bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth of Epitaxial Al2O3 Films on Silicon by Ionized Beam Deposition
Authors: Whangbo SangWoo , Choi YunKi , Chung Kwun Bum , Jang HongKyu , Whang ChungNam 
Published: April 2011

AbstractEpitaxial Al2O3 films have been successfully grown on an oxidized silicon substrate by the ionized beam deposition using an Al ion beam in oxygen environments. The crystalline quality dependence of the Al2O3 films on the growth temperatures was investigated. Using in situ reflection high energy electron diffraction, the orientation relationships between epitaxial Al2O3 films and Si substrate were found to be (100) Al2O3//(100) Si with [110] Al2O3//[110] Si and (111) Al2O3//(111) Si with [112] Al2O3//[112] Si. The stoichiometry of the films was found to be similar to that of sapphire from XPS measurements.
AFM and TEM Examination of Surface Grains in LPCVD Silicon Films
Authors: Kharas Dave , Gambino R. J. , Golubovic-Liakopoulos N. 
Published: April 2011

AbstractPolycrystalline silicon is an important technological material in microelectronics, and more recently in microelectromechanical systems (MEMS). For MEMS applications polysilicon films with residual tensile stress are often used, requiring film growth in the transition zone from 550-600°C. In this study polysilicon films were grown in a hot walled LPCVD reactor at 590°C to a thickness of 450 nm. The tensile as-deposited stress in the wafers was found to decrease with distance from the reactor front and served as a marker for the changing microstructure and surface roughness of the film as measured by Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM). It was found that the surface contained a high density (≍30 /µm2) of grains that protruded 30 nm above the mean film surface. The size and volume of these grains increased linearly with decreasing stress until the surface saturated and became uniformly rough. The nature of these surface grains, their spatial characteristics, and their annealing behavior is discussed.
Nano-Scale Heteroepitaxy Control of Magnetic Oxide Thin Films on Ultra-Smooth Sapphire Substrates
Authors: Takakura Masahiro , Miyahara Takafumi , Tashiro Junichi , Sasaki Atsushi , Furusawa Mitsuyasu , Yoshimoto Mamoru 
Published: April 2011

AbstractWe have examined the novel heteroepitaxy of magnetic oxide thin films on ultra-smooth sapphire substrates by laser MBE for fabrication of low-dimensional structures. Employing the atomically controlled substrate surfaces with atomic steps and terraces, we demonstrate the deposition of magnetic oxide nanowires (~0.5 nm high and ~20 nm wide) and nanodots of (Mn, Zn) ferrite, Fe3O4 and NiO.
Thermodynamics and Kinetics of Shear Induced Melting of a thin Lubrication film Trapped between Solids
Authors: Popov V.L. , Persson B.N.J. 
Published: April 2011

AbstractShear melting of a thin layer trapped between two crystalline solids is considered in the frame ofü the Landau's theory of phase transitions. Kinetics of melting and solidifying by static and periodic loading is analyzed.
Bismuth Contribution to the Improvement of the Positive Electrode Performances in Ni/Cd and Ni/MH Batteries
Authors: Pralong V. , Delahaye-Vidal A. , Beaudoin B. , Tarascon J-M. 
Published: April 2011

ABSTRACTIn this study we investigated the evolution of nickel hydroxide, which acts at the positive electrode of the Ni/Cd, Ni/MH and Ni/H2 alkaline batteries. We found that the addition of bismuth oxide in the course of the active material preparation prevents the dissolution-re-crystallization processes of the nickel hydroxide that are harmful to the electrode efficiency. From XRD and SEM studies, it is shown that treatment of the bismuth doped-nickel hydroxide by hydrogen in 5 N KOH electrolyte prevents metallic nickel formation. Moreover, it appears to stabilize the α-type nickel hydroxide structure, preventing its transformation into the β-Ni(OH)2 phase. Finally, an implementation of these findings towards the most efficient use of nickel positive electrodes is shown.
Mechanism of Quality Factor Compensation by Nb2O5 Addition for Dielectric Properties of Low-T Sintered ZST Microwave Ceramics
Authors: Park Yong H. , Shin Moo Y. , Kim Hyung H. , Ko Kyung H. 
Published: April 2011

ABSTRACTIt has been known that some additives such as Nb2O5 are efficient quality factor compensators to potential additives for low-T sintering of (Zr0.8Sn0.2)TiO4such asZnO. The compensation mechanism of Nb2O5was analyzed in the light of its effects on the Zn incorporation in grains. ZST ceramics were prepared by conventional mixed oxide method and their microwave dielectric properties including quality factor, permittivity and temperature coefficient frequency (TCF) were measured at X-band. After sintering at 1350 and 1400oC, samples were post-annealed at 900∼1100oC. It was found that as Nb2O5 was added, the quality factor of 6 mol % ZnO-ZST specimens increased from 24000 to 44000 without any sacrificing of other dielectric properties such as permittivity and TCF. According to TEM and XRD, Nb addition tends to enhance Zn diffusion toward grain boundaries while Nb moved in the opposite direction. Due to the fact that no second phases were formed, it was assumed that the redistribution of Zn and Nb could play a major role in the enhancement mechanism of quality factor. Post-annealing can also be a secondary booster for the quality factor of ZST. After annealing at 900∼1100oC, the quality factor of a specimen with additives, increased again up to 48000 due to further decrease of oxygen vacancies resulting from further out-diffusion of Zn toward grain boundaries and incorporation of Nb into the grain.
Solid-State NMR Investigation Of Mixed-Alkali Distribution In Phosphate Glasses
Authors: Prabakar S. , Mueller K.T. 
Published: April 2011

ABSTRACTThe correlation between 31P and 23Na (or 133Cs) nuclei in a mixed-alkali phosphate glass has been investigated by TRAnsfer of Populations by DOuble Resonance (TRAPDOR) NMR spectroscopy. The variation in spatial proximity between 31P nuclei in phosphate tetrahedra and sodium (or cesium) modifier ions has been demonstrated in a phosphate glass with molar composition 25 Cs2O: 31 Na2O: 44P2O5. Interactions between 31P and 23Na (or 133Cs) nuclei are shown to exist even at low dephasing times indicating the short-range nature of these couplings. The ratios of resonance intensities from Q1 and Q2 phosphate units show different trends depending on whether couplings to 23Na or 133Cs are investigated, demonstrating the differing structural roles of the modifier alkali cations within the glass.
Modification of Ferroelectric Properties of TGS Crystals Grown under a dc Electric field
Authors: Arunmozhi G. , Nogueira E. , Gomes E.de Matos , Lanceros-Mendez S. , Margarida M. , Costa R. , Criado A. , Mano J. F. 
Published: April 2011

ABSTRACTFerroelectric triglycine sulphate crystals have been grown under the influence of an intense electric field of 6×104 V/m. Relative to crystals grown under ambient conditions (TGS) the crystals grown under the electric field (TGS-E) display a dielectric permittivity a factor of two lower. Significant differences are observed in the Curie-Weiss behavior of the ferroelectric phase, in the x-ray diffraction patterns and in the differential calorimetry measurements.
Transition Metal Based Zeotypes: Inorganic Materials at the Complex Oxide – Zeolite Border
Authors: Henry Paul F. , Hughes Robert W. , Weller Mark T. 
Published: April 2011

ABSTRACTThe synthesis of compounds of the type CsAIIIMIVO4 and (Cs,Rb)AIIPO4 (AIII = Al, Ga, Fe; AII = Ni, Co, Cu; M = Si, Ge, Ti,), using gel decomposition techniques at high temperatures is described. Several new materials in this family have been characterised using powder X-ray diffraction and are shown to adopt the zeolite ABW framework topology. Evidence for the large monovalent cation templating the formation of the ABW framework is presented. Extension of the method to other AIII and MIV (A = Mn, Co, B, In; M = Sn, Zr) framework cations, which are known to adopt tetrahedral geometry in other structures, has proved unsuccessful.
Preparation of New Bismuth Oxides by Hydrothermal Reaction
Authors: Kumada N. , Takei T. , Kinomura N. , Sleight A. W. 
Published: April 2011

ABSTRACTHydrothermal reactions using NaBiO3·nH2O produced a variety of newbismuth oxides that were not prepared by high temperature reaction. Some of them have pentavalent bismuth such as Bi2O4O, LiBiO3, ABi2O6 (A = Mg, Zn) and AgBiO3. When using transition metal or rare-earth metal solutions, new bismuth oxides with trivalent bismuth were obtained. In the case of Cr(NO3)3 solution a chromium bismuth oxyhydroxide, HBi3(CrO4)2O3, was prepared at 180°C, while in A2CrO4 (A = Li, Na, K) solution a new bismuth chromium oxide, Bi8(CrO4)O11, was prepared above 180°C. When A2MoO4 (A = Li, Na, K) solution was used, a new phase appeared above 220°C. By using A2WO4 (A = Li, Na, K) solution β-Bi2O3 and Bi2WO6 were obtained above 220°C.
Lithium deintercalation in LiNi0.30Co0.70O2: Redox processes, electronic and ionic mobility as characterized by7Li MAS NMR and electrical properties
Authors: Carlier D. , Ménétrier M. , Delmas C. 
Published: April 2011

ABSTRACTLiNi1-yCoyO2 materials are particularly interesting as positive electrode in lithium-ion batteries. Their 7Li MAS NMR spectra are sensitive to the presence of paramagnetic Ni3+ cations as nearest and next-nearest neighbors. These contact shift (or Fermi contact) interactions are used to yield information on the lithium environment in terms of paramagnetic cations.Electrochemically deintercalated LixNi0.30Co0.70O2 phases have been characterized by XRD, 7Li MAS NMR, electronic conductivity and thermoelectronic power. Ni3+ oxidation to Ni4+ occurs at the beginning of deintercalation, leading to a Ni3+/Ni4+ hopping which causes an exchange of the 7Li NMR signals of the Li ions interacting with nickel. For higher deintercalation amounts, the signal due to Li ions with only cobalt as first and second neighbor is also involved in the exchange upon heating, showing the onset of ionic hopping. For x close to 0.70, an increase of the NMR shift with temperature is observed, which is assigned to a hopping between Ni4+ and Co3+. Therefore, the question as to which ion is actually oxidized during deintercalation is somewhat irrelevant around this composition. Finally, for x < 0.70, the presence of Ni hinders a true long-range electronic delocalisation between Co4+/Co3+ (LS) as it happens in LixCoO2(x < 0.70). However, electrons are clearly delocalized in restricted zones, as seen from NMR and thermoelectronic power coefficient.
Quantitative Modelling of Nucleation Kinetics in Experiments for Poly-Si Growth on Sio2 by Hot-Wire Chemical Vapor Deposition
Authors: Swiatek Maribeth , Holt Jason K. , Atwater Harry A. 
Published: April 2011

ABSTRACTWe apply a rate-equation pair binding model of nucleation kinetics [1] to the nucleation of Si islands grown by hot-wire chemical vapor deposition on SiO2 substrates. Previously, we had demonstrated an increase in grain size of polycrystalline Si films with H2 dilution from 40 nm using 100 mTorr of 1% SiH4 in He to 85 nm with the addition of 20 mTorr H2. [2] This increase in grain size is attributed to atomic H etching of Si monomers rather than stable Si clusters during the early stages of nucleation, decreasing the nucleation density. Atomic force microscopy (AFM) measurements show that the nucleation density increases sublinearly with time at low coverage, implying a fast nucleation rate until a critical density is reached, after which grain growth begins. The nucleation density decreases with increasing H2 dilution (H2:SiH4), which is an effect of the etching mechanism, and with increasing temperature, due to enhanced Si monomer diffusivity on SiO2. From temperature-dependent measurements, we estimate the activation energy for surface diffusion of Si monomers on SiO2 to be 0.47 ± 0.09 eV. Simulations of the temperature-dependent supercritical cluster density lead to an estimated activation energy of 0.42 eV ± 0.01 eV and a surface diffusion coefficient prefactor of 0.1 ± 0.03 cm2/s. H2-dilution-dependent simulations of the supercritical cluster density show an approximately linear relationship between the H2 dilution and the etch rate of clusters.
Changes in hydrogenated amorphous silicon upon extensive light-soaking at elevated temperature
Authors: Hata N. , Fortmann C. M. , Matsuda A. 
Published: April 2011

ABSTRACTPreviously a through the substrate ellipsomtery technique was used to study the high temperature dynamics of light induced reversible changes in amorphous silicon thin films [1]. Since this technique was based on above gap optical changes it is sensitive to the structural aspects of the light induced effects, differently from the below-gap absorption techniques which detect dangling-bond defect states [2-3]. It was found that high intensity light soaking at an elevated temperature causes surprising large, reversible, changes [1]. By comparing these optical changes with the changes in dangling bond concentrations probed by electronic and below gap methods, a fuller picture of temperature dependent light-induced defect creation and annealing dynamics emerges. A high temperature high intensity light soaking method is developed which reduces saturation times, decreases the saturated dangling bond density, as well as decreases the annealing activation energy. These results are discussed in terms of the coupling between network disorder and its relaxation with respect to defect concentrations at high temperature.
Importance of Defect Density near the p-i Interface for a-Si:H Solar Cell Performance
Authors: Korevaar B.A. , Smit C. , Swaaij R.A.C.M.M. van , Schram D.C. , Sanden M.C.M. van de 
Published: April 2011

ABSTRACTA cascaded arc expanding thermal plasma is used to deposit intrinsic hydrogenated amorphous silicon at growth rates larger than 2 Å/s. Implementation into a single junction p-i-n solar cell resulted in initial efficiencies of ∼7%, although all the optical and initial electrical properties of the individual layers are comparable with RF-PECVD deposited films. The somewhat lower efficiency is due to a smaller fill factor. Spectral response measurements, illuminated J,V- measurements, and simulations indicate that a higher local defect density in the region near the p-i interface might be responsible for the smaller fill factor in comparison with conventional low- rate RF-PECVD. The higher defect density is most likely caused by the initial growth in the first 10 to 50 nm. Therefore, controlled initial growth of the intrinsic layer is suggested for good solar cell performance.
Controlling The Lateral Photoeffect In a-Si:H Heterojunction Structures: The Influence of The Band Offset Analysed Through A Numerical Simulation
Authors: Fantoni A. , Fernandes M. , Louro P. , Schwarz R. , Vieira M. 
Published: April 2011

ABSTRACTWhen an a-Si:H p-i-n structure is locally illuminated by a light spot, the non uniformity of light causes the appearance of a gradient in the carrier concentration between the illuminated and the dark zone. Carrier start to flow in agreement with such gradients, and when equilibrium is reached, the lateral diffusion process is counterbalanced by the appearance of a lateral component of the electric field vector in addition to the transverse usual one. The lateral fields act as a gate for the lateral flow of the carriers and small lateral currents appears at the transition region between the illuminated and the dark zone.Such lateral photoeffect depends on the incident light wavelength, light intensity and on the device operation condition (mainly the applied bias). The introduction of carbon in the doped layers modifies the intensity and the extension of these lateral effects through the potential barriers deriving from the band banding at the interfaces.We have used the 2D numerical simulator ASCA to analyze the behavior of an a-Si:H p-i-n structure under local illumination with the goal of observing the appearance of the lateral components of the electric field and current density vectors. Different homo and heterojunctions have been simulated, outlining how the band offset at the interfaces influences the induced lateral photoeffect and aiming to explain how a correct device design and engineering can, depending on the foreseen application, alternatively enhance or reduce the intensity of such lateral effects.
Photocapacitance of Hydrogenated Amorphous Silicon Phototransistors
Authors: Caputo D. , Cesare G. de , Lemmi F. , Nascetti A. , Palma F. , Roca F. , Tucci M. 
Published: April 2011

ABSTRACTAmorphous silicon-based phototransistors are studied as an alternative solution to replace pixel-level amplifiers simplifying large-area imaging systems. We report electrical characterization by means of current-voltage and capacitance measurements. The measured capacitance increases with decreasing frequency of the probe signal and values largely exceeding the geometrical one at low frequencies have been achieved both in the dark and under illumination. In particular, values in excess of 200 μF/cm2 are measured under 220 μW/cm2 illumination at 600 nm at 100 mHz. The capacitance dependence on frequency is interpreted in terms of trapping and release kinetics processes in the base and of the gain of the device.
Control of Medium Range Order in Amorphous Silicon via Ion and Neutral Bombardment
Authors: Gerbi Jennifer E. , Voyles Paul. M. , Treacy Michael M. J. , Gibson J. Murray , Chen Wangchun , Heuser Brent J. , Abelson J. R. 
Published: April 2011

ABSTRACTWe have observed the existence of medium range order via fluctuation microscopy in amorphous silicon grown at 230°C. We hypothesize that this structure develops during the highly non-equilibrium growth process; high densities of ordered surface nuclei are produced which are subsequently buried and forced into an unfavorable energy state. These nm sized regions are distorted in the bulk due to strain, but remain topologically crystalline. In this work, we alter the growth energetics both at the surface and sub-surface during magnetron sputter film deposition with two kinds of particle bombardment, respectively: a controllable flux of low-energy (20eV) Ar+ ions, and higher energy (100eV) D vs. H neutrals. With this method, we demonstrate for the first time control over the intensity of this medium-range structural order at a constant substrate temperature as seen primarily with fluctuation electron microscopy, but also Raman scattering, spectroscopic ellipsometry, and SAXS. We suggest that these bombardments can increase adspecie surface mobility or drive local sub-surface restructuring (“kinetic annealing”), thus increasing or decreasing the size, density and/or strength of the ordered regions.
Determination of the Mobile-Hydrogen Charge State in Hydrogenated Amorphous Silicon
Authors: Nelsona Brent P. , Xu Yueqin , Reedy Robert C. , Crandall Richard S. , Mahan A. Harv , Branz Howard M. 
Published: April 2011

ABSTRACTWe find that hydrogen diffuses as H+, H0, or H- in hydrogenated amorphous silicon depending on its location within the i-layer of a p-i-n device. We annealed a set of five p-i-n devices, each with a thin deuterium-doped layer at a different location in the i-layer, and observed the D-diffusion using secondary ionmass spectrometry (SIMS). When H-diffuses in a charged state, electric fields in the device strongly influence the direction and distance of diffusion. When D is incorporated into a device near the p-layer, almost all of the D-diffusion occurs as D+, and when the D is incorporated near the n-layer, most of the D-diffusion occurs as D-. We correlate the preferential direction of D-motion at given depth within the i-layer, with the local Fermi level (as calculated by solar cell simulations), to empirically determine an effective correlation energy for mobile-H electronic transitions of 0.39 ± 0.1 eV. Using this procedure, the best fit to the data produces a disorder broadening of the transition levels of ∼0.25 eV. The midpoint between the H0/+ and the H0/- transition levels is ∼0.20 ± 0.05 eV above midgap.
EVALUATION OF MICROCRYSTALLINE SILICON FILMS DEPOSITED BY ULTRAFAST THERMAL PLASMA CVD
Authors: Chae Yongkee , Ohno Hiromasa , Eguchi Keisuke , Yoshida Toyonobu 
Published: April 2011

ABSTRACTThis research is the first attempt at applying thermal plasma chemical vapor deposition (TPCVD) for the ultrafast deposition of Si films for solar cells. A conventional deposition process of Si films, such as plasma-enhanced chemical vapor deposition (PECVD), is capable of a maximum deposition rate of approximately 5 Å/s and it takes a relatively long time to deposit an intrinsic layer. In this paper we report a novel ultrafast deposition approach using dc-rf hybrid TPCVD. The extreme improvement of stability, controllability, and cleanliness of the process enabled the deposition of microcrystalline Si films at the ultrafast rate of over 1000 nm/s, which is about 2000 times faster than that by conventional CVD. Moreover, a minimum defect density of 7.2×1016 cm−3was achieved by post-treatment of the film in 2 Torr H2/Ar plasma. Monte-Carlo simulation and step coverage analysis suggested that the precursor is an approximately 1 nm cluster with a sticking probability of about 0.6. The success of this research will lead to the development of commercially viable technology in a roll-to-roll system in the near future, and will fundamentally change the established concepts of Si deposition technology.
Ion-assisted Sputter Deposition of Microcrystalline Silicon Films with Pulsed-DC Plasma Excitation
Authors: Reinig P. , Fenske F. , Selle B. , Fuhs W. 
Published: April 2011

ABSTRACTWe have applied a novel Ion-Assisted Sputter Deposition (IASD) method to deposit microcrystalline silicon (µc-Si) thin films with high deposition rates. An unbalanced magnetron sputter source together with an asymmetrical bipolar pulsed-DC plasma excitation operating in the frequency range 50-250 kHz was used for realizing high ion fluxes to the growing film. µc-Si films of high crystallinity are obtained at T > 400 °C with growth rates of up to 90 nm/min. The crystallinity of the films is characterized by the thickness-independent ratio of the optical thickness n·d determined by FTIR measurements and the atomic area density N·d as given by RBS analysis.
Stability and Nanostrucure of Heterogeneous Amorphous Silicon Thin-Film Synthesized Under High Chamber Pressure (500 To 2200 Mtorr) Regime of Rf Pecvda
Authors: Middya A. R. , Hamma S. , Hazra S. , Ray S. , Longeaud C. 
Published: April 2011

ABSTRACTWe report on improvement in stability of a new type of amorphous silicon films, synthesized (growth rate > 0.1 nm/s) by driving the plasma condition close to the powder regime (or “γ-regime”) of rf PECVD. These films exhibit high mobility-lifetime products [(μτ)annld ∼ 10−4 cm2/V, σph/σd ∼ 5-10×105, Ea ≍ 0.7 - 0.9 eV ], compact network structure [CH ≍ 7 to 8 at%, nanovoid density < 0.01 %, ρ ≍ 2.23 ± 0.01 gm/cm3], new features of optical properties and density-of-state (DOS) above EF is significantly lower than that of state-of-the art films. The kinetics of light-induced (AM 1.5) degradation of μτ is very fast and saturated μτ ∼ 10−6cm2/V, a value similar to that of conventional a-Si:H films at annealed state. The improved stability of “new” a-Si films, henceforth it will be denoted as “quasi-amorphous silicon (qm-Si) thin- film”, will be correlated with its specific nanostructure.