bluuebunny/crossref_metadata_2025_split huggingface dataset:
Epitaxy of Iron on Various Ruthenium Surfaces: Occurence of a New Fe Phase.
Authors: Piecuch Michel , Ravet Marie Françoise , Maurer Marc 
Published: March 2011

AbstractWe have deposited Fe on (0001) and (1122) Ru surfaces. The RHEED patterns of Fe layers on these two different surfaces show perfect 2 dimensionnal epitaxy. The symmetry of the RHEED patterns is clearly 6 fold in the case of the (0001) growth direction. The RHEED patterns in the case of Fe deposited on (1122) surface are the same as those obtained from the clean Ru surface. The structure of the Fe surface is then exactly pseudomorphous to the Ru surface in both cases. Superlattices of these new Fe atomic layers with Ru have been achieved. We have deduced from X-ray diffraction, the average interplanar spacing d and we have demonstrated the hexagonal close packed stacking sequence of the entire superlattice. Plots of d versus the average atomic composition are used to determine the value of Fe interplanar spacing as 2.075Å and 1.08Å for the (0001) and the (1122) plane respectively. We are then able to determine the average Fe atomic volume, 12.8Å3. We propose that Fe is in an expanded new metastable hexagonal phase.
Epitaxy of TiO2 Thin Film on Sapphire by MOCVD
Authors: Chang H. L. M. , You H. , Parker J. C. , Lam D. J. 
Published: March 2011

AbstractEpitaxial TiO2 films have been successfully grown on sapphire substrate at temperatures from 400 to 800°C by thermally decomposing titanium isopropoxide in the presence of O2 in a cold wall low pressure MOCVD system. Rutile film was grown on sapphire (1120) at 800°C with (101) being the growth plane and 〈010〉 being parallel to sapphire 〈0001〉. Anatase film was grown on sapphire (0001) at 400°C with (112) being the growth plane and 〈112〉 being parallel to sapphire 〈1100〉. The film structure as a function of substrate surface orientation and growth temperature is discussed in detail.
X-Ray Double Crystal Diffraction Characterization of Epitaxial Magnetic Transiton Metal Difluorides
Authors: Lui M. , King A. R. , Jaccarino V. , Farrow R. F. C. , Parkins S. S. P. 
Published: March 2011

AbstractEpitaxial films of a variety of magnetic transition metal difluoride films have been grown by molecular beam epitaxy techniques. The structural quality of these films have been characterized using X-ray double crystal rocking curve analysis. The observed rocking curve linewidths were compared to their intrinsic values as calculated by dynamical diffraction theory. The degree of crystalline perfection as judge by the rocking curves have been correlated with the amount of lattice mismatch between the various epitaxial films and substrates. In the well lattice match case (Δa/a < 0.2%) of epitaxial films of FeF2 and CoF2 grown on (001) ZnF2 substrates, the rocking curve line widths approached their intrinsic limit indicative of extremely high quality material. This work represents some of the best epitaxial magnetic insulating films grown to date.
Molecular Dynamics Study of (001) and (111) Thin Fcc Films
Authors: Streitz F.H. , Sieradzki K. , Cammarata R. C. 
Published: March 2011

AbstractWe report on the results of molecular dynamics simulations of thin unsupported fcc films ranging in thickness from 20 layers to a monolayer. The films were oriented with either (001) or (111) free surface normals. The atomic interactions were modelled using a standard Lennard-Jones potential and a short range analytic form of the embedded atom potential. The elastic moduli of the films were determined by measuring their response to very low levels of applied stress.We find that the embedded atom and Lennard-Jones results are in relative agreement for (001) films and qualitative disagreement for (111) oriented films. We relate these differences to the nature of the interatomic potential and the thermodynamic instability of the (001) surface.
Stability and Decomposition of IV-VI Semiconductor Films.
Authors: Salamanca–Riba L. , Nahm S. , Wuttig M. 
Published: March 2011

AbstractPb1−xEuxTe alloys with 0.41 ≤ x ≤ 0.51 have been observed to be unstable when grown at a temperature of 573K on BaF2 substrates. The alloys are stabilized when a buffer layer of PbTe is grown prior to the growth of the Pb1−xEuxTe alloy. In this work, we have observed tha the solid solution of Pb1−xEuxTe with x ≈ 0.5 can also be stabilized by increazing the growth temperature to 623K. Our results suggest that the critical temperature for decomposition is in the range 573–623K. We present a qualitative phase diagram for Pb1−xEuxTe alloy films.
Optimizing Process Parameters for the Growth of YBa2Cu3O7−δ thin-films
Authors: Norton M. Grant , Carter C. Barry , Moeckly Brian H. , Russek Stephen E. , Buhrman Robert A. 
Published: March 2011

ABSTRACTLaser deposition is widely used to fabricate thin-films of the YBa2Cu3O7−δ superconductor due to its ease of operation and its reproducibility. The films thus formed do not require post-deposition annealing to be superconducting. The processing route involves many variables which would be expected to exert an influence on the early stages of the film growth and thereby the final microstructure. The parameters which have been varied are the laser energy, laser pulse repetition rate and laser wavelength. The films have been examined using transmission electron microscopy (TEM) in order to determine the film orientation, composition and microstructure.
Preparation and Properties of Superconducting thin Films by Excimer Laser Ablation
Authors: Geusic Michael E. , Stewart Alan F. , Pederson Larry R. , Weber William J. , Marken Kenneth R. , Li Kin 
Published: March 2011

ABSTRACTExcimer laser ablation with an in situ heat treatment was used to prepare high quality superconducting YBa2Cu3O7−x thin films on (100)-SrTiO3 and (100)-LaAlO3 substrates. A pulsed excimer laser (XeCl; 308 nm) was used to ablate a rotating, bulk YBa2Cu3O7−x target at a laser energy density of 2–3 J/cm2. Based on four-probe dc resistance measurements, the films exhibited superconducting transition temperatures (Tc, midpoint) of 88 and 87K with 2K (90–10%) transition widths for SrTiO3 and LaAlO3, respectively. Transport critical current densities (Jc) measured at 77K were 2 × 106 and 1 × 106 A/cm2 in zero field for SrTiO3 and LaAlO3, respectively. X-ray diffraction (XRD) analysis showed the films to be highly oriented, with the c-axis perpendicular to the substrate surface.
Effects of Substrate Bias Voltages on Preparation of YBa2Cu3O7-δ Thin Films by Laser Ablation
Authors: Ohata K. , Izumi H. , Hase T. , Suzuki K. , Morishita T. , Tanaka S. 
Published: March 2011

ABSTRACTSuperconducting films of YBa2Cu3O7-δ have been fabricated by pulsed laser deposition technique applying bias voltage to a substrate up to +/-500 V. It has been found that substrate bias voltages are effective for preparing the fidms with high Tc and high crystalline quality at lower substrate temperatures. Positive bias is more effective than negative one. Time resolved observation has been carried out in order to investigate the influence of biasing on the plume and revealed three kinds of light emission. The first is an ordinary plume with a velocity of 6×105 cm/s, which is independent of biasing. It suggests that most of the luminous particles in the plume are electrically neutral. The second is oxygen plasma with a short life time, which is triggered by laser pulse under the positive bias and triggered by arrival of the plume in 8 ps after the laser pulse under the negative bias. The third is an additional plume with a velocity of 3×105 cm/s. The oxygen plasma and additional plume have improved superconducting properties of films deposited with biasing to the substrate.
In Situ Growth of PbZrxTi1-xO3 Thin Films by Pulsed Laser Deposition
Authors: Chrisey D. B. , Horwitz J. S. , Grabowski K. S. 
Published: March 2011

ABSTRACTWe have investigated the composition and structure of thin films of PbZrxTi1-xO3 (x-0.54) produced in situ by pulsed excimer laser deposition from a stoichiometric pressed oxide target. Thin films were deposited onto (100) MgO and SrTiO3 substrates as a function of substrate temperature between room temperature and 750 °C, and oxygen background pressures between vacuum and 300 mtorr. The deposited films were very smooth with particulates covering less than 0.5% of the surface. Elastic backscattering spectroscopy was used to determine the relative atomic fractions. In the deposited films, the Pb stoichiometry was found to be very sensitive to both the substrate temperature and the O2 background pressure. Above ∼600 °C, the Pb content dropped rapidly with increasing substrate temperature for a 50 mtorr 02 background. At 550 °C the Pb content was near-stoichiometric for O2 background pressures between 200 and 300 mtorr but dropped monotonically to ∼20% of the expected value for depositions in a vacuum (i.e., no O2 background). Over this entire range of pressures and temperatures the Ti/Zr stoichiometry ratio was relatively uneffected. The structure and orientation of the deposited films, as determined by x-ray diffraction, followed the Pb deficiency via the production of other phases and orientations. Crystallation of the deposited film was observed at temperatures as low as 400 °C for 200 mtorr O2 background. At 550 °C and 200 –300 mtorr, (100) oriented PbZrxTi1-xO3 was observed on SrTiO3 substrates.
Structural Implications for Optimizing A-Sige:H Alloys
Authors: Schubert M.B. , Eberhardt K. , Bauer G.H. 
Published: March 2011

ABSTRACTDetailed structural investigations have been performed on a-Si1−xGex:H in 0 ≤ × ≤ l namely Raman, X-ray Photoelectron, and Photothermal Deflection Spectroscopies, which reveal the silicon sub-matrix to be considerably more rigid than the germanium one. In Si-Ge dominated networks distinct deviations from an overall random distribution of Si and Ge atoms can be deduced from a semi-quantitative analysis of the Raman data.
Hydrogen Bonding in a-Si:H Prepared by Remote Hydrogen Plasma Deposition
Authors: Ready S. E. , Boyce J. B. , Johnson N. M. , Walker J. , Stevens K. S. 
Published: March 2011

ABSTRACTNuclear magnetic resonance (NMR) has provided essential information on the local atomic bonding and microstructure of hydrogen in hydrogenated amorphous silicon (a-Si:H). Here we describe results from NMR and Raman spectroscopy on the hydrogen distribution and bonding in a-Si:H prepared by remote hydrogen plasma (RHP) deposition and contrast the results with those from a-Si:H prepared by conventional glow discharge (GD) deposition. The films prepared by the two techniques have similar H bonding except for the presence in the RHP sample of about 1 atomic % molecular hydrogen, a factor of ten higher than in GD material. For RHP samples prepared from a deuterium plasma rather than a hydrogen plasma, substantial differences in the hydrogen NMR spectra, hydrogen spin lattice relaxation time and Raman spectra are observed. The hydrogen which necessarily originates from the silane has a dramatically altered spectra.
Hydrogen Incorporation in A-Si:H: Temperature and Doping Type Dependence
Authors: Pruppers M.J.M. , Maessen K.M.H. , Habraken F.H.P.M. , Bezemer J. , Van Der Weg W.F. 
Published: March 2011

ABSTRACTPhosphorus, boron and compensation doped hydrogenated amorphous silicon films were deposited in a glow discharge at different substrate temperatures in the range 50–330°C. Gas phase doping levels were 1%. At the lower temperatures the hydrogen concentration in the B doped and compensated doped films is larger than in the P and undoped films. For higher deposition temperatures the H concentration of the B doped films appeared to be smaller than in the other materials. The difference in hydrogen content of the doped and undoped material, deposited at various temperatures, is considered as a function of the measured activation energy for conduction in these films. This difference varies in much the same way with the activation energy as the hydrogen content in films deposited at one substrate temperature, but with varying gas phase dopant levels. This represents strong evidence that, apart from the deposition temperature, the hydrogen concentration in glow discharge a-Si:H is determined by the position of the Fermi level.
Deep Levels and Hydrogen Evolution in Hydrogenated Amorphous Silicon
Authors: Zafar Sufi , Schiff E. A. 
Published: March 2011

ABSTRACTTwo hydrogen-mediated models are applied to predicting the density of deep levels in hydrogenated amorphous silicon (a-Si:H) under variations in the material’s temperature and total hydrogen content. Both models depart from the assumption that hydrogen is bonded at two classes of sites, dangling bonds and weak bonds. The predictions of the two models for the temperature-dependence of the deep-level density are similar. The models differ in their treatment of the origins of the weak bonds; a model associating the weak bonds with the clustered phase of bonded hydrogen observed by nuclear magnetic resonance also appears to be in agreement with hydrogen evolution experiments.
Study of Bandgap Profiling Control on Photovoltaic Performance in the Three Stacked Amorphous Solar Cells
Authors: Nakata Y. , Sannomiya H. , Moriuchi S. , Yokota A. , Inoue Y. , Itoh M , Itoh H 
Published: March 2011

ABSTRACTA series of systematic experiments has been made on a bandgap profiling control using a-SiGe and a-SiC cells to clarify the cause for the improvement of the photovoltaic performance by the bandgap profiling in the photovoltaic active layer. It has been shown from the analysis that the most important contribution to the cell performance is an optimization of the ambipolar carrier collection by the bandgap profiling. On the basis of the results, an efficiency of 10.1% was obtained at the promising a-SiC/a-Si/ a-SiGe multi-bandgap stacked cell by the bandgap profiling.
Hopping of Electrons in Hybrid Band Tails of a-Si1-xGex:H
Authors: Nebel C. E. , Weller H. C. , Bauer G.H. 
Published: March 2011

ABSTRACTThe thermalization of electrons in the medium temperature range (120K ≤ T ≤ 200K) is investigated by time-of-flight experiments on a-SiGe:H mim structures. The evaluation of the pre-transit current decay reveals a dual slope characteristic which reflects an initial hopping down (I ∼ t−1) followed by a thermally activated (I ∼ t−p 0 < p < 1) process. The transition time from hopping down to multiple trapping sensitively depends on temperature and alloy composition. The experimentally deduced features can be explained by the increased tail state density at the conduction band mobility edge of a-SiGe:H samples compared to a-Si:H.
Band Tails and Thermal Disorder in Doped and Undoped Hydrogenated Amorphous Silicon and Silicon-Germanium Alloys
Authors: Aljishi Samer , David Cohen J. , Jin Shu , Ley Lothar 
Published: March 2011

ABSTRACTThe energy distribution and temperature dependence of the conduction and valence band tail density of states in a-Si:H and a-Si,Ge:H alloys is determined via total yield photoelectron spectroscopy. All films are observed to possess purely exponential conduction and valence band tail densities of states; however, the characteristic energy of the conduction band tail increases much more rapidly with temperature in the range of 300K to 550K than that of the valence band tail. This indicates that over that temperature range the conduction band tail is considerably more susceptible to thermal disorder than to structural disorder whereas the reverse holds for the valence band tail.
Cathodoluminescence of Diamond-Like and Hydrogenated Amorphous Silicon Carbide Materials
Authors: Alvarez F. , Koropecki R.R. , Fajardo F. , Fragnito H.L. , Santos P.V. 
Published: March 2011

ABSTRACTThe room temperature cathodoluminescence (CL) of diamond-1ike materials produced by glow discharge is reported. The CL spectra of these samples (4 eV optical gap) display two bands located at 2.3 eV and 2.8 eV which are frequently found in natural and synthetic diamond. X-ray diffraction spectra (before electron bombardment) are identical to those obtained in natural powder diamond, confirming the existence of crystalline particles. The room temperature CL of phosphorous doped samples is also reported.Structural changes in amorphous silicon carbide samples (3.0 eV optical gap) associated with electron bombardnent are presented and elucidated by IR studies.
Analysis of the Amorphous Silicon Carbide/Crystalline Silicon Interface
Authors: Rahman M. M. , Harjono T. , Lui K. H. , Pagaduan F. E. , Inokawa H. , Yang C. Y. , Sugiarto Dian 
Published: March 2011

ABSTRACTThe performance and reliability of silicon-based hetero-structure devices depend critically on their interfacial characteristics. Here we present high-resolution TEM (HRTEM) results for the a-SiC:H/c-Si (100) interface, substrate doping, and interface electrical characteristics derived from an Al/undoped a-SiC:H/p-Si metal-insulator-semiconductor (MIS) structure. The HRTEM study reveals an interface with a maximum asperity of three atomic planes. The substrate dopant profile for depths less than an extrinsic Debye length from the interface is computed from an iterative fit to the C-V data. A density of interface traps (Dit) of 1011 eV−1cm−2 at midgap is obtained.
Molecular Dynamics Simulations of the Structural, Vibrational and Electronic Properties of Amorphous Silicon
Authors: Biswas R. , Kwon I. , Soukoulis C. M. 
Published: March 2011

ABSTRACTAmorphous silicon models have been computer-generated by melt-quenching and film deposition molecular dynamics simulations, employing classical interatomic Si-potentials. The structural, vibrational and electronic properties of these models is described. Dangling-bond gap states are well localized whereas, floating bonds gap states are considerably less localized with wavefunction amplitudes on the neighbors of the five-coordinated atom. In contrast to melt-quenched models, the a-Si films displayed voids, a 15–28% lower density than c-Si, and no five- coordinated atoms. A-Si:H models with 5 and 22% hydrogen, and both monohydride and dihydride species, have also been developed.
Prospects of a-Sige:H Alloys for Solar Cell Application
Authors: Fortmann C.M. 
Published: March 2011

ABSTRACTThe transport properties of intrinsic a-SiGe films are found to be limited by poor electron mobility. The relationship between electronic transport and composition (Si, Ge and H content) is established. The electron mobility decreases with increasing hydrogen content for a given Ge content. The relation between growth conditions and film composition is developed. Growth conditions that reduce the extent of gas phase polymerization as well as the flux of hydrogen radical to the growth surface yield the best electronic transport. The best a-SiGe:H alloys of 1.3 eV band gap are used to study the effects of band gap grading on solar cell performance. Solar cells analysis is used to determine both hole and electron transport. Cell designs that minimize performance loss due to poor electron mobility are considered.
A Comprehensive Defect Model for Amorphous Silicon
Authors: Hata N. , Larson E. , Liu J. Z. , Okada Y. , Park H. R. , Wagner S. 
Published: March 2011

ABSTRACTBased upon the thermal-equilibration theory and the annealing of defects introduced at the growing surface of amorphous silicon, the distribution of defect-states in energy and in space is calculated for a comprehensive set of deposition and post-deposition treatment parameters. We include the growth temperature, growth rate, illumination time, illumination intensity, annealing temperature, and annealing time. We compare the theoretical results with experimental data for the dark-conductivity-activation energy and for the fill factor of a solar cell. Agreement between the modelled and the experimental results reconfirms the validity of the assumptions made, and encourages further application of the model to analyses of a wide variety of amorphous silicon devices.
Observation of Quantized Ballistic Transport in Amorphous Silicon Memory Structures
Authors: Hajto J. , Rose M.J. , LeComber P.G. , Owen A.E. , Snell A.J. 
Published: March 2011

ABSTRACTWe present experimental results showing that the ON state of amorphous silicon memory structures exhibits ballistic electron transport associated with a quantised resistance, h/2ie2, where i is the number of occupied one dimensional conducting channels (sub-bands) and the spin degeneracy is two (in the case when no magnetic field is applied). Conduction in the memory ON state is restricted to a narrow conducting channel through which the electrons can travel ballistically i.e. no collisions occur. As the applied voltage is increased, the width of the conducting channel is broadened. This results in additional conducting channels (sub-bands) passing through the Fermi energy and consequently the resistance drops by quantised values. In the presence of a magnetic field additional steps occur corresponding to the split levels at values of h/2(i + ½)e2. A particular feature of this quantised resistance is that the effect can be observed at relatively high temperatures effect can be observed at relatively high temperatures (from 4.2 K up to ∼190K).
A-Si:H Thin Film Transistors and Logic Circuits Fabricated in an Integrated Multichamber System
Authors: Kim S. S. , Wang C. , Parsons G. N. , Lucovsky G. 
Published: March 2011

ABSTRACTHydrogenated amorphous silicon (a-Si:H) thin-film-transistors (TFT’s) and logic circuits have been fabricated using a simple 3-mask process. Inverted staggered TFT structures were prepared in a multichamber UHV-compatible system that provides: 1) sequential deposition of dielectrics, and intrinsic and doped a-Si:H by remote plasma-enhanced chemical-vapor deposition (Remote PECVD) in a single deposition chamber; 2) in-situ surface analysis by Auger Electron Spectroscopy (AES); and 3) dry etching of deposited thin films by Remote plasma-enhanced etching, Remote PEE. A field-effect electron mobility of 0.74 cm2/V-s, and a threshold voltage of 2.5 Volts have been measured at room temperature in the TFTs. The on/off current ratio of the TFT exceeds 106. The a-Si:H TFT logic circuits, 2-transistor inverters and addressable 6-transistor static memory cells, operate at a supply voltage of as low as 8 Volts. The experimental results indicate that high performance a-Si:H thin film devices can be fabricated by sequential Remote plasma processing in a multichamber integrated system.
Photoelectronic Properties of the Pipi... Multilayers and their Implications for the Operation of Solar Cells
Authors: Yang L. , Balberg I. , Skibo S. 
Published: March 2011

ABSTRACTWe have studied the photoelectronic properties of pipi... multilayers made of a-SiC:H p-layers (∼ 100Å) alternating with a-Si:H i-layers (500Å to 4000Å). A large enhancement in d.c. coplanar photoconductivity (more than an order of magnitude) over that of bulk a-Si:H was observed with decreasing i-layer thickness of the multilayer. On the other hand, the ambipolar diffusion length was observed to decrease with decreasing i-layer thickness. These observations can be explained by the effect of charge separation due to the strong built-in electric field in the i-layer. The insertion of an ultrathin SiC layer at the p/i interface is shown to appreciably reduce the built-in field which may be directly related to the observed decrease in fill factor when such a buffer layer is used in a solar cell.