bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pseudo-MOS Operation of Ultra-Narrow Polycrystalline Silicon Wires: Electrical Characterization and Memory Effects
Authors: Anghel C. , Hefyene N. , Ionescu A.M. , Declercq M. , Tringe J.W. , Plummer J.D. 
Published: April 2011

AbstractThis paper presents a new method for the electrical characterization of polycrystalline silicon wires based on the pseudo-MOS effect. The investigated devices are ultra-narrow (0.1- 0.2μm), four-contact polycrystalline silicon wires composed of several individual grains in series. The pseudo-MOS static operation allow the examination of interface and bulk characteristics via MOSFET modeling in terms of electrical parameters (carrier mobility, flat band and threshold voltages, mobility reduction coefficient). Additionally, the measurement of 1/f noise is shown to be a useful complementary characterization tool for material investigation. Particular attention is paid to the exploration of transient phenomena in the dynamic pseudo-MOS operation. A significant I-V hysteresis is experimentally revealed when high voltages are applied on the substrate acting as a gate. Long current relaxation (>100s) in accumulation and depletion, in darkness and under illumination, demonstrate the dominance of carrier trapping at grain boundaries over oxide charging and/or SRH generation-recombination intra-grain phenomena. The dynamic regime analysis shows remarkable data retention duration and suggest further investigations of polycrystalline silicon wires for memory applications may be useful.
Si/Ge Intermixing and Island-Island Interaction in Ge/Si(100) Self-Assembled Islands
Authors: Capellini G. , Seta M. De , Evangelisti F. 
Published: April 2011

AbstractIn this paper we present a study of the influence of the growth rate and deposition temperature on the growth dynamic of self-assembled Ge/Si(100) islands. By combining AFM and XPS measurements we show that the main effect of rising the deposition temperature is an enhancement of the Ge-Si intermixing. The actual composition of the Ge islands as a function of deposition temperature has been measured in the 450 °C- 850 °C range: the Ge content x in the alloyed epilayer was found to decrease from x=1 to x=0.28. By changing the growth rate at fixed deposition temperature we were also able to modify the island density. The influence of the island density on the island size has been investigated. We found that an increase of the island density from 109 to 2×1010 cm−2 at T=600 °C brings about a change of the mean island size from 85 to 55 nm. This reduction is explained in terms of island-island interaction effects on the growth dynamic.
Atomically Sharp Artificially Reordered Structures in Si(100)
Authors: Sen P. , Akhtar J. 
Published: April 2011

AbstractThe ability to organize materials in two or three dimensional structures forms the basis for approach worldwide to construct nanometer sized arrangements. Here we show the interaction of 200 MeV silver ions with a Si( 100) single crystal lattice which has been studied to look for defects with atomic resolution. Employing scanning tunnelling microscopy (STM), we demonstrate that the deposited energy is not stored as random defected arrangements at the irradiation site but as spatially extended structures at predetermined locations. These artificially reordered structures consist of random Si atoms, placed atomically sharp next to the single crystalline lattice.
Shock Synthesis of Nanocrystalline High -Pressure Phases in Semiconductors by High-Velocity Thermal Spray
Authors: Goswami R. , Parise J. , Herman H. , Sampath S. , Gambino R. , Zhu Y. , Welch D. 
Published: April 2011

AbstractShock synthesis of nanocrystalline Si, Ge and CdTe was accomplished using high- velocity thermal spray. Si or Ge powders were injected into a high energy flame, created by a thermal spray gun, where the particles melt and accelerate to impact on a substrate. The shock wave generated by the sudden impact of the droplets propagated through the underlying deposits, which induces a phase transition to a high pressure form. The decompression of the high-pressure phase results in the formation of several metastable phases, as evidenced by transmission electron microscopy and x-ray diffraction studies. The peak pressure is estimated to be ≈23GPa with a pulse duration of 1-5 ns. Transmission electron microscopy revealed that the metastable phases of Si with a size range of 2 to 5 nm were dispersed within Si-I. In Ge, a metastable phase, ST-12, was observed. This is a decompression product of Ge-II which possesses the β-Sn type of structure. In the case of CdTe, a fine dispersion of hexagonal CdTe particles, embedded in cubic-CdTe with an average size of 2 nm was obtained.
Nanostructured TiO2 and W:TiO2Thin Films by a Novel Sol-Gel Processing for Alcohol Sensing Devices
Authors: Garzella Carlotta , Comini Elisabetta , Bontempi Elza , Depero Laura E. , Frigeri Cesare , Sberveglieri Giorgio 
Published: April 2011

AbstractTiO2and W:TiO2 thin films have been prepared by a chemically modified sol-gel technique, that implies hydrolysis and condensation of tetraethylortotitanate in the presence of a polymer dissolved in ethanol. Oxide-polymer films were deposited by dip-coating. Annealing at 500°C results in nanosized structurally stable oxides films. For doping tungsten(V)ethoxide was used in concentration that led to a final W/Ti atomic ratio of 1/33, 5/33, 10/33. The morphological and structural characteristics of thin films were studied through microraman, GIXRD, SEM and TEM. A microstructural comparison between pure and doped TiO2 layers is reported. Ethanol and methanol sensing properties are tested.
Photoluminescence from n-(p-) type impurity doped Si nanocrystals
Authors: Fujii Minoru , Mimura Atsushi , Hayashi Shinji , Kovalev Dmitri , Koch Frederick 
Published: April 2011

AbstractEffects of impurity (P and B) doping on the photoluminescence (PL) properties of Si nanocrystals (nc-Si) in SiO2 thin films are studied. It is shown that with increasing P concentration, PL intensity first increases and then decreases. In the P concentration range where PL intensity increases, quenching of the defect-related PL is observed, suggesting that dangling-bond defects are passivated by P doping. On the other hand, in the range where PL intensity decreases, optical absorptiondue to the intravalley transitions of free electrons generated by P doping appears. The generation of free electrons andthe resultant three-body Auger recombination of electron-hole pairs is considered to be responsible for theobserved PL quenching. In the case of B doping, the behavior is much different. With increasing B concentration, PL intensity decreases monotonously. By combining the results obtained for P and B doped samples, theeffects of donor and acceptor impurities on the PL properties of nc-Si are discussed.
Low-noise, Low-dark-current GaN Diodes for UV Detectors
Authors: Deelman Peter W. , Bicknell-Tassius Robert N. , Nikishin Sergey , Temkin Henryk 
Published: April 2011

ABSTRACTWe report mesa-isolated Schottky barrier photodetectors fabricated on n-GaN. Single-element detectors were constructed from nitride epilayers grown by gas source molecular beam epitaxy (GSMBE) on Si(111). Chlorine-based reactive ion etching was used to form two-level mesas. The detectors were front-illuminated through 100 Å Pd semitransparent Schottky contacts on the upper mesas; ohmic contact on the lower mesas was made using standard Ti/Al/Ti/Au metallurgy. Silicon dioxide grown by plasma-enhanced chemical vapor deposition provided both surface passivation and electrical isolation. The dark current of an 86 × 86 µm2 single-element detector is 2.10 × 10−8 A/cm2 at –2 V bias, and the zero-bias noise power density at 1Hz is as low as 9 × 10−29 A2/Hz. In addition, we present preliminary results for p-n diodes fabricated from epilayers grown on sapphire. The dark current of a 50 × 50 µm2 single-element detector is 1.6 × 10−6 A/cm2 at –2 V bias.
Analysis of strain in sub-grains with variable misorientation in GaN epilayers by digital processing of HRTEM images
Authors: Kret S. , Ruterana P. , Chen J. , Nouet G. 
Published: April 2011

ABSTRACTIn epitaxial GaN layers on (0001) sapphire, the distance between edge dislocations in sub-grain boundaries is variable. The strain state in such sub-grains is quantitatively measured by processing of HRTEM images. The dislocation core distribution maps and in plane Burgers vectors components are derived from experimental strain tensor by applying the continuum dislocation theorem. For image simulationsthe atomic models of edge dislocations are calculated using a modified Stillinger-Weber potential. It is shown that the strain field extracted from simulated images matches that from experimental ones. The corresponding dislocation density peaks are larger and more splitted than those from simulated images.
Nitride-Rich Hexagonal GaNP Growth Using Metalorganic Chemical Vapor Deposition
Authors: Yoshida Seikoh , Itoh Yoshiteru , Kikawa Junjiroh 
Published: April 2011

ABSTRACTThe growth of GaNP using laser-assisted metalorganic chemical vapor deposition (LA-MOCVD) was carried out for the fabrication of a light-emitting diode (LED). We used an Ar-F laser in order to decompose the source gases at lower temperatures. Trimethylgallium (TMG), ammonia (NH3) and tertialybuthylphosphine (TBP) were used for the growth. GaNP growth was carried out at different temperatures. After that, annealing was carried out at 1273-1373 K to improve the crystal quality.As a result, N-rich GaNP could be grown at 1123-1223 K. The surface morphologies of GaNP were improved when the growth temperature was increased to above 1173 K. We investigated the photoluminescence (PL) of GaNP. The band-edge emission of GaNP was observed at 77 K upon applying thermal annealing at 1323 K. This peak shifted to about 0.2 eV compared with the GaN band-edge emission. Furthermore, a GaNP LED was fabricated and the electoluminescence spectra were investigated. The band-edge emission at 420 nm was observed.
Optical Properties of a Quantum Well of A1−x Bx Alloy Semiconductor in the Coherent Potential Approximation
Authors: Shinozuka Yuzo , Kida Hirotsugu , Watarikawa Masanori 
Published: April 2011

ABSTRACTWe have theoretically studied optical properties of a quantum well (QW) in which the well region is constructed from a binary alloy semiconductor A1−xBx in the coherent potential approximation (CPA). A tight binding model is used for a single particle (electron, hole, Frenkel exciton) in the well composed by a rectangular array of NxxNyxNz sites. The effect of the diagonal randomness is reduced to the coherent potential σ(E), which is assumed to be the same for all sites, and is selfconsistently determined with the average Green's function. For a slab (∞, ∞, Nz) and wire (∞, Ny, Nz), the density of states (E) is composed of Nz (or NyxNz) subbands, each shows the two (one)-dimensional van-Hove singularity. When x (or 1−x) is small, a B (A) impurity-band always appears at the lower (higher) energy side of the lowest (highest) host-band. The change of (E) and the absorption spectrum by changing the well-width and the dimensionality is discussed in detail.
Luminescence And Structural Properties Of InGaN Epilayer, Quantum Well And Quantum Dot Samples Using Synchrotron Excitation
Authors: O'Donnell K.P. , Martin R.W. , White M.E. , Tobin M.J. , Mosselmans J.F.W. , Watson I.M. , Damilano B. , Grandjean N. 
Published: April 2011

ABSTRACTThe Daresbury synchrotron radiation source (SRS) provides bright, tunable x-rays for scattering and absorption probes of local structure. Scanning confocal microscopy and luminescence decay measurements employ the SRS in alternative ways, as a tunable luminescence excitation engine and as a source of weak, 160 ps pulses with a large pulse-topulse separation, respectively. This report first describes local atomic structure studies of InGaN epilayers by extended x-ray absorption fine structure (EXAFS). In addition, we report photoluminescence (PL) imaging, PL microspectroscopy and photoluminescence decay studies of various nitride samples, including tailored InGaN quantum wells and discs.
Improvement of Thin Palladium and Platinum Silicide Films On (100) Si Substrates By Incorporating Phosphorus Dopant
Authors: Juang M. H. , Ou-Yang C. I. , Cheng H. C. , Lin C. T. 
Published: April 2011

AbstractEffects of phosphorus dopant on thin Pd and Pt silicide films on (100) Si substrates have been studied. As for the samples formed by implanting BF2 dopant into thin Pd films deposited on Si substrates and then annealing, the thermal stability of thin Pd2Si films can be improved relative to the control samples without dopant incorporation. The degree of improvement is affected by the fluorine concentration around the silicide/Si interface and thus the BF2 implant energy. On the other hand, as for the samples formed by implanting phosphorus dopant into thin Pd films and then annealing, both the thermal stability and the silicide conductivity of thin Pd2Si films can be significantly enhanced. The large improvements in the thermal stability and the silicide conductivity are nearly independent of the phosphorus implant energy, and which are primarily due to the formation of textured Pd2Si structures. In addition, the Pt silicides formed by implanting phosphorus dopant into thin Pt films and then annealing also show considerably improved thermal stability.
Effects of Surface Hydrogenation on Initial Reaction Processes of Transition-Metal Adatoms on Silicon Surfaces
Authors: Higai Shin'ichi , Ohno Takahisa 
Published: April 2011

AbstractWe studied the effects of the surface hydrogenation on the adsorption, penetration, and silicidation, i.e., the initial reaction processes of the transition-metal Ni and Ti adatoms on the Si surfaces by the first-principles theoretical calculations. We found for both Ni and Ti that the surface hydrogenation changes the most stable surface site and reduces the adsorption energy. In addition, it blocks the penetration, and thus prevents the silicidation. Furthermore, we newly propose its interesting effects from our results, i.e., impurity metal atoms existing in the Si subsurface are extracted onto the surface by the surface hydrogenation. Thereby, highly pure and atomically flat Si surfaces are expected to be obtained.
Microstructure and Coarsening in Mazed Bicrystal Films of Au Grown on Ge Substrates
Authors: Radetic Tamara , Dahmen Ulrich 
Published: April 2011

AbstractThin films of gold (Au) were grown on single crystal germanium (Ge) or silicon (Si) substrates using physical vapor deposition (PVD). The resulting microstructure was that of a mazed bicrystal in which two equivalent grain orientations, related to each other by a 90° rotation, are arranged in a morphology of irregularly shaped, convoluted grains. Quantitative morphological analysis showed a strong dependence of grain shape on size, with larger grains being more convoluted and smaller grains more compact. The evolution of grain size, anisotropy and shape during heating in the temperature range from 300-340 °C was studied by in-situ transmission electron microscopy (TEM).
The nature of islanding in the InGaAs / GaAs epitaxial system
Authors: Walther T. , Cullis A.G. , Norris D. J. , Hopkinson M. 
Published: April 2011

AbstractThe interest in the phenomenon of islanding in a range of semiconductor systems is in part due to the fundamental importance of the Stranski-Krastanow transition but also driven by potential device applications of self-organized quantum dot arrays. However, the mechanism underlying the island formation is still to a significant degree unclear. In the present work, we focus on the epitaxial InGaAs / GaAs(001) system, with layer deposition by molecular beam epitaxy. Atomic force microscopy is used to measure the surface topography of nominally 4nm thick InxGa1-xAs films. It is shown that the growth mode switches abruptly from flat layer to island growth if a critical Indium composition of x(In)≍0.25 is reached. The structure of such layers during early stages of growth is examined using energy-filtered transmission electron microscopy. Indium gradients in the islanded layers are measured and the driving force for the islanding transition itself is considered.
Kinetic properties of adatoms in Sine-Gordon model
Authors: Baryakhtar I.V. 
Published: April 2011

AbstractThe model for describing kinetic properties of adatoms on an anisotropic substrate is proposed. The kinetic equation for 1D adatom localized structures is constructed in the frame of the Sine-Gordon model. The self-diffusion coefficient for adatoms is calculated and the process of their homogenization is discussed.
Velocity Distribution of Electrons Escaping from a Potential Well
Authors: Lavine James P. 
Published: April 2011

AbstractElectron escape over a one-dimensional potential barrier is treated with a Monte Carlo method that incorporates simple models for the electron-phonon interaction. The consequences of these models are considered here through the calculation of the escaping electron velocity distribution and the electron energy distribution before escape. Effective temperatures are derived from both distributions. The numerical results are compared with those from the classical model of thermionic emission.
Determination of TN for Ba6Mn4MO15 (M = Cu, Zn) by Neutron Diffraction
Authors: Battle P. D. , Cussen E. J. 
Published: April 2011

ABSTRACTThe Néel temperatures of Ba6Mn4MO15 (M = Cu, Zn) have been determined by neutron powder diffraction to be ∼ 6 K. In both cases, short-range magnetic coupling within the individual chains of this pseudo-1D crystal structure produces a susceptibility maximum at a temperature somewhat higher than that at which the frustrated interchain interactions establish long-range magnetic order.
Synthesis of Mesophase Cerium(IV) Oxides via Surfactant Templating
Authors: Inagaki Masahiko , Hozumi Atsushi , Yokogawa Yoshiyuki , Kameyama Tetsuya 
Published: April 2011

ABSTRACTMesostructured cerium(IV) oxides were directly synthesized via the hexamethylenetetramine (HMT) homogeneous precipitation method. Cerium(III) nitrate, a templating agent, HMT and water were mixed in a molar ratio of 1: 0.1-2: 1-15: 100-1000 and kept at 65 to 95°C for 10 to 40 hours. 1-Hexadecanesulfonic acid sodium salt was used as the templating agent. Low-angle XRD patterns showed that the as-prepared powders had a lamellar structure with d100=4.1 nm. Wide-range (2θ=10-70°) XRD patterns also exhibited reflection peaks of CeO2 with a fluorite structure. However, the low-angle reflection peaks disappeared in calcined specimens.
A Novel Route For The Synthesis of LiAlxCo1−xO2 Battery Materials And Their Structural Properties
Authors: Tomar M. S. , Hidalgo A. , Dobal P. S. , Katiyar R. S. , Dixit A. , Melgarejo R. E. , Kuenhold K. A. 
Published: April 2011

ABSTRACTLiCoO2 is an important cathode material for rechargeable batteries. Al substitution on Co sites was recently found to enhance its intercalation voltage. We have developed a reliable and less expensive method for the synthesis of such LiAlxCo1−xO2 compositions using simple salts of the constituent elements and organic solvents. X-ray diffraction and Raman spectroscopy were used for structural characterization of these materials at various annealing temperatures. The phase evolutions in LiAlxCo1−xO2 compositions were studied using micro-Raman spectroscopy and a phase diagram is proposed based on the observations. The phase diagram suggests that thin films of these materials can be deposited at substrate temperature at about 650°C
Reducibility study of the LaMxFe1−xO3 (M = Ni, Co) perovskites
Authors: Estournès C. , Provendier H. , Bedel L. , Petit C. , Roger A.C. , Kiennemann A. 
Published: April 2011

ABSTRACTSolid solutions of LaMxFe1−xO3 (with M = Ni and Co) have been used in the Fischer- Tropsch reaction (CO + H2 → Hydrocarbons + CO2) and in the partial oxidation of methane (CH4 + 1/2 O2 → CO + 2 H2). In both catalytic reactions, the active catalyst is reported to be reduced metal particles; their size and their interactions with the support induce large differences in the product distribution.In the nickel system, after total reduction by TPR all catalysts exhibit ferromagnetic behavior at room temperature. In situ magnetization in 1 Tesla on cooling the sample under reducing atmosphere shows one magnetic transition for each sample indicating one Curie temperature. These Curie temperatures are in between those known for bulk nickel and iron and decrease with the initial nickel content of the perovskite. This indicates that nickel is reduced first and induces the reduction of iron, leading to the formation of an alloy.In the cobalt system, in situ magnetization on heating the sample shows a sharp increase of the magnetization only for x = 0.25, 0.40 and 1, corresponding to the formation of metallic cobalt nanoparticles. All other materials present only one increase of the magnetization for temperatures similar to those observed for the second reduction in TPR corresponding to the formation of CoFe alloys.
Conversion of an Aurivillius Phase Bi2SrNaNb3O12 into Its Protonated Form via Treatment with Various Mineral Acids
Authors: Shirata Masashi , Tsunoda Yu , Sugimoto Wataru , Sugahara Yoshiyuki 
Published: April 2011

ABSTRACTA protonated form of a layered perovskite was prepared from an Aurivillius phase Bi2SrNaNb3O12via acid treatments, and the effect of the type of mineral acids was investigated. The treatment with HX (X = Cl, Br, I) resulted in the formation of a protonated form H1.8[Sr0.8Bi0.2NaNb3O10], while no reactions were observed for HNO3 and H2SO4 under the present experimental conditions. All the products obtained by HX-treatments exhibited layered structures and the structures of the perovskite-like slabs were preserved.
Two Different Interactions between Oxygen Vacancies and Dopant Cations for Ionic Conductivity in CaO-Doped CeO2 Electrolyte Materials
Authors: Zhou Yuanzhong , Chen Xi 
Published: April 2011

ABSTRACTThe electrical measurement has demonstrated that conductivity of CaO-doped CeO2 has higher activation energy for low temperature and lower activation energy for high temperature. A model with two different kinds of defect interactions between oxygen vacancy and doped cations has been used to interpret the phenomenon. Diffusion based on hopping of oxygen ions was assumed as the mechanism of electrical conduction. The analysis indicated that at high temperature free oxygen vacancies are dominant and the activation energy is only for oxygen ion hopping. At low temperature, however, oxygen vacancies associated with dopant calcium ions are dominant for high CaO content and the activation energy is the energy for hopping of an oxygen ion plus half of the association energy between one oxygen vacancy and one calcium ion. For low level doping, both free and associated oxygen vacancies are important.
Piezoresistive Sensors on Plastic Substrates Using Doped Microcrystalline Silicon
Authors: Alpuim P. , Chu V. , Conde J. P. 
Published: April 2011

ABSTRACTThe piezoresistive behavior of optimized n-type and p-type microcrystalline silicon films deposited on polyethylene terephthalate plastic substrate by hot-wire and radio-frequency plasma-enhanced chemical vapor deposition, at a substrate temperature of 100 °C, is studied. A 4-point bending jig allowed the application of positive and negative strains in the films. Repeated measurements of the relative changes in the resistance of the samples during the strained condition showed reversible behavior, with p-type microcrystalline films having positive gauge factor in the range from 25 to 30 and n-type [.proportional]c-Si:H films having negative values of gauge factor from -40 to -10. The induced strain in the films was in the range between 0 and ±0.3%. A sensor utilizing the piezoresistive property of doped [.proportional]c-Si:H was used to map a contour with the shape of an Archimedes' spiral.