bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling of Gas-Phase and Surface Kinetics in Movpe of GaAs and AlxGal-xAs
Authors: Mountziaris T.J. , Ingle N.K. , Kalyanasundaram S.
Published: March 2011

We present detailed chemical reaction mechanisms that describe the deposition of GaAs films from tertiary-butyl-arsine (TBA) and trimethyl-gallium (TMG) as well as the deposition of AlxGa1-xAs (0≤x≤1) films from trimethyl-aluminum (TMAl), TMG and arsine during metalorganic vapor phase epitaxy (MOVPE). The kinetic models include both gas-phase and surface reactions, whose rates are used to predict production or consumption of the participating species as well as the growth rate of the film. Two-dimensional simulations of flow, heat and mass transfer in horizontal MOVPE reactors have been coupled with the kinetic models to provide a realistic picture of the process. The predicted growth rates at different operating conditions as well as the predicted incorporation ratio, x, of Al in the AlxGal-xAs films are in good agreement with experimental observations.
Bromine-Methanol Etching of Cadmium Telluride in a Rotating Disk Reactor
Authors: Gentzler Michael B. , Ko Edmond I. , Sides Paul J. , Bowman Paul T.
Published: March 2011

The kinetics of the bromine-methanol etching of CdTe were studied in a rotating disk reactor as a function of temperature, bromine concentration, substrate orientation, and rotation rate. The results indicated that the etching process is mass transfer controlled from -20°C to 40°C and to a maximum rotation rate of 1200 RPM. A one-dimensional transport model was used to obtain effective diffusion coefficients for bromine in methanol. The diffusion coefficient of the etchant in methanol is given by 3.7×10-8 (T/η) cm2/s over the range of 2.5°C to 23°C.
Properties of Doped a-Si:H Films Deposited by Ecr Plasma CVD
Authors: Murai H. , Hayama M. , Kobayashi K. , Yamazaki T.
Published: March 2011

Phosphorous doped hydrogenated amorphous silicon films were deposited by microwave electron cyclotron resonance (ECR) plasma CVD at a substrate temperature of 100°C. Electrical, optical and hydrogen-incorporation properties of the films have been investigated. By optimizing the deposition condition, the dark conductivity of 3×10−4S/cm is realized without subsequent annealing. Relations between the film properties and ECR plasma properties have been studied by means of optical emission spectroscopy (OES) and quadrupole mass spectroscopy (QMS).
Hydrogen--Halogen Exchange Reactions on Silicon (100)
Authors: Thomas R.E. , Rudder R.A. , Markunas R.J.
Published: March 2011

Using thermal mass desorption and LEED we have studied interactions of H, C12, and F2 with a silicon (100) surface, and exchange reactions of the gases with adsorbates on the silicon (100) surface. Thermal desorption spectra were measured for surfaces dosed with H, C12, and F2 singly and then for surfaces dosed first with a halogen and then atomic hydrogen. Finally, the reverse sequence was studied, with atomic hydrogen dosing and then the halogen exposure. Results indicate that the molecular halogens C12 and F2 are not effective at removing H from a Si (100) surface. However, for the reverse reaction, atomic hydrogen appears quite effective at removing the halogens.
Process and Surface Characterization of Hydrogen Plasma Cleaning of Si(100)
Authors: Schneider T. P. , Cho J. , Weide J. Vander , Wells S.E. , Lucovsky G. , Nemanich R.J. , Mantini M.J. , Rudder R.A. , Markunas R.J.
Published: March 2011

This study details low pressure and low temperature cleaning of Si(100) surfaces. The properties of Si surfaces exposed to variations in plasma generated H are described. The diagnostic techniques used to study the processing conditions are residual gas analysis (RGA) and emission spectroscopy. The surface is characterized by low energy electron diffraction (LEED) and angle resolved uv-photoemission spectroscopy (ARUPS). During the cleaning, Si complexes are formed which indicates the removal of species from the Si(100) surface. Plasma cleaning at 300°C results in a Si(100) surface with 2×1 surface diffraction patterns as detected by LEED. Measurements by ARUPS with He I radiation show the absence of Si surface states on the Hpassivated surface. The ARUPS measurements also indicate that the H begins to desorb from the Si(100) H-passivated surface at ∼500°C.
Surface Chemistry of CVD Reactions Studied by Molecular Beam/Surface Scattering
Authors: Yu Ming L. , Memmert Ulrich , Buchan Nicholas I. , Kuech Thomas F.
Published: March 2011

A molecular beam/surface scattering experiment in an ultrahigh vacuum is conceptually a simulation of a CVD reactor without the interference from gas phase and wall reactions. The surface chemistry can be studied in real-time during the deposition reaction at the desired temperature. In our experiment, we used pulsed molecular beams of the reactants and a mass spectrometer to monitor In real-time the reaction products evolving from the substrate surface. With this arrangement, the reaction probability of the molecules can readily be determined by measuring the unreacted fraction of the molecular beam. The reaction pathways can be deduced from the Identification of the reaction products, while their time-evolutions give the kinetic parameters. We shall illustrate this technique by our study on the reactions of trimethylgallium and triethylgallium on GaAs as related to the metalorganic CVD and atomic layer epitaxy of GaAs.
Decomposition Of Trimethylgallium Multilayers On Si(100)
Authors: Lin R. , Gow T. R. , Masel R. I.
Published: March 2011

In previous work, we found that the decomposition of trimethylgallium (TMGa) on a clean silicon substrate was dominated by interactions with the silicon substrate. In this paper, TPD, XPS, and molecular beam techniques were used to explore how the surface chemistry changes as gallium, trimethylgallium, and hydrocarbon overlayers are deposited onto the substrate. At low coverages, gallium and carbon have little effect on the TPD spectrum. However, at coverages in the order of a monolayer, the chemistry changes substantially. While on clean silicon the metal containing species are all strongly bound, on covered surfaces there are TPD peaks at 580 K and 700 K corresponding to di- and mono- methyl gallium. Dimethylgallium desorption is also observed in the beam system. There is also evidence for desorption of methyl radicals from the covered surfaces, while only methane desorption is seen with clean silicon. These results show that changes in the substrate composition can have a substantial, influence on TMGa decomposition. Hence some care must be taken when extrapolating data from UHV studies to actual growth conditions.
Organometallic Chemical Vapor Deposition of Copper from a New Organometallic Precursor
Authors: Fine Stephen M. , Dyer Paul N. , Norman John A. T. , Muratore Beth A. , Iampietro Robert L.
Published: March 2011

Thin copper films have been grown on a variety of substrates using Cu(nona-F)2, (bis[4-(2,2,2-trifluoroethyl)imino-1,1,1,5,5,5-hexafluoro-2-pentanonato] copper(II)), a new volatile organometallic copper precursor, and the results are compared with those obtained using copper(II) betadiketonates. Copper films were grown in a cold wall reactor at reduced pressure at temperatures between 270°C and 350°C. For Cu(nona-F)2, films which are pure as determined by Auger electron spectroscopy and have a resistivity of 2.1 micro-ohm cm were deposited at temperatures above 270°C, 40°C lower than was possible using Cu(hfac)2. At low deposition temperatures, Cu(nona-F)2 shows some selectivity towards silicon oxide surfaces in preference to metals. The effects of CVD process parameters on the deposition rate and microstructure of the films were studied with a designed experiment and were statistically modeled. Deposition rates up to 70 nm/min were measured. The standard enthalpy of vaporization of Cu(nona-F)2 was found to be 9.6 kcal/mol.
Synthesis of New Copper(I) β-Diketonate Compounds for CVD of Copper
Authors: Shin H.K. , Chi K.-M. , Hampden-Smith M.J. , Kodas T.T. , Farr J.D. , Paffeif M.F.
Published: March 2011

A series of (0β-diketonate) copper(l) trimethylphosphine compounds has been prepared. These species exist either as liquids or low-melting solids at room temperature. The utility of these compounds as precursors for Chemical Vapor Deposition (CVD) of copper has been examined under a variety of conditions. High purity films with low resistivities have been deposited under a variety of conditions. Selective copper deposition was observed as a function of the substrate, precursor and substrate temperature. Evidence consistent with thermallyinduced disproportionation of the title compounds to form copper metal and copper(II) (β-diketonate)2 during deposition was observed.
Self-Induced Repair: a New Concept in Chemical Microprocessing
Authors: Chen C. Julian
Published: March 2011

Self-induced repair (SIR) is a new concept in chemical microfabrication of microelectronic interconnections. It is based on local chemical processes (deposition or etching) induced by certain local electrical phenomena at defect sites (Joule heat, concentration of electrical field or current density, etc.). It has been demonstrated on four types of defects: near-opens, small opens, near-shorts, and thin shorts. The example of the SIR of near opens, or constrictions in interconnections, is discussed in detail.
Synchrotron Photoemission Studies of the Structure of Thermally Grown Si3N4 ON Si(100)
Authors: Peden C. H. F. , Rogers J. W. , Kidd K. B. , Tsang K. L. , Shinn N. D.
Published: March 2011

Synchrotron photoemission measurements of the Si(2p) and N(ls) levels have been made on Si3N4 thin films grown in-situ by high temperature reaction of Si(100) with NH3. The tunability of the excitation photons allowed the mean-free-path of the emitted photoelectrons to be varied, thereby providing the capability to determine not only the types of chemical species present, but their location within the film as well. The structure of these films consists of an outer monolayer (ML) of Si atoms on top of stoichiometric Si3N4. In addition, there are a smaller number (1/2 ML) of Si atoms with intermediate oxidation states at the Si3N4/Si interface.
In-Situ Ftir and Mass Spectrometric Studies of Gallium Arsenide Metalorganic Chemical Vapor Deposition: Trimethyl Gallium and Tertiary-Butyl Arsine on GaAs(100)
Authors: Annapragada Ananth V. , Jensen Klavs F.
Published: March 2011

Low pressure (∼10−5 Torr) studies of the adsorption and decomposition of tertiarybutyl arsine (t-BAs) on three different GaAs(100) surfaces (Ga-rich, H-atom treated and high temperature t-BAs treated) are presented. Mass spectrometric studies indicate that the primary gas-phase products of t-BAs decomposition on GaAs(100) are the tertiary-butyl radical and incomplete arsenic hydrides (predominantly AsH2). Infrared spectroscopic studies show that on H-atom treated and high-temperature t-BAs treated surfaces, t-BAs decomposes leaving behind very small quantities of alkyl groups. On Ga-rich surfaces however, significant amounts of alkyl products are observed. The surface species resulting from the adsorption of trimethyl gallium (TMG) are shown to be different at room temperature and high temperature.
Characterization of Spin on Glass Using Thermo Analytical Techniques and Ftir Spectroscopy
Authors: Speciale M. , Rosa C. La , Grasso D. , Porto A. , Lanza P. , Magro C.
Published: March 2011

The curing of a commercial ethoxymethyl-phosphosiloxane at different temperatures and under various gas ambients was characterised using NMR, thermoanalytical techniques, and FTIR spectroscopy. DSC (Differential Scanning Calorimetry) and DTG (Differential Thermo Gravimetry) were employed to characterize the reactions that occur during thermal treatments in O2 or N2 atmospheres. FTIR spectroscopy and CP (Cross Polarization) 133C - NMR were used to detect the presence of the hydroxyl and organic groups in the cured samples. The experimental results identified three different temperatures (400,580,700°C) that define important stages of the curing reaction. In particular, for annealing at temperatuires up to 580°C in 02, DSC, DTG and FTIR spectra showed the elimination of the organic groups. However, when the annealing was carried out in N2 up to 700°C, these groups are retained.
Synthesis and Characterization of PbTiO3 Thin Films Grown by Chemical Beam Deposition
Authors: Hsieh K.Y. , Rou S.H. , King L.L.H. , Kingon A.I.
Published: March 2011

A new deposition technique for PbTiO3 films utilizing chemical beams of metalorganic sources in an ultrahigh vacuum chamber is demonstrated. Ozone is introduced to provide a source of active oxygen. The role of active oxygen in controlling the surface chemical reactions is discussed. Fine grained, single phase PbTiO3 films have been deposited on MgO (100) and SiO2/Si substrates at substrate temperatures as low as 350°C. Films were characterized by XRD, SEM, and TEM. The results suggest that the chemical beam deposition technique provides another method for the fabrication and integration of ferroelectric thin films with silicon (or GaAs) devices.
Preceramic Polymers for Aluminum Oxides
Authors: Rees William S. , Hesse Werner
Published: March 2011

The utilization of recently discovered aluminum-oxygen-carbon backbone polymers in the preparation of various phases of A12O3 is presented. The structure of the polymers has been examined by ss 27AI NMR, TGA, MS, SEM, XRD, and EDAX. The solid pyrolysis products of these polymers have been characterized by ss 27AI NMR, XRD, SEM, and EDAX. The volatile products of pyrolysis have been studied by trapping, TGA and MS.
Aes and Xps Studies of Sulfur-Treated ALxGA1−xas Surfaces
Authors: Ohno Hirotaka , Kawanishi Hidenori , Akagi Yoshiro , Koba Masayoshi , Hijikata Toshiki
Published: March 2011

Passivation of AlxGa1−xAs surfaces by ammonium sulfide treatment has been investigated. Enhancement of photoluminescence intensity and dramatic reduction of oxide peaks in spectra acquired by X-ray photoelectron spectroscopy on AlxGa1−x.As surfaces prepared by this treatment lead to the reduction of surface state density. It was found that sulfur atoms were mainly bonded to Al atoms in an Al-enriched specimen of AlxGa1−xAs(x=0.78). The surface compositions of Al-enriched specimen(x=0.43, 0.78) were also found to be As-rich as a result of both sulfur treatment and the preferential etching of metallic atoms by an acidic solution, which prevents the initial oxidation of the surface of A1xGa1−xAs.
Atmospheric Pressure Chemical Vapor Deposition of Gallium Nitride Thin Films
Authors: Gordon Roy G. , Hoffman David M. , Riaz Umar
Published: March 2011

The atmospheric-pressure chemical vapor deposition of gallium nitride films from hexakis(dimethylamido)digallium, Ga2(NMe2)6, and ammonia precursors at 200 °C with growth rates up to 1000 Å/min is described. The films were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry. Rutherford backscattering analysis showed that the N/Ga ratio was 1.12–1.17. The films were crystalline with ≃ 5–15 nm crystallites.
On the Formation of Martensite in In0.77TL0.23.
Authors: Wuttig M. , Zhou X. , Nahm S. , Li J.
Published: March 2011

It has been proposed that martensite is formed by heterogeneous nucleation and growth or evolves from a precursor. In order to examine these theories, high resolution X-ray diffraction experiments have been performed on In0.77Tl0.23. It is known that the transformation of the alloy is close to second order and tweed has been observed which could be a possible precursor structure. Our experimental results do show precursors but of a different nature: satellites around the 220 Bragg peak have been detected up to 15 degrees above the transformation temperature. They develop reversibly at the angular positions of the product phase. The results are not compatible with the “crest-riding-peridon” model but rather show an equilibrium two phase mixture above the transformation temperature in which the second phase is structurally equal to the product phase. We have also investigated the mechanical response of the high temperature phase and found that both shear ‘elastic constants’ soften. This result can be understood in terms of twin boundary or stacking fault motion.
Solid State Amorphization of a Ni-B Alloy by Mechanical Alloying
Authors: Nasu T. , Koch C.C. , Nagaoka K. , Sakurai M. , Suzuki K.
Published: March 2011

The main purpose of this work was to investigate the possibility of solid state amorphization of Ni-B crystal powder. A Ni-B alloy powder was obtained by mechanical alloying of Ni and B powder using a conventional ball milling machine. X-ray diffraction and EXAFS measurements were made for the mechanically alloyed samples as a function of milling time. An amorphization reaction was observed in Ni64B36 at 400 h of milling time. The long range order of the crystalline Ni phase diminished with an increase of solution of B into the Ni matrix. This suggests that the solution of B atoms into the Ni crystalline phase, forced by mechanical alloying, plays an important role in the crystalamorphous transformation.
Solid-State Reactions in Multilayer Ni/Ti Thin Film Composites
Authors: Winters Gillian E. , Unruh K.M. , Swann C.P. , Patt M.E. , White B.E. , Cotts E.J.
Published: March 2011

Multilayer films, consisting of alternating layers of crystalline Ni and Ti, have been prepared by RF sputter deposition over a range of modulation wavelengths corresponding to an overall composition of Ni50Ti50. These films have been characterized by xray diffraction and Rutherford backscattering measurements. The solid-state transformation by interdiffusional mixing of the individual layers has been directly studied by differential scanning calorimetry and correlated with structural measurements. These measurements indicate that the solid-state reaction of Ni and Ti multilayers proceeds through the formation of a metastable solid solution of Ti in Ni followed by the formation of intermetallic equilibrium compounds. No direct calorimetric or structural evidence for the formation of an amorphous Ni-Ti phase has been found in these samples.
Structural Transformations During the Mechanical Alloying of Nickel and Ruthenium Elemental Powders
Authors: Neste A. Van , Kaliaguine S. , Trudeau M. , Schulz R.
Published: March 2011

The structural evolution of a mixture of elemental Ni and Ru powders during high energy ball milling has been studied as a function of milling time using X-ray diffraction and transmission electron microscopy. On the Ni-rich side of the phase diagram (Ni70Ru30) we observe, during the milling, the diffusion of Ru in the Ni and an expansion of the Ni fcc lattice. After about 20 hours of milling, all the Ru has diffused into the Ni and we are left with an oversaturated Ni(Ru) fcc structure with a lattice parameter about 3.6% larger than the one of pure Ni. The Ni does not seem to diffuse into Ru during the process. On the Ru-rich side (Ni43Ru57) we observe initially the same diffusion process taking place but more rapidly. After about 8 hours of milling, the incorporation of Ru in the Ni has driven the fcc Ni lattice to its limit of stability (about 3.9% expansion) and the fcc structure transforms, upon further milling, into a new hcp structure. In the later stage of the process the remaining Ru diffuses into this new phase.
Polymorphic Crystallization of Metal-Metalloid-Glasses above the Glass Transition Temperature
Authors: Köster U. , Schünemann U. , Stephenson G.B. , Brauer S. , Sutton M.
Published: March 2011

Crystallization of metal-metalloid glasses is known to proceed by nucleation and growth processes. Using crystallization statistics in partially crystallized glasses, at temperatures below the glass transition temperature, time-dependent heterogeneous nucleation has been found to occur at a number of quenched-in nucleation sites [1]. Close to the glass transition temperature crystallization proceeds so rapidly that partially crystallized microstructures could not be obtained. Initial results from fully crystallized glasses exhibit evidence for a transient homogeneous nucleation process at higher temperatures [1,2].
A Study of the Diffusion of Phosphorus in Ni/amorphous NiPx and a-NiPx/a-NiPy. Multilayers
Authors: Ross C. A. , Goldman L. M. , Barnard J. A. , Spaepen F.
Published: March 2011

An x-ray technique has been used to measure the diffusion of phosphorus in crystalline Ni/amorphous NiPx and amorphous NiPx/NiPy multilayer thin films produced by electrodeposition. The films have repeat lengths in the range 30–80Å and P contents x, y < 25at.%. A value for the interdiffusivity in amorphous NiPx is derived from measurements on fully amorphous films. The behaviour of partially crystalline films is described in terms of phosphorus diffusion into the nickel grain boundaries.
Coherency Strain Energy in any Crystal System: Applications to in Situ Observations of Cigm in Calcite
Authors: May R.S. , Evans B.
Published: March 2011

In situ observations of CIGM in CaCO3 bicrystals with a SrCO3 solute source were made. The change in boundary orientation and migration rate were compared with solute concentration. The liquid film model for coherency strain Induced migration was generalized to any non-cubic system and applied to CaCO3-SrCO3. The coherent layer was modeled as a thin film on an infinite half-space. The strain energy was found from solution of the Hooke's law expressions transformed to the appropriate coordinate system. For triclinic or monoclinic films the strain tensor was found by an eigenvector decomposition of the transformation matrix that defined the lattice parameter change with composition. High anisotropy of Vegard's law constants for CaCO3-SrCO3 caused (111) to have the lowest coherency strain per unit solute. Surfaces perpendicular to (111) in coherent equilibria were predicted to have half the solute concentration and three times the migration driving force of those perpendicular to (111). However, no correlation between solute concentration and boundary orientation was observed. Ambiguous and contradictory evidence for a relationship between solute concentration, boundary orientation, and migration rate was found. The self-stress state of a grain boundary in a solute diffusion field may be better modelled as hydrostatic rather than plane stress. Hydrostatic compression may interact with the boundary excess volume and cause a PV driving force for migration. Predictions based on coherent equilibrium at a surface have not been tested for that geometry in calcite; they should be tested before they are applied to grain boundaries.
Raman Studies of Pressure and Temperature Induced Phase Transformations in Calcite
Authors: Exarhos Gregory J. , Hess Nancy J.
Published: March 2011

Phase stability in the calcium carbonate system was investigated as a simultaneous function of pressure and temperature up to 40 kbar and several hundred degrees Kelvin using micro-Raman techniques to interrogate samples constrained within a resistively heated diamond anvil cell. Measured spectra allow unequivocal identification of crystalline phases and are used to refine the P, T phase diagram. Calcium carbonate was found to exhibit both reversible and irreversible transformation phenomena among the four known phases which exist under these conditions. Time-dependent Raman intensity variations as the material is perturbed from its equilibrium state allow real-time kinetics measurements to be performed. Evidence suggests that the order of certain observed transformations may be pressure dependent. The utility of Raman spectroscopy to follow transformation phenomena and to estimate fundamental thermophysical properties from the stress dependence of vibrational mode frequencies is demonstrated.
Crystallization Processes of Heterogeneous Systems Followed in Time Resolved X-ray Powder Diffraction
Authors: Christensen Axel NØrlund
Published: March 2011

Time resolved X-ray powder diffraction was used to follow the crystallization processes in the systems MgO-MgCl2-H2O and MgO-H2O. A Stoe X-ray powder diffractometer with a position sensitive detector was used. The crystalline reaction products are [Mg2(OH)3(H2O)2]C1.H2O and Mg(OH)2 dependent upon the MgC12 concentrations in the heterogeneous systems. Mg(OH)2 was the product in a 1.50 M MgCl2 solution and [Mg2(OH)3(H2O)3]Cl.H2O was formed in 3.00 and 5.17 M MgCl2 solutions at 20°C.
Application of Solid Phase Epitaxy for Measuring Dangling Bond Densities and Impurity Ionization in Amorphous Silicon
Authors: Walser R. M. , Jeon Young-Jin
Published: March 2011

According to a recent model [1], the enhancement in the rate of the solid phase epitaxial regrowth (SPER) of silicon produced by implanted impurities is determined by the superposition of reconstruction at sites that capture neutral, and ionized, three-fold coordinated dangling bond states. Considerable support for this model is derived from experiments on ionization-enhanced SPER in silicon. In this paper we discuss how this dangling bond model (DBM) could be used to determine the densities of neutral dangling bonds and ionized impurities in amorphous silicon from these experimental results. Both densities, determined by a self-consistent calculation, are in good agreement with those measured by other types of experiments. This result provides further support for the DBM and indicates that simultaneous SPER and ESR measurements could make it possible to depth profile low concentrations of ionized impurities in amorphous silicon.
Structural Relaxation of Amorphous Silicon Induced by High Temperature Annealing
Authors: Wit L. De , Roorda S. , Sinke W.C. , Saris F.W. , Berntsen A.J.M. , Van Der Weg W.F.
Published: March 2011

Structural relaxation of amorphous Si is studied in the temperature range 500-850 °C using Raman spectroscopy. The minumum value for the Raman peakwidth that can be obtained is inversely proportional to the anneal temperature. The relaxation process is basically the same in a-Si prepared by ion implantation and by vacuum evaporation.
New Insight into the Banded Microstructure of Rapidly Solidified Ag-Cu Alloys : Experiment and Theory
Authors: Yankov E. Y. , Copley S. M. , Todd J. A. , Yankova M. I.
Published: March 2011

A transmission electron microscopy study has revealed that the banded microstructure produced in Cu-61.7 at. pct. Ag after surface laser melting and resolidification is not due to a cellular breakdown of the interface as previously thought, but consists of alternating regions of the extended metastable solid solution, y, and a coupled growth structure containing thin plates of y and the copper-rich phase β'. The spacing of this coupled growth structure is approximately 100 Å, which is less than half the minimum spacing yet observed for coupled growth from the melt in Ag-Cu.

In order to explain the banded microstructure a theoretical model has been developed based on a finite elements solution of the diffusion equation in the melt, the interface response functions for continuous growth derived by Aziz and Kaplan and a recently developed theory for coupled growth that includes far-from-equilibrium regimes by Yankov et al..
The Planar to Cellular Transition and the Long Time Scale Dynamics of Pattern Formation During Thin-Film Directional Solidification
Authors: Lee John T.C. , Brown Robert A.
Published: March 2011

Experimental observations of the melt/crystal interface in the directional solidification of a thin sample of a binary alloy are reported for conditions only slightly beyond those for the onset of morphological instability. Spectral analysis for long times shows dynamics leading to a band of most probable wavelengths with sharply selected peaks at wavelengths significantly below the most dangerous wavelength predicted by linear stability theory. These large-amplitude cells develop first in packets that spread to fill the interface.
Numerical Studies of Precipitate Coarsening Phenomena
Authors: Lavine James P. , Hawkins Gilbert A.
Published: March 2011

A three-dimensional Monte Carlo computer program is used to study the time-dependent coarsening of a precipitate population in a solid. The emphasis is on the influence of the escape rate of solute atoms from a precipitate on the coarsening behavior. Three models for the escape attempt frequency are compared. The time when coarsening is observed and the extent of coarsening depend on the model as does the percentage of solute precipitated in a given time. The qualitative results of the present calculations are compared with earlier findings.
Kinetics of an Order-Disorder Transition in the Presence of Elastic Energies
Authors: Elder K. R. , Morin B. , Grant M. , Desai R. C.
Published: March 2011

An approximate late time solution to the dynamics of phase separation for a nonconserved ordering order parameter (ø) coupled to a stable conserved field (c) is presented. In the Halperin Hohenberg(1) classification scheme this model is known as Model C with a symmetric coupling between nonconserved and conserved fields. The different time dependences of long (i.e., domain size lengths ∼ power law in time) and short wavelength (i.e., interfacial lengths ∼ exponential decay in time) fluctuations imply a simple relationship between the two fields. In essence ø controls the growth of the long wavelength fluctuations, and c modifies the interfacial profile. Asymptotically the dynamic structure factor (Sø(k,t)≡<Ø(k,t)Ø*(k,t)>) for the nonconserved field is shown to scale in the form Sø(k,t) = tdnfø(ktn), with n = 1/2. Similarly the structure factor for the conserved field (Sc(k,t)) is shown to obey the scaling law Sc(k,t) = tdn−1fc(ktn), with n = 1/2. Explicit expressions for the scaling functions fc(z) and fø(z) are presented for arbitrary dimension. These predictions can be tested through scattering experiments.
Specific Heat and Melting Temperature of Relaxed and Unrelaxed Si Amorphous States
Authors: Grimaldi M.G. , Baeri P. , Malvezzi M.A.
Published: March 2011

Direct picosecond laser measurements of the critical fluence for melting have been performed for the first time, giving unambiguously consistent differences in the energy required for surface melting of relaxed and unrelaxed amorphous silicon. The different optical coupling cannot account for this variation which can only be explained in term of different melting temperatures. Heating of unrelaxed amorphous silicon samples at temperatures close to the melting point may result in relaxation of the material even when the treatment occurs in the nanosecond time scale. However nanosecond UV irradiation of relaxed and unrelaxed amorphous silicon samples have provided informations on the specific heat of the two amorphous states. The melting temperature of unrelaxed amorphous silicon has been derived independently via both picosecond data and via free energy calculations.
Formation of Micro-Precipitates at the Melt-Solid Interface in Semiconductors
Authors: MÖller H.J.
Published: March 2011

A theory is developed for the formation of precipitates in very dilute hypereutectic two phase systems during solidification. It is based on a mechanism for the growth of microdefects at the melt -interface. The model presents a solution of the diffusion problem for the solute atoms in the melt and provides an analysis of the factors which determine the particle size and their mean distance. The possibility of microdefect nucleation in front of the melt -interface, which can lead to very large precipitates, is discussed. The model is suitable to describe the formation of microdefects in semiconductors where impurity concentrations are generally low but may exceed the solubility limit in the melt. The results of the theory are compared with experimental investigations of the silicon carbide formation in carbon rich silicon crystals grown from the melt.
The Effect of Hydrogen on the Kinetics of Solid Phase Epitaxy in Amorphous Silicon
Authors: Roth J. A. , Olson G. L. , Jacobson D. C. , Poate J. M. , Kirschbaum C.
Published: March 2011

This paper discusses the intrusion of H into a-Si layers during solid phase epitaxy and the effect of this H on the growth kinetics. We show that during annealing in the presence of water vapor, H is continuously generated at the oxidizing a-Si surface and diffuses into the amorphous layer, where it causes a reduction in the epitaxial growth rate. The measured variation of growth rate with the depth of the amorphous/crystal interface is correlated with the concentration of H at the interface. The diffusion coefficient for H in a-Si is determined by comparing measured depth profiles with calculated values. Hydrogen intrusion is observed even in layers annealed in vacuum and in inert gas ambients. Thin (<;5000 Åthick) a-Si layers are especially susceptible to this effect, but we show that in spite of the presence of H the activation energy for SPE derived earlier from thin-layer data is in good agreement with the intrinsic value obtained from thick, hydrogen-free layers.
Numerical Simulation of Scanning Speed and Supercooling Effects During Zone-Melting-Recrystallization of Soi Wafers
Authors: Yoon Sharon M. , Miaoulis Loannis N.
Published: March 2011

The effects of scanning speed and supercooling were studied during zone-meltingrecrystallization (ZMR) of silicon-on-insulator (SOI) wafers. Using finite difference methods, a numerical simulation of the ZMR process was developed which captures all of the optical and thermal property changes during phase transformation. The effects of supercooling and scanning speed on the temperature profiles, the total width of the melt-zone and the width of ‘slush’ region were investigated. The melt-zone width increases for increasiongf thdee gfrreeeezsi nogf supercooling and decreases for increasing strip heater velocities. The combined effects on the melt-zone width were shown for various scanning speeds and degrees of supercooling. Supercooling also had a significant effect on the size of the freezing ‘slush’ region which was shown to decrease for increasing degrees of supercooling.
Effect of Low Level Photoionization in Solid Phase Epitaxial Regrowth of Amorphous Silicon
Authors: Jeon Young-Jin , Becker M. F. , Walser R. M.
Published: March 2011

In this work we searched for evidence of low level photoionization effects in the solid phase epitaxial regrowth (SPER) of intrinsic amorphous silicon on (100) silicon during isothermal furnace annealing. We used in situ cw laser interferometry to measure the changes in the rate at 500 °C as the laser power was varied from 20 mW-80 mW. Calculation showed that laser heating increased the sample temperature by a maximum of 6 °C at 80 mW. The measured change of the SPER rate with laser power in this range was always smaller than the change computed from an Arrhenius calculation using the measured activation energy, and the calculated value of the laser-produced increment in the sample temperature. The result indicates that there are negligible low level photoionization effects in silicon SPER.
Evolution of the Microstructure During Laser-Induced Amorphization of Si
Authors: Yater J.A. , Thompson Michael O.
Published: March 2011

The interface growth dynamics of Si leading to laser-induced amorphization have been studied as a function of incident energy density and crystallographic orientation using tran-smission electron microscopy (TEM). Using lithographic and dry etching techniques, cross sectional TEM specimens across the entire melt region were produced. These samples allowed observation of the evolution of the amorphous thickness and crystal defect structure from shallow anmorphous Si (a-Si) formation near the melt threshold energy density to crystallized material (c-Si) at higher energy densities. For surfaces near [111] orientations, marked differences in the solidification behavior were observed as compared to [001] or [110] orientations. The transition to a-Si growth at the moving liquid/crystal interface is discussed in terms of interface response function kinetics and crystallization models. A growth instability model, arising from the shape of the interface response function, is proposed to explain the observed nmicrostructure.
Electronic Structures of Icosahedral C60 and C60X (X=K, O and Cl) Clusters
Authors: Saito Susumu
Published: March 2011

I report the electronic structures of “buckminsterfullerene”, C60 cluster with truncated-icosahedron geometry, and C60X where X is a foreign atom trapped at the center of the C60 cage (X=K, O, and Cl). The local-density approximation with Xα exchange-correlation potential is used. The obtained electronic structure of C60 has a rather large energy gap between the completely occupied highest-occupied state and the lowest-unoccupied state, in accord with previous calculations. In the case of C60K, a valence electron of an alkali-metal atom is found to transfer to the outer C60 surface. On the other hand, in C60O and C60Cl, 2p state of O and 3p state of Cl appear inside the energy gap of the pure C60 cluster. Such variety of results indicates great possibilities of C60X as constructing units of new materials.
Quantum-Size Variation in Optical Transition Energies of CdTe Crystals in Glass
Authors: Potter B. G. , Simmons JH
Published: March 2011

We examine the effects of finite crystallite size on the energies of optical transitions originating from states located at two different critical points of the semiconductor Brillouin zone. Using a versatile, dual source, R.F. sputtering technique, CdTe-glass composite thin films have been produced possessing average crystal sizes ranging from 24 to 125 Å in films containing up to 30 vol% semiconductor. Analysis of quantum-size induced transition energy shifts, monitored by optical absorption, indicates the persistence of significant Coulomb interactions between carriers at the gamma point of CdTe in crystallite sizes 0.3 times the size of the bulk exciton. L-point transition energy shifts support the existence of 2-D bound electron-hole pair states whose center-of-mass motion is confined in the semiconductor crystals.
Surface Melting and Surface Diffusion on Clusters
Authors: Cheng Hai-Ping , Stephen Berry R.
Published: March 2011

Surface melting on clusters is investigated by a combination of analytic modeling and computer simulation. Homogeneous, argon-like clusters bound by Lennard-Jones forces and Cu-like clusters bound by ‘embedded atom’ potentials are the systems considered. Molecular dynamics (MD) calculations have been carried out for clusters with 40–147 atoms. Well below the bulk melting temperature, the surfaces become very soft, exhibiting well-defined diffusion constants even while the cores remain nearly rigid and solid-like. The simulations, particularly animations, of atomic motion reveal that the surface melting is associated not with amorphous, random surface structures in constant, irregular motion, but rather in large-amplitude, organized, collective motion of most of the surface atoms accompanied by a few “floaters” and holes. At any time, a few of the surface atoms move out of the surface layer, leaving vacancies; these promoted particles wander diffusively, the holes also but less so, and occasionally exchange with atoms in the surface layer. This result is the basis for an analytic, statistical model. The caloric curves, particularly the latent heats, show that surface melting of clusters is a “phase change” different from the bulk melting of clusters.
The Formation and Growth of Nanoscale Particles by Rapid Condensation of A Sputtered Vapor
Authors: Chow G. M.
Published: March 2011

Some factors influencing the formation, growth and convective transport of the particles by the rapid condensation of a vapor produced by high pressure sputtering in an inert gas are discussed.
Symmetry and High Magnetic Moment Clusters
Authors: Dunlap B. I.
Published: March 2011

High-spin 13-atom transition metal cluster are studied using the linear-combination-of-Gaussian-type-orbital, local-density-functional, all-electron method. The high degeneracy associated with high symmetry is exploited to find geometry optimized clusters that have the highest contribution by spin to the magnetic moment subject to a constraint. The constraint is that the cluster not distort by the Jahn-Teller mechanism and thus have the lowest possible orbital-angular-momentum component of the magnetic moment. Pure 13-atom nickel and iron clusters are approximately icosahedral because of increased symmetry-required orbital degeneracy for electrons of different spins in this largest point group. The central atom of the icosahedral iron cluster has been varied to optimize the spin of the cluster keeping the orbital contribution to the magnetic moment quenched. Varying the central atom under this constraint can alter the magnetic moment by 20%, relative to the pure iron cluster.
Molecular-Dynamics Simulations of Collisions of Buckminsterfullerene with Diamond Surfaces
Authors: Mowrey R.C. , Brenner D.W. , Dunlap B.I. , Mintmire J.W. , White C.T.
Published: March 2011

We have performed molecular dynamics simulations using a recently developed empirical many-body potential energy function to study the collision of the C60 isomer buckmin-sterfullerene with a hydrogen-terminated diamond surface. The simulations indicate that the cluster can react with the surface and has a larger probability of gaining atoms from the surface than of losing atoms to the surface. We have investigated the dependence of the reaction probability on the initial center-of-mass translational velocity of the cluster. The structures and energy distributions of the product clusters have been determined. Both inelastically and reactively scattered clusters have large amounts of internal energy which suggests that gas-phase dissociation is likely.
Production of Ultra-Thin Metal Films Using Neutral Cluster Beams
Authors: Ramachandra A. , Vaziri M. , Andres R.P.
Published: March 2011

Gold clusters (diam. = 1.0 ± .5 nm) are prepared in a gas aggregation source (MECS), expanded into a vacuum chamber to form a neutral cluster beam, and deposited at low impact velocity on room temperature substrates. When several monolayers of these clusters are deposited on clean substrates (nitrocellulose, glass, mica, NaCl), they form smooth ultra-thin films. These cluster-assembled films appear to be similar in quality to those produced by the Takagi-Yamada ion cluster beam process. They exhibit finite electrical conductivity at thicknesses much smaller than is the case with atomically evaporated films. They are extremely uniform and smooth with a surface height that typically varies less than 1 nm across the entire film.
In Situ Ellipsometry of Ge Clusters and Ultrathin Films
Authors: Yang B.-Y. , Gu T. , Yu R.Q. , Lannin J.S. , Collins R.W.
Published: March 2011

The evolution of the nanostructure of a-Ge sputter-deposited onto naturally oxidized c-Si and disordered carbon substrates is characterized by in situ ellipsometry, with the focus of attention being on the initial stage when clusters are in evidence. The structural data deduced from ellipsometry are reproducible, are a sensitive function of the preparation parameters, and are also consistent with data deduced from less sensitive Auger electron spectroscopy. The information provided by ellipsometry is of critical importance in studying the effects of average size on the electronic and vibrational properties of clusters by ultraviolet photoelectron spectroscopy and Raman spectroscopy. Other structural probes of clusters for this system, including transmission electron microscopy, have failed to yield reliable results due to the small cluster size.
Nanometer-Scale Composite Structures Formed by Simultaneous Oblique Sputter-Deposition of Two Materials from Different Directions
Authors: Motohiro Tomoyoshi , Takeda Yasuhiko , Watanabe Yoshihide , Noda Shoji
Published: March 2011

Oblique depositlon(OD) provides an attractive anisotropic structure In nm-scale as a promising host structure to form anisotropic nm-scale composites(ANSC). Among a variety of possible methods to introduce a guest material Into the host structure of OD, we have attempted simultaneous oblique deposition of a guest and a host material from two different directions. The computer simulation for ballistic deposition, which had greatly contributed to the understanding of the morphology evolution in OD, has been carried out again here to design possible ANSC structures and to survey their variations. A typical ANSC structure obtained here is a composite of slender clusters of the guest and the host materials, which can be regarded as an anisotropic version of the well-known isotropic structures of the metal-insulator or semiconductor-insulator cermets for magneto-optical or nonlinear optical applications. This appears when the host and the guest materials are deposited from the directions of the same polar angle of 70° but from the reverse azimuthal directions. In accordance with this result, a specially designed sputtering apparatus has been constructed. Structures and optical anisotropy of the films of several composites' systems such as ZnTe-SiO2 and Cu-SiO2 formed by this apparatus have indicated that our attempt has hit the mark.
Magnetic Behavior of Nanocomposites Prepared in a Vitreous Alumina Gel
Authors: Shull R. D. , Ritter J. J. , Shapiro A. J. , Swartzendruber L. J. , Bennett L. H.
Published: March 2011

Homogeneous gelled composites of iron and vitreous alumina containing 10-40% Fe have been prepared by room temperature polymerization of aqueous aluminum alkoxide solutions containing ferric nitrate and nitric acid at low pH. Scanning electron microscopy, x-ray diffraction, and Mossbauer spectroscopy demonstrated that this bulk material is comprised of nanometer-sized regions of iron compounds embedded in a vitreous alumina gel matrix. Magnetization data showed that in the as-cured condition these nanocomposites are paramagnetic at room temperature and become either superparamagnetic or ferromagnetic on cooling to 10 K. The magnetic susceptibility increased with the Fe content and with decreasing temperature. Analysis of the temperature dependence of the magnetic susceptibility indicated the magnetic moment per Fe atom was 1.87 µB for the 10% Fe nanocomposite and that it increased linearly with composition to 1.96 µB for the 40% Fe material. Mössbauer effect data showed that subsequent treatment of these materials in a gaseous environment of hydrogen at elevated temperatures (T<400 C) changed the form of the iron in the magnetic regions. These results are compared to that observed for similar nanocomposites prepared using a silica gel matrix.
Microprobe Analysis of Nanophase Metal-Oxides using Inelastic Light Scattering
Authors: Parker J. C. , Siegel R. W.
Published: March 2011

Nanophase TiO2 and ZnO were investigated with a Raman microprobe in order to determine the spatial variations in material composition, oxygen stoichiometry, and phase. Calibration of the oxygen stoichiometry of nanophase TiO2 was determined through a combination of Raman scattering and thermogravimetric analysis.
High-Resolution Electron Microscopy Study of Iron Nanocrystals Prepared by High-Energy Mechanical Crystallization
Authors: Trudeau M.L. , Van Neste A. , Schulz R.
Published: March 2011

Recently, there has been a growing interest on materials called “nanocrystalline solids”. These materials are made of crystals with sizes ranging typically from 1 to 10 nm. Several methods have been used to produce these solids. One of them is the high energy mechanical deformation (HEMD) process. Indeed, we have shown recently that some iron-based amorphous alloys crystallize completely into a nanocrystalline structure when they are subjected to HEMD. In this work, we present a TEM study of the nanocrystals formed by the mechanical crystallization of Fe66Co18si1B15 amorphous metallic ribbons.