bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of Kinetic Mechanisms of Three-component Photoinitiator Systems for Visible-light Free Radical Polymerizations
Authors: Kim Dongkwan , Stansbury Jeffrey W 
Published: April 2011

ABSTRACTThree-component photoinitiator systems generally include a light-absorbing photosensitizer (PS), an electron donor and an electron acceptor, which is usually an onium salt. To investigate the key factors involved with visible-light free radical polymerizations of three-component photoinitiators, we used thermodynamic feasibility and kinetic considerations with three-component photoinitiator systems containing either rose bengal (RB) or fluorescein (FL) as the photosensitizer. The Rhem-Weller equation was used to verify the thermodynamic feasibility for the photo-induced electron transfer reaction. Using the thermodynamic feasibility, we suggest three different kinetic mechanisms, which are i) photo-reducible series mechanism, ii) photo-oxidizable series mechanism and iii) parallel-series mechanism.
Novel Applications of the QCM Technique in Biomaterials Science
Authors: Silva Candida Costa , Lin David C , Horkayne-Szakaly Iren , Basser Peter J , Horkay Ferenc 
Published: April 2011

ABSTRACTA quartz crystal microbalance (QCM) has been used to investigate polymer samples. The vapor sorption of three different polymer samples (poly(vinyl acetate), polybutadiene and polydimethylsiloxane) was studied. The change in resonance frequency of the quartz sensor uniformly coated with polymer films was measured as a function of the film thickness and water absorption at different temperatures. The range of linear frequency vs. mass response was determined in the absence of absorbed water. The glass transition temperature of thin poly(vinyl acetate) films (10 nm <thickness< 1000 nm) was found to be in reasonable agreement with published values for macroscopic samples.
Dynamics and Transport of Molecules in Polymer and Colloidal-Rod Networks
Authors: Kang Kyongok 
Published: April 2011

ABSTRACTRe-orientational dynamics of liquid crystal molecules in a polymer network subjected to an electric field is studied by means of light diffraction [1]. When the optical pitch of the electric-field induced cholesteric phase is small compared to the optical wavelength of light, dynamic light scattering (DLS) can be performed to extract the relaxation dynamics of the chiral nematic molecules in the presence of the polymer network. Intriguingly, the reactive mesogenic type of polymer network exhibits a confinement effect, which can be probed within the limited range of scattering angles that comply with the structural correlation length in the system [2].Diffusive mass transport of molecules through a rod network can be studied via fluorescence correlation spectroscopy (FCS) and DLS. Long time self-diffusion of tracer spheres (silica and proteins) in isotropic and nematic colloidal-rod networks (fd-viruses) is systematically studied for various tracer-sphere sizes as compared to the mesh size of the network [3]. In addition, by varying the salt concentration, the relative contribution of electrostatic interactions can be varied. A theory is developed where the diffusion coefficient is expressed in terms of the hydrodynamic screening length of the highly entangled rod-network. The hydrodynamic screening length of rod networks is extracted from diffusion data as a function of the rod concentration both for isotropic and nematic networks [4-5].
Computer Simulation of Compressive Failure in Silica Aerogels
Authors: Good Brian S. 
Published: April 2011

ABSTRACTHistorically, the low thermal conductivity of silica aerogels has made them of interest to the aerospace community for applications such as cryotank insulation. However, recent advances in the application of conformal polymer coatings to these gels have made them significantly stronger, and potentially useful as lightweight structural materials. In this work, we perform multiscale computer simulations to investigate the compressive strength and failure behavior of silica aerogels.The gels' nanostructure is simulated via the diffusion limited cluster aggregation (DLCA) process, which produces fractal aggregates that are structurally similar to experimentally observed gels. The largest distinct feature of the clusters is the so-called secondary particle, typically tens of nm in diameter, which is composed of primary particles of amorphous silica an order of magnitude smaller. The secondary particles are connected by amorphous silica bridges that are typically smaller in diameter than the particles they connect.We investigate compressive failure via the application of a uniaxial compressive strain to the DLCA clusters. In computing the energetics of the compression, the detailed structure of the secondary particles is ignored, and the interaction among secondary particles is described by a Morse pair potential parameterized such that the potential range is much smaller than the secondary particle size; an angular potential contribution is included in some of the simulations as well. The Morse and angular parameters are obtained by atomistic simulation of models of the interparticle bridges, with the compressive and bending behavior of these bridges modeled via molecular statics. We consider the energetics of compression and compressive failure, and compare qualitative features of low-and high-density gel failure.
A light scattering study of interactions of oppositely charged proteins in solution
Authors: Ramasamy Perumal Radha , Elmaghrabi Raafat , Halada Gary , Rafailovich Miriam 
Published: April 2011

ABSTRACTIn experiments involving electrophoresis of proteins in gels, it was observed that the mobility of FITC tagged albumin (FITC albumin) was greater than that of TRITC tagged albumin (TRITC albumin). To further understand the effects of tagging proteins with fluorescent dyes, interactions of anionic proteins FITC albumin and untagged bovine serum albumin (BSA), with cationic protein ploy-L-lysine was studied using dynamical light scattering. It was found that aggregates formed by the interaction of FITC albumin with poly-L-lysine were larger than those formed by the interaction between poly-L-lysine and BSA. Using zeta potential measurements it was observed that irrespective of the fluorescent tags attached to them, the zeta potential values of cationic proteins changed from negative to positive with increasing amounts of poly-L-lysine. It was also observed that addition of small amounts of poly-L-lysine to solutions containing FITC albumin decreased the zeta potential drastically. To explain this data, we are proposing a model that suggests that low concentrations of poly-L-lysine serve as scaffold - like structures on which several FITC albumin molecules anchor. We conclude that FITC appears to change the surface charge of albumin significantly and thereby influencing its behavior in solution and its interaction with cationic poly-L-lysine.
Stronger and Longer Synthetic Collagen
Authors: Raines Ronald T. 
Published: April 2011

ABSTRACTCollagen is the most abundant protein in the human proteome. The post-translational modification of collagen by the enzyme prolyl 4-hydroxylase increases markedly the conformational stability of the collagen triple helix. We have discovered that a previously unappreciated force—stereoelectronic effects—is responsible for this increased stability. By exploiting these stereoelectronic effects (e.g., the gauche effect and n→π* interaction) and reciprocal steric effects, we have created synthetic collagen of unprecedented stability. We have also used the molecular self-assembly of triple-helical fragments to create synthetic collagen of unprecedented length. These synthetic collagens have numerous applications in biotechnology and biomedicine.
A Bacterium's Sense of “Touch”
Authors: Yongsunthon Ruchirej , Lower Brian H. , Fowler Vance G. , Alexander Emily , Lower Steven K. 
Published: April 2011

ABSTRACTThe sheer number of bacteria living on solid surfaces makes a compelling argument for the existence of surface sensing mechanisms. However, surface sensing abilities have not been widely studied in bacteria, because such abilities are not macroscopically observable in attached organisms with limited mobility. We report experimental evidence that attachedStaphylococcus aureuscells recognize the steep gradient near their substrate interface and localize substrate-specific biomolecules toward that region. We present Atomic Force Microscopy-based affinity maps which reflect the cells' biochemical sensory response to the substrate and provide a unique view of regions indicating specific binding activity and bond resilience.
Analysis of Human Spleen Contamination
Authors: Kopani Martin , Weis Martin , Dekan Julius , Jakubovsky Jan , Miglierini Marcel 
Published: April 2011

ABSTRACTWe identified both crystalline and amorphous phase of human spleen particles. The silicon particles in the spleen were 10-30 μm large. Silicon, silicon-aluminium and silicon-calcium particles by EDX were found. We assume that the silicon must enter the organism from the external environment and the presence of silicon in the human spleen is consequence of the cleaning function of human spleen.Mössbauer spectroscopy of studied tissues revealed different phase of iron oxide in the human spleen. On the ground of this consideration we can claim all samples of investigated tissues exhibit presence of two different paramagnetic iron phases, both based on three-valent (Fe3+) atoms. Consequently only 4 different iron-oxides correspond with experimental results. Multielemental composition of iron particles was found by EDX analysis. We suppose that pH and time are significant factors influence biomineralization of iron in the human spleen.
Radiochemical Synthesis of Au/Iron-oxide Composite Nanoparticles Using PEG
Authors: Seino Satoshi , Kinoshita Takuya , Iida Juinichi , Shibata Yujin , Nakagawa Takashi , Ueno Koji , Yamamoto Takao A 
Published: April 2011

ABSTRACTComposite nanoparticles consisting of gold and iron-oxide were radiochemically synthesized in aqueous solution systems by using polyethylene glycols. The gold particles with average diameter of 3 nm were firmly immobilized on the surface of the support iron-oxide nanoparticles. The composite nanoparticles specifically adsorbed sulfur-containing amino acids by a Au-S bonding.
Encapsulation of Neural Cells in Nano-Featured Polymer Scaffolds through Co-axial Electrospinning
Authors: Pareta Rajesh A , Webster Thomas J 
Published: April 2011

ABSTRACTEncapsulation of PC12 cells (neural cell model) in alginate hydrogels with a protective coating of poly(lactic-co-glycolic acid) (PLGA) was achieved in the present study using co-axial electrospinning. Co-axial electrospinning consists of two concentric capillaries compared to only one capillary in conventional electrospinning. This allows for the processing of two liquid solutions simultaneously. Neural cells suspended in hydrogels were injected in the inner capillary, while the carbon nanotubes (added for conductivity) suspended in PLGA were injected in the outer capillary at controlled flow rates. On the application of a high voltage, a compound jet formed at the capillary exits and resulted in a co-electrospun fiber of nerve cells encapsulated in PLGA with carbon nanotubes. Carbon nanotubes were included to make the outer shell conductive to stimulate the PC12 cells. In this study, the voltage varied from 0 to 15 kV and various flow rates were tested to achieve a stable cone-jet mode in electrospinning. The cell density in the media varied from 0.5 to5 million cells/ml and the polymer solution (PLGA) concentration varied from 1 to 10 mg/ml. This resulted in a three dimensional conductive scaffold with nano-features (due to carbon nanotubes) on the polymer surface, which were collected on the grounded substrate. PC12 cells were found to be viable inside microspheres after 3 days. The size of the microspheres was quite uniform and less than 200 μm. This technique may be very useful for the development of cell encapsulated scaffolds which mimic natural body tissue organization for tissue engineering applications such as nervous system regeneration.
Conducting Polymer-based Aptamer Biosensor for in situ Monitoring of Cytokine
Authors: Liao Wei , Randall Bradly , Alba Nicolas , Cui Xinyan Tracy 
Published: April 2011

ABSTRACTNeural prostheses often suffer from undesired chronic inflammatory tissue response. Therefore; a sensitive and real-time biosensor for inflammatory cytokine detection would provide invaluable information toward solving this problem. Such a biosensor based on an aptamer probe doped in polypyrrole and subsequent electrochemical impedance spectroscopy (EIS) has been developed. PDGF, an important inflammatory cytokine, has been successfully measured in both offline EIS characterization and real-time impedance monitoring. For in situ detection of PDGF, the best sensitivity of 10 ng/ml has been achieved.
Evolution of Film Crystalline Structure During the Ultrafast Deposition of Crystalline Si Films
Authors: Jia Haijun , Kuraseko Hiroshi , Fujiwara Hiroyuki , Kondo Michio 
Published: April 2011

ABSTRACTBy using a high density microwave plasma source, an ultrafast deposition rate over 1000 nm/s has been achieved for polycrystalline silicon (poly-Si) film deposition. We find that crystalline structure of the deposited film evolves along the film growth direction, i.e. large grains in surface region while small grains in the bottom region of the film. Systematic study of the deposition process has been performed as a function of the deposition duration. Based on the observed results, a possible mechanism, the annealing-assisted plasma-enhanced chemical vapor deposition, is proposed to describe the film growth process.
Improved Passivation of a-Si:H / c-Si Interfaces Through Film Restructuring
Authors: Burrows Michael Zanoni , Das U. K. , Bowden S. , Hegedus S. S. , Opila R. L. , Birkmire R. W. 
Published: April 2011

ABSTRACTThe as-deposited passivation quality of amorphous silicon films on crystalline silicon surfaces is dependent on deposition conditions and resulting hydrogen bonding structure. However the initial surface passivation can be significantly improved by low temperature post-deposition anneal. For example an improvement in effective lifetime from 780 μsec as-deposited to 2080 μsec post-anneal is reported in the present work. This work probes the hydrogen bonding environment using monolayer resolution Brewster angle transmission Fourier transform infrared spectroscopy of 100 Å thick films. It is found that there is significant restructuring at the a-Si:H / c-Si interface upon annealing and a gain of mono-hydride bonding at the c-Si surface is detected. Calculations show an additional 3.56 − 4.50 × 1014 cm−2 mono-hydride bonding at c-Si surface due to annealing. The estimation of the surface hydride oscillator strength in transmission mode is reported for the first time to be 7.2 × 10−18 cm on Si (100) surface and 7.5 × 10−18 cm on Si (111).
Probing Carrier Depletions on Grain Boundaries in Polycrystalline Si Thin Films by Scanning Capacitance Microscopy
Authors: Jiang Chunsheng , Moutinho H.R. , To B. , Dippo P. , Romero M.J. , Al-Jassim M.M. 
Published: April 2011

ABSTRACTGrain boundaries (GBs) in polycrystalline Si thin-film solar cells are believed to limit the photovoltaic efficiencies. In this paper, we report on a nanometer-resolution measurement of the carrier depletion at the GBs, using scanning capacitance microscopy (SCM). The SCM images exhibit the following features: (1) Carrier concentrations are lower at locations around the GBs than on center regions of the grains; (2) The depletion width at the GBs varies considerably, between 0 and 100 nm, depending on individual GBs; (3) Intra-grain carrier depletion was also observed at point and line defects; and (4) The faceted features that were observed on the topography of the as-grown film surface appeared on the SCM images even after the film surface was polished flat. The direct measurement of the carrier depletion on the GBs demonstrates that the GBs in Si thin films indeed create charged gap states. The nonuniformity of the carrier depletions suggests that the gap states depend on specific GB structures, which should relate directly to the grain orientations and grain facets adjacent to the GB. The depletion around the intragrain defects indicates that the defects are charged and can be recombination centers, and thus, harmful to device performance. This paper reports the first step of our studies toward understanding the relationships between the electronic and structural properties on specific GBs.
Nanostructures with Group IV Nanocrystals Obtained by LPCVD and Thermal Annealing of SiGeO Layers
Authors: Morana Bruno , Rodríguez Andrés , Sangrador Jesús , Rodríguez Tomás , Martínez Óscar , Jiménez Juan , Kling Andreas 
Published: April 2011

ABSTRACTNanocrystals embedded in an oxide matrix have been fabricated by annealing SiGeO films deposited by LPCVD. The composition of the oxide layers and its evolution after annealing as well as the presence and nature of nanocrystals in the films have been studied by several experimental techniques. The results are analyzed and discussed in terms of the main deposition parameters and the annealing temperature.
Micro Crystalline Silicon TFT by the Metal Capped Diode Laser Thermal Annealing Method
Authors: Arai Toshiaki , Morosawa Narihiro , Inagaki Yoshio , Tatsuki Koichi , Urabe Tetsuo 
Published: April 2011

ABSTRACTA novel crystallization method for silicon based thin film transistor (TFT) is proposed for the fabrication of high performance large size flat panel displays. In spite of using almost the same TFT fabrication process as that of hydrogenated amorphous silicon (a-Si:H) TFT, the proposed metal capped laser thermal annealing method realizes the formation of uniform and dense micro crystalline silicon (μc-Si), and provides mobility of 3.1 cm2/V•s, threshold voltage (ΔVth) of 2.3 V, and sub threshold slope (S) of 0.93 V/decade. Moreover, proposed stacked n+ amorphous silicon structure realizes extremely low off-current maintaining high on-current. As the reliability of TFT, a threshold voltage sift (ΔVth) under the high current bias stress test (BTS) condition was investigated, and realized the assumed ΔVth of +1.77 V after 100,000 hours stress of 10 μA and 50°C. This value is 2 orders smaller than that of a-Si:H TFT and only three times larger than that of low temperature poly silicon (LTPS) TFT.We believe that our μc-Si TFT technology is the suitable solution for the high quality, large size flat panel display mass-production.
Micro Photovoltaic Modules for Micro Systems
Authors: Wyrsch Nicolas , Dunand Sylavain , Ballif Christophe 
Published: April 2011

ABSTRACTAmorphous silicon based solar modules are very attractive for the powering of various microsystems for both indoor and outdoor applications. This technology offers a lot of flexibility in terms of module design, output voltage, shape, size, choice of substrates and offers also the possibility to embed sensors such as photodiodes. This paper focuses on the development of micro-solar modules with area ≤0.15 cm2. Several micro-modules with output voltage of up to 60 V (form 0.1 cm2) were designed and fabricated. The performance limitation introduced by the segment monolithic interconnection and the design of the latter is presented and discussed. An example of a micro-module with a total size of 3.9×3.9 mm2 developed for a micro-robot with dual voltage outputs and embedded photodiodes is also presented.
Quality and Growth Rate of Hot-wire Chemical Vapor Deposition Epitaxial Si Layers
Authors: Teplin Charles W , Martin Ina T. , Jones Kim M. , Young David , Romero Manuel J. , Reedy Robert C. , Branz Howard M. , Stradins Paul 
Published: April 2011

ABSTRACTFast epitaxial growth of several microns thick Si at glass-compatible temperatures by the hot-wire CVD technique is investigated, for film Si photovoltaic and other applications. Growth temperature determines the growth phase (epitaxial or disordered) and affects the growth rate, possibly due to the different hydrogen coverage. Stable epitaxy proceeds robustly in several different growth chemistry regimes at substrate temperatures above 600°C. The resulting films exhibit low defect concentrations and high carrier mobilities.
Influence of the Structural Properties of Microcrystalline Silicon on the Performance of High Mobility Thin-Film Transistors
Authors: Chan Kah Yoong , Knipp Dietmar , Carius Reinhard , Stiebig Helmut 
Published: April 2011

ABSTRACTThe influence of the crystalline volume fraction of hydrogenated microcrystalline silicon (mc-Si:H) on the performance of thin-film transistors (TFTs) processed at temperatures below 180 °C was investigated. TFTs employing mc-Si:H channel material prepared near the transition to amorphous growth exhibit the highest electron charge carrier mobilities exceeding 50 cm2/Vs. The influence of the crystalline volume fraction of the intrinsic mc-Si:H material on the transistor parameters like the charge carrier mobility and the contact resistance will be discussed.
Mechanical Properties and Reliability of Amorphous vs. Polycrystalline Silicon Thin Films
Authors: Gaspar Joao , Paul Oliver , Chu Virginia , Conde Joao Pedro 
Published: April 2011

ABSTRACTThis paper presents the mechanical characterization of both elastic and fracture properties of thin silicon films from the load-deflection response of membranes, also known as the bulge test. Properties extracted include the plane-strain modulus, prestress, fracture strength and Weibull modulus. Diaphragms made of low-temperature, hydrogenated amorphous and nanocrystalline silicon films (a-Si:H and nc-Si:H, respectively) deposited by plasma enhanced chemical vapor deposition (PECVD) and, for comparison, membranes composed of high-temperature polycrystalline silicon (poly-Si) deposited by low pressure chemical vapor deposition (LPCVD) have been fabricated and characterized. The structures are bulged until failure occurs. From the stress profiles in the diaphragms at fracture, the brittle material strength is analyzed using Weibull statistics. The bulge setup is fully automated for the sequential measurement of several membranes on a substrate realizing the high-throughput acquisition of data under well controlled conditions. A comprehensive study of the mechanical properties of low-temperature silicon films as a function of deposition parameters, namely substrate temperature, RF power, hydrogen dilution and doping, is presented.
Temperature and humidity effects on the stability of on-plastic a-Si:H thin film transistors with various conduction channel layer thicknesses
Authors: Chen Jian Z , Cheng I-Chun 
Published: April 2011

ABSTRACTStability is an important issue for the application of TFTs. In this paper, we present the effects of humidity and temperature on the stability of inverted-staggered back-channel-cut a-Si:H TFTs with various conduction channel layer thickness. We evaluated the stability of on-plastic TFTs of different conduction layer thicknesses made at a process temperature of 150°C on 51-μm thick Kapton polyimide foil substrates.. With conduction channel layer thickness of 50nm, humidity reversibly varies the characteristics of TFTs, but TFTs of conduction layer thickness greater than 100 nm is pretty immune to the humidity change. The temperature dependent stability and characteristics of TFTs were analyzed from 20°C to 60°C. Rising temperature from 20°C to 56°C, the threshold voltage (Vt) drops about 2 volts; on-off current ratio decreases by one order of magnitude mainly due to thermally excited carriers in the off-region.