bluuebunny/crossref_metadata_2025 huggingface dataset:
Reprocessing Silicon Carbide Inert Matrix Fuel by Molten Salt Corrosion
Authors: Cheng Ting , Baney Ronald , Tulenko James
Published: August 2010

Silicon carbide is one of the prime matrix material candidates for inert matrix fuels (IMF) which are being designed to reduce plutonium and long half-life actinide inventories through transmutation. Since complete transmutation is impractical in a single in-core run, reprocessing the inert matrix fuels becomes necessary. The current reprocessing techniques of many inert matrix materials involve dissolution of spent fuels in acidic aqueous solutions. However, SiC cannot be dissolved by that process. Thus, new reprocessing techniques are required.

This paper discusses a possible way for separating transuranic (actinide) species from a bulk silicon carbide (SiC) matrix utilizing molten carbonates. Bulk reaction-bonded SiC and SiC powder (1 μm) were corroded at high temperatures (above 850 °C) in molten carbonates (K2CO3 and Na2CO3) in an air atmosphere to form water soluble silicates. Separation of Ceria (used as a surrogate for the plutonium fissile fuel) was achieved by dissolving the silicates in boiling water and leaving behind the solid ceria (CeO2).
Thermal Conductivities of Cs-M-O (M= Mo or U) Ternary Compounds
Authors: Tokushima Kazuyuki , Tanaka Kosuke , Kurosaki Ken , Gima Hiromichi , Muta Hiroaki , Uno Masayoshi , Yamanaka Shinsuke
Published: August 2010

Thermal conductivities of Cs-M-O (M= Mo or U) ternary compounds, observed in the pellet-cladding gap region and in the pellet periphery in irradiated oxide fuels with high oxygen potentials, were investigated. Bulk samples of Cs2MoO4and Cs2UO4were prepared by hot pressing or spark plasma sintering, and their thermal diffusivities were measured by the laser flash method from room temperature to 823 K for Cs2MoO4and to 900 K for Cs2UO4. The thermal conductivities were evaluated from the thermal diffusivity and bulk density, and the specific heat capacity values available in the literature. The thermal conductivities of Cs2MoO4and Cs2UO4were quite low compared with UO2(e.g. 0.5 Wm−1K−1at 800 K for Cs2MoO4).
Thermal and Mechanical Properties of Hf Hydrides with Various Hydrogen Content
Authors: Kurosaki Ken , Ito Masato , Kitano Yuki , Muta Hiroaki , Uno Masayoshi , Konashi Kenji , Yamanaka Shinsuke
Published: August 2010

Fine bulk samples of delta-phase Hf hydride with various hydrogen contents (CH) ranging from 1.62 to 1.72 in the atomic ratio (H/Hf) were prepared, and their thermal and mechanical properties were characterized. In the temperature range from room temperature to around 650 K, the heat capacity and thermal diffusivity of the samples were measured and the thermal conductivity was evacuated. The elastic modulus was calculated from the measured sound velocity. The Vickers hardness was measured at room temperature. Effects of CH and/or temperature on the properties of Hf hydrides were discussed. At room temperature, the thermal conductivity values of the Hf hydrides were 23 Wm−1K−1. The Young's and shear moduli and the Vickers hardness of Hf hydride decreased with increasing CH.
Oxygen Potential of (Th0.7Ce0.3)O2-x
Authors: Osaka Masahiko , Tanaka Kosuke , Miwa Shuhei , Kurosaki Ken , Uno Masayoshi , Yamanaka Shinsuke
Published: August 2010

Oxygen potentials of (Th0.7Ce0.3)O2-x were experimentally determined by means of thermogravimetric analysis as a function of non-stoichiometry at 1173 and 1273 K. Oxygen potentials of (Th0.7Ce0.3)O2-x at each temperature increased with increase of oxygen to metal (O/M) ratio (=2-x) and steep increases of the oxygen potentials when approaching O/M ratio = 2 were observed. These characteristics are typical for non-stoichiometric fluorite-type actinide dioxides. The oxygen potentials of (Th0.7Ce0.3)O2-x were similar to those of CeOO2-x when they were plotted as a function of average Ce valence.
Thermal Aging of Primary Circuit Piping Materials in PWR Nuclear Power Plant
Authors: Wang Xitao , Li Shilei , Li Shuxiao , Xue Fei , Shu Guogang
Published: August 2010

The reserved cast austenitic stainless steels (CASS) for primary circuit piping in Daya Bay Nuclear Power Plant were studied. The changes of microstructure, mechanical properties and fracture behavior were investigated using SEM, EPMA, TEM and nanoindentation after accelerated aging at 400°C for up to 10000 h. Microhardness of ferrite increased rapidly in the early stage and then increased slowly later. The impact energy of materials declined with the aging time and reduced to a very low level after aging for 10000 hours. Fracture morphology displayed a mixture of cleavage in ferrite along with dimple and tearing in austenite. Two kinds of precipitations were observed in ferrite by TEM after long periods of aging. The fine Cr-enriched α′ phases precipitated homogeneously in ferrite, and a few larger G phases were observed as well. The precipitation of α′ phases was considered to be the primary mechanism of thermal aging embrittlement in CASS.
Micromechanical Testing of Nanostructured NbTiNi Hydrogen Permeation Membranes
Authors: Kusuno Tetsuya , Shimada Yusuke , Matsuda Mitsuhiro , Otsu Masaaki , Takashima Kazuki , Nishida Minoru , Ishikawa Kazuhiro , Aoki Kiyoshi
Published: August 2010

Nb-Ti-Ni alloy is one of the candidates for hydrogen permeation membranes. The hydrogen permeability of a membrane depends on its thickness, and mechanical properties such as the fracture toughness of the membrane are important to ensure reliability and durability. In the present work, micro-mechanical tests have been carried out for melt-spun Nb-Ti-Ni thin films consisting of amorphous and nano-crystalline phases. The relationship between the mechanical properties of the melt-spun films and the microstructural changes occurring in the films due to heat treatment has been also discussed. The Nb-Ti-Ni alloy thin films were prepared by the melt-spun technique and then heat-treated at 873-1173 K. Micro-sized cantilever specimens with dimensions of 10 × 10 × 50 μm3 were prepared by focused ion beam (FIB) machining. Fracture tests were carried out using a mechanical testing machine for the micro-sized specimens; the testing machine was developed by us. In addition, microstructures were observed by transmission electron microscopy (TEM). The fracture toughness (KQ) value decreased up to 823 K, and it increased above 1173 K. The specimen heat-treated above 1173 K showed ductile fracture. The fracture morphology of the specimen heat-treated up to 1023 K showed grain boundary fracture characteristics, and that of the specimen heat-treated at 1173 K changed to transgranular fracture.
Size-Dependent Mechanical Properties of Polymer-nanowires Fabricated by Two-photon Lithography
Authors: Shoji Satoru , Nakanishi Sana , Hamano Tomoki , Kawata Satoshi
Published: August 2010

Two-photon lithography allows us to fabricate arbitrary three-dimensional structures with micro/nano-spatial resolution. The intrinsic three-dimensional spatial resolution of two-photon lithography is a promising tool for developing a variety of novel photonic and mechanical nano-devices. In addition, two-photon lithography makes it possible to study the properties of polymers of micro/nano-meter dimension [1-4]. In this presentation, we show the evidence that the elasticity and the transition temperature of polymers start to show size-dependent characteristics when the size of the polymer decreases down to a few hundreds of nanometers. We fabricated free-standing polymer nano-wires in the shape of coil spring by two-photon lithography, and measured the elasticity of the nano-wires by applying a mechanical tension onto the springs through laser trapping technique under temperature control. From the stretching length of the spring generated by a certain optical force, the spring constant of the spring and the shear modulus of polymer were calculated from simple Hook’s law. The material we used is a compound of methyl-methacrylate, dipentaerythritol hexaacrylate, benzil, and 2-benzyl-2-(dimethylamino)-4’-morpholino-butyrophenone. We scanned a light spot of a Ti:Sapphire laser at 780 nm with a pulse width of 80 fs focused by a 1.4 NA microscope objective to shape the polymer nano-wires suspended by a thick pillar. We observed that the elasticity of the polymer, which is usually an invariable coefficient, changes according to the thickness of the polymer wire. Furthermore, we changed the temperature of the entire polymer structures from -20 to 40 °C with measuring the elasticity of the springs. We observed phase transition of polymer wires with a rapid change of the share modulus, which also shows a size-dependent behavior. Recently, the similar experimental results, i.e. the drop of the glass transition temperature, were also reported in thin polymer nano-films. Our result is a clear evidence of such a nano size-effect of mechanical properties in polymers confirmed from free-standing polymer nanostructures. [1]S. Nakanishi, H. Yoshikawa, S. Shoji, Z. Sekkat, and S. Kawata, J. Phys. Chem. B 112, 3586-3589 (2008). [2] S. Nakanishi, S. Shoji, S. Kawata, and H.-B. Sun, Appl. Phys. Lett. 91, 063112 (2007). [3]H. Ishitobi, S. Shoji, T. Hiramatsu, H.-B. Sun, Z. Sekkat, and S. Kawata, Opt. Express 16, 14106-14114 (2008). [4]S. Kawata, H.-B. Sun, T. Tanaka, and K. Takada, Nature, 412, 697 (2001).
Elastic Properties of Mimetically Synthesized Model Nanoporous Carbon
Authors: Mi Xi , Shi Yunfeng
Published: August 2010

Activated carbon is widely used for its attractive diffusion, adsorption and reaction properties. However, its mechanical behavior has received much less attention. We present a molecular dynamics simulation study on the elastic properties of activated carbon with nanometer-sized pores. The nanoporous carbon sample is composed of curved and defected graphene sheets, which is synthesized using quench molecular dynamics (QMD) method [1]. One unique feature of the current model is the mechanical stability, thus the bulk modulus, Young’s modulus, shear modulus and Poisson’s ratio can be obtained from simulated mechanical tests. By varying the density of the nanoporous carbon model, it was further found that the bulk modulus vs. density relation follows Gibson-Ashby type power law with exponents of 2.80 at low densities and 1.65 at high densities.
Ultra-fast Time-Resolved Electron Diffraction of Strongly Driven Phase Transitions on Silicon Surfaces
Authors: Möllenbeck Simone , Hanisch-Blicharski Anja , Schneider Paul , Ligges Manuel , Zhou Ping , Kammler Martin , Krenzer Boris , Horn-von Hoegen Michael
Published: August 2010

The dynamics of strongly driven phase transitions at surfaces are studied by ultra-fast time-resolved reflection high energy electron diffraction. The surfaces are excited by an intense fs-laser pulse (pump) and probed by an ultra-short electron pulse with variable time delay. The order-disorder phase transition from a c(4×2) to a (2×1) of the bare Si(001) surface shows a transient decrease of the intensity of the c(4×2) spots which recovers on a time scale of a few hundred picoseconds indicating the excitation of the phase transition. On Si(111) a monolayer of Indium induces a (4×1) reconstruction which undergoes a Peierls like phase transition to a (8×“2”) reconstruction below 100 K. Upon laser excitation at a temperature of 40 K the phase transition was strongly driven. The (8×“2”)-diffraction spots instantaneously disappears, while the intensity of the (4×1)-spots increases. This increase of the (4×1) spot intensity excludes an explanation by the Debye-Waller-Effect and is evidence for a true structural phase transition at a surface.
Ultrafast All-optical Switching and Laser Action in Rotaxane
Authors: Mroz Marta M. , Perissinotto Stefano , Virgili Tersilla , Salerno Marco , Sforazzini Giuseppe , Anderson Harry L. , Lanzani Guglielmo
Published: August 2010

Linear and non-linear optical properties of conjugated polymers are often masked by the inter-chain network in solid state. The formation of aggregates may trap excitons, reduce oscillator strength and modify relaxation processes. The control of the inter-chain interaction is the main reason for developing “threaded” polymers, where supra-molecular encapsulation should reduce aggregation. Here, we investigate the influence of the encapsulation with β-cyclodextrin (β-CD) macrocycles on the photophysics of the polyfluorene-alt-biphenylene (PFBP) using femtosecond non-linear spectroscopy. Upon threading we observe enhancement of the stimulated emission (SE) in the visible range and reduction of the charge absorption. These phenomena are ascribed to the reduced inter-chain interaction. In more isolated chains the dynamics of intra and inter-chain charge states are distinguished. In addition, we performed three-beam experiments in which a first pulse (pump) creates singlet excited states; a second (push) pulse re-excite the singlet state and a broadband probe pulse detects the induced changes in transmission. This technique shows: (i) charges are generated from higher lying singlet states also in isolated chains (ii) ultrafast optical gain switching is possible in threaded chain. Finally, we demonstrate that ASE occurs in films of threaded polymers and lasing can be achieved with much lower threshold than the neat polymer chain in the DFB configuration. All our findings point out the potential role of rotaxanes in photonics, as amplifiers and reopen the route to the electrically pumped organic lasers and all-optical logic devices.
Short-pulse Laser Induced Transient Structure Formation and Ablation Studied with Time-resolved Coherent XUV-scattering
Authors: Sokolowski-Tinten Klaus , Barty Anton , Boutet Sebastien , Shymanovich Uladzimir , Chapman Henry , Bogan Mike , Marchesini Stefano , Hau-Riege Stefan , Stojanovic Nikola , Bonse Jörn , Rosandi Yudi , Urbassek Herbert M. , Tobey Ra'anan , Ehrke Henri , Cavalleri Andrea , Düsterer Stefan , Redlin Harald , Frank Matthias , Bajt Sasa , Schulz Joachim , Seibert Marvin , Hajdu Janos , Treusch Rolf , Bostedt Christoph , Hoener M. , Möeller Thomas
Published: August 2010

The structural dynamics of short-pulse laser irradiated surfaces and nano-structures has been studied with nm spatial and ultrafast temporal resolution by means of single-shot coherent XUV-scattering techniques. The experiments allowed us to time-resolve the formation of laser-induced periodic surface structures, and to follow the expansion and disintegration of nano-objects during laser ablation.
The Role of Thermal and Electronic Pressure in the Picosecond Acoustic Response of Femtosecond Laser-excited Solids
Authors: Shymanovich Uladzimir , Nicoul Matthieu , Kähle Stefan , Lu Wei , Tarsevitch Alexander , Zhou Ping , Wietler Tobias , Horn-von Hoegen Michael , von der Linde Dietrich , Sokolowski-Tinten Klaus
Published: August 2010

Ultrafast time-resolved X-ray diffraction has been used to study the dynamics of coherent acoustic phonons in fs laser-excited Ge and Au, with the particular goal to clarify the interplay of the electronic and thermal pressure contributions. For semiconductors it is usually assumed that the electronic pressure is the dominant driving force. Our measurements reveal that in Ge the relative strength of the electronic pressure decreases with increasing laser fluence. Only for low fluences the electronic pressure dominates, while at high fluences the thermal pressure exceeds the electronic pressure. For the case of Au the data are well described within the established theoretical framework using the known values for those material parameters which determine the laser-induced pressure, namely the energy relaxation time and the electronic and lattice Grüneisen parameters.
Synthesis of LNF Nano Particles for Fuel Cell Applications
Authors: Bateni Reza , Nasirpour Maryan , Kesler Olivera
Published: August 2010

The aim of the present work is to understand the effect of different parameters such as the molar ratio of metallic ions to fuel in sol-gel solution, pH of the solution, and calcining temperature on the efficiency of the combustion synthesis technique in preparing submicron lanthanum nickel ferrite using metal nitrate-citrate/glycine mixtures. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) was used to evaluate the powder morphology and elemental composition. The crystal structure of the calcined powders was evaluated by X-ray diffraction (XRD) and the thermal characteristics of the LNF precursors were examined by thermo-gravimetric analysis (TGA) in air, to identify suitable processing conditions. It was found that by increasing the molar ratio of fuel to metallic ions in the precursor solution, calcining could take place at lower temperatures. However, by increasing the molar ratio of fuel to metallic ions, the yield of the combustion process was decreased. Furthermore, the pH value of the precursor solution did not have any influence on the process efficiency over the range examined.
Modification of Aluminium Surface Using Picosecond Laser for Printing Applications
Authors: Ansari Imtiyaz Ahmed , Watkins Kennith G. , Sharp Martin C. , Hutchinson Richard , Potts Rodney
Published: August 2010

Ultrafast picosecond laser pulses of wavelength of 1064nm have allowed the surface modification of anodised aluminium plate for potential industrial application. The interaction of the laser with the substrate created a hydrophilic surface, giving a contact angle of less than 10 degrees. On examination under a Scanning Electron Microscope (SEM), it was observed that these surfaces have an interesting ‘lotus-leaf’ like structure. It has been found that these laser processed hydrophilic surfaces revert with time. The potential for application in the printing industry is strong due to the reusability and sustainability of the process materials; initial trials confirm this. This technology would offer extra advantages as a non-chemical process without the need for developer, thereby reducing the overall cost and time of printing.
Quantitative Kelvin Probe Force Microscopy
Authors: Baumgart Christine , Helm Manfred , Schmidt Heidemarie
Published: August 2010

In this paper we report on the investigation of electrostatic forces between a conductive probe and semiconducting materials by means of Kelvin probe force microscopy measurements. Due to the formation of an asymmetric electric dipole at the semiconductor surface, the measured KPFM bias is related with the energy difference between Fermi energy and respective band edge. Quantitative Kelvin probe force microscopy measurements on semiconductors, namely on a conventional dynamic random-access memory cell and on a cross-sectionally prepared Si epilayer structure, are presented.
The Development of Silicon Carbide Based Electrode Devices for Central Nervous System Biomedical Implants
Authors: Frewin Christopher , Oliveros Alexandra , Locke Christopher , Filonova Irina , Rogers Justin , Weeber Edwin , Saddow Stephen E.
Published: August 2010

Brain machine interface (BMI) technology has been demonstrated to be a therapeutic solution for assisting people suffering from damage to the central nervous system (CNS), but BMI devices using implantable neural prosthetics have experienced difficulties in that they are recognized by glial cells as being foreign material, which leads to an immune response cascade process called gliosis. One material, cubic silicon carbide (3C-SiC), may provide an excellent solution for the generation of an implantable neural prosthetic interface component of a BMI system. We have recently reported on the biocompatibility of 3C-SiC with immortalized cells, and have extended this work by demonstrating neural cell action potential instigation via an electrode type device. Biocompatibility assessment of 3C-SiC was accomplished using in vitro methodology. 96 hour MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assays were performed to determine neural cell viability. Atomic force microscopy (AFM) was used to quantify attached cell morphology and determine lamellipodia/ filopodia interaction with the surface of the semiconductor. It was seen that neurons show excellent viability, cell morphology, and good lamellipodia/ filopodia permissiveness when interacting with 3C-SiC. A neuronal activation device (NAD), based on the planar Michigan microelectrode probe, was constructed from 3C-SiC with the goal of activating an action potential within a neuron. In order to illicit an action potential, neurons were seeded on the NAD device and then they were subjected to a biphasic square pulse signal. Successful action potential activation was recorded through the use of Rhod-2, a Ca2+ sensitive fluorescent dye. Based on these results, 3C-SiC may be an excellent material platform for neural prosthetics.
Endothelial Cell Attachment and Proliferation Studies on Modified Metal Stent Surfaces
Authors: Davè Vipul , Buensuceso Charito , Colter David , Zhao Jonathon , Falotico Robert
Published: August 2010

Flat coupons prepared from cobalt chromium alloy (CoCr) were modified using different methods (low energy excimer laser processing, electron beam irradiation, and immobilized covalently-bound heparin coating). Human coronary artery endothelial cell (HCAEC) attachment and growth kinetics were investigated on unmodified and modified metal surfaces. Results showed that HCAEC attach to unmodified CoCr coupons and surface-modified CoCr coupons. No change in cell number was observed when cells were grown on CoCr coupons and heparin coated coupons throughout the 72h study period. A decrease in cell number was observed for excimer treated coupons. HCAEC seeding on CoCr stents indicated that cells attached and proliferated on the stents over a ten day study period. This research showed that physical modifications did not improve cell proliferation. Very few non-viable cells were observed for unmodified and surface bound heparin coupons, and cells attached to the surface up to 72h. This shows that heparin can be coated on a stent surface to provide anti-thrombotic properties without any negative effect on cell attachment and proliferation. In vitro screening method of testing endothelial cell attachment and proliferation on modified metal stent surfaces can be used to gain insight for developing next generation drug eluting stents with improved endothelialization behavior.
Semiconductor Quantum Dots for Cell Imaging
Authors: Aguilar Zoraida Pascual , Xu Hengyi , Jones Ben , Dixon John , Wang Andrew
Published: August 2010

Nanotechnology is currently undergoing unprecedented development in various fields. There has been a widespread interest in the application of nanomaterials in medicine with its promise of improving imaging, diagnostics, and therapy. The recent advances in engineering and technology have led to the development of new nanoscale platforms such as quantum dots, gold nanocrystals, superparamagnetic nanocrystals, and other semiconductor nanoparticles. Literature on the applications of quantum dots in life sciences has recently increased in number. This may have led to predictions that nanotechnology in life sciences research will contribute $3.4 billion by 2010 while institutions have predicted that the market for nanotechnology and corresponding products will reach $1 trillion in 2012 (1).

Ocean NanoTech is at the height of developmental stages of nanoparticle production for biological applications. Ocean’s high quantum-yield quantum dots (QDs) is currently being tested and used for cell imaging, as wells as for the detection of proteins, DNA, whole cells, and whole organisms. Imaging of cells involves conjugation of QDs to highly sensitive and specific antibody to form QD˜Ab conjugates that attach to specific protein target on the cell surface. Attachment of the QD˜Ab on the cell surface allows imaging of the cell under a fluorescence microscope. QD based imaging can be used in a multiplex immunoassay detection of several types of cells (or microorganisms) in a single sample when several size tunable quantum dots are used as reporter probes.

We report the QD imaging of breast cancer cells. Using the breast cancer cell line SK-BR3, which expresses high levels of her2 antigens on the cell surface, anti-her2 were conjugated to Ocean’s quantum dots, QSH620. To eliminate non-specific binding of the QD˜20Ab Ocean’s super blocking buffer BBB and BBG were used. Preliminary results of in vitro studies indicated that QD based systems can be used to image cells. We anticipate that this system can be transferred to in vivo detection.
Encapsulation of BSA within Gelatin Nanoparticles-laden Biopolymer Film
Authors: Zhang Jin , Zhu Jesse , Akhter Kazi Farida , Thomas Anu Alice
Published: August 2010

This research project aims at the development of new biopolymer nanocomposites which enable to act as a critical component to next generation medical device. In this paper, we developed an in situ method to encapsulate model protein, bovine serum albumin (BSA), within gelatin nanoparticles (NPs). The results demonstrate that the average diameter of the BSA-containing gelatin NPs is approximately 180 nm±10 nm. They can absorb up to 70% of water. The gelatin- nanoencapuslated BSA afterwards were loaded in the biopolymer film with thickness around 150 μm composed of poly(2-hydroxyethyl methacrylate) (pHEMA) through the photopolymerization. The release kinetics of BSA from the nanoparticles and the nanoparticle-laden p(HEMA) were studied through UV-Vis spectrometry, respectively. The releasing concentration of BSA increased with time (t), and about 80% of the encapsulated BSA was released in 80 hrs; while, the releasing profile of BSA from the gelatin nanoparticles-loaded hydrogel can be monitored up to10 days. These studies show that the gelatin nanoparticles are able to encapsulate water-soluble protein. The hydrogel film, pHEMA, enable to further prolong the releasing profile for the water soluble protein. It is expected that this new biodegradable polymer nanocomposites can be an alternative materials for consisting of implant medical device for protein therapy.
Photoluminescent Nanofibers for Solid-State Lighting Applications
Authors: Davis Lynn , Han Li , Hoertz Paul , Guzan Kim , Mills Karmann C. , Walls Howard J. , Walker Teri A. , Magnus-Aryitey Damaris
Published: August 2010

Photoluminescent nanofibers (PLN) can be formed by combining electrospun polymeric nanofibers and luminescent particles such as quantum dots (QD). The physical properties of PLNs are dependent upon many different nanoscale parameters associated with the nanofiber, the luminescent particles, and their interactions. By understanding and manipulating these properties, the performance of the resulting optical structure can be tailored for desired end-use applications. For example, the quantum efficiency of quantum dots in the PLN structure depends upon multiple parameters including quantum dot chemistry, the method of forming the PLN nanocomposites, and preventing agglomeration of the quantum dot particles. This is especially important in solution-based electrospinning environments where some common solvents may have a detrimental effect on the performance of the PLN. With the proper control of these parameters, high quantum efficiencies can be readily obtained for PLNs. Achieving high quantum efficiencies is critical in applications such as solid-state lighting where PLNs can be an effective secondary conversion material for producing white light. Methods of optimizing the performance of PLNs through nanoscale manipulation of the nanofiber are discussed along with guidelines for tailoring the performance of nanofibers and quantum dots for application-specific requirements.
Electrospun Nanofiber Networks for Electronics and Optics
Authors: Tanioka Akihiko , Matsumoto Hidetoshi , Tsuboi Kazuma
Published: August 2010

In this paper, we report on the preparation and applications of nanofiber networks, particularly in the area of optelectronics. The major topics are (i) carbon nanotubes grown on carbon nanofibers for a field emitter, (ii) dye-sensitized ZnO nanowires grown on carbon nanofibers for a photoelectrochemical cell, (iii) nanofiber coatings for coloring, and (iv) nanofiber coatings on gold substrate for surface plasmon resonance. The results presented here reveal the potential use of nanofiber networks for various optoelectronic devices.
Thin Film Silicon Photovoltaic Technology – From Innovation to Commercialization
Authors: Guha Subhendu , Yang Jeffrey
Published: August 2010

The last decade has witnessed tremendous progress in the science and technology of thin film silicon (amorphous and nanocrystalline) photovoltaic. The shipment of solar panels using this technology was about 200 MW in 2009; based on announcement of new or expanded production capacity, the shipment is projected to grow ten-times in the next 3-5 years. The key factor that will determine the wide-scale acceptance of the products will be the cost of solar electricity achieved using this technology. Efficiency of solar modules and throughput of production equipment will play a key role. In this paper, we discuss our roadmap to improve the product efficiency and machine throughput.
Advanced Light Trapping in Thin-film Silicon Solar Cells
Authors: Zeman Miro , Isabella Olindo , Jaeger Klaus , Santbergen Rudi , Liang Renrong , Solntsev Serge , Krc Janez
Published: August 2010

Photon management is one of the key issues for improving the performance of thin-film silicon solar cells. An important part of the photon management is light trapping that helps to confine photons inside the thin absorber layers. At present light trapping is accomplished by the employment of the refractive-index matching layers at the front side and the high-reflective layers at the back contact of the solar cells and scattering of light at randomly surface-textured interfaces. In this article key issues and potential of light management in thin-film silicon solar cells are addressed. Novel approaches for light trapping are presented such as i) surface textures based on periodic diffraction gratings and modulated surface morphologies for enhanced scattering and anti-reflection, ii) metal nano-particles introducing plasmonic scattering, and iii) one-dimensional photonic-crystal-like structures for back reflectors.
Amorphous Silicon Solar Cells With Silver Nanoparticles Embedded Inside the Absorber Layer
Authors: Santbergen Rudi , Liang Renrong , Zeman Miro
Published: August 2010

A novel light trapping technique for solar cells is based on light scattering by metal nanoparticles through excitation of localized surface plasmons. We investigated the effect of metal nanoparticles embedded inside the absorber layer of amorphous silicon solar cells on the cell performance. The position of the particles inside the absorber layer was varied. Transmission electron microscopy images of the cell devices showed well defined silver nanoparticles, indicating that they survive the embedding procedure. The optical absorption of samples where the silver nanoparticles were embedded in thin amorphous silicon layer showed an enhancement peak around the plasmon resonance of 800 nm. The embedded particles significantly reduce the performance of the fabricated devices. We attribute this to the recombination of photogenerated charge carriers in the absorber layer induced by the presence of the silver nanoparticles. Finally we demonstrate that the fabricated solar cells exhibit tandem-like behavior where the silver nanoparticles separate the absorber layer into a top and bottom part.
Synthesis of Silicon Nano-particles for Thin Film Electrodes Preparation
Authors: Munao David , Erven Jan van , Valvo Mario , Vons Vincent , Evirgen Alper , Kelder Erik
Published: August 2010

The present work concerns novel approaches to fabricate silicon-based electrodes. In this study silicon nano-particles are synthesized via two aerosol routes: Laser assisted Chemical Vapour Pyrolysis (LaCVP) and Spark Discharge Generation (SDG). These two techniques allow the generation of uniformly sized particles, with a good control over the composition and the range of sizes. Herein, particles with size ranging from 2 to 70 nm were obtained. Starting from these nano-particles, nano-structured porous thin films are produced either by electrospraying a polymeric solution in which LaCVP-produced particles were previously dispersed, or by inertial impacting the SDG-produced particles directly from gas phase onto a substrate. The Electro- Spray (ES) is used to produce composite films for Li-ion battery applications, whereas the Inertial Impaction (II) is used to produce pure silicon films for other purposes (i.e.: sensors).
Float Foil Growth of Si-Foils for Solar Cell Applications
Authors: Cohen Uri , Roitberg Michael
Published: August 2010

A new Float Foil Growth (FFG) technique has been demonstrated for growing thin Si foils from molten metal solvent, such as molten indium (In) or tin (Sn), at temperatures below 1,000°C. Si source is first dissolved to saturation (or close to saturation) in a molten metallic bath (or solvent) at a temperature T2 (T2 ≤ 1,000°C), and the molten bath is then cooled to T1, where T2 » T1. Due to lower solubility of Si at T1 than at T2, Si separates (or is driven) out of solution and, due to its much lower density than that of the molten metallic bath, it floats to the top of the melt to form a floating thin Si-foil. The thickness of the Si foil is determined primarily by T2, the dissolution temperature (i.e., Si solubility at T2), and the depth of the molten bath. This paper reports preliminary results demonstrating the utility of the FFG technique for growing Si-foils. Si foils with thickness range of 50-200μm were obtained from molten In baths. The Si foils were multicrystalline with crystalline (or grain) size of several millimeters, having a strong <111> preferred orientation. The Si-foils were very pure; with In (solvent) content as low as 14ppb. Other metallic impurities were below 0.1ppm, oxygen content was as low as 1.8ppm, and carbon content was below the detection level (50ppb). It is expected that large FFG thin Si-foils, when produced on large scale, will offer significant Si material cost and energy savings (> 80%), compared with conventional sliced Si wafers, with similar photovoltaic conversion efficiency.
Influence of Embedded a-Si:H Layer Location on Floating-gate a-Si:H TFT Memory Functions
Authors: Kuo Yue , Coan Mary
Published: August 2010

The influence of the location of the embedded a-Si:H layer in the gate dielectric film of the floating-gate a-Si:H TFT on the charge trapping and detrapping mechanisms has been investigated. The thin channel-contact SiNx gate dielectric layer favors both hole and electron trappings under the proper gate voltage condition. The sweep gate voltage affect the locations and shapes of forward and backward transfer characteristics curves, which determines the memory function. In order to achieve a large memory window, both the location of the embedded a-Si:H layer and the gate voltage sweep range need to be optimized.
Measure of carrier lifetime in nanocrystalline silicon thin films using transmission modulated photoconductive decay
Authors: Simonds Brian J. , Yan Baojie , Yue Guozhen , Dunlavy Donald , Ahrenkiel Richard K. , Taylor Craig
Published: August 2010

We present results of extremely short carrier lifetime measurements on a series of hydrogenated nanocrystalline silicon (nc-Si:H) thin films by a novel, non-destructive, non-contact method. Transmission modulated photoconductive decay (TMPCD) is a newly developed technique which appears to have high enough sensitivity and time resolution to measure the extremely short carrier lifetimes on the order of a nanosecond. As a proof of this, we measure various nc-Si:H samples of varying crystalline volume fraction as well as a fully amorphous sample. To ascribe an effective lifetime to the materials, we use a simple model which assumes a single exponential decay. By using this model, effective lifetimes can be deconvoluted from our pump beam giving nanosecond lifetimes. Lifetimes of between 1.9 and 0.9 nanoseconds are reported and trend to decreasing lifetimes as crystalline volume fraction is increased.
Molecular Dynamics Modeling of Stress and Orientation Dependence of Solid Phase Epitaxial Regrowth
Authors: Lai Haoyu , Sea Stephen M , Kennel Harold , Dunham Scott T
Published: August 2010

Solid Phase Epitaxial Regrowth (SPER) is of great technological importance in semiconductor device fabrication. A better understanding and accurately modeling of its behavior are vital to the design of fabrication processes and the improvement of the device performance. In this paper, SPER was modeled by Molecular Dynamics (MD) with Tersoff potential. Extensive MD simulations were conducted to study the dependence of SPER rate on growth orientation and uniaxial stress. The results were compared with experimental data. It was concluded that MD with Tersoff potential can qualitively describe the SPER process. For a more quantitatively accurate model, a better interatomic potential are needed.
Threshold Voltage Shift Variation of a-Si:H TFTs With Anneal Time
Authors: Indluru Anil , Venugopal Sameer M , Allee David R , Alford Terry L
Published: August 2010

Hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) are widely used in many areas and the most important application is in active matrix liquid crystal display. However, the instability of the a-Si:H TFTs constrains their usability. These TFTs have been annealed at higher temperatures in hope of improving their electrical performance. But, higher anneal temperatures become a constraint when the TFTs are grown on polymer-based flexible substrates. This study investigates the effect of anneal time on the performance of the a-Si:H TFTs on PEN. Thin-film transistors are annealed at different anneal times (4 h, 24 h, and 48 h) and were stressed under different bias conditions. Sub-threshold slope and the off-current improved with anneal time. Off-current was reduced by two orders of magnitude for 48 hours annealed TFT and sub-threshold slope became steeper with longer annealing. At positive gate-bias-stress (20 V), threshold voltage shift (∆Vt) values are positive and exhibit a power-law time dependence. High temperature measurements indicate that longer annealed TFTs show improved performance and stability compared to unannealed TFTs. This improvement is due to reduction of interface trap density and good a-Si:H/insulator interface quality with anneal time.
Al-mediated Solid-Phase Epitaxy of Silicon-On-Insulator
Authors: Sakic Agata , Civale Yann , Nanver Lis K. , Biasotto Cleber , Jovanovic Vladimir
Published: August 2010

Silicon-on-insulator (SOI) regions have been grown on lithographically predetermined positions by Al-mediated Solid-Phase Epitaxy (SPE) of amorphous silicon (α-Si). A controllable Si lateral overgrowth is induced from windows formed in silicon dioxide (SiO2) to the crystalline Si substrate. The resulting hundred of-nanometer large areas of high-quality monocrystalline SOI are formed at the temperatures that can be as low as 400 °C. The as-obtained SOI regions were found to take on the same crystal orientation as the (100) Si substrate and have the ability to merge seamlessly over the oxide.
N-type Microcrystalline Silicon Oxide (μc-SiOx:H) Window Layers with Combined Anti-reflection Effects for n-i-p Thin Film Silicon Solar Cells
Authors: Smirnov Vladimir , Boettler Wanjiao , Lambertz Andreas , Astakhov Oleksandr , Carius Reinhard , Finger Friedhelm
Published: August 2010

We will describe the development and application of n-type microcrystalline silicon oxide (μc-SiOx:H) alloys as window layers in thin film silicon solar cells with microcrystalline silicon (μc-Si:H) absorber layers. Cells are prepared in n–i–p deposition sequence with illumination through the n-side. The layers were deposited by radio-frequency plasma enhanced chemical vapour deposition (RF-PECVD) at 185°C substrate temperature, using a mixture of phosphine (PH3), silane (SiH4), carbon dioxide (CO2) and hydrogen (H2) gases, at CO2flows varied between 0.5 and 2 sccm and different thickness. Films were characterised by dark conductivity measurements, Photothermal Deflection Spectroscopy (PDS) and Raman spectroscopy to evaluate optical band gap E04, refractive index n and crystallinity ICRS, respectively. The results were compared with the data of alternative optimised window layers, such as n-type μc-Si:H and silicon carbide (μc-SiC:H) films. Also solar cells with conventional illumination through the p-side window were investigated for comparison. Solar cells were prepared with μc-SiOx:H n-layers of varied compositions and characterised by current-voltage (J-V) measurements under AM 1.5 illumination (and also under modified AM 1.5 illumination with red (OG590) and blue (OG7) filters) and reflectance measurements. The effects of the μc-SiOxn-layer composition and thickness on the performance of n-i-p cells were investigated and correlated with the optical, electrical and structural properties of the μc-SiOx:H n-layers. The results indicate that n-type μc-SiOx:H provides a sufficient combination of conductivity (up to 0.1 S/cm) and crystallinity (ICRS up to 30%) to function well as a doped layer for the internal electric field and the carrier transport and as a nucleation layer for the growth of the μc-Si:H i-layer. As a window layer, it also results in an enhanced spectral response, particularly in the long wavelength part of the spectrum of the solar cells, in comparison with the cells containing alternative window layers. An improved short circuit current density (Jsc) can be attributed to the wide optical gap E04 (around 2.3 eV) in the μc-SiOx:H window layers and reduced reflection in the long wavelength region of the spectrum. A minimum total reflectance of only 6% at 570nm wavelength was achieved with such μc-SiOx:H window layers. Using optimised n-type μc-SiOx:H as a window layer, an efficiency of 8.0% for 1cm2cell area was achieved with 1 μm thick μc-Si:H absorber layer and Ag back reflector.
Defect Reduction in SiC Growth Using Physical Vapor Transport
Authors: Hansen Darren , Loboda Mark J , Drachev Roman Victorovich , Sanchez Edward , Zhang Jie , Carlson Eric P , Wan Jianwei , Chung Gil
Published: August 2010

4H SiC is a promising material because of its mechanical, electrical, and physical properties. However, SiC material defects have had a rate limiting effect on the widespread adoption of SiC. Micropipes, basal plane dislocations (BPD), elementary screw dislocations (SDD) and threading edge dislocations (TED) have all been identified as limiting to device operation and/or performance. An ideal PVT strategy for manufacturing SiC crystals would be capable of driving defects out the crystal via a combination of thermal field control and defect dissociation pathways. In this work a PVT technology was realized which is capable of continuously improving the crystal quality. A low defect PVT process was conceived and optimized using iterative experiment and simulation methods. During the maturation of the process it was observed that the crystal defect density repeatedly decreased relative to the seed crystal, as evaluated by x-ray topography, x-ray diffraction, and molten salt etching. The process improvements were leveraged successfully to achieve 4H n+ SiC wafers at 76-100 mm diameter with MPD <1 cm-2, SDD <500 cm-2, and BPD <500 cm-2. This paper will illustrate the defect reduction pathways leading to state of the art defect density 4H SiC crystals and the impact of the improved crystal on epitaxy defects and simple device experiments.
a-SiC:H Based Devices as Optical Demultiplexers
Authors: Louro Paula , Vieira Manuela , Costa João , Vieira M. A. , Fernandes Miguel , Fantoni Alessandro , Barata Manuel
Published: August 2010

In this paper we present results on the use of a multilayered a-SiC:H heterostructure as a wavelength-division demultiplexing device (WDM) for the visible light spectrum. The WDM device is a glass/ITO/a-SiC:H (p-i-n)/ a-SiC:H(-p) /Si:H(-i)/SiC:H (-n)/ITO heterostructure in which the generated photocurrent at different values of the applied bias can be assigned to the different optical signals.

The device was characterized through spectral response measurements, under different electrical bias. Demonstration of the device functionality for WDM applications was done with three different input channels covering wavelengths within the visible range. The recovery of the input channels is explained using the photocurrent spectral dependence on the applied voltage. The influence of the optical power density was also analysed.

An electrical model, supported by a numerical simulation explains the device operation. Short range optical communications constitute the major application field, however other applications are also foreseen.
Diffusivity of Si in the 3C-SiC Buffer Layer on Si(100) by X-ray Photoelectron Spectroscopy
Authors: Chen Wei-Yu , Lin Jian-You , Hwang Jenn-Chang , Huang Chih-Fang
Published: August 2010

A void free 3C-SiC film grown on Si(100) can be achieved by low pressure chemical vapor deposition using the modified four-step method. The diffusion step plays an important role to enhance the quality of the 3C-SiC buffer layer on Si(100). X-ray photoelectron spectroscopy was used to characterize the bonding characteristics of the 3C-SiC buffer layer of about 10 nm thick. The Si-C bonds are partially formed on the as-carburized Si(100) before the diffusion step. The ratio of C-C to Si-C bonds on the as-carburized Si(100) is about 7:3, which can be lowered to about 1:9 after the diffusion step at 1350 oC for 5 min or at 1300 oC for 7 min. According to XPS data and Fick's second law, the diffusivity of Si across the 3C-SiC interlayer are determined to be 2.2×10-16 cm2/s and 3.13×10-16 cm2/s at 1300°C and 1350°C, respectively. The derived activation energy is 1.6 eV for the diffusion of Si atoms in the 3C-SiC buffer layer.
Phosphorus Oxide Assisted n-type Dopant Diffusion in 4H-Silicon Carbide
Authors: Mendis Suwan P , Tin Chin-Che
Published: August 2010

Phosphorus is an important n-type dopant for both silicon and silicon carbide. Although solid-state diffusion of phosphorus in silicon has been well documented and experimentally proven, not much is known about phosphorus solid-state diffusion in silicon carbide, especially at lower temperatures. A convenient source of phosphorus for solid-state diffusion in silicon carbide is phosphorus oxide. The possibility of using phosphorus oxide as a dopant source for silicon carbide is investigated by considering the probable reactions between silicon carbide and phosphorus oxide at temperatures below 1700 K using published thermodynamic data. By considering the standard free energies of reactions, it can be shown that phosphorus can be introduced in silicon carbide at temperatures below 1700 K using phosphorus oxide. A successful development of low temperature dopant incorporation in silicon carbide would reduce the need for high temperature processes and prevent process-induced thermal degradation of critical device structures such as the oxide-semiconductor interface. Experimental results showing phosphorus impurity incorporation and activation in 4H-SiC are presented.
Planarization Specification for 22nm and Beyond BEOL CMP
Authors: Choi Jihong , Wang Changan , Wei Yayi , Zielinski Eden , Tseng Wei-tsu , Moon Yongsik , Kelling Mark , Economikos Laertis
Published: August 2010

This study discusses topography specifications for 22 nm and beyond CMP process and presents recent experimental data. We evaluated local topography impact on CD development in the subsequent layer using specially designed 22-nm test patterns. A wide range of localized erosions were generated in CMP within a single exposure field to avoid any focus-correction effect by the scanner or any other scanner-induced focus change between different levels of local erosion. Local erosions were measured by atomic force microscopy (AFM) after each process step from CMP to lithography to identify the local planarization effect from other film coatings between CMP and lithography. Post-litho CD inspection was done in the subsequent layer over the local erosion areas. Using experimental results, the paper also discusses BEOL pattern design rule for maximizing the process window.