bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microfabrication of Asymmetric, Homogeneous Cell-laden Hydrogel Microcapsules
Authors: Dang Tram T. , Xu Qiaobing , Bratlie Kaitlin M , O'Sullivan Esther S , Chen Xiao Y , Langer Robert , Anderson Daniel G. 
Published: August 2010

AbstractCell encapsulation has been broadly investigated as a technology to provide immunoprotection for transplanted endocrine cells. Here we develop a new fabrication method that allows for rapid, homogenous microencapsulation of insulin-secreting cells with varying microscale geometries and asymmetrically modified surfaces. Micromolding systems were developed using polypropylene mesh, and the mesh material/surface properties associated with efficient encapsulation were identified. Cells encapsulated using these methods maintain desirable viability and preserve their ability to proliferate and secrete insulin in a glucose-responsive manner. This new cell encapsulation approach enables a practical route to an inexpensive and convenient process for the generation of cell-laden microcapsules without requiring any specialized equipment or microfabrication process.
Biomaterials Nano Geometry for Control of Stem Cell Differentiation
Authors: Brammer Karla , Oh Seunghan , Jin Sungho 
Published: August 2010

AbstractTwo important goals in stem cell research are to control the cell proliferation without differentiation, and also to direct the differentiation into a specific cell lineage when desired. Recent studies indicate that the nanostructures substantially influence the stem cell behavior. It is well known that mesenchymal stem cells (MSCs) are multipotent stem cells that can differentiate into stromal lineages such as adipocyte, chondrocyte, fibroblast, myocyte, and osteoblast cell types. By examining the cellular behavior of MSCs cultured in vitro on nanostructures, some understanding of the effects that the nanostructures have on the stem cell’s response has been obtained. Here we demonstrate that TiO2 nanotubes produced by anodization on Ti implant surface can regulate human mesenchymal stem cell (hMSC) differentiation towards an osteoblast lineage in the absence of osteogenic inducing factors. Altering the dimensions of nanotubular-shaped titanium oxide surface structures independently allowed either augmented human mesenchymal stem cell (hMSC) adhesion at smaller diameter levels or a specific differentiation of hMSCs into osteoblasts using only the geometric cues. Small (˜30 nm diameter) nanotubes promoted adhesion without noticeable differentiation, while larger (˜70 - 100 nm diameter) nanotubes elicited a dramatic, ˜10 fold stem cell elongation, which induced cytoskeletal stress and selective differentiation into osteoblast-like cells, offering a promising nanotechnology-based route for novel orthopaedics-related hMSC treatments. The fact that a guided and preferential osteogenic differentiation of stem cells can be achieved using substrate nanotopography alone without using potentially toxic, differentiation-inducing chemical agents is significant, which can be useful for future development of novel and enhanced stem cell control and therapeutic implant development.
Fabrication of (Ti-O-N-Si)/Ti Composite Coating on NiTi Shape Memory Alloy Using PIIID and Coating Evaluation
Authors: Sun Tao , Wang Langping , Wang Min 
Published: August 2010

AbstractA compact and uniform (Ti, Si, O, N)/Ti composite coating was fabricated on the surface of a NiTi shape memory alloy (SMA) (containing 50.8 at.% Ni) using plasma immersion ion implantation and deposition (PIIID) with radio-frequency (RF) magnetron sputtering. The coating and coated NiTi SMA were studied using various techniques. Analysis showed that the Ni content was drastically reduced on the surface of coated samples due to coating formation. This could greatly improve the biocompatibility of NiTi SMA. There was no TiO2 or TiN formation in the coating. The shape memory ability of NiTi SMA samples was no deteriorated by the coating process. The coating significantly improved the corrosion resistance and wear resistance of NiTi SMA and also rendered the material bioactive.
Electrochemical Deposition of Apatite/Collagen Composite Coating on NiTi Shape Memory Alloy and Coating Properties
Authors: Wang Min , Sun Tao 
Published: August 2010

AbstractIn this investigation, an apatite/collagen composite coating was formed at 37C on a NiTi shape memory alloy (SMA) through electrochemical deposition using double-strength simulated body fluid (2SBF) which contained dissolved collagen. Surface characteristics, wettability and stability of the composite coating were subsequently studied. Scanning electron microscope (SEM) examination of the surface of composite coatings revealed that many collagen fibers were embedded in apatite with flake-like structure and apatite nanocrystals nucleated and grew on collagen fibrils. Energy dispersive X-ray (EDX) spectroscopy analysis showed that the Ca : P ratio of the composite coating was about 1.35, which is close to that of octocalcium phosphate. Transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) analysis were also conducted for the composite coating. Compared to bare NiTi SMA samples, the potentiodynamic polarization curves of NiTi SMA samples with the composite coating displayed lower corrosion current density, more positive corrosion and breakdown potential, suggesting that the composite coating was chemically stable and provided corrosion resistance for NiTi SMA.
Syntheses of Hydroxyapatite Nanospheres Through a Facile Sol-gel Method
Authors: Li Kai , Tjong Sie Chin 
Published: August 2010

AbstractHydroxyapatite (HA) nanospheres were synthesized via the sol-gel route in the presence of poly(vinyl alcohol) (PVA). The HA nanospheres were formed from the reaction between (NH4)2HPO4 and CaCl2 in ethanol/PVA sol-gel system, in which ammonia solution (NH3•H2O) was added to adjust the pH of solution. The as-synthesized products were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDAX). XRD patterns and FTIR spectra showed that the HA nanospheres exhibit the crystalline structure and vibration bands of HA. The Ca/P molar ratio of HA nanospheres (50˜70nm) approached the stoichiometric value of 1.67, on the basis of EDAX results. Simulated Body Fluid (SBF) immersion test for three weeks demonstrated that the apatite layer can be formed on the HA nanospheres sintered at 550°C.
Quantitative Investigations of Nanoscale Elasticity of Nanofibrillar Matrices
Authors: Tiryaki Volkan M , Khan Adeel Ahmed , Pastor Alicia , Alduhaileb Raed A , Delgado-Rivera Roberto , Ahmed Ijaz , Meiners Sally A , Ayres Virginia M 
Published: August 2010

AbstractRecent research indicates that nanophysical properties as well as biochemical cues can influence cellular re-colonization of a tissue scaffold. It has also been shown nanoscale elasticity can strongly influence cellular responses. In the present work, quantitative investigations of the elasticity of a nanofibrillar matrix scaffold that has demonstrated promise for spinal cord injury repair are compared with complementary transmission electron microscopy investigations, performed to assess nanofiber internal structures. Interpretive model improvements are identified and discussed.
Optical Properties of Electrospun Nanofiber Substrates
Authors: Davis Lynn , Walls Howard J , Mills Karmann C. , Guzan Kim , Yaga Robert , Ensor David S 
Published: August 2010

AbstractLight impinging upon electrospun nanofiber substrates encounters a complex media where a multitude of factors controls the transmittance and reflectance of light through the structure. The chemical composition of the nanofiber plays a significant role in that it determines the index of refraction of individual fibers. However, the surrounding media (e.g., air, encapsulating polymer, etc.) also plays an equally important role. In addition, physical effects such as fiber diameter, fiber morphology, fiber packing density (i.e., structure void volume), and substrate thickness play a large role in determining the light management properties of nanofibers. Our research has demonstrated that the transmittance and reflectance of undoped nanofibers can be adjusted through proper manipulation of these factors. For example, similar electrospinning formulations can produce either highly transmitting or highly reflecting light structures depending upon fabrication parameters that impact the final properties of the nanofiber substrates. In addition, a degree of wavelength dependent reflectance and transmittance can be imparted simply by adjusting the physical properties of the nanofibers to promote preferential light scattering below selected frequencies. This paper provides an overview of various factors impacting the light management properties of nanofiber substrates and the importance of controlling these factors to meet end-use applications.
Nontoxic Silicon Nanocrystals and Nanodiamonds as Substitution for Harmful Quantum Dots
Authors: Fucikova Anna , Valenta Jan , Pelant Ivan , Brezina Vitezslav 
Published: August 2010

AbstractThe commercially available semiconductor quantum dots have been proven to be slightly to significantly toxic by recent publications depending on the chemical composition. We are developing new non-toxic fluorescent labels based on (i) nanocrystalline silicon, suitable for in vivo studies due to their biodegrability, and on (ii) nanodiamonds, intended mainly for in vitro use due to their long-term stability and nondegradilibity.
P-layer Optimization in High Performance a-Si:H Solar Cells
Authors: Xu Yueqin , Nemeth Bill , Hasoon Falah , Hong Lusheng , Duda Anna , Wang Qi 
Published: August 2010

AbstractWe report our progress toward high-performance hydrogenated amorphous silicon (a-Si:H) solar cells fabricated in NREL's newly installed multi-chamber film Si deposition system. The a-Si:H layers are made by standard radio frequency plasma-enhanced chemical vapor deposition. This system produces a-Si:H p-i-n single-junction devices on Asahi U-type transparent conducting oxide glass with >10% initial efficiency. The importance of the p-layer to the cell is identified: it plays a critical role in further improving cell performance. Our optimization process involves changing p-layer parameters such as dopant levels, bandgap, and thickness in cells as well as applying a double p-layer. With the optimized p-layer, we are able to increase the fill factor of our cells to as high as 72% while maintaining high open-circuit voltage.
Silicon Germanium Oxide (SixGeyO1-x-y) Infrared Sensitive Material for Uncooled Detectors
Authors: Anvari Reza , Cheng Qi , Hai Muhammad Lutful , Bui Truc Phan , Syllaios A. J. , Ajmera S. K. , Almasri Mahmoud F. 
Published: August 2010

AbstractThis paper presents the formation and the characterization of silicon germanium oxide (SixGeyO1-x-y) infrared sensitive material for uncooled microbolometers. RF magnetron sputtering was used to simultaneously deposit Si and Ge thin films in an Ar/O2 environment at room temperature. The effects of varying Si and O composition on the thin film's electrical properties which include temperature coefficient of resistance (TCR) and resistivity were investigated. The highest achieved TCR and the corresponding resistivity at room temperature were -5.41 %/K and 3.16×103 ohm cm using Si0.039Ge0.875O0.086 for films deposited at room temperature.
High Mobility a-Si:H TFT Fabricated by Hot Wire Chemical Vapor Deposition
Authors: Hsueh Chun-Yuan , Yang Chieh-Hung , Lee Si-Chen 
Published: August 2010

AbstractThe hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) having a very high field-effect mobility of 1.76 cm2/V-s and a low threshold voltage of 2.43 V have been fabricated successfully using the hot wire chemical vapor deposition (HWCVD).
Biaxial Texturing of Inorganic Photovoltaic Thin Films Using Low Energy Ion Beam Irradiation During Growth
Authors: Groves James , Hayes Garrett J , Li Joel B , DePaula Raymond F , Hammond Robert , Salleo Alberto , Clemens Bruce M 
Published: August 2010

AbstractWe describe our efforts to control the grain boundary alignment in polycrystalline thin films of silicon by using a biaxially textured template layer of CaF2 for photovoltaic device applications. We have chosen CaF2 as a candidate material due to its close lattice match with silicon and its suitability as an ion beam assisted deposition (IBAD) material. We show that the CaF2 aligns biaxially at a thickness of ~10 nm and, with the addition of an epitaxial CaF2 layer, has an in-plane texture of ~15°. Deposition of a subsequent layer of Si aligns on the template layer with an in-plane texture of 10.8°. The additional improvement of in-plane texture is similar to the behavior observed in more fully characterized IBAD materials systems. A germanium buffer layer is used to assist in the epitaxial deposition of Si on CaF2 template layers and single crystal substrates. These experiments confirm that an IBAD template can be used to biaxially orient polycrystalline Si.
Research Progresses on High Efficiency Amorphous and Microcrystalline Silicon-Based Thin Film Solar Cells
Authors: Geng Xinhua , Zhao Ying , Zhang Xiandan , Hou Guofu , Ren Huizhi , Ge Hong , Chen Xinliang 
Published: August 2010

AbstractThis paper reviews our research progresses of hydrogenated amorphous silicon (a-Si:H) and microcrystalline (μc-Si:H) based thin film solar cells. It coves the three areas of high efficiency, low cost process, and large-area proto-type multi-chamber system design and solar module deposition. With an innovative VHF power profiling technique, we have effectively controlled the crystalline evolution and made uniform μc-Si:H materials along the growth direction, which was used as the intrinsic layers of pin solar cells. We attained a 9.36% efficiency with a μc-Si:H single-junction cell structure. We have successfully resolved the cross-contamination issue in a single-chamber system and demonstrated the feasibility of using single-chamber process for manufacturing. We designed and built a large-area multi-chamber VHF system, which is used for depositing a-Si:H/μc-Si:H micromorph tandem modules on 0.79-m2 glass substrates. Preliminary module efficiency has exceeded 8%.
Boule Shape Dependence of Shear and von-Mises Stress Distributions in Bulk SiC during Sublimation Growth
Authors: Drachev Roman Victorovich , Hansen Darren , Loboda Mark J 
Published: August 2010

AbstractAn analytical study of the dependence of shear and von-Mises stress distributions, which develop during PVT (Physical Vapor Transport) growth of 4H-SiC, has been executed. The key parameters investigated include thermal conditions of the crystal growth and parameters of the growing boule geometry. The evaluation was conducted via a 24 full factorial DOE (Design of Experiments). Parameters of the growing boule geometry, i.e. seed diameter, growth front height, inclination angle and height of the side surface were set as the DOE factors, while responses were calculated using numerical simulations. It is found that unique SiC boule growth conditions, which simultaneously minimize both the shear stress and von Mises stress magnitudes, cannot be achieved. Optimization of the shear stress distribution favors longer SiC boules with small seed diameters, small expansion angles and flat growth fronts. Alternatively, optimization of von-Mises stress favors short crystals with small seed diameters and small expansion angles but with curved growth fronts. Consequently, optimization of stress components in SiC crystals involves careful investigation of the interaction and compromise of the reaction cell geometry and growth conditions.
Analysis of Dislocation Behavior in Low Dislocation Density, PVT-Grown, Four-Inch Silicon Carbide Single Crystals
Authors: Dudley Michael , Byrappa Shayan , Wang Huanhuan , Wu Fangzhen , Zhang Yu , Raghothamachar Balaji , Choi Gloria , Sanchez Edward , Hansen Darren , Drachev Roman , Loboda Mark 
Published: August 2010

AbstractSynchrotron White Beam X-ray Topography studies are presented of dislocation behavior and interactions in a new generation of one hundred millimeter diameter, 4H-SiC wafers grown using Physical Vapor Transport (PVT) under specially designed low stress conditions. Such low stress growth conditions have, for example enabled reductions of basal plane dislocation (BPD) densities by two or three orders of magnitude compared to previous levels down to just a few hundred per square centimeter. This provides a unique opportunity to discern details of dislocation behavior which were previously precluded due to complications of image overlap at higher densities. Among the phenomena observed in these studies is the deflection of threading dislocations onto the basal plane producing various stacking fault configurations. Analysis of the contrast from these faults enables determination of their fault vectors which, in turn, provides insight into their possible formation mechanisms.
Self-aligned Process for SiC Power Devices
Authors: Borsa Tomoko , Van Zeghbroeck Bart 
Published: August 2010

AbstractSilicon carbide is a semiconductor with desirable material properties, such as a wide bandgap and high thermal conductivity. It is an excellent material for constructing power switching devices operating in harsh environments where conventional semiconductors cannot adequately perform. One example of such a power device is a bipolar junction transistor (BJT). While the potential of the SiC BJT is recognized, appropriate techniques for producing devices is lacking due to its difficulty.For example, in order to achieve a high voltage 4H-SiC BJT switch with nanosecond switching time, the device must have a low base resistance. The simulation results indicate that for an emitter width of 2.0 μm and a base width of 1.2 μm the distance between the two should be 0.4 μm or less to meet the requirement for base resistance. To produce the above-described geometries and spacing, it is desirable to construct the device in a self-aligned manner. Self-alignment in this context means that the relative spacing of features of the device, such as contacts, is automatically controlled by the processing sequence and process parameters, rather than by the careful alignment prior to exposure of a photo sensitive layer. For this purpose, we developed a novel self-aligned process for SiC BJT devices, that enables the fabrication of the design with high yield, as standard silicon self-aligned technique are not applicable.The newly developed process starts with the deposition of the emitter contact metal, which provides the metal mask for the etching of the emitter ridges. Next, the wafer is planarized with photoresist and etched, so that only the emitter contacts are exposed. Electroless plating is then used to enlarge the contacts, and after removal of the resist, the plating provides an overhang, suitable for lift-off of the base contact metal. After the base contact metal deposition, the structure is planarized and etched, this time with a silicon dioxide layer, again exposing the plated emitter contacts and the lift-off step is the wet etching of the plated metal. The emitters are then all connected with a blanket wiring level, which also forms the base contact pad. This process is simpler and more robust than the process we developed to date. The main difference is the inclusion of a sacrificial lift-off overhang, created by electroless plating. It enables a well controlled overhang independent of steepness of the SiC ridge profile and the height of the emitter mesa. We successfully fabricated the overhang structure on 4H-SiC substrates.In conclusion, we report the demonstration of a new self-aligned process, which provides a self-aligned emitter contact, a self-aligned base contact and eliminates the need for via holes smaller than the emitter stripe widths. We consider this new process a major improvement over existing processes to fabricate SiC BJT devices.
Ohmic Contacts to Wurtzite Silicon Carbide Using Polarization Technology
Authors: Praharaj Choudhury Jayant 
Published: August 2010

AbstractWe present theoretical calculations for ohmic contact technology to wurtzite Silicon Carbide using thin Indium Gallium Nitride and Aluminium Indium Nitride cap layers. Spontaneous and piezoelectric polarization in Indium Gallium Nitride and Aluminium Indium Nitride cap layers gives rise to bound interface sheet charge density of the order of 1013 electrons per cm2, and built-in electric fields of the order of MV per cm. For Si-face p-type SiC, the large compressive strain in very thin InGaN and AlInN cap layers results in negative sheet charge densities and much lower tunneling widths for holes compared to bulk contacts. For C-face p-type SiC, pseudomorphic nitride layers yield no benefit over bulk contacts since positive interface sheet charge densities repel holes and give higher contact resistances. However, thick, relaxed cap layers lead to spontaneous polarization-based negative charge densities that attract holes, leading to lower contact resistances. The contributions of the heavy, light and split-off band holes to the total tunneling flux is taken into account in our calculations. All tunneling probabilities are calculated within the Wentzels-Kramers-Brillouin approximation. The presence of the appropriate cap layers leads to several orders of magnitude improvement in tunneling transmission probabilities, and in many cases, makes ohmic technology to SiC feasible. While the major difficulties are encountered for contacts to p-type SiC, the effect of cap-based polarization technology on contacts to n-type layers is also discussed in this paper. Our calculations have relevance to contact technology for bipolar devices built from wide band-gap wurtzite semiconductors like heterojunction bipolar transistors, light-emitting diodes and lasers.
Near-interface Traps in n-type SiO2/SiC MOS Capacitors from Energy-resolved CCDLTS
Authors: Basile Alberto F , Dhar Sarit , Rozen John , Chen Xudong , Williams John , Feldman Leonard C. , Mooney Patricia M. 
Published: August 2010

AbstractSilicon Carbide (SiC) Metal-Oxide-Semiconductor (MOS) capacitors, having different nitridation times, were characterized by means of Constant Capacitance Deep Level Transient Spectroscopy (CCDLTS). Electron emission was investigated with respect to the temperature dependence of emission rates and the amplitude of the signal as a function of the filling voltage. The comparison between the emission activation energies of the dominant CCDLTS peaks and the filling voltages, led to the conclusion that the dominant trapping behavior originates in the Silicon-dioxide (SiO2) layer. Moreover, a model of electron capture via tunneling can explain the dependence of the CCDLTS signal on increasing filling voltage.