bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Nano-Micro-Macro-Structured Porous Nickel Electrodes for use in Supercapacitors
Authors: Manning Jason , Campbell Roger , Woo Renee , O'Neil Brenda , McKenzie Leigh , Bakker Martin Gerard , Montoya Velma , Havrilla George
Published: April 2011

The extremely high surface areas required for supercapacitors has limited the use of metal based electrodes, despite the other advantages such electrodes might have. Self-assembling surfactants and block co-polymers can be used as templates to produce nanostructured thin films that readily give 60-140 fold increases in surface area on both planar and three-dimensional substrates. However, even when relatively high surface area porous metal substrates such as nickel foam are used as a starting point, the resultant material still has surface area density well short of that available in other types of materials. Micro-emulsions offer a method of generating microstructure that bridges the gap between the 100 micron scale structures of foamed metals and the 10-50 nm scale structure of self-assembling block co-polymers. Electrodeposition of nickel and cobalt from micro-emulsions of Tween surfactants gives rise to structure on the 0.1-10 micron length scale. The scale of the microstructure is strongly influenced by the metal ion concentration and the potential at which the electrodeposition. The nature of the metal ion also strongly effects the ease with which the microstructure can be generated and the distribution of the microstructured film on foamed nickel electrodes. For microstructured nickel films ten fold surface area increases can be achieved. The microstructured films are expected to be compatible with a number of the nanostructuring methods to yield cumulative surface area increases of 1000-2000 fold.
Exciton Lifetime in PbS Quantum Dots in Glass
Authors: Persans Peter D , Filin A. , Berry N. E. , Huang F. , Chan E.
Published: April 2011

We report experimental measurements and analysis of HOMO-LUMO transition photoluminescence and photoinduced bleaching magnitude and decay kinetics in lead sulfide quantum dots in glass. We find that the radiative lifetime is independent of temperature from 77K to 500K. The lifetime of the HOMO-LUMO state decreases dramatically for T>300K, indicating thermally activated nonradiative recombination. The excitation decay time is much greater than the radiative lifetime and increases monotonically with decreasing temperature with decay times of 2 μs at room temperature and 4-10 μs at 77K.
Electron Tomography of SPM Probes, Nanoparticles and Precipitates
Authors: Xu Xiaojing , Saghi Zineb , Yang Guang , Peng Yong , Inkson Beverley , Gay Ralph , Möbus Günter
Published: April 2011

Nanoscale tomographic reconstructions from objects with diameters of 100nm or smaller can only be achieved non-destructively with transmission electron tomography. The application of this technique to W tips, which are common probes for scanning tunneling microscopy and nanoindentation, is demonstrated with emphasis on visualizing oxide layers and functionally attached nanoparticles. For the reconstruction of facetted free-standing catalyst nanoparticles, such as CeO2 octahedra, we propose a combination of energy-filtered (EF) and bright field (BF) TEM tomography to achieve high fidelity of the projection relationship via EFTEM, due to its incoherent imaging mode, and high resolution definition of the particle circumference from the edge-enhancement effects of the BF tomogram. Finally, electron tomography applications to CeO2 nanoprecipitates embedded in a multicomponent oxide glass matrix are shown, which comprises the first tomographic 3D reconstruction of a nanoscale dendrite.
Dependence of the Electronic Properties of Hot-Wire CVD Amorphous Silicon-Germanium Alloys on Oxygen Impurity Levels
Authors: Datta Shouvik , Cohen J. David , Xu Yueqin , Mahan A. H. , Branz Howard M.
Published: April 2011

We report the effects of intentionally introducing up to ∼ 5×1020/cm3 oxygen impurities into hydrogenated amorphous silicon-germanium alloys (of roughly 30at.% Ge) grown by the hot-wire chemical vapor deposition (HWCVD) method. Deep defect densities determined by drive-level capacitance profiling (DLCP) indicated a modest increase with increasing oxygen content (up to a factor of 3 at the highest oxygen level). Transient photocapacitance (TPC) spectra indicated a clear spectral signature for an optical transition between the valence band and an additional defect level which is attributed to oxygen impurities. The oxygen impurity related defect transition has an optical threshold around 1.4eV above the valence band and also results in a negative contribution to the TPC signal. This initially led us to believe that the bandtail for the higher oxygen samples was much narrower than it actually is. Surprisingly, this additional oxygen related defect level appears to have only a very minor effect upon the estimated minority carrier collection fraction. The effects of light-induced degradation upon some of these oxygen contaminated samples were also examined. We infer the existence of a significant thermal barrier to explain the observed spectral signatures of this oxygen impurity defect.
Stability of Amorphous Silicon Thin Film Transistors under Prolonged High Compressive Strain
Authors: Chen Jian-Zhang , Cheng I-Chun , Wagner Sigurd , Jackson Warren , Perlov Craig , Taussig Carl
Published: April 2011

We studied the effect of prolonged mechanical strain on the electrical characteristics of thin-film transistors of hydrogenated amorphous silicon made at a process temperature of 150°C on 51-μm thick Kapton polyimide foil substrates. Effects are observed only at very high compressive strain of 1.8%. Tensile strain up to fracture at 0.3% to 0.5% does not show any effect, nor does compressive strain substantially less than 1.8%. The TFTs were stressed for times up to 23 days by bending around a tube with axis perpendicular to the channel length, and were evaluated in the flattened state. The changes observed are small. The threshold voltage is increased, the “on” current and the field effect mobility remain essentially constant, and the subthreshold slope, “off” current and gate leakage current drop somewhat. Overall, the observed changes are small. We conclude that mechanical strain caused by roll-to-roll processing and permanent shaping will have negligible effects on TFT performance.
Amorphous Silicon Based TFT and MIS Nonvolatile Memories
Authors: Kuo Yue , Nominanda Helinda
Published: April 2011

The amorphous silicon (a-Si:H) TFT and MIS capacitor, which include an a-Si:H layer embedded in the silicon nitride gate dielectric layer, have been prepared and characterized for memory functions. Large shifts of the threshold voltage and flat band voltage were detected in the current-voltage and capacitance-voltage hysteresis measurements. The embedded a-Si:H film functioned as a charge retention medium that stores and releases injected carriers. The devices memory capacity varied with the thickness of the embedded a-Si:H layer and the sweep voltage. These low-cost memory devices can be used in many low-temperature prepared circuits.
&[mu]-Watt Enhanced Electroluminescent Power of Silicon Nanocrystal Light-Emitting Diodes Made on Nano-Scale Silicon-Tip-Array Substrate
Authors: Lin Gong-Ru , Lin Chun-Jung
Published: April 2011

A Si nanocrystal based metal-oxide-semiconductor light-emitting diode (MOSLED) on Si nano-pillar array is preliminarily demonstrated. Rapid self-aggregation of Ni nanodots on Si substrate covered with a thin SiO2 buffered layer is employed as the etching mask for obtaining Si nano-pillar array. Dense Ni nanodots with size and density of 30 nm and 2.8×10 cm-2, respectively, can be formatted after rapid thermal annealing at 850°C for 22 s. The nano-roughened Si surface contributes to both the relaxation of total-internal reflection at device-air interface and the Fowler-Nordheim tunneling enhanced turn-on characteristics, providing the MOSLED a maximum optical power of 0.7 uW obtained at biased current of 375 uA. The optical intensity, turn-on current, power slope and external quantum efficiency of the MOSLED are 140 μW/cm2, 5 uA, 2+-0.8 mW/A and 1×10-3, respectively, which is almost one order of magnitude larger than that of a same device made on smooth Si substrate.
Advanced Deposition Phase Diagrams for Guiding Si:H-Based Multijunction Solar Cells
Authors: Collins Jason , Podraza Nikolas J. , Li Jian , Cao Xinmin , Deng Xunming , Collins Robert W.
Published: April 2011

Phase diagrams have been established to describe very high frequency (vhf) plasma-enhanced chemical vapor deposition (PECVD) processes for intrinsic hydrogenated silicon (Si:H) and silicon-germanium alloy (Si1-xGex:H) thin films using crystalline Si substrates that have been over-deposited with n-type amorphous Si:H (a-Si:H). The Si:H and Si1-xGex:H processes are applied for the top and middle i-layers of triple-junction a-Si:H-based n-i-p solar cells fabricated at University of Toledo. Identical n/i cell structures were co-deposited on textured Ag/ZnO back-reflectors in order to correlate the phase diagram and the performance of single-junction solar cells, the latter completed through over-deposition of the p-layer and top contact. This study has reaffirmed that the highest efficiencies for a-Si:H and a-Si1-xGex:H solar cells are obtained when the i-layers are prepared under maximal H2 dilution conditions.
Laser Crystallization of Silicon for Large Area Electronics
Authors: Sameshima Toshiyuki
Published: April 2011

Laser crystallization of silicon is discussed for forming polycrystalline silicon thin films used to fabricate polycrystalline silicon thin film transistors (poly-Si TFTs). Laser-induced rapid heating is important for crystalline film formation with a low thermal budget. Structural and electrical properties of poly-Si films are discussed. Reduction of electrical active defects located at grain boundaries is essential for achieving poly-Si TFTs with high performances. The internal film stress is attractive to increase the carrier mobility. Recent development in laser crystallization methods with pulsed and continuous wave (CW) lasers is then reviewed. Control of the heat flow results in crystalline grain growth in the lateral direction, which is essential for fabrication of large crystalline grains. We also report an annealing method using a high power infrared semiconductor laser. High power lasers will be attractive for rapid crystallization of silicon films over a large area and activation of doped regions.
Defect characterization of polycrystalline silicon layers obtained by aluminum-induced crystallization and epitaxy
Authors: Van Gestel Dries , Gordon Ivan , Carnel Lodewijk , Beaucarne Guy , Poortmans Jef
Published: April 2011

To reduce the harmful influence of grain boundaries in polycrystalline Si layers we make absorber layers on foreign substrates with columnar grains with a grain width larger than the grain thickness. Such layers with a grain size in the range of ~1-100 µm can be obtained by aluminum-induced crystallization and epitaxy. Until now however, the open-circuit voltage of solar cells made from such layers was quasi-independent of the grain size. To understand this fact, defect etching and Electron Backscattered diffraction (EBSD) measurements were performed to investigate the crystallographic defects. A very large density (~ 109 cm-2) of intra-grain defects (IGD) was found. Room temperature Electron Beam Induced Current (EBIC) measurements were done to localize and investigate the electrically active defects. The intra-grain defects found with defect etching showed a strong recombination activity. These results indicate that the unexpected quasi-independence on the grain size of the open-circuit voltage of our pc-Si solar cells is due to the presence of numerous electrically active intra-grain defects.
Influence of Amorphous Layers on Performance of Nanocrystalline/Amorphous Superlattice Si Solar Cells
Authors: Madhavan Atul , Ghosh Debju , Noack Max , Dalal Vikram
Published: April 2011

Nanocrystalline Si:H is an important material for solar cells. The electronic properties of the material depend critically upon the degree of crystallinity, the efficacy of passivation of the grain boundaries and impurities, particularly oxygen, in the material. In this paper, we examine different degrees of passivation of grain boundaries by amorphous Si, by deliberately introducing various thicknesses of amorphous tissue layers at the grain boundaries. The device structure consisted of a p+nn+ cell on stainless steel where the base n layer was fabricated using alternating layers of amorphous (a-Si) and crystalline (nc-Si) phases, creating a superlattice structure. The thicknesses of the amorphous and crystalline phases were varied to study their influence on structural and electrical properties such as grain size and diffusion length. We find that <111> grain continued to be nucleate independently of the thickness of the amorphous layer, but the grain size in <220> grain decreased when the thickness of the tissue layer became very large. We also find that as the thickness of the amorphous tissue layer increased, the quantum efficiency at 800 nm decreased and the open circuit voltage increased. For significant thickness of amorphous layer, the transport properties degrade dramatically, causing an inflection in the I-V curve, probably because of difficulty of holes tunneling across the barriers.
Computational Solid Mechanics Modeling of Asperity Deformation and Pad-Wafer Contact in CMP
Authors: Jiang Bo , Muldowney Gregory P.
Published: April 2011

Asperity-scale pad deformation and dynamic pad-wafer contact area are crucial to the fundamental understanding of material removal and defect formation mechanisms in CMP. Pad asperity stress and strain are also central to characterizing pad wear rate during polishing and cut rate during conditioning. While it is very difficult to isolate and measure stress and strain in individual asperities, finite element modeling may be used in conjunction with experimental surface characterization to predict asperity-scale deformation and pad-wafer contact. Asperity sub-domains up to 1270 microns across are reproduced from three-dimensional point cloud data on porous polyurethane CMP pads obtained by confocal microscopy, meshed to high resolution, and analyzed using ABAQUS finite element software. Physical properties are derived from dynamic mechanical experiments. Pad stacks are simulated both with and without sub-pads. Results show that while a sub-pad increases pad-wafer contact area overall, it limits the local spreading of individual contact regions as polishing load increases. This finding identifies a direct mechanical origin of the trade-off in pad design between wafer-scale and die-scale planarity. As expected, the real contact area between a pad and wafer is much smaller than the cross-sectional or “bearing” area, but the difference is notably greater when a sub-pad is present. Values of asperity stress and strain under typical CMP polishing pressures reveal that plastic deformation takes place both on and beneath the contacting surface. Hence upon release of the polishing load the asperities do not fully rebound to their pre-compressed shapes. Each pass under the wafer thus reshapes the pad asperities such that a slightly different texture is presented upon the next pass. These deformation mechanics clarify the impact of top pad and sub-pad properties on real contact area, allowing better optimization of CMP pad performance.
Influence of Microstructure on Aggressive Chemical Mechanical Planarization Processes for Thick Copper Films
Authors: Andersen Patrick J. , Frary Megan
Published: April 2011

Novel die-stacking schema using through-wafer vias may require thick electrodeposited copper and aggressive first-step chemical mechanical planarization (CMP). However, the effect of microstructural parameters, including surface orientation and grain size, on the CMP behavior of thick electrodeposited copper is not well understood. Here we explore the relationship be-tween the surface orientation of copper grains and local CMP removal parameters using electron backscatter diffraction and topography correlation techniques. In the present work, solid copper disks are studied which are annealed to produce samples with differing grain sizes. In addition, aggressive CMP is performed on copper films (30 μm) electrodeposited on silicon. At the bulk level, the slurry composition is found to have the greatest effect on the removal rate and surface roughness. At the microstructural level, the nature of the grain boundaries (e.g. coincidence site lattice (CSL) vs. non-CSL boundaries) is shown to impact the depth of grooving at the grain boundaries. A relationship between surface orientation and local removal rate is found.
High Rate Silicon Carbide Polishing to Ultra-smooth Surfaces
Authors: White Michael , Moeggenborg Kevin , Batllo Francois , Gilliland Jeffrey , Naguib Nevin
Published: April 2011

Silicon Carbide has a unique combination of properties that include a nearly diamond-like hardness, intrinsic electrical semiconductivity and a high thermal conductivity. This combination of properties has led to it's use in a number of applications including substrates for Light Emitting Diodes (LEDs), power, RF (radio frequency) and other electronic devices in addition to mirror substrates and optical devices as well as stop layers in integrated circuit chip manufacture. In addition, the chemical inertness and high hardness of SiC has historically resulted in low removal rates during chemical mechanical Planarization (CMP). Recent efforts in our labs have led to being able to polish single crystal silicon carbide at removal rates up to 400 nm/hr yielding a root mean squared roughness on the order of a nanometer as determined by AFM and interferometry. The high rates and smoothness obtained are expected to translate to other types of silicon carbide. Fundamental studies by FTIR, streaming potential and ESCA have been done to elucidate the mechanism of silicon carbide polishing.
Nano-scale Characterization of Surface Defects on CMP-finished Si Wafers by Scanning Probe Microscopy Combined with Laser Light Scattering
Authors: Arima Kenta , Shigetoshi Takushi , Inoue Haruyuki , Kawashima Tsukasa , Hirokane Takaaki , Kataoka Toshihiko , Morita Mizuho
Published: April 2011

Scanning probe microscopy has been widely used to evaluate surface microroughness on Si wafers after chemical mechanical polishing (CMP) processes. In this article, we utilize atomic force microscopy (AFM) combined with laser light scattering to detect nano-scale surface defects called microscratches on CMP-finished Si wafers. We find that most microscratches detected by the combined method are very shallow trenches with widths and depths of 80–200 nm and 0.1–0.2 nm, respectively. The dependence of scattered-light intensity on the size of microscratches agrees with theoretical calculations within one order of magnitude.
Shallow Junction Engineering by Phosphorus and Carbon Co-implantation: Optimization of Carbon Dose and Energy
Authors: Cagnat Nathalie , Laviron Cyrille , Mathiot Daniel , Rando Chris , Juhel Marc
Published: April 2011

Carbon co-implantation after pre-amorphization implantation (PAI) has been studied for Boron shallow implants and can be also used to reduce Phosphorus diffusion. The expected role of Carbon is to trap Si interstitials responsible of Phosphorus diffusion. A known drawback of this kind of co-implantation is junction leakage caused by Carbon deep levels. To find a compromise between diffusion reduction and leakages, it is necessary to optimize the location and the amount of Carbon with respect to Si interstitials.

In this work, we present full sheet experiments optimizing Carbon implanted energy and dose in order to minimize Phosphorus diffusion. First, we performed a PAI with Germanium. Then Carbon was implanted at several energies and doses to locate its projected range (Rp) at various locations with respect to the Phosphorus peak and the amorphous/crystalline interface. Finally the Phosphorus implant was placed completely within the amorphized area. Dopants were activated by a spike anneal at 1080°C, 1055°C or 1000°C. SIMS analysis and Rs measurements were used to understand Carbon action on Phosphorus diffusion and activation. The role of C in suppressing P diffusion is discussed in regards of the specificities of P diffusion mechanism.
Fabrication of Multi – Oxides Thin Film on Iron – Base Metal by Laser Color Marking Technique
Authors: Kano S. , Niino H. , Sato T. , Itagaki K. , Togashi T. , Shimura H.
Published: April 2011

Coloring on stainless steel by pulsed laser irradiation seemed like anodic oxidation surface but drawing fine art. The coloring area shows monochromatic surface, not optical interference coloring. Usually color marking by laser showed rainbow color, but in this technique the coloring area showed monochromatic.... why?
Surface Engineering in Microfluidic Devices for the Isolation of Smooth Muscle Cells and Endothelial Cells
Authors: Murthy Shashi , Plouffe Brian , Radisic Milica
Published: April 2011

Microfluidic cell separation systems have emerged as attractive alternatives to traditional techniques in recent years. These systems offer the advantages of being able to handle small sample volumes and at the same time achieve highly selective separation. Conventional separation techniques, including both fluorescence-activated cell sorting (FACS) and magnetic-activated cell sorting (MACS), typically require a pre-processing incubation step to attach ligated tags (such as fluorescent dyes or magnetic beads) to cell surfaces prior to separation. These techniques are also constrained by infrastructure and high cost. Microfluidic devices with surface-immobilized adhesion molecules eliminate the need for pre-processing incubation and are a low cost alternative.

We describe the selective adhesion of smooth muscle cells and endothelial cells in microfluidic devices coated with adhesion peptides. The device geometry is such that the shear stress varies linearly as a function of flow channel length, allowing simultaneous evaluation of the effects of surface chemistry and fluid shear on cell adhesion. The adhesion peptides, val-ala-pro-gly (VAPG) and arg-glu-asp-val (REDV), are known to bind selectively to smooth muscle cells and endothelial cells, respectively. These peptides were tethered to the device surface using silane chemistry and NHS-ester coupling. Cell adhesion was examined in a shear stress range of 1.3-4.0 dyn/cm2. Under these conditions, endothelial cells show significantly higher adhesion to REDV-coated devices compared to smooth muscle cells and fibroblasts. Correspondingly, smooth muscle cell adhesion in VAPG-coated devices is much greater than that of endothelial cells and fibroblasts. This selective binding behavior is also observed when mixed suspensions of the three cell types are flowed into both types of peptide-coated microfluidic devices. These results suggest that microfluidic devices coated with REDV and VAPG can be used as effective separation tools in various applications, such as tissue engineering. Specific examples of applications in cardiac and skin tissue engineering will be discussed.
Polymerization Kinetics of Methacrylic Groups in Organic-Inorganic Hybrid Polymeric Thin Films
Authors: Zha Congji , Luo Xinshi , Luther-Davies Barry
Published: April 2011

In this paper, the polymerization kinetics of unsaturated double bonds (C=C) in TiO2- and ZrO2-doped hybrid polymeric thin films during UV irradiation and thermal curing is studied by monitoring the variation of C=C absorption band at 1630 cm-1 using FT-IR spectroscopic technique. Experimental results showed that polymerization of the unsaturated C=C groups in the TiO2- and ZrO2-doped hybrid polymers can be realized by either photo-irradiation or thermal treatment. The UV-induced polymerization process is much faster than thermal curing, but a full conversion of C=C groups into polyacrylate chains cannot be achieved without thermal treatment. The catalytic effect of TiO2 and ZrO2 on promoting the polymerization of C=C groups was observed, and the time of UV exposure and thermal curing for cross-linking C=C bonds was found to decrease with the increase of the concentration of TiO2 and ZrO2. The activation energy of the hybrid material containing varied concentration of TiO2 and ZrO2 was calculated, and the results indicated that TiO2 is more active than ZrO2 in promoting the polymerization of the unsaturated C=C bonds. Finally, the mechanisms for TiO2 and ZrO2 enhancing the material's photosensitivity (i.e. promoting polymerization of C=C bonds) have been proposed and discussed.
Controlled silica deposition on soft-lithography fabricated poly-L-lysine templates
Authors: Butler Randall , Ferrell Nicholas , Naik Rajesh R. , Hansford Derek J.
Published: April 2011

We describe the combination of soft-lithographic patterning and biomolecule-induced deposition to create microscale patterns of silica on a diverse array of substrates. A soft lithographic technique was used to create a sacrificial layer of the polymer poly(n-propyl methacrylate) (PPMA) on the desired substrate. Subsequently, poly-L-lysine was deposited on the substrate, after which removal of the PPMA yielded a pattern of PLL on the substrate. Exposure of the PLL template to a silicic acid solution resulted in silica deposition in the pattern spatially and geometrically controlled by the PLL. With this procedure, we have created both continuous and discontinuous silica patterns on metallic, ceramic, and polymer substrates. While morphology of the deposited silica varied between substrates, the ability to pattern silica through this templated growth was demonstrated on all investigated substrates. EDS, optical micrography, and SEM analysis verified the controlled deposition of silica on the PLL template patterns. This PLL template-mediated induction of silica formation may facilitate the incorporation of silica in new microdevices and serve as a prototype process for controlled deposition with other biomolecule-material systems.
Visible-Range Luminescence Study in Indium Oxide Nanowires
Authors: Calestani Davide , Zha Mingzheng , Mazzera Margherita , Lazzarini Laura , Zappettini Andrea , Salviati Giancarlo , Paorici Carlo , Zanotti Lucio
Published: April 2011

The interest in semiconducting metal oxide nanowires for gas sensing devices is today very high. Besides common materials such as SnO2 or ZnO, also In2O3 has been obtained in this quasi-1D morphology . In the present work In2O3 nanowires have been grown by vapor transport process starting from 6N pure In. For a better knowledge of the fundamental properties and the sensing mechanism of In2O3 nanowires, the obtained samples have been investigated by different techniques, focusing mainly on the optical characterization. Their morphology and structure have been studied by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-Ray diffraction. The optical properties have been investigated as well, mainly by means of photo- (PL) and Cathodo-luminescence (CL) both applied in the UV-Visible range. A complex emission spectrum has been revealed and assigned to specific defects thanks to a deep analysis of the bands as functions of temperature (varying from 20 to 300K) and to suitable thermal treatments (in oxygen rich atmosphere at 1000°C). Moreover, the effects of electron beam irradiation have been pointed out by performing CL spectra on a single In2O3 nanowire after different irradiation times. The possible influence of the substrate has been verified by measuring low temperature spectra on In2O3 nanowires grown both on alumina and silicon substrates.
Novel Approach for Fabricating Highly Ordered Colloidal Crystals using Fluorinated Solvent
Authors: Takeda Satoshi , Wiltzius Pierre
Published: April 2011

A novel technique for fabricating highly ordered colloidal photonic crystals has been developed. In this method, a droplet of water containing polystyrene microspheres was added to the surface of a fluorinated solvent bath. Consequently, the two liquids remained separated and the colloidal particles self-assembled into close-packed structures at the interface between them. By transferring the droplet onto a glass slide, a highly ordered crystal was obtained. This technique offers a new, potentially easier, and more effective approach than currently used. We believe that it will open new ways for fabricating materials based on colloidal crystals as well as applying the colloidal photonic crystals to optical devices.
Single-Walled Carbon Nanotube Scaffolds Promote Stem Cell Differentiation into Bone Forming Cells
Authors: Tu Xiaomin , Skinner Charles M , Chen Xiao-Dong , Zhao Wei
Published: April 2011

The use of carbon nanotubes for tissue engineering has become one of the most fascinating applications. The exquisite electronic and mechanical properties of carbon nanotubes may provide a three-dimensional (3D) microenvironment that closely mimics in vivo situation for facilitating the use of stem cells in the tissue regeneration. Therefore, it is important to know whether carbon nanotubes enhance the adhesion, proliferation, and differentiation of stem cells. Here, we hypothesized that the carbon nanotubes promote the differentiation of osteoblast progenitors into mature osteoblasts. To test this hypothesis, we quantified the differentiation of murine osteoblast progenitors, with and without pro-differentiating growth factor Bone Morphogenetic Protein-2 (BMP-2), cultured on the 3D scaffolds made by single-walled carbon nanotubes (SWNTs). Three types of SWNT samples, chitosan functionalized SWNTs, acid-oxidized SWNTs, and surfactant-free pristine SWNTs were used for the construction of these 3D microarchitectures. Osteoblast progenitors were harvested from calvariae from 3∼5-day-old mice, and cultured on the 3D scaffolds made by carbon nanotubes until ∼ 80% confluent. Then the cells were treated with BMP-2 (100 ng/ml) for 5 days. It was found that osteoblast progenitors cultured on the SWNTs dramatically increased the level of mature osteoblastic marker osteocalcin in either the absence or the presence of BMP-2, as compared to the cells cultured on the regulate tissue culture plastic plates. The results suggested that SWNTs highly promote osteoblast progenitor differentiation into mature osteoblasts. The finding indicates that SWNTs may provide an ideal scaffold for facilitating the differentiation of osteoblast progenitors in the repair of bone defects.
Si Whisker Growth by Hydrogen Radical using Hot Filament CVD Reactor
Authors: Nagayoshi Hiroshi , Nishimura Suzuka , Terashima Kazutaka , Matsumoto Nobuo , Ulyashin Alexander G.
Published: April 2011

This paper describes the growth mechanism of silicon whisker on a silicon substrate using hot filament CVD reactor. Only hydrogen is used as source gas. The particle layer could be obtained at high filament current condition under hydrogen ambient. XPS analysis result suggests that the particle is composed of tungsten silicide. The deposition condition of the particle layer is much depended on the substrate size, surface condition and the distance between the substrate and the filament. The experimental results suggest that the silicon hydride, which generated at the silicon surface by hydrogen radical etching, react with the tungsten filament material around the filament, depositing on the silicon substrate. The silicon surface is etched by hydrogen radical and its resultant surface morphology is much depended on the particle deposition pattern. Many silicon whiskers, which diameter is varied from 10 to 50 nm, are observed on the textured silicon surface when the residence time of the source gas in the reactor is long. Each whisker has a silicon particle on their tip. The silicon hydride generated by the hydrogen radical etching is much absorbed to the silicide particle when the source gas residence time is long, enabling the silicon whisker growth from the particle. The results suggest that nm size whisker structure is much stable compare to the bulk silicon against etching reaction.
Silicon Nanowire Electromechanical Switch for Logic Device Application
Authors: Li Qiliang , Koo Sang-Mo , Edelstein Monica D. , Suehle John S. , Richter Curt A.
Published: April 2011

In this paper, we have reported the fabrication and characterization of nanowire electromechanical switches consisting of chemical-vapor-deposition grown silicon nanowires suspended over metal electrodes. The devices operate as transistors with the suspended part of the nanowire bent to touch metal electrode via electromechanical force by applying voltage. The reversible switching, large on/off current ratio, small subthreshold slope and low switching energy compared to current CMOSFET make the switches very attractive for logic device application. In addition, we have developed a physical model to investigate the switching characteristics and extract the material properties.
Spatially Resolved Characterization of Plastic Deformation Induced by Focused-Ion Beam Processing in Structured InGaN/GaN Layers
Authors: Barabash R. , Ice G. , Kroger R. , Lohmeyer H. , Sebald K. , Gutowski J. , Bottcher T. , Hommel D. , Liu W. , Chung J.-S.
Published: April 2011

In this study the results of polychromatic X-ray microbeam analysis (PXM) of the structural changes caused by FIB in nitride heterostructures are presented and discussed in connection with micro-photoluminescence (μ-PL), fluorescent analysis, scanning electron (SEM) and transmission electron microscopy (TEM) data. It is shown that FIB processing distorts the lattice in the InGaN/GaN layer not only in the immediate vicinity of the processed area but also in the surroundings. A narrow amorphidized top layer is formed in the direct ion beam impact area.
Dynamics of Ion Beam Stimulated Surface Mass Transport to Nanopores
Authors: Hoogerheide David P. , Golovchenko Jene A.
Published: April 2011

We explore the ion beam-induced dynamics of the formation of large features at the edges of nanopores in freestanding silicon nitride membranes. The shape and size of these “nanovolcanoes”, together with the rate at which the nanopores open or close, are shown to be strongly influenced by sample temperature. Volcano formation and pore closing slow and stop at low temperatures and saturate at high temperatures. Nanopore volcano size and closing rates are dependent on initial pore size. We discuss both surface diffusion and viscous flow models in the context of these observed phenomena.
MeV Ion Beam Fabrication of Nanopores
Authors: Minamisawa Renato Amaral , Zimmerman Robert Lee , Muntele Claudiu , ILA Daryush
Published: April 2011

We have used MeV ion beams to fabricate nanopores in Poly(tetrafluorethylene-co-perfluoro-(propyl vinyl ether)) (PFA) fluoropolymer membranes. We have developed an in house system to produce nanopores. Using MeV ion beams we developed a method to produce pores from nanometers to one-micron diameter. A thin film of the PFA polymer was mounted to cover a window to a gas filled chamber and then exposed to a uniformly scanned MeV ion beam masked to define the exposed area. The gas leak rate through the fabricated pores was monitored by an in situ RGA system both during and after each bombardment to correlate the leakage with the total area of the pores produced. In this project we used MeV light and heavy ions to best define the pore diameter through each hole and the pore entrance and exit dimensions in the membranes.
Fluence Dependence of Thermoelectric Properties Induced By Ion Bombardment of Zn4Sb3 and CeFe2Co2Sb12 thin films
Authors: Smith C.C. , Budak S. , Guner S. , Muntele C. , Minamisawa R. A. , Zimmerman R. L. , ILA D.
Published: April 2011

Thermoelectric power generation is a promising technology for increasing the efficiency of electrical and optical electrical devices. We prepared samples by Electron Beam evaporating Zn4Sb3 and CeFe2Co2Sb12 thin films on silicon dioxide (silica) substrates. The materials were co-evaporated and then were prepared for gold over-coating. Following electron deposition we performed post ion bombardment at a constant energy of 5 MeV while varying fluence from 1×1012, 1×1013, 1×1014, 1×1015 ions/cm2, respectfully. The production of nano-clusters generated from the MeV Si ions bombardment modifies the electrical and phonon interactions in the materials. Also, we will report on the fluence dependence of the figure of merit, Seebeck Coefficient, thermal conductivity and electrical conductivity. In addition, Rutherford backscattering spectrometry (RBS) was used to analyze the elemental composition and the thickness of the deposited material.
Sudden Olivine LiFePO4 Nanocrystallisation by Progressive Introduction of Li into Ferrous Phosphate Structure
Authors: Sundarayya Y. , Kumaraswamy K.C. , Sunandana C. S.
Published: April 2011

Homogeneous sub-micron sized particles of surface carbon coated phase pure LiFePO4 are synthesized by a novel non-aqueous oxalate-based sol-gel route. X-ray diffractogram of LiFePO4 reveals nanocrystals with average crystallite size 32(7) nm. The very large QS (nearly five times greater than that of Fe3+) value observed from Mossbauer spectrum is due to high spin configuration of 3d electrons and the asymmetric local environment at Fe site in LiFePO4. A uniform particle size distribution with grain size 100 - 150nm was observed in SEM with few irregular growths. Our synthetic route successfully overcomes the incidence of Fe3+, effectively controls undesirable particle growth and has the potential for upscaling and application as Li-ion battery cathodes. Progressive evolution of olivine structure by the interlock of FeO6 octahedra and PO4 tetrahedra with Li concentration is studied by introducing lithium in to LixFePO4 (0.0 × 1.0 ). A fairly abrupt phase transformation from monoclinic Fe3(PO4)2 to orthorhombic LiFePO4 shows up for x∼0.2 accompanied by structural disorder which gets stabilized at x 0.35. A systematic study of X-ray diffractograms shows nanocrystal nucleation and growth from an unstable low symmetry crystalline phase with considerable disorder.
Electronic Structure Investigation of MAX-Phases by Soft X-ray Emission Spectroscopy
Authors: Magnuson Martin
Published: April 2011

The electronic structure of nanolaminate Ti2AlC and Ti2AlN thin films, so-called MAX-phases, were investigated by soft X-ray emission spectroscopy. These nanolaminated carbide and nitride compounds represent a class of layered materials with a combination of properties from both metals and ceramics. The bulk-sensitive soft X-ray emission technique is particularly useful for detecting detailed electronic structure information about internal monolayers and interfaces. The Ti-Al bonding is manifested by a pronounced peak in the Ti L-emission of Ti2AlC and Ti2AlN that is not present in the binary TiC system. The spectral shape of Al L-emission in the MAX-phase is strongly modified in comparison to metallic Al. By replacing or partly exchanging C with N, a change of the electron population can be achieved causing a change of covalent bonding between the laminated layers, which enables control of the material properties.
Diffraction Microscopy using 20-kV Electron Beam for Multi-Wall Carbon Nanotubes
Authors: Kamimura Osamu , Kawahara Kota , Doi Takahisa , Dobashi Takashi , Abe Takashi , Gohara Kazutoshi
Published: April 2011

Diffraction microscopy (or diffractive imaging) with iterative phase retrieval was performed using a low-energy (20-keV) electron beam to verify the possibility of high-resolution imaging with low specimen damage. Diffraction patterns of fine and uniform multi-wall carbon nanotubes (MWCNT) were recorded without a post-specimen lens. One- and two-dimensional phase retrievals were processed from the diffraction pattern alone. The reconstructed object images reflected the characteristic structure of the MWCNT. These results show the possibility of high-resolution imaging with a low-energy electron beam.
Electron Microscopy Investigation of Magnetization Process in Thin Foils and Nanostructures
Authors: Bayle-Guillemaud Pascale , Masseboeuf Aurelien , Cheynis Fabien , Toussaint Jean-Christophe , Fruchart Olivier , Gatel Christophe , Marty Alain , Bayle-Guillemaud Pascale
Published: April 2011

This paper presents investigations of magnetization configuration evolution during in-situ magnetic processes in materials exhibiting planar and perpendicular magnetic anisotropy. Transmission electron microscopy has been used to perform magnetic imaging. Fresnel contrasts in Lorentz Transmission Electron Microscopy (LTEM) and phase retrieval methods such as Transport of Intensity Equation (TIE) solving or electron holography have been implemented. These techniques are sensitive to magnetic induction perpendicular to the electron beam and can give access to a spatially resolved (resolution better than 10 nm) mapping of magnetic induction distribution and could be extended to dynamical studies during in-situ observation. Thin foils of FePd alloys with a strong perpendicular magnetic anisotropy (PMA) and self-assembled Fe dots are presented. Both are studied during magnetization processes exhibiting the capacities of in-situ magnetic imaging in a TEM.
Interlayer Exchange Coupling in Single Crystal Magnetic Tunnel Junctions Studied by Electron Holography
Authors: Snoeck Etienne , Tiusan Coriolan , Greullet Fanny , Benassayag Gerard , Baules Pierre , Schuhl Alain
Published: April 2011

Ion irradiation has been performed on epitaxial Fe/MgO/Fe magnetic tunnel junctions exhibiting antiferromagnetic exchange coupling. Electron holography and VSM experiments show that the amplitude and the nature of the coupling are modified by the irradiation. We demonstrate that the roughness induced by the irradiation at the Fe/MgO interfaces destroys the AF coupling. The biquadratic coupling experimentally observed in the irradiated samples is the result of the competition between local antiferromagnetic and ferromagnetic coupling. For the largest irradiation doses, the net coupling becomes ferromagnetic.
Reliable and Cost-Effective Dispensing Technology for Large-Area Patterning
Authors: Li Bo , Clark Patrick A. , Church Kenneth H.
Published: April 2011

It is reported that the global market for flexible electronics will reach 250 billion dollars by 2025, driven by the products on a human scale (the so called “electronics for life”). These devices such as LCDs cannot be made smaller. However, this field is immature and significant research and development is being conducted for the synthesis, manufacture and characterization of these kinds of devices. The manufacturing process has been identified as the bottleneck of the advancement of these products. High throughput, reliable and yet cost effective technologies are greatly needed for the developing of affordable and functional devices. Researchers and engineers at nScrypt have developed enabling tools and processing solutions for patterning components on large areas with great accuracy and repeatability. In this paper, we will present innovative printing/dispensing solutions as well as novel pumping technologies (smart pump) for the manufacturing and packaging on large areas. In addition to the smart pump, we have a mixer head and spray attachment for the developing of new materials and covering large area.
Theoretical Limits on the Minimal Switching Field and the Switching Current in Magnetization Reversal
Authors: Wang Xiangrong , Sun Zhouzhou
Published: April 2011

Recent theoretical limits of the minimal switching field and current for uniaxial magnetic nano-structures are reviewed. The results include also the optimal field and current pulses for the fastest magnetization reversal. Contrary to the general belief, the precessional magnetization reversal is not the fastest one, and its critical switching field is neither the lowest one.
Atomic-Scale Segregation and Fluctuations in Chemical Ordering FePt Thin Films
Authors: Torres Karen L , Srivastava Chandan , Martens Richard L , Thompson Gregory B
Published: April 2011

A series of atom probe and transmission electron microscopy (TEM) studies have been performed to quantify minute compositional fluctuations in Fe55Pt45 thin films during the A1 to L10 phase transformation. The atom probe specimens were analyzed in an Imago Local Electrode Atom Probe (LEAP®) at a target evaporation of 0.5%, a pulse fraction of 20% and a temperature of 120K. We noted a propensity of fracture failures in the LEAP with this material at lower temperatures. The atom probe reconstruction showed small levels of Pt segregation at grain boundaries in the as-deposited films. Fresnel-contrast TEM imaging confirmed high density fluctuations in these boundaries. Upon annealing at 600°C for 10 minutes, the film transformed from A1 to L10 and the grain boundaries become Fe enriched as compared to the as-deposited film.
Liquid-phase Epitaxial Growth of BiFeO3 Thick Films using an Infrared Irradiation
Authors: Kawae Takeshi , Shiomoto Mitsuhiro , Tsuda Hisashi , Yamada Satoru , Nagao Masanori , Morimoto Akiharu , Kumeda Minoru
Published: April 2011

Epitaxial BiFeO3 (BFO) thick films were fabricated on SrTiO3 (STO) substrates by a simple liquid-phase epitaxy (LPE) growth technique. To avoid the evaporation of Bi, in this process, we used the lid substrate. As starting materials, we used calcined powder or amorphous films deposited by pulsed laser ablation. The fabricated films were found to have a single perovskite phase and be (100)-oriented. Cube-on-cube epitaxial growth of film on the STO substrate was also confirmed by ϕ-scan measurements. The films grown on the substrate display a multigrain structure with a maximum in-plane size of approximately 100μm, and the film thickness was about 3-35 μm. The interface structure between the film and the substrate was relatively smooth. These results indicate that the proposed simple LPE technique is highly suitable for the fabrication of BFO thick films.
Properties of Zinc Oxide Doped Indium, Magnesium and Aluminum Oxide Films used on Flexible Substrates
Authors: Hsiao Shih Hsiu , Tanaka Yoshikazu , Ide-Ektessabi Ari
Published: April 2011

Zinc oxide was considered to be substitute for indium tin oxide (ITO) as the transparent conductive oxide (TCO) films used in display industry according to indium is a rare and expensive metal. For the flexible display, the polymeric materials used as the flexible substrates are more bendable and lighter weight compared to the glass substrates used in flat panel display. However, the thermal sensitivity of polymer affects the properties of TCOs layers when it was deposited at room temperature. In this study, we doped the different ratio of indium oxide, magnesium oxide and aluminum oxide into zinc oxide to improve the properties of zinc oxide used as the TCOs films deposited by the sputtering method. The polyethylene terephthalate (PET) was used as the flexible substrate without thermal process and the glass was used as the comparison substrate with annealing. The light transmittance and the surface resistivity were measured. The chemical composition and the crystal structure were analyzed by using Rutherford backscattering spectrometry and X-ray diffraction measurement.
Tunneling Spectroscopy of Magnetic Impurities (=Mn,Fe,Co) in ZnO
Authors: Tamura Takashi , Kim Changman , Oikawa Yasushi , Ozaki Hajime
Published: April 2011

The first observations have been made on the electronic density of states of Mn, Co and Fe-doped ZnO by tunneling spectroscopy. For Mn- and Co-doped ZnO, rising of DOS were observed around 2.8eV and 3.2eV below the bottom of the conduction band, respectively. In these cases, the Fermi level lay at the bottom of the conduction band. For Fe-doped ZnO, the DOS with about 1.2eV width was observed around the Fermi level in the mid-gap. The result reproduced the recent theoretical calculation.