for propulsion, power, and life-support is an essential requirement for missions into space. Efficient and reliable insulation materials are key to the success of these missions. The required insulation material must outperform the current standard multi-layer insulation (MLI) for thermal insulation and provide additional features such as durability, micrometeoroid orbital debris protection, and flexibility, all in one single-layer material. Ultra-low density and highly hydrophobic fiber reinforced aerogel material integrated with MLI has the potential to offer a great insulation package which will overcome several issues that the current standard MLI alone suffers from such as: 1) damage during installation, 2) high cost, and 3) degradation over time. The hybrid aerogel/MLI solution affords a more reliable alternative because it is robust, and will outperform the MLI in cases of vacuum loss. Low density and highly resilient methylsilicate aerogel will contribute less solid conductivity to the overall heat transfer within the aerogel/MLI system. Sol-gel optimization of low density and low dust methylsilicate aerogels will be presented. Thermal performance of two prototypes of hybrid aerogel/MLI composites and a baseline MLI system (1 inch thick, 90 layers) fabricated by Aerospace Fabrication and Materials (AFM) and tested at cryogenic temperatures under different vacuum level conditions (at Cryogenic Laboratory, NASA KSC) will also be presented.
Design and Functionalization of Magnetic Core-Shell Oxide Nanoparticles Exhibiting Exchange Bias Features
Authors: Mammeri Fayna , Mamèche Faïza , Kataya Zeinab , Yaacoub Nader , Slawska-Waniewska Anna , Menguy Nicolas , Grenèche Jean-Marc , Ammar Souad
Published: September 2011

Core-shell magnetic nanoparticles (CSNPs) composed of a ferrimagnetic core (CoFe2O4) embedded in an antiferromagnetic shell (CoO) were produced using seed mediated growth in a polyol. Different core sizes and shell thicknesses were considered. The structural and magnetic properties of assemblies of these nanoparticles were characterized by means of X-ray Diffraction, Transmission Electron Microscopy, dc-magnetometry (SQUID) and 57Fe Mössbauer spectrometry. The measured EB magnetic field values, at low temperature, are found to be weak whatever the microstructural characteristics of the studied CSMNPs. Simultaneously, both the magnetization and the interparticle interaction (mainly dipolar) appear clearly reduced when the shell thickness increases.
Effects of direct lateral Current Injection on the Performance, Overall Efficiency and Emission Distribution in GaN LED structures: a 2D Computational Study
Authors: Kivisaari Pyry , Oksanen Jani , Tulkki Jukka
Published: September 2011

We study and demonstrate the potential benefits of using a transverse junction structure in GaN LEDs by simulating and comparing the structure with conventional vertical injection structures.The direct current injection component enabled by the transverse structure significantly reduces the height of the polarization-induced potential barriers and facilitates the electron flow into the active material, improving the overall efficiency. In addition, the transverse junction structure enables a more even radiative recombination distribution from different quantum wells. We estimate the attainable optical output efficiency and also discuss the influence of the active layer design on the quantum efficiency. Based on the obtained results, shifting from the conventional 1-dimensional LED structures to genuinely 2-dimensional structures may allow new possibilities to optimize LED performance.
Electromechanical Response of Multilayered Polymer Films for High Energy Density Capacitors
Authors: Wolak Mason A. , Shirk James S. , Mackey Matt , Carr Joel , Hiltner Ann , Baer Eric
Published: September 2011

Multilayered films comprising alternating layers of polycarbonate (PC) and poly(vinylidene fluoride-hexafluoropropylene) (P[VDF-HFP]) show an enhanced dielectric strength (EB> 750 kV/mm) and an increased energy storage density (Ud ~ 13.5 J/cm3) compared to monolithic PC and P[VDF-HFP] films. Here the role of electromechanical effects in the breakdown of multilayer films is explored both by imaging the changes in the layer structure caused by electrical fields below the breakdown field and by a direct measurement of the strain in multilayer PC/ P[VDF-HFP] films subjected to similar fields. Focused Ion Beam (FIB)/ Scanning Electron Microscopy (SEM) images of the layer structure in films subjected to repeated cycles at near-breakdown fields showed local changes in the thickness of individual layers, suggesting that mechanical forces arising from field-induced compression may play a role in the steps preceding the breakdown. The directly measured field induced strain showed evidence for both an elastic and a flow component to the strain. The mechanical responses of films with ≤ 50 vol% P[VDF-HFP] were modeled as simply the sum of an elastic and viscous flow. The observed electromechanical properties vary with the layer structure. This suggests that multilayering polymers may provide a means to mitigate deleterious electromechanical effects in low modulus, high dielectric materials.
The Study about the Control of Defect Factors to Improve Properties of P(VDF-TeFE) Thin Film
Authors: Jeong Jong-Hyeon , Terashima Daiki , Kimura Chiharu , Aoki Hidemitsu
Published: September 2011

In order to apply P(VDF-TeFE) piezoelectric polymer to micro-generator as a membrane, the polymer is deposited on a substrate by spin-coating method. Since a solvent affects the film properties and surface stability, we have carried out the thermal process at a temperature higher than melting point. In the annealing process of a P(VDF-TeFE) thin film, electrical properties of the film was improved by an application of an electric field. The established study was the investigation of variations in characteristics by an application of a certain electric field. We have attempted to measure about the critical intensity of an electric field and investigate what the influences of the application is caused using a XPS spectrum in this study. Moreover, in order to control the intrusion of impurities, we have used the vacuum chamber to carry out the annealing process in it.
Characterization and Optimization of Fluid Flow in a High Biot Number System
Authors: Wlezien Richard , Prapas Jason , Briggs Sarah , Hodes Marc , Manno Vincent , Matson Douglas , Chiesa Luisa
Published: September 2011

Experiments and analysis have been conducted to characterize flow separators used in applications where heated fluid passes between layers of solid material such as in the manufacturing of gelatinous materials. The Biot number of the configuration is the key parameter, and must be taken into account when optimizing performance. It is shown that most prior work was for low Biot number systems, and the particular configurations under consideration operate at high Biot number. Existing designs developed for lower Biot number (such as membrane filter spacers) are shown to perform poorly for this application. An experimental apparatus was designed and fabricated to quantitatively assess pressure drop through the system using different separation strategies. These results were compared with a simplified two-term model based on the physics of viscous drag in these devices. Channels without separators behave like classical Poiseuille flow. Channels with separators can be modeled with a two-term equation: a baseline Poiseuille term and a form drag term. A variety of separator designs are compared and their overall performance is discussed. We also illustrate the high sensitivity to gap height in all configurations.
A Hexagonal Pillar Array of Thermo-responsive Soft Actuators Prepared by Nanoimprinting
Authors: Wu Ching-Mao , Lin Szu-Yin , Huang Kuo-Tung
Published: September 2011

Thermo-responsive actuation (thermomechanical effects) based on nematic liquid crystal elastomers (LCEs) have become a research priority in the preparation of soft actuators. Nematic LCEs combine the anisotropic features of liquid crystal phases with the rubber elasticity of polymer network. When heated at nematic to isotropic phase transition temperature (N-to-I temp.), a uniaxial thermomechanical deformation of LCEs will undergo at nearly constant volume due to a change of LC director order. Recently, an array of the micro-sized LCE pillars related to such thermomechanical effects have been successfully constructed through a soft lithography technology (i.e., replica molding). The prepared LCE pillars are mono-dispersive and micro-sized. They also possess N-to-I temp. higher than 100°C, largely limiting the available application. By contrast, the present study will report a hexagonal array of nano-sized thermo-responsive pillar actuators that are able to contract and expand in response to temperature changes around a lower N-to-I temp. is manufactured via using reactive rod-like liquid crystal and ultraviolet nanoimprinting technology. According to atomic force microscope (AFM) observation, a hexagonal array of pillars can be easily constructed by nanoimprinting and a responsive surface with a thermo-stimuli-driven roughness change is achieved. The room-temperature AFM scans quantitatively represent the single pillar shows a diameter of ca. 270 nm and 140 nm in depth, and the pitch meaning the averaged inter-pillar distance is measured as ca. 425 nm, thus lying in a nano-sized range. Furthermore, temperature-variable AFM is also utilized to demonstrate the pillar behaves as a thermally-stimulated nano-sized actuator. In our case, when heated above N-to-I phase transition temperature (ca. 65°C), it is clearly observed that the pillar diameter is expanded in the order of over 12-15 % and then reversibly contracted in response to temperature drop.
A Patterned Conducting Polyaniline Layer on a Non-Conducting Polymer Matrix
Authors: Song Edward , Choi Jin-Woo
Published: September 2011

Polyaniline is one of the most studied conducting polymers and its properties have been used in many sensor applications including gas sensors and pH sensors. In this work, we present a method that is able to embed a conducting polyaniline film in a desired pattern onto a nonconducting polymer matrix. We have developed an embedded polyaniline film on a polydimethylsiloxane (PDMS) matrix using a cast molding technique. The polyaniline film was grown by electrochemically polymerizing polyaniline from an electrolyte containing sulfuric acid and aniline monomer. A three-electrode cell system was used with a standard Ag/AgCl reference electrode, a gold auxiliary electrode, and a patterned gold working electrode. After the polyaniline film was formed on the patterned working electrode, PDMS was poured atop and cured. Cured PDMS was then debonded along with the polyaniline film embedded on the PDMS layer or block. The gold layer of the working electrode can be patterned using a photolithography steps so that the designed pattern can be transferred by the polyaniline growth on the working electrode. The greenish color of the polyaniline film indicated that the embedded polyaniline was in the conducting state (emeraldine salt form) and the conductivity of the polyaniline has also been verified by applying a DC voltage across the film and measuring the current through the polyaniline layer. The measured conductivity of the PANi layer at room temperature was in the range of 4.5 ~ 4.6 S/m. The advantage of this technique is that the PDMS matrix holds the polyaniline in place while allowing the polyaniline film to undergo reversible doping/dedoping chemistry when electrolyte solution comes into contact with the surface of the film. The developed technology can be used for various chemical sensor applications, for example, a pH sensor or gas sensors where a flexible and all-polymer apparatus is needed.
Temperature-adaptive Insulation Based on Multicomponent Fibers of Various Cross-sections
Authors: DeCristofano Barry S. , Fossey Stephen A. , Welsh Elizabeth A. , Perry Jeffrey , Archambault Deana
Published: September 2011

We have developed a thermal insulation based on bi-component fibers that adapts to its thermal environment, providing greater insulation at low temperatures than at warmer temperatures. The analysis of bi-metallic strips done by Timoshenko [1] for strips of rectangular cross-section concluded that “…curvature is proportional to the difference in elongation of the two metals and inversely proportional to the thickness of the strip.” We have extended Timoshenko’s formulation and applied it to bi-component fibers of circular and triangular cross-sections. In each case, the curvature resulting from the balance of the axial forces and bending moments has been brought into a standard form inversely proportional to (A+Bn+C/n) where n is the ratio of the moduli and A, B, and C are functions of the geometry of the two components. An important consequence of this result is that for any “n” there is a maximum curvature where (A+Bn+C/n) is a minimum. We have used the process of melt-spinning to produce fibers with circular and triangular cross-sections, varying the proportion of the two components. The polymers used have widely different coefficients of thermal expansion. These fibers spontaneously form mats at room temperatures. The experimentally measured thickness changes are in good agreement with the analytical results for fiber bending. The most effective samples to date change thickness by more than 1.5% per degree C (30% over a temperature range from approximately 20°C to 0°C).
Electron Phase Microscopy of Magnetic Fields in Ferromagnets and Superconductors
Authors: Tonomura Akira
Published: September 2011

Highly sensitive electron phase microscopy based on the Aharonov-Bohm (AB) effect principle has been used to observe microscopic distributions of magnetic fields in ferromagnets and superconductors. The observation examples include the unconventional behaviors of interlayer Josephson vortices in anisotropic layered high-Tc superconducting YBa2Cu3O7-δ (YBCO) thin films, which are produced when the applied magnetic field is greatly tilted to the layer plane, and the magnetic-field distributions of tiny magnetic heads for perpendicular recording and of colossal magnetoresistance (CMR) materials.
Influence of Heat Treatment on the Physical Transformations of Flint Used by Neolithic Societies in the Western Mediterranean
Authors: Roqué-Rosell J. , Torchy L. , Roucau C. , Lea V. , Colomban Ph. , Regert M. , Binder D. , Pelegrin J. , Sciau Ph.
Published: September 2011

The Neolithic period Chassey culture in southern France from 4200 to 3500 Cal. BC developed a specialized lithic technology for flint bladelets that used a heating process as an essential part of the production. Experimental archaeology demonstrated that the heating should take place at low temperature somewhere around 250°C. To identify and quantify the physical transformations of flint at low temperature, laboratory and synchrotron experiences have been carried out on a set of heated Barremo-Bedoulian flint samples. According to our measurements, this flint consists of a nanocrystalline matrix of quartz and moganite. Evolution of mesoporous structure was observed during heat treatment. The flint transformed between 200-300°C, resulting in a reduction in the size and volume of porosity. The densification of flint is linked to changes on the nanocrystalline grain boundaries, and it is thought to have a direct impact on the improved mechanical properties from the Chassey culture lithic productions.
Flash-Lamp-Induced Lateral Solidification of Thin Si Films
Authors: Omori K. , Ganot G.S. , Chung U.J. , Chitu A.M. , Limanov A.B. , Im James S.
Published: September 2011

In this paper we show that a flash lamp can be employed to induce controlled lateral solidification of a-Si thin films. Specifically, a dual xenon-arc-lamp-based system was utilized to induce location-controlled complete melting by shaping the incident beam using a contact mask. The resulting laterally solidified microstructure consisted of exceptionally long grains (~10s to ~100s of μm) that were relatively free of intragrain-defects. With further development and optimization, the approach may lead to cost-effective/high-throughput processes and systems that can capture and enhance the advantages of laser-based/melt-mediated crystallization techniques.
Flexible, Lightweight, Amorphous Silicon Based Solar Cells on Polymer Substrate for Space and Near-Space Applications
Authors: Beernink K. , Banerjee A. , Yang J. , Lord K. , Liu F. , DeMaggio G. , Pietka G. , Worrel C. , Guha S.
Published: September 2011

United Solar Ovonic has leveraged its history of making amorphous silicon solar cells on stainless steel substrates to develop amorphous silicon alloy (a-Si:H)-based solar cells and modules on ∼25 μm thick polymer substrate using high-throughput roll-to-roll deposition technology for space and near-space applications. The solar cells have a triple-junction a-Si:H/a-SiGe:H/a-SiGe:H structure deposited by conventional plasma enhanced CVD (PECVD) using roll-to-roll processing. The cells have distinct advantages in terms of high specific power (W/kg), high flexibility, ruggedness, rollability for stowage, and irradiation resistance. The large area (23.9 cm x 32.1 cm) individual cells manufactured in large quantity can be readily connected into modules and have achieved initial, 25 °C, AM0 aperture-area efficiency of 9.8% and initial specific power of 1200 W/kg. We have conducted light-soak studies and measured the temperature coefficient of the current-voltage characteristics to determine the stable values at an expected operating temperature of 60 °C. The stable total-area efficiency and specific power at 60 °C are 7.2% and 950 W/kg, respectively. In this paper, we review the challenges and progress made in development of the cells, highlight some applications, and discuss current efforts aimed at improving performance.
Properties of amorphous silicon passivation layers for all back contact c-Si heterojunction solar cells
Authors: Zhang Lulu , Das Ujjwal , Appel Jesse , Hegedus Steve , Birkmire Robert
Published: September 2011

Low temperature deposited Interdigitated All Back Contact a-Si:H/c-Si Heterojunction (IBC-SHJ) devices are a promising approach for high efficiency, low cost solar cells on thin wafers. Thin intrinsic a-Si:H films (i-a-Si:H) deposited below 300°C provide excellent surface passivation and high Voc. However, the optical properties of a-Si:H layers and electronic band alignment at the heterointerface are critical to reduce optical losses and transport barriers in IBC-SHJ solar cells. At the front illumination surface, a wide band gap (Eg) i-a-Si:H layer with good passivation is desirable for high Voc and Jsc while at the rear surface a narrower Eg i-a-Si:H layer with good passivation is required for higher FF and Voc as seen in 2D numerical simulation. Various substrate temperature, H2/SiH4 dilution ratio and plasma power conditions were explored to obtain i-a-Si:H with good passivation and desired Eg. All the deposited films are characterized by Variable Angle Spectroscopic Ellipsometry (VASE) to determine Eg and thickness and by Fourier Transform Infrared spectroscopy (FTIR) to estimate hydrogen content and microstructure factor. Passivation qualities are examined by quasi-steady state photoconductance (QSS-PC) measurement. The i-layer Eg, was varied in the range from ~1.65eV to 1.91eV with lifetime >1 ms. Lowest Eg is obtained just prior to the structure transition from amorphous to epitaxial-like growth. The FF of IBC-SHJ devices improved from 20% to 70% as Eg of the a-Si:H rear passivation layer decreased from 1.78 to 1.65 eV.
Thin Film Si Photovoltaic Devices on Photonic Structures Fabricated on Steel and Polymer Substrates.
Authors: Pattnaik S. , Chakravarty N. , Bhattacharya J. , Biswas R. , Slafer D. , Dalal V.L.
Published: September 2011

In this paper, we report on the growth and fabrication of thin film Si photovoltaic devices on photonic structures which were fabricated on steel and PEN and Kapton substrates. Both amorphous Si and thin film nanocrystalline Si devices were fabricated. The 2 dimensional photonic reflector structures were designed using a scattering matrix theory and consisted of appropriately designed holes/pillars which were imprinted into a polymer layer coated onto PEN, Kapton and stainless steel substrates. The photonic structures were coated with a thin layer of Ag and ZnO. Both single junction and tandem junction (amorphous/amorphous and amorphous/nanocrystalline) cells were fabricated on the photonic layers. It was observed that the greatest increase in short circuit current and efficiency in these cells due to the use of photonic reflectors was in nanocrystalline Si cells, where an increase in current approaching 30% (compared to devices fabricated on flat substrates) was obtained for thin (∼ 1 micrometer thick i layers) films of nano Si deposited on steel structures. The photonic structures (which were nanoimprinted into a polymer) were shown to stand up to temperatures as large as 300 C, thereby making such structures practical when a steel (or glass) of kapton substrate is used. Detailed measurements and discussion of quantum efficiency and device performance for various photonic back reflector structures on steel, kapton and PEN substrates will be presented in the paper.
Analysis and Control of Plating Baths in the Electrodeposition of Copper Indium Gallium Selenide (CIGS) Films with Ion Chromatography
Authors: Kleiman-Shwarsctein Alan , Aksu Serdar , Cetiner Tuncay , Lastella Sarah , Pinarbasi Mustafa
Published: September 2011

Cu(In,Ga)Se2(CIGS) is one of the most advanced absorber materials with conversion efficiencies reaching up to about 20%. Electrodeposition of CIGS precursors is highly attractive due to its low cost, efficient utilization of raw materials and scalability to high-volume manufacturing, however, a strict chemistry control of the plating baths is required in a manufacturing environment to ensure a consistent plating process with high yields. In the present study, we tested the use of ion chromatography (IC), for the quantitative analysis of both the cationic and anionic species in a variety of aqueous alkaline electroplating solutions we developed for the fabrication of CIGS precursors. Using ion chromatography we were able to precisely determine the concentrations of several key anions commonly employed in the plating baths including chloride, sulfate, selenite, selenate, tartrate, citrate, gluconate, and ethylenediaminetetraacetate. Our results indicated IC might not be a suitable method to determine the cationic concentrations for Cu, In, Ga ions when complexing species, such as ethylenediaminetetraacetate, are present in the electroplating solutions. We determined that inductively coupled plasma optical emission spectroscopy (ICP-OES) could be used instead for the precise determination of the cationic concentrations.
Organosiloxane Transparent Aerogels and Hierarchically Porous Monoliths
Authors: Kodera Yasunori , Hayase Gen , Kanamori Kazuyoshi , Nakanishi Kazuki , Hanada Teiichi
Published: September 2011

A transition of porous structures in monolithic poly(methylsilsesquioxane) (PMSQ, CH3SiO1.5) gels from uniform mesopores to hierarchical pore structures consisting of macro- and mesopores, has been investigated using a sol-gel system containing surfactant Pluronic F127. A broad variation of porous morphology is controlled by changing the concentration of F127. Sufficient concentrations of F127 inhibit the occurrence of macroscopic phase separation of hydrophobic PMSQ condensates and lead to well-defined mesoporous transparent aerogels with high specific pore volume. Mesopores are developed through microscopic phase separation of PMSQ colloid-surfactant complexes in the solvent. Macroscopic phase separation regulates well-defined macropores in the micrometer range on decreasing concentrations of F127, in which microscopic phase separation concurrently takes place in the PMSQ-rich gelling phase after the onset of macroscopic phase separation. Monolithic PMSQ gels with hierarchical macro- and mesopore structures are consequently obtained.
Polychloroprene: a new material for Dielectric Elastomer Actuators.
Authors: Waché Rémi , Risse Sebastian , Schulze Manuel , Kofod Guggi
Published: September 2011

Dielectric Elastomer Actuators (DEAs) consist of an elastomeric layer sandwiched between two compliant electrodes. An electric field applied between the two electrodes will lead to a compression of the elastomer due to the Maxwell’s pressure. DEA can be used for many active applications such as pumps, muscles and so on, where the voltage drives the motion, but they can also operate inversely for energy harvesting or for sensor applications, when the displacement of charges due to a change in thickness is stored or detected. Energy harvesting systems like buoys using wave energy or shoe soles extracting energy from walking have been demonstrated. In this contribution we investigate polychloroprene (CR) as a new material for DEA and describe its potential for use in energy harvesting. To this end, a full characterization of the material properties was undertaken. We find that the very high permittivity combined with good mechanical properties makes this material a promising novel candidate for the energy harvesting application.
New Multilayer Architectures for Piezoelectric BaTiO3 Cantilever Systems
Authors: Vasta Giuseppe , Jackson Timothy J. , Bowen James , Tarte Edward J.
Published: September 2011

The fabrication and characterization of released cantilevers in new multilayer thin films architectures is reported. In contrast to previous works, the cantilevers are produced without etching of the substrate and are based on lead free piezoelectric materials. The three architectures are: SrRuO3/BaTiO3/MgO/SrTiO3/YBa2Cu3O7, SrRuO3/BaTiO3/SrRuO3/YBa2Cu3O7 and SrRuO3/BaTiO3/SrRuO3/SrTiO3/YBa2Cu3O7. It is shown that the different architectures allow a choice of the orientation of the polar axis in piezoelectric layers, in plane (d33 mode) or out of plane (d31 mode). Both configurations may be utilized in piezoelectric energy harvesting devices. Released cantilevers with the above layer sequences have been produced with lengths ranging from, 100 μm to 250 μm. The residual stress after the release of the cantilevers produces an upward bending, the distance between the cantilever tips and the substrate varies between 20 μm and 45 μm. This distance would allow the sufficient vibration amplitude to enable the cantilevers to be used as micro-generators. Measurements of Young Modulus of the cantilevers and of polarization hysteresis loop are reported.
Recent Progress in Downsizing FeFETs for Fe-NAND Application
Authors: Van Hai Le , Takahashi Mitsue , Sakai Shigeki
Published: September 2011

Sub-micrometer ferroelectric-gate field-effect transistors (FeFETs) of 0.56 μm and 0.50 μm gate lengths were successfully fabricated for Fe-NAND cells. Gate stacks of the FeFETs were Pt/SrBi2Ta2O9(SBT)/Hf-Al-O/Si. The gate stacks were formed by electron beam lithography and inductively coupled plasma reactive ion etching (ICP-RIE). Ti and SiO2 hard masks were used for the 0.56 μm- and 0.50 μm-gate FeFETs, respectively, in the ICP-RIE process. Steep SBT sidewalls with the angle of 85° were obtained by using the SiO2 hard masks while 76° sidewalls were shown using Ti hard masks. All fabricated FeFETs showed good electrical characteristics. Drain current hysteresis showed larger memory windows than 0.95 V when the gate voltages were swung between 1±5 V. The FeFETs showed stable endurance behaviors over 108 program/erase cycles. Drain current retention properties of the FeFETs were good so that the drain current on/off ratios did not show practical changes after 3 days.
Understanding the Role of Process Parameters on the Characteristics of Transition Metal Oxide RRAM/Memristor Devices
Authors: Long Branden , Li Yibo , Jha Rashmi
Published: September 2011

In this report, we studied the role of the oxygen concentration in TiOx layer of Ni/TiOx/TiO2/Ni stack based 2-terminal resistive random access memory (RRAM) devices. The sample with oxygen deficient TiOx layer showed Schottky diode type J-V characteristics in the as-fabricated state while the sample with higher oxygen content in TiOx demonstrated MIM or back-to-back connected diode behavior. The Capacitance-Voltage (C-V) profiling was performed and doping density vs. depletion width characteristic was obtained. The conductance technique was implemented to study the interface state density. The RRAM type switching behavior of these samples was studied. The sample with high oxygen in TiOx showed filament based switching after electroforming while the sample with low oxygen in TiOx showed switching governed by the charge trapping.