bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-throughput characterization of shape memory thin films using automated temperature-dependent resistance measurements
Authors: Thienhaus Sigurd , Zamponi Christiane , Rumpf Holger , Hattrick-Simpers Jae , Takeuchi Ichiro , Ludwig Alfred 
Published: April 2011

AbstractShape memory alloy (SMA) thin films are used as actuator materials in MEMS due to their unique properties. Binary thin films with a composition close to Ni50Ti50 are well-established materials, whereas ternaries like NiTiCu, NiTiPd, NiTiHf are less studied. Furthermore, new alloys are being developed which show a magnetic shape memory effect, e.g. Ni2MnGa. For the optimization of known, and the development of new, SMA thin films, a fast and reliable characterization technology is needed, which rapidly identifies the transformation temperatures (i.e. martensite and austenite start and finish temperatures) for a range of material compositions deposited on a whole wafer. In this paper, automated temperature-dependent resistance measurements are discussed as a means which yields the thermal hysteresis of the investigated thin films. Results of monitoring the uniformity of shape memory film depositions on the wafer level, as well as results on the use of this method as a tool for screening for new SMA films by characterization of materials libraries are reported.
Focused ion beam microscope as an analytical tool for nanoscale characterization of gradient-formulated polymeric sensor materials
Authors: Dovidenko Katharine , Potyrailo Radislav A. , Grande Games 
Published: April 2011

AbstractIn this study, we are demonstrating localized nano-scale analysis of sensor materials which are developed using combinatorial gradient approach. Our technique based on Focused Ion Beam cross-sectioning at specific locations affords establishing metal nano-particles concentrations at best-performing area(s) of gradient-formulated polymer samples. We have achieved three-dimensional characterization/mapping of nano-fillers (30-100 nm metal particles) in composite thin films on variety of substrates.
Computational DFT Study of ZrSiO4 Polymorphs: Microelectronic, Nuclear Safety and Geological Implications
Authors: Korkin Anatoli , Kamisaka Hideyuki , Yamashita Koichi , Safonov Andrey , Bagatur'yants Alexander 
Published: April 2011

AbstractZirconium silicate is an extremely durable materials with the variety of useful optical and electronic properties and broad range of existing and potential applications. Using Density Functional Theory (DFT) in local density approximation (LDA) and generalized gradient approximation (GGA) with plane wave (PW) basis set we have revealed eight new polymorphs of ZrSiO4 within the energy range ∼1 eV above the most stable zircon which have higher and lower density than experimentally known zircon and reidite. Two structures, which have both silicon and zirconium atoms six-fold coordinated, orthorhombic AlTaO4-like (alumotantite) and monoclinic PbWO4-like (raspite), have similar energies at GGA level ∼0.35 eV above reidite and density intermediate between zircon and reidite. Among two low-density structures, which can be potentially revealed experimentally in the nanocrystalline thin films, the orthorhombic CaSO4-like form has energy similar to reidite but much lower density. We also conducted a comparative study of existing ZrO2 and SiO2 polymorphs, which demonstrates the higher accuracy of GGA approach.
Information-Based Development of New Radiation Detection Materials
Authors: Ferris Kim , webb-robertson bobbie-jo m , jones dumont m 
Published: April 2011

AbstractWith our present concern for a secure environment, the development of new radiation detection materials has focused on the capability of identifying potential radiation sources at increased sensitivity levels. As the initial framework for a materials-informatics approach to radiation detection materials, we have explored the use of both supervised (Support Vector Machines – SVM and Linear Discriminant Analysis – LDA) and unsupervised (Principal Component Analysis – PCA) learning methods for the development of structural signature models. Application of these methods yields complementary results, both of which are necessary to reduce parameter space and variable degeneracy. Using a crystal structure classification test, the use of the nonlinear SVM significantly increases predictive performance, suggesting trade-offs between smaller descriptor spaces and simpler linear models.
Tuning the Elasticity of Biopolymer Gels for Optimal Wound Healing
Authors: Georges Penelope , McCormick Margaret , Flanagan Lisa , Ju Yo-El , Sawyer Evelyn , Janmey Paul 
Published: April 2011

AbstractSoft polymer networks with large mesh size, not flat rigid surfaces, are the normal environment for most animal cells. Cell structure and function depend on the stiffness of the surfaces on which cells adhere as well as on the type of adhesion complex by which the cell binds its extracellular ligand. Many cell types, including fibroblasts and endothelial cells, switch from a round to spread morphology as stiffness is increased between 1000 and 10,000 Pa. Coincident with the change in morphology are a host of differences in protein phosphorylation levels, expression of integrins, and changes in cytoskeletal protein expression and assembly. In contrast, other cells types such as neutrophils and platelets do not require rigid substrates in order to spread, and neurons extend processes better on soft (50 Pa) materials than on stiffer gels. We compare the stiffness sensing of four cell types: platelets, neurons and astrocytes, a glial cell type derived from embryonic rat brain, and melanoma cells. Astrocytes switch from a round to spread morphology as substrate stiffness increases, but do so over a stiffness range 10 times softer than that over which fibroblasts alter morphology. Stiffness-dependent morphologic changes observed from studies of cells grown on surfaces of protein-laminated polyacrylamide gels that have linear elasticity are also seen when cells are on matrices of natural biopolymers such as fibrin. Biopolymer gels like fibrin can be formed with appropriate stiffness to optimize for neuronal cell survival and patterning, and may have utility for repair of damaged neural tissues. The complex non-linear rheology of fibrin and other gels formed by semi-flexible biopolymers that exhibit strain-stiffening provide additional mechanisms by which cells can respond to and actively remodel the mechanical features of their environment.
Solvent behavior in hydrophobic silica nanotubes
Authors: English Douglas , Luckett Charles , Jayaraman Karthik , Lee Sang Bok , Son Sang Jun , Okamoto Kenji 
Published: April 2011

AbstractTemplate-synthesized silica nanotubes offer a unique and interesting opportunity for studying fluids in confined spaces. Their versatility stems from our ability to independently vary the inside diameter and surface chemistry. In this work we investigated capillarity for binary mixtures of water and methanol in hydrophobic nanotubes with internal diameters of both 30 and 170 nm. An improved sol-gel template synthesis process was used to prepare silica nanotubes with smooth and uniform walls within the pores of alumina template membranes. The pore diameter and thickness of the template membrane determined the outer diameter and length of the nanotube, respectively. The number of deposition cycles controlled the wall thickness. An octadecylsilane coating was selectively applied to the nanotube interior while leaving the nanotube exterior unmodified. The interiors of hydrophobic nanotubes prepared in this way were then labeled with trace amounts of adsorbed dyes. The diffusion of the dye molecules inside individual immersed nanotubes was investigated using fluorescence recovery after photobleaching (FRAP) experiments. Dye diffusion was used to determine the wettability of the nanotube interior as a function of solvent composition. Several important observations are reported here. First, a clear transition is observed in which all nanotubes change from non-wetting to wetting when the methanol mole fraction approaches 0.5. This transition appears at the same solvent composition for both nanotube sizes. Interestingly, the Young-Laplace equation fails to accurately predict the wetting transition. The difference between the observed and predicted wetting transition may be due to reliance on macroscopic values of contact angles or surface tensions in our predictions or may be related to the presence of liquid phase instability, dry-layers or non-spherical menisci within the hydrophobic pore.
Synchrotron X-Ray Scattering Studies of the Surface Structure and Dynamics of Liquids and Liquid Films
Authors: Kim Hyunjung , Jiang Zhang , Lee Heeju , Lee Young Joo , Jiao Xuesong , Li Chunhua , Lurio Laurence , Hu Xuesong , Lal Jyotsana , Rafailovich Miriam , Sinha Sunil K 
Published: April 2011

AbstractThe dynamics of surface fluctuations in thin supported polystyrene films have been investigated using x-ray photon correlation spectroscopy (XPCS) in reflection geometry. The results from the films thicker than four times of the radius of gyration (Rg) of polystyrene show the behavior of the capillary waves expected in viscous liquid. However, thinner films show a deviation indicating the need to account for viscoelasticity. Theoretical considerations with viscoelastic liquid model has been performed by introducing frequency dependent viscosity and compared with Fredrickson’s brush model (Macromolecules, 25, 2882 (1992)). The theory has been extended to the surface and interfacial modes in a bilayer film system. The results will be discussed in terms of surface tension, viscosity, and shear modulus.
Creating Nanostructures with Controllable Sidewall Profiles for Mechanical Sensor Applications
Authors: Zhao Yi , Zhang Xin 
Published: April 2011

ABSTRACTThis paper presents a novel approach to create silicon nanostructures with controlled sidewall profiles. The nanostructures are fabricated by alternating the reactive ion etching process and the exposure process to the atmosphere with moisture. The air exposure is believed attributed to the sidewall passivation by facilitating the fast formation of a thin SiO2/SiOxFy layer. Using this approach, three types of representative nanostructures are demonstrated, namely: nanopillars with vertical sidewall, nanopillars with narrowed necks, and suspending nanocantilevers. Without requiring expensive facilities and extensive expertise, this work is expected to provide an alternative for developing nanostructures with a variety of geometric profiles for mechanical sensing applications.
Vanadium Oxide Nanostructures: Growth, Characterization and Applications
Authors: Mathur Sanjay , Ruegamer Thomas 
Published: April 2011

ABSTRACTVanadium oxide nanostructures (V2O5 and VO2) were obtained by chemical vapor deposition of the alkoxide precursor [VO(OPri)3]. The nanomaterials were studied with respect to their morphological features (HR-SEM) and phase structure (XRD) followed by characterization as resisitive-type gas sensors. Given the high surface area, vanadium oxide (VOx) nanostructures show significant sensor response via resistance change upon reaction induced by carbon monoxide and desorption of adsorbed oxygen at 400 °C. Tin-doped VOx showed enhanced sensitivity of the films which suggests a higher number of active sensing sites or alternations in the intrinsic electrical properties of VOx by addition of SnO2 as dopant.
Microstructure and ferroelectric properties of ultrathin PbTiO3 films by MOCVD
Authors: Fujisawa Hironori , Horii Toru , Takashima Yoshiyuki , Shimizu Masaru , Kotaka Yasutoshi , Honda Koichiro 
Published: April 2011

AbstractWe report on microstructure and ferroelectric properties of ultrathin PbTiO3 films epitaxially grown on SrTiO3(100), La-doped SrTiO3(100) and SrRuO3/SrTiO3(100) by MOCVD. High angle annular dark field scanning transmission electron microscopy, atomic force microscopy, x-ray diffraction and x-ray reflectivity measurements demonstrated that 1-20 monolayer (ML)-thick epitaxial PbTiO3 films had high-crystallinity, atomically flat surface and sharp interface at an atomic scale. The epitaxial relationship and thickness were also confirmed by these methods. Kelvin force probe microscopy and contact resonance piezoresponse force microscopy revealed that a 7ML (2.7nm)-thick PbTiO3 film grown on SrRuO3/SrTiO3 had the ferroelectric polarization.
Influence of Crystal Phase and Orientation on Electro-Optic Effect of PLZT Epitaxial Films
Authors: Sato Keisuke , Ishii Masatoshi , Kondo Masao , Kurihara Kazuaki 
Published: April 2011

AbstractLanthanum-modified lead zirconate titanate and lead zirconate titanate epitaxial films with (100) and (111) orientations are grown respectively on (100) and (111) niobium, lending conductivity to strontium titanate through chemical solution deposition. This study investigates changes in the ordinary and extraordinary refractive index no and ne induced by the electric field in these films using the prism-coupling method. Anisotropic electrooptic effects arise from Pockels effect and switching among polar clusters. Isotropic electrooptic effect is realized on PLZT 8/65/35 and PZT 70/30 of (100) epitaxial films.
The effects of PBB on the dielectric properties of BST film
Authors: Kim Jin Cheol , Oh Jun Rok 
Published: April 2011

AbstractThe mixture of PbO-Bi2O3-B2O3 (PBB) were formed on the Ba0.5Sr0.5TiO3 (BST) film and the effects of PBB phase on the dielectric properties of the BST film were investigated. The amorphous PBB layer was deposited on the BST film using rf magnetron sputtering and diffused into the film by heat treatment. The PBB phase in BST film was identified by energy dispersive spectrometer (EDS). Dielectric properties of BST film were significantly improved after the diffusion of PBB. The leakage current density of BST film decreased from 3.24×10-5 A/cm2 to 9.45×10-8 A/cm2 at 1.5 V and the dielectric constant increased from 238 to 533. These results show that the diffusion of insulating metal oxide into the ferroelectric thin film can improve the dielectric properties of the film.
Phase Transition Temperature of Ferroelectric Thin Film Evaluated by Four-State Potts Model
Authors: Chung Wing Yee Winnie , Lo Veng Cheong 
Published: April 2011

AbstractAn epitaxial ferroelectric thin film can be modeled by a two-dimensional array of dipoles. The orientation of each dipole is assigned to one of the four possible states which are mutually perpendicular to each other. Consequently, the whole film can be divided into domains with both 90° and 180° domain walls. The dominant switching mechanism for individual dipole is implemented by a 90° rotation. Two different conditions have been considered. For the first one (model A), every dipole inside the film is allowed to rotate, provided that it is thermally activated. For the second (model B), only the dipole rotation is restricted to those at the domain walls. The phase transition temperatures under these two models have been evaluated. Furthermore, the effects of sample size and boundary condition are discussed.
Silicon Carbide Growth: C/Si Ratio Evaluation and Modeling
Authors: Pons Michel , Nishizawa Shin-Ichi , Wellmann Peter , Blanquet Elisabeth , Chaussende Didier , Dedulle Jean Marc 
Published: April 2011

AbstractModeling and simulation of the SiC growth processes, Physical Vapor Transport (PVT), Chemical Vapor Deposition (CVD) and hybrid techniques, are sufficiently mature to be used as a training tool for engineers as well as a growth machine design tool, e.g. when building new process equipment or up-scaling old ones. It is possible (i) to simulate accurately temperature and deposition distributions, as well as doping (ii) to quantify the limiting phenomena, (iii) to understand the important role of different precursors in CVD and hydrogen additions in PVT. The first conclusion of this paper is the importance of the "effective" C/Si ratio during CVD epitaxy in hot-wall reactors and its capability to explain the doping concentrations. The second conclusion is the influence of the C/Si ratio in alternative bulk growth technique involving gas additions. Preliminary results show that fine tuning of H2 or precursor additions allow a better control of concentrations of residual and intentional doping.
Characterization of SiC Materials and Devices by SIMS
Authors: Li Yupu , Gao Yumin 
Published: April 2011

AbstractBased on the various implanted standards, we have used SIMS (Secondary Ion Mass Spectrometry) to characterize SiC materials and devices. We develop the SIMS analysis on 2'' and 3'' full SiC wafers using our customized sample load chamber at a Cameca 4f magnetic sector SIMS tool. This feature is particularly useful for the on-line control of the wafer processing. With our special mounting skills, we provide SIMS analyses on small patterned area (say 50 microns × 50 microns or larger) of the tiny or large SiC dies. The detailed comparison between the implanted profiles for the major dopants (such as B, Al, and N) measured by SIMS and the simulated profiles by SRIM code [1] will be discussed. The detection limits for selected elements will also be discussed. In addition, it is well know that nitrogen has a very high ionization potential and zero electronic affinity. Therefore, nitrogen is normally profiled with a Cs+ primary beam and monitored negative molecular ions of (matrix+N)- [such as (Al+N)- in Al [2], (Si+N)- in Si, and (C+N)- in SiC]. However, such negative molecular detection mode cannot be applied to the multi-layers with different matrix elements (such as Al/SiC and Cu/SiC samples). Fortunately, like to detect nitrogen in Cu [3], we have found that using a Cs+ primary ion beam and monitoring (Cs2N)+ molecular ions by Cameca magnetic sector SIMS tools, nitrogen in the multi-layer samples including SiC layer can be detected by the (Cs2N)+ detection model [3,4] with a very low profiling energy (such as 2.5keV).
Development of PECVD SiC for MEMS Using 3MS as the Precursor
Authors: Du Jiangang , Singh Neha , Summers James B. , Zorman Christian A. 
Published: April 2011

AbstractThis paper reports our effort to develop amorphous hydrogenated silicon carbide (a-SiC:H ) films specifically designed for MEMS applications using a semiconductor-grade organosilane known as trimethylsilane (3MS) as the precursor. In our work, the a-SiC:H films were deposited in a commercial PECVD system at a fixed temperature of 350&#730;C using 3MS diluted in helium (He). Films with thicknesses from ~ 100 nm to ~ 2μm, a typical range for MEMS applications, were deposited. Deposition parameters such RF power, deposition pressure, and 3MS-to-He ratio were explored to obtain films with low residual compressive stresses. Low temperature, post-deposition annealing at 450&#730;C was used to convert the as-deposited compressive residual stresses to moderate tensile stresses, which are desired for micromachined bridges, membranes and other anchored structures. Compositional analysis indicated that films with a Si-to-C ratio of 1 could be deposited under certain conditions. Mechanical properties such as Young's modulus and fracture strength were derived from the load-deflection behavior of micromachined freestanding membranes. Nanoindentation was used to verify the Young's modulus and determine the hardness. As expected, the films exhibit insulating properties with a relative dielectric constant at 3.90 for as-deposited films and 2.69 after annealing at 1100&#730;C, as determined from C-V measurements. Chemical inertness was tested in aqueous, corrosive solutions such as KOH and HNA. Prototype structures were fabricated using both surface micromachining and bulk micromachining techniques to demonstrate the potential of the a-SiC:H films for MEMS applications.
A Study of V3+/4+ Levels in Semi-insulating 6H-SiC using Optical Admittance and Electron Paramagnetic Resonance Spectroscopies
Authors: Lee Wonwoo , Zvanut Mary E 
Published: April 2011

AbstractThe purpose of this study is to identify the vanadium acceptor levels in semi-insulating (SI) 6H-SiC using optical admittance spectroscopy (OAS) and electron paramagnetic resonance (EPR) spectroscopy. OAS conductance peaks near at 0.67 ± 0.02 eV and 0.70 ± 0.02 eV are identified as V3+/4+ levels at the quasi-cubic sites. An OAS peak at 0.87 eV is assigned to the same transition at the hexagonal site. EPR measurements before illumination revealed the characteristic spectrum of V3+. The presence of the V3+ signal supports the identification of the OAS peaks as transitions from the V3+/4+ level to the conduction band. Photo-induced EPR measurements reveal a change in the intensity of V3+ and V4+ at 0.8 ± 0.1 eV, where the amplitude of the V3+ charge state decreases and that of V4+ increases by approximately equal amounts. Although the individual sites are not resolved in the photo-induced EPR data, the 0.8 eV feature strongly supports the assignment of the three OAS peaks as acceptor levels.
Ion Implanted p+/n 4H-SiC Junctions: effect of the Heating Rate during Post Implantation Annealing
Authors: Nipoti Roberta , Carnera Alberto , Bergamini Fabio , Canino Mariaconcetta , Poggi Antonella , Solmi Sandro , Passini Mara 
Published: April 2011

AbstractStructural, morphological and electrical characteristics of Al-implanted p+/n 4H-SiC diodes are compared for the same implantation process and post implantation annealing with identical stationary and cooling cycles but different heating velocity. Al+ ions were implanted at 400°C, with energies in the range 250-350 keV and total fluence of 1.2×1015 cm−2. Post implantation annealing processes were done at 1600°C for 30 min with a constant heating velocity in the range 7 – 40°C/sec and an abrupt cooling cycle. Gas in the annealing ambient was high purity Ar. The Al depth profile of annealed and as implanted samples were equal except for concentrations below 10E17 cm−3 where the former profiles showed a diffusion tail. With the increase of the heating velocity of the post implantation annealing process, sheet resistance of the Al implanted layer and diode leakage currents decrease while the surface roughness increases.
Effects of Different Defect Types on the Performance of Devices Fabricated on a 4H-SiC Homoepitaxial Layer
Authors: Chen Hui , Raghothamachar Balaji , Vetter William , Dudley Michael , Wang Y. , Skromme B. J. 
Published: April 2011

AbstractAn 8° off-axis 4H-SiC wafer with circular Schottky contacts fabricated on a CVD grown 4H-SiC homoepitaxial layer was studied to investigate the influence of various defects, including small (closed-core) screw dislocations (Burgers vector of 1c or 2c), hollow-core (micropipes; Burgers vector larger than 2c), threading edge dislocations (from conversion of basal plane dislocations from the substrate into the epilayer), grain boundaries and triangular defects, on the device performance in the form of breakdown voltages. The defects were examined using synchrotron white beam x-ray topography (SWBXT) based techniques and molten KOH etching. The devices commonly contained basal plane dislocations, small screw dislocations and threading edge dislocations, the latter two of which could give rise to low breakdown voltages for the devices. In addition, less commonly observed defects such as micropipes, grain boundaries and triangular defects are much more destructive to device performance than closed-core screw dislocations and threading edge dislocations.