bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two-Dimensional Silicon/Ferroelectric Liquid Crystal Spatial Light Modulators
Authors: Drabik Timothy J. 
Published: April 2011

AbstractSpatial light modulator (SLM) technology based on commodity silicon fabrication processes and employing a thin, ferroelectric liquid crystal light modulating layer at the chip's surface, has advanced to the point of producing high-performance, practically useful devices. Electrically addressed display devices with 256 × 256 resolution, 100: 1 contrast, and 10 kHz frame rate, as well as optically addressed, “smart” SLMs that perform spatio-temporal filtering on images, have resulted in the course of the author's involvement with Displaytech, Inc.The silicon technology infrastructure is a juggernaut that produces regular and significant advances in capability. An optoelectronics technology based on foundry silicon can exploit these advances directly and realize rapid improvements. The gains in the density, speed, and optical performance of the Si/FLC devices presented here, illustrate this perspective.The favorable speed-power performance of these devices is due to an excellent match in the “terminal characteristics” of FLC materials with those of fine-line MOSFETs. The impact of these characteristics on overall device performance is discussed in some depth.
The Growth of Optical Quality LiNbo3 Thin Films On Sapphire and LiTao3 Substrates Using Solid-Source Mocvd
Authors: Lee S. Y. , Route R. K. , Feigelson R. S. 
Published: April 2011

AbstractHigh quality lithium niobate (LiNbO3) epitaxial thin films have been grown on c-plane sapphire and LiTaO3 substrates by solid-source MOCVD using the tetramethyl-heptanedionate sources, Li(thd) and Nb(thd)4. Phase content was controllable, and stoichiometric films were reproducibly deposited over a broad temperature range from a Li(thd)-rich source. Using sapphire substrates, with which the occurrence of multiple in-plane orientations is typically a problem, LiNbO3 films with only one in-plane orientation could be prepared within a narrow range of growth conditions. XRD rocking curve FWHM values as low as 0.04°, and optical waveguiding losses near 2dB/cm (1200Å thick film, TMo mode, 632.8nm) were obtained. However, film thicknesses on sapphire were limited to 2000Å because of cracking caused by the large thermal expansion mismatch, and in such thin films, optical confinement is poor.In contrast, LiTaO3 has almost same lattice constants and thermal expansion coefficients as LiNbO3, making it a potentially superior substrate material. Lithium niobate films up to 6000Å were successfully deposited on LiTaO3 substrates without cracking. Film quality was greatly improved, with FWHM values as low as 0.01°, and rms surface roughness less than 10 Å. Preliminary optical waveguiding losses less than 6 dB/cm for the TEo mode have been achieved.
The Effect of Co-Dopants on the Photoluminescence of Er3+ in Silicon
Authors: Pradissitto J. J. , Federighi M. , Pitt C. W. , Gillin W. P. , James A. G. , Wilson R. J. 
Published: April 2011

AbstractThis paper presents the results of our investigation into the possibility of increasing both the radiative cross-section and the electrical activation efficiency in erbium (Er3+) doped silicon (Si). The energy levels of the isolated Er3+ have been theoretically predicted, employing the Thomas-Fermi method. The behaviour of these levels in Si was then investigated using a Kronig-Penney approach. Initial theoretical results imply that fluorine (F), in addition to Er3+ in Si, increases the radiative cross-section of Er3+ by at least an order of magnitude, and that co-doping appears to enhance the mixing of the 4f and 5d levels and causes the Er3+ energy levels to overlap with those of the host. Photoluminescence spectra of Er3+ in Si co-doped with F also indicate an interaction with the host lattice which appears to be dependent on its electrical characteristics.
Cationic Gelatin as a Gene Carrier
Authors: Brown K. E. , Bathon J. , Huang C. H. , Dalai R. , Leong K. W. 
Published: April 2011

AbstractCationic gelatin was evaluated as a non-viral vector for cell transfection. We hypothesized that cationic gelatin would be a nontoxic alternative to already existing viral and non-viral cationic vectors. Cationic gelatin was synthesized by modifying gelatin with hexanediamine. Complexation of cationic gelatin with psv-β-gal plasmid caused an electrophoretic mobility shift of the plasmid. Cationic gelatin/DNA complexes were optimized in terms of transfection efficiency in CHODUK XB1 and COS 7 cell lines. Maximal gene expression for both cell types occurred in serum free medium with chloroquine (100 μM) at cationic gelatin/DNA ratios of approximately 2 and 7. In comparison with DEAE dextran, polylysine and Lipofectamine, cationic gelatin was the most efficient in transfecting COS 7 cells, with up to 18% cells transfected. In a dye reduction cytotoxicity assay, cationic gelatin caused < 5% of cells to become nonviable at a concentration of 100 μg/ml, while the other transfection reagents tested at the same concentration caused 25–100% of cell death. These results suggest that cationic gelatin holds promise as an effective vehicle for gene delivery to mammalian cells.
Gallium Incorporation Kinetics During GSMBE of GaN
Authors: Jones Charles R. , Lei Ting , Kaspi Ron , Evans Keith R. 
Published: April 2011

ABSTRACTThe kinetics of Ga incorporation during gas-source molecular beam epitaxy of GaN are investigated for varying substrate temperature and incident ammonia flux. Incident Ga atoms eventually either: 1) react with NH3 to form GaN, 2) accumulate on the film surface, or 3) desorb. Low substrate temperatures lead to significant Ga surface accumulation due to the temperature-dependent reactivity of NH3 towards Ga. High substrate temperatures give rise to significant Ga desorption. Increasing NH3 flux retards both Ga surface accumulation and Ga desorption. The GaN formation rate variation with substrate temperature peaks near 750°C and increases with NH3 flux. The observation of two distinct and very low activation energies for Ga desorption suggests a relatively complex surface chemistry and a strong likelihood that hydrogen is playing an important role.
Plasma-Assisted MBE of GaN and AlGaN on 6H SiC(0001)
Authors: Sinharoy S. , Agarwal A. K. , Augustine G. , Rowland L. B. , Messham R. L. , Driver M. C. , Hopkins R. H. 
Published: April 2011

ABSTRACTThe growth of undoped and doped GaN and AlGaN films on off-axis 6H SiC substrates was investigated using plasma-assisted molecular beam epitaxy (MBE). Smooth and crack-free GaN and AlGaN films were obtained; the best results occurred at the highest growth temperature studied (800°C) and with a 40 to 50 nm A1N buffer layer grown at the same temperature. Carrier concentrations of up to n = 4 × 1020 cm−3 were accomplished with silicon, with a 40 to 50% activation rate as determined by secondary ion mass spectrometry (SIMS). Unintentionally doped AlxGa,.xN (x≈0.1) was n-type with a carrier concentration of 7 × 1018 cm−3. N-type AlGaN (x≈0.1)/p-type 6H SiC (0001) heterostructures showed excellent junction characteristics with leakage currents of less than 0.1 nA at 5 V reverse bias at room temperature and 0.5 nA at 200°C operating temperature.
Optoelectronic and Structural Properties of High-Quality GaN Grown by Hydride Vapor Phase Epitaxy
Authors: Molnar R.J. , Aggarwal R. , Liau Z.L. , Brown E.R. , Melngailis I. , Götz W. , Romano L.T. , Johnson N.M. 
Published: April 2011

ABSTRACTGallium nitride (GaN) films have been grown by hydride vapor phase epitaxy (HVPE) in a vertical reactor design. We report on GaN growth directly on sapphire using a GaCl surface pretreatment. The electrical properties of these films compare favorably with the highest values reported in the literature for GaN. Specifically, a room temperature Hall mobility as high as 540 cm2 /V-s, with a corresponding carrier concentration of 2×1017 cm−3, have been attained. Additionally, the vesical reactor design has assisted in reducing nonuniformities in both film thickness as well as in transport properties due to depletion effects, as compared with horizontal designs. The dislocation density in these films has been determined by plan-view transmission electron microscopy to be ∼3×l08 cm−2 .Photoluminescence spectra obtained at 2 K show intense, sharp, near-bandedge emission with minimal deep level emissions. Stimulated emission has been observed in these films, utilizing a nitrogen laser pump source (λ=337.1 nm) with a threshold pump power of ∼0.5 MW/cm2 . These results suggest that HVPE is viable for the growth of high-quality nitride films, particularly for the subsequent homoepitaxial overgrowth of device structures by other growth methods such as OMVPE and MBE.
An Atomic Force Microscopy Study of the Initial Nucleation of GaN on Sapphire
Authors: Richards-Babb M. , Buczkowski S. L. , Yu Zhonghai , Myers T. H. 
Published: April 2011

ABSTRACTPreliminary results of a study of GaN nucleation and growth by molecular beam epitaxy using a nitrogen rf plasma source are presented. Nucleation layers and 3000 Å thick layers were investigated by atomic force microscopy and x-ray diffraction. Growth under gallium-rich conditions both increased nucleation island size and promoted two-dimensional growth.
Low Temperature Growth of Oriented Gallium Nitride using Pulsed Laser Deposition
Authors: Leuchtner Robert , Brock W. , Li Y. , Hristakos L. 
Published: April 2011

ABSTRACTOriented GaN has been successfully grown at low substrate temperatures (∼480°C) on a- and r-planes of sapphire, using the pulsed laser deposition process. We have examined the effects of several deposition parameters on film growth, including substrate temperature (∼50–500°C), ambient pressure (1×10−3 – 10 torr of NH3), and target material (Ga or GaN). The film deposition rate was typically ∼3–4 μm/hr. Film characterization was performed using x-ray diffraction (XRD), optical microscopy, x-ray photoelectron spectrometry (XPS), and atomic force microscopy (AFM). In the case of the Ga metal target, a plasma (∼500V) between the target and substrate was necessary to promote formation of the GaN phase. The ammonia ambient enhanced the nitrogen content in the films compared to vacuum deposition. In general, the GaN target yielded better quality films (smaller rocking curve widths and smoother film morphology) compared to the Ga metal target. These results suggest that pulsed laser deposition is a promising approach to fabricating high quality films of this potentially important semiconducting material.
Electronic Structures of Wide Band-Gap (AlN)m(GaN)n[001] Superlattices
Authors: Tian Z.-J. , Dharma-Wardana M.W.C. , Lewis L.J. 
Published: April 2011

ABSTRACTWide bandgap III-V nitrides, such as GaN and AlN, have become topical in the near-term technology of blue lasers. We report detailed electronic band-structure calculations for (AlN)m(GaN)n [001] zinc-blende superlattices (SL), with m + n ≤ 12, using the all-electron full-potential linear-muffin-tin-orbital method. For n ≥ 3, the SL are found to have a direct band gap. For n ≤ 2 and m ≥ 3, all the band gaps are indirect. In ultrathin SL, m ≤ 3 and n ≤ 2, only (m, n)= (3,1) is found to have an indirect gap. The band offsets are estimated by calculating the core-level shifts of nitrogen atoms in the central planes of the GaN and A1N layers. The calculated densities of states, electron- and hole- effective masses (m), etc., as a function of m and n, are reported; a remarkable dependence of m on the number of layers is revealed.
ScAlMgO4: An Oxide Substrate for GaN Epitaxy
Authors: Hellman E. S. , Brandle C. D. , Schneemeyer L. F. , Wiesmann D. , Brener I. , Siegrist T. , Berkstresser G. W. , Buchanan D. N. E. , Hartford E. H. 
Published: April 2011

ABSTRACTWe report the use of ScAlMgO4 as a substrate for the epitaxial growth of wurzitic GaN. The low misfit (+1.8%) allows coherent epitaxy of GaN, as observed by RHEED. The congruent melting of ScAlMgO4 makes Czochralski growth possible, suggesting that large, high quality substrates can be realized. Boules about 17mm in diameter are reported. We have used nitrogen-plasma molecular beam epitaxy to grow GaN epitaxial films onto ScAlMgO4 substrates. Band-gap photoluminescence has been observed from some of these films, depending primarily on the deposition conditions. A 3×3 superstructure has been observed by RHEED on the GaN surfaces. Structural analysis by x-ray diffraction indicates very good in-plane alignment of the GaN films. We also report thermal expansion measurements for ScAlMgO4.
The Effect of Hydrogen-Based, High Density Plasma Etching on the Electronic Properties of Gallium Nitride
Authors: Eddy C.R. , Molnar B. 
Published: April 2011

ABSTRACTDevelopment of devices based on the wide gap semiconductor gallium nitride (GaN) requires the realization of reliable, high fidelity, low damage pattern transfer processes. In this work, GaN thin films grown by OMVPE have been subjected to both chlorine- and methane/hydrogen-based etch chemistries in an electron cyclotron resonance microwave plasma reactive ion etching system. Both n-type and semi-insulating thin films have been utilized to examine the effect of these etch processes on the electronic properties of the materials. The methane/hydrogen-based etch system (CH4/H2/Ar) induced considerable changes in the electrical properties of both n-type and semi-insulating films, causing the former to become more insulating and the latter to become conducting. In both cases, the original electrical properties were recoverable after a short, high temperature anneal. In the chlorine-based etching system (Cl2), no changes in the electrical properties were observed and etch rates five times greater than in the methane/hydrogen-based system were achieved. Proposed mechanisms responsible for the observed behavior will be discussed. These results show that pattern transfer processes based in chlorine etch chemistries are more suitable for the generation of high performance GaN devices.
Schottky Barrier Heights of Ni, Pt, Pd, and Au on n-type GaN
Authors: Schmitz A.C. , Ping A.T. , Asif khan M. , Adesida I. 
Published: April 2011

ABSTRACTSchottky barrier heights of Ni, Pt, Pd, and Au on n-type GaN were measured using current-voltage and capacitance-voltage techniques. Measurements from the I-V technique yielded barrier heights of 0.95, 1.01, 0.94, and 0.87 eV for Ni, Pt, Pd, and Au, respectively. Barrier heights of 1.13,1.16, 1.07, and 0.98 eV, for Ni, Pt, Pd, and Au, respectively, were obtained using C-V measurements.
Recent Progress in AlGaN/GaN Based Optoelectronic Devices
Authors: Khan M. A. , Chen Q. , Sun C. J. , Yang J. W. , Shur M. S. 
Published: April 2011

ABSTRACTWe review our recent results on GaN based optoelectronic devices, which include InGaN-AlGaN Light Emitting Diodes (LEDs), GaN photoconductive, Schottky barrier, and p-n junction ultraviolet detectors, and optoelectronic AlGaN-GaN Heterostructure Field Effect Transistors. GaN-based optoelectronic devices cover a wide spectral range and demonstrate visible blind operation. A high quality of the epitaxial layers, the recent development of high performance GaN-based heterostructure field effect transistors, and transparent substrates make this material system uniquely suited for optoelectronic integrated circuits operating in visible and ultraviolet range.
Laser-Induced Voltages at Room Temperature in YBa2Cu3O7 and PrxY1-xBa2Cu3O7 Thin Films
Authors: Habermeier H.- U. , Jisrawi N. , Jäger-Waldau G. , Sticher U. , Leibold B. 
Published: April 2011

ABSTRACTRecent reports on high transient transverse voltages at room temperature in YBa2Cu3O7 and PrxYl-xBa2Cu3O7 thin films grown on SrTiO3 single crystal substrates, with a tilt angle between the [ 001 ] cubic axis and the substrate surface plane, have been interpreted by thermoelectric fields transverse to a laser-induced temperature gradient which are caused by the non-zero off diagonal elements of the Seebeck tensor. We have studied this effect in epitaxially grown Pr- doped, as well as undoped YBa2Cu3O7, thin films and observed for a 2 mm long YBa2Cu3O7 strip exposed to a UV photon fluence of 100 mJ/cm2 signals as large as 30 V. The unexpected high values for the signals and their doping dependence are discussed within the frame of a model based on a thermopile arrangement, the growth induced defect structure and the doping induced modifications of the material properties.
Giant Magnetoresistance Phenomenon in Laser Ablated La0.6y0.07ca0.33mnox Thin Films
Authors: Kumar Dhananjay , Kalyanaraman R. , Narayan J. , Christen David K. 
Published: April 2011

ABSTRACTMicrostructural and magnetoresistance properties of La0.6Y0.07Ca0.33MnOx (Y-doped LCMO) thin films grown in-situ by pulsed laser ablation have been studied. Transmission election microscopy and x-ray diffraction measurements have shown that the Y-doped LCMO thin films grow epitaxially on (100) LaAl03 substrates and are cubic with a lattice parameter of 3.849 ?. The as-deposited films exhibited a metal-insulator transition at 130 K and a giant magnetoresistance (GMR) at 125 K with a MR ratio (dR/RH) of 1500% in the presence of a magnetic field of 6 Tesla. Such a colossal value of MR ratio for as-deposited Y-doped LCMO films is quite promising keeping in view the fact that these films were unannealed and not optimized. We ascribe this magnetoresistance to spin-dependent electron scattering coupled with the presence of intervening O2. ions across Mn3+ and Mn4+ with suppressed separation between Mn-O layers caused by smaller sized Y-dopant. The effect of annealing on the positive-shift of metal-insulator transition temperature and the improvement in GMR ratio has also been discussed. We also report a non-ohmic response in the Y-doped LCMO films which is observed only in the region of the resistance peak and lends support to a conduction mechanism in these materials based on spin-dependent scattering of electrons.
Laser Induced Avalanche Ionization and Electron-Lattice Heating of Silicon with Intense Near IR Femtosecond Pulses
Authors: Pronko P.P. , VanRompay P.A. , Singh R.K. , Qian F. , Du D. , Liu X. 
Published: April 2011

ABSTRACTA two temperature finite difference model has been developed and is used to describe the response of materials under ultrafast femtosecond laser pulses in the energy regime where melting and vaporization can occur. In applying this model to silicon it is observed that, for 800 nm light, laser pulse intensities that are just sufficient to achieve threshold for vaporization are also at the level of optical electric field strength where electron avalanche breakdown at the surface of the material can occur. For sub-picosecond pulses the physical response of the material is associated with a strongly temperature dependent coupling coefficient connecting electron and phonon thermal distributions. The results of these analyses demonstrate that a very thin near solid density plasma, caused by avalanche ionization, is responsible for the surface heating and subsequent thermodynamic response of the material. This interpretation is consistent throughout the pulse duration range from 80 femtoseconds to 0.2 nanoseconds. The proposed mechanism for absorption, at the near infra-red wavelength being used here, is very different from the types of mechanisms usually considered for nanosecond laser heating of semiconductors. Surface damage threshold is determined by atomic force microscopy and the threshold for plasma optical emission by photomultiplier detection . Melt deths are probed with SIMS impurity diffusion profiles and high resolution cross sectional TEM.
Test of Kinetic Models for Interface Velocity, Temperature, and Solute Trapping in Rapid Solidification
Authors: Kittl J.A. , Aziz M.J. , Brunco D.P. , Thompson M.O. 
Published: April 2011

ABSTRACTDuring rapid solidification, deviations from local interfacial equilibrium are manifested by solute trapping and interfacial undercooling. Both the solute trapping function and the interface velocity-temperature function have been measured in the Si:As alloy system following pulsed laser melting, permitting us to test models for nonequilibrium interface kinetics. The results are consistent with the Continuous Growth Model “without solute drag” of Aziz and Kaplan and are inconsistent with models that incorporate solute drag effects during solidification.
Kinetic Analysis of Nonisothermal Crystallization
Authors: Kelton K. F. 
Published: April 2011

ABSTRACTA realistic computer model for polymorphic crystallization under isothermal and nonisothermal conditions, which takes proper account of time-dependent nucleation behavior and cluster-size-dependent growth, is presented. A new correction to the standard Johnson-Mehl-Avrami-Kolmogorov (JMAK) statistical analysis that takes account of finite sample size is incorporated to simulate data taken from fine particles and nano-structured materials. Model predictions compare well with experimental data obtained from calorimetric studies of the polymorphic crystallization of lithium disilicate glass. The computer model is employed to evaluate commonly used methods of analysis for calorimetric data and to suggest new approaches for extracting kinetic parameters.
The Time Cone method for Nucleation and Growth Kinetics on a Finite Domain
Authors: Cahn John W. 
Published: April 2011

ABSTRACTThe Kolmogorov-Johnson-Mehl-Avrami theory is an exact statistical solution for the expected fraction transformed in a nucleation and growth reaction in an infinite specimen, when nucleation is random in the untransformed volume and the radial growth rate after nucleation is constant until impingement. Many of these restrictive assumptions are introduced to facilitate the use of statistics. The introduction of “phantom nuclei” and “extended volumes” are constructs that permit exact estimates of the fraction transformed. An alternative, the time cone method, is presented that does not make use of either of these constructs. The method permits obtaining exact closed form solutions for any specimen that is convex in time and space, and for nucleation rates and growth rates that are both time and position dependent. Certain types of growth anisotropies can be included. The expected fraction transformed is position and time dependent. Expressions for transformation kinetics in simple specimen geometries such as plates and growing films are given, and are shown to reduce to expected formulas in certain limits.
Kinetics of Phase Transitions in Superionic Pbsnf4 Versus Temperature
Authors: Denes Georges , Madamba M. Cecilia , Milova Galina 
Published: April 2011

ABSTRACTPbSnF4 is the highest performance fluoride ion conductor known to date and is starting to be used for the fabrication of chemical sensors. Although several phase transitions have been reported, with conflicting results from different groups, the exact sequence of phase transitions versus temperature and the kinetics of the phase transformations remain unclear. We have prepared the three phases that can be stabilized at ambient temperature, i.e. o-, α- and β-PbSnF4, and studied the stability of each phase versus temperature. It appears that some of the phases transform very slowly to another under prolonged heating at constant temperature. This is very important since the conductivity is not necessarily the same for each phase, and therefore, a phase transition taking place slowly in the PbSnF4 used for the fabrication of a device, might not be detectable by a short time evaluation but, it could well alter its properties after prolonged use.