bluuebunny/crossref_metadata_2025 huggingface dataset:
A Monte-Carlo Study of B2 Ordering and Precipitation on a Bcc Lattice
Authors: Athènes M. , Bellon P. , Martin G. , Haider F.
Published: April 2011

Atomistic Monte-Carlo simulations of precipitation and B2 ordering in a binary alloy on a BCC lattice via vacancy mechanism are presented. Evolution of simulated patterns is in good agreement with the experimentally observed morphologies. Moreover, it is observed that the very early stages of ordering are strongly dependent on atomic mobility parameters. Depending on the relative exchange frequency of vacancies with A and B atoms, two extreme regimes oiordering are identified, leading either to localized or delocalized ordering.
Hysteresis of Long-Range Ordering in CuAu
Authors: Chalupa B. , Chmelik F. , Sima V. , Sprusil B. , Spanl M. , Lang H. , Pfeiler W.
Published: April 2011

The effect of heating and cooling on the long-range order transformation in stoichiometric CuAu is investigated by several complementary measuring methods. Measurements of heat flow, resistometry and acoustic emission are done dynamically by linear heating/cooling. It is shown that measuring dynamically yields the expected effect of undercooling, which decreases with decreasing cooling rate. The dependence of undercooling on cooling rate is compared with the concept of continuous cooling for glass forming. A small influence of heating rate on disordering temperature is reported (retro-effect).
Growth of Transition Metal Films on AL(110) Surfaces
Authors: Smith R.J. , Saleh Adli A. , Shutthanandan V. , Shivaparan N.R. , Krasemann V.
Published: April 2011

The growth of thin Pd, Ni, Fe and Ti films on Al(110) surfaces has been studied using high-energy ion scattering (HEIS), x-ray photoemission spectroscopy and photoelectron diffraction techniques. Of these four metals, only Ti grows as an epitaxial overlayer, while the other metals mix with the substrate to form surface alloys. In the HEIS experiments the backscattered ion yield from Al surface atoms is measured as a function of metal coverage on the Al surface. A decrease in the Al scattering is observed for Ti deposition while the other metals result in increased Al scattering, attributed to alloy formation. An explanation for the exceptional growth behavior of Ti on Al is provided using a model of surface strain associated with aluminide formation.
Morphological Transition of Epitaxial Rhodium (111)
Authors: Tsui Frank , Wellman Joanne , Uher Ctirad , Clarke Roy
Published: April 2011

We report a global morphological transition in the nucleation and growth of epitaxial Rh (111). The transition occurs near 600 K, about 1/4 of the Rh melting temperature, and is signaled by a change in the shape of the surface features from fingered to compact. The transition appears to be related to a change in the critical nucleation size from 1 to 2 atoms. On both sides of the transition, there lies a regime of persistent layer-by-layer growth indicated by a minimum in surface roughness and by the presence of RHEED oscillations. The general surface features exhibit well defined length scales that are not self-affine, and as growth proceeds they increase in size following a power-law dependence on film thickness with a temperature-independent exponent of 0.33 ± 0.03. The results suggest a general pathway to the layer-by-layer growth of close-packed metals.
Correlation between Extended Defects and Surface Morphology in MBE Grown InAs/GaAs Heterostructures
Authors: Bruni M.R. , Padeletti G. , Simeone M.G. , Francesio L. , Franzosi P. , Gennari S. , Nasi L. , Salviati G.
Published: April 2011

InAs single layers were grown by Molecular Beam Epitaxy on nominally (001) oriented GaAs substrates at growth temperatures ranging from 350 °C to 500 °C and thicknesses between 1 nm and 6 μm. A systematic study of the influence of growth temperature and thickness on crystal defects and surface morphology is discussed by comparing High Resolution X-Ray Diffraction, Transmission Electron Microscopy and Atomic Force Microscopy investigations.

Surface hexagonal shaped holes were observed to develop at the lowest temperatures starting from an heterolayer thickness of 50 nm. Both misfit and threading dislocations were revealed; moreover the correlation between hexagonal shaped surface holes and mixed dislocations, with the component of the Burgers vector (b) along the growth axis larger than the minimum interatomic distance, is discussed. The holes increase in size and decrease in density by increasing the layer thickness. An almost complete surface planarization is observed at a thickness of 6 μm by increasing the growth temperature up to 500 °C.
Crossover from Dimer Nucleation to Adatom Exchange During Submonolayer Epitaxy
Authors: Bales G.S.
Published: April 2011

The nucleation and growth of islands in the early stages of epitaxial growth is studied with kinetic Monte Carlo Simulations and self-consistent mean field rate equations. Specifically, adatom exchange and irreversible dimer formation are allowed to compete equally as the origin of two-dimensional islands. The island size distribution and number density are found to satisfy a dynamic crossover scaling form. The critical island size evolves from one to zero with increasing temperature, decreasing flux, and increasing coverage.
Morphological Evolution During Ge/Si(100) Heteroepitaxy
Authors: Espada Loren I. , Chaparro Sergio , Aguilar Jose , Dorrance Melissa , McKay Michael , Payne Ken , Drucker Jeff
Published: April 2011

We have investigated the morphological evolution of islanded Ge/Si(100) samples formed by > 3 monolayer (ML) Ge deposition. Ge was deposited onto Si(100) surfaces cleaned by flash desorption of the native oxide at rates near 1/2 ML per minute. Growths were performed in an ultra-high vacuum system with a base pressure of < 10−9 Torr. Substrate temperature during growth was 500 °C. Post-deposition processing ranged from no additional treatment to 1 hour at 560 °C anneals. Samples removed from the growth chamber were processed using standard transmission electron microscopy (TEM) specimen preparation techniques and characterized using plan-view TEM. Micrographs were computer analyzed to generate island size distributions (histograms of island size). These size distributions fall into general classes. First, samples with only coherent Ge islands exhibit relatively narrow size distributions. Secondly samples with both coherent and incoherent islands presented bi-modal size distributions with coherent islands populating the smaller radii. These results will be discussed in the context of a model which includes elastic as well as surface and interface energies as driving forces for ripening.
Strain Relaxation in GaAs on Si by Two Groups of Misfit Dislocations
Authors: Tamura M. , Saitoh T. , Yodo T.
Published: April 2011

High-resolution cross-sectional and conventional plan-view transmission electron microscope observations have been carried out for molecular beam epitaxially grown GaAs films on vicinal Si (001) as a function of film thicknesses and observation directions between two orthogonal <110> directions before and after annealing. Two groups of misfit dislocations are characterized by analyzing whether their extra half planes exist in the film and the substrate side. The group I misfit dislocations due to a stress caused by a lattice misfit between GaAs and Si consist of partial and, 60° and 90° complete dislocations in an as-grown state. After annealing partial dislocations almost disappear and 90° perfect dislocations are predominantly observed. The group II misfit dislocations due to a thermal-expansion misfit-induced stress are all of the 60° type complete dislocations, independent of film thickness and annealing.
Phase Evolution During Crystallization of Amorphous Titanium Aluminide Thin Films: Effect Mn and Nb Additions
Authors: Banerjee R. , Swaminathan S. , Wheeler R. , Fraser H. L.
Published: April 2011

Thin films of Ti-aluminides have been sputter deposited using a binary γ-TiAl based target and a quaternary γ-TiAl based target containing alloying additions of Nb and Mn. The as-deposited binary film consisted of microcrystalline agglomerates of α-Ti(Al) embedded in an amorphous matrix whereas the as-deposited quaternary film was found to be amorphous. These films have been annealed in a furnace under a protective Ar atmosphere (referred to as ex situ annealing) as well as on a hot stage in a transmission electron microscope (TEM), referred to as in situ annealing, to study the crystallization behavior of these films and also the effect of Nb and Mn additions on the same. Ex situ annealing of both binary and quaternary films resulted in a nanocrystalline microstructure consisting of primarily γ-TiAl with a small amount of finely dispersed α2-Ti3Al. During in situ annealing of the binary film, at 753 K (stage temperature), growth of the α-Ti(Al) phase was observed together with crystallization of a second phase in relatively thicker regions of the specimen. The first crystalline phase to appear during in situ annealing of the quaternary film was a surface crystallized metastable tetragonal phase at 873 K. Prolonged annealing at the same temperature resulted in the transformation of the amorphous region between grains of the tetragonal phase into γ-TiAl. Formation of the tetragonal and intergranular γ-TiAl phases were also observed in the thin regions of the binary film when it was heated to 873 K.
Kinetic Roughening of Interfaces and Mixing in Alloys Under Shear or Irradiation
Authors: Bellon P. , Partyka P.
Published: April 2011

Both irradiation and plastic deformation can induce the stabilization of non-equilibrium phases in alloys. A simple kinetic atomistic model is used for describing these two situations, when the external forcing is acting in competition with thermally activated diffusion. Monte Carlo simulations are performed on alloys with positive heats of mixing. Both situations share common features : random solid solutions are stabilized at high enough forcing intensity (i.e. irradiation flux or shearing rate), while at moderate forcing intensities interfaces exhibit kinetic roughening. However, major differences are observed : alloys under irradiation undergo dynamical transitions between steady-states, such as a dynamical roughening transition at interfaces and a precipitation-dissolution transition in the bulk ; in alloys under shear such transitions are not observed ; instead the steady-state microstructure of a two-phase alloy is continuously refined on increasing the shearing rate. These differences originate from the size of the perturbation induced by the external forcing : the perturbation is of microscopic size for alloys under irradiation, while it is of macroscopic size for alloys under shear. Results obtained for the shearing case provide a rationalization scheme of ball milling experiments showing chemical mixing of immiscible elements. The fact that such systems consist of nanograins should also contribute to prevent the existence of 1st order phase transitions on varying the milling conditions.
Nanosized Metallic Sn Precipitates in Si, Formed Upon Ion Implantation
Authors: Barancira T. , De Wachter J. , Milants K. , Verheyden J. , Deweerd W. , Odeurs J. , Pattyn H.
Published: April 2011

In this work we firstly established the optimal conditions to preferentially form nanosized β-Sn inclusions from a supersaturated solid solution of Sn in Si, formed by a high dose ion implantation. Afterwards we tried to elucidate the origin of the strongly enhanced recoilless fraction of Sn nuclei inside these precipitates, thereby making a link to the observed shift in isomer shift value. This is tentatively interpreted in terms of a local compression of the inclusion to about 200 kbar.
Formation of Epitaxial CoSi2 Layers Grown from the Interaction of Co/Ti Bilayers with Si <100> Substrates
Authors: Cardenas J. , Zhang S.-L. , Svensson B. G. , Petersson C. S.
Published: April 2011

The redistribution of titanium during the growth of epitaxial CoSi2 from the reaction of Co(20nm)/Ti(lOnm)/Si<100> structures has been investigated. The concentration of Ti in the CoSi2 layers versus annealing temperature has been determined. Emphasis is placed on the formation of inhomogeneities in the epitaxial CoSi2 layers, and the role of Ti with respect to the thermal stability of the layers. The fundamental mechanism for the development of inhomogeneities in the epitaxial CoSi2 layers will be discussed.
Phase Formation Between Codeposited Co-Ta Thin Film and Single Crystal Silicon Substrate
Authors: Riskin G. , Pelleg J. , Talianker M.
Published: April 2011

A combination of near-noble and refractory metal silicides was considered for shallow contacts to silicon in VLSI circuits [1]. The objective of the present work is to investigate formation of phases between codeposited Co-Ta film, of 150 nm thickness, and n-type silicon substrates of (100) or (111) orientation. Characterization of the specimens annealed in the temperature range of 600–1100°C was done by X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that in addition to the silicide phases of Co and Ta, the intermetallic compound Co2 Ta was also formed. Co2 Ta appears only in the lower temperature range of about 600–800°C. At temperatures of 900–1100°C only the silicon rich phases were present. These are the low resistivity phases useful for devices. No ternary phases have been observed. Silicide formation occurs at a faster rate on (111) oriented silicon substrates.
Reaction of Amorphous Silicon with Cobalt and Nickel Silicides Before Disilicide Formation
Authors: Maa Jer-Shen , Hsu Sheng Teng
Published: April 2011

A method is introduced to reduce substrate Si consumption of the salicide process by supplying extra Si from an amorphous Si film. Si is introduced into cobalt silicide and nickel silicide at the time when the silicide is converted into the disilicide phase. The reaction rate with amorphous Si is higher than that with single crystal Si if the amorphous Si has a low oxygen content.
A Low Temperature Single-Step RTA Process to form Ultrathin CoSi2 for Mosfet Applications
Authors: Sherony Melanie J. , Sriram T. S. , England Craig , Pelillo Aldo , Harris William C. , Miller Stephen J. , Bill Steven A. , Yang Isabel Y. , Wei Andy , Antoniadis Dimitri A.
Published: April 2011

A single-step, low temperature self-aligned CoSi2 process using Ti/Co source material has been developed for use in extreme submicrometer MOSFET applications. Ultra-thin CoSi2 films (∼ 20 nm) were obtained from a single-step RTA anneal at 550°C for 30 sec using Ti/Co source material on patterned n+ implanted (100) Si. X-ray diffraction was used to verify CoSi2 formation. Highresolution SEM and TEM examination showed the silicide to be microstructurally smooth and the devices showed no lateral growth of the silicide at the polysilicon spacer edge. Some voiding and lateral overgrowth was observed at the LOCOS isolation edge and this effect was exacerbated at higher anneal temperatures. This single-step low temperature CoSi2 process is a promising technology for deep-submicron MOSFET applications.
Application of Cobalt Salicide in Sub-Quarter Micron Ulsi
Authors: Bai G. , Stivers A.
Published: April 2011

A thin Ti-siuicide film is widely used today as the low resistance shunt in a semiconductor chip. As the feature size in the chip shrinks to sub-quarter micron, the thin Ti-silicide film formed on such narrow lines transforms from C49 to C54 at increasing temperatures and agglomerates at decreasing temperatures, closing the process window for Ti-salicide process. In contrast, low resistivity Co-silicide thin films can be formed on narrow lines below the agglomeration temperature. In addition, an epitaxial CoSi2 with a flat interface can be formed in source/drain areas, enabling the formation of very shallow junctions with low leakage current. Experimental results on formation of silicides from Co/Ti bilayers and thermal stability of the CoSi2 films will be presented, with special emphasis on the sheet resistance of the silicide film versus poly-line width down to 0.15 umn. Interaction between dopants and silicide films will also be discussed.
Tungsten Silicide Films Based on Dichlorosilane Chemistry for sub 0.5 Micron Applications
Authors: Ozkan Cengiz S. , Moinpour Mansour
Published: April 2011

CVD WSix, films have found widespread use as ultra thin gate, wordline and bitline interconnects due to the lower resistance that polycide offers. For submicron technologies, WSix films based on the monosilane chemistry shows limitations due to the incorporation of high concentrations of Fluorine ions and poor step coverage. Recent work has shown that, WSix films based on the dichlorosilane (DCS) chemistry minimizes these problems. One of the major issues in DCS WSix films is the in-depth compositional non uniformity, especially those deposited on poly-Si substrates. The formation of a W-rich region at the WSix/poly-Si interface can cause localized stresses which can result in cracking and adhesion problems. In this paper, we report the composition and structure of DCS WSix, films deposited on undoped, doped and in situ doped poly-Si and oxide substrates. We have investigated the effect of different processing conditions on Si/W uniformity and the formation of W-rich and Si-rich interfaces, and the role of the nucleation step in modulating the Si/W ratio at the WSix/poly-Si interface. The impact of a Si-rich region at the WSix/poly-Si interface on silicide film properties has also been explored. RBS measurements were used to determine the composition profile through the depth of the film and Si/W uniformity in terms of Si-rich and W-rich interfaces. SIMS measurements were used to determine the impurity content in the silicide film and at the film/substrate interface.
GeSi Infrared Detectors Using Selective Deposition
Authors: Strong R. , Greve D. W. , Weeks M. M.
Published: April 2011

Heterojunction p++ GeSi / Si internal photoemission (HIP) detectors deposited by ultra high vacuum chemical vapor deposition (UHV/CVD) were investigated as alternatives to silicide Schottky-barrier type detectors for infrared focal plane arrays. HIP structures were grown using SiH4, GeH4, and B2H6 source gases on (100) p- Si substrates patterned with thermal oxide windows. Selective epitaxy was maintained over a range of boron concentrations (6×1019 – 6.5×1020 cm-3) and Ge fractions (0.38–0.50), and a maximum selective thickness of ~300Å was determined for silicon growth at 550°C. These structures were fabricated into IR detectors using techniques compatible with standard Si focal plane array processing technology. Photoresponse data were analyzed according to the modified Fowler equation, indicating cut-off wavelengths of 5–12 (μm) and Cl values of 8–21 (%/eV) depending on sample parameters. I(V) characteristics were also measured at various temperatures, yielding electrical barrier heights consistent with optical measurements.
Heteroepitaxy of CoSi2 on Patterned Si(100) Substrates
Authors: Karpenko O. P. , Eaglesham D. J. , Yalisove S. M.
Published: April 2011

This study has addressed the effect of starting surface topography on the nucleation and growth of epitaxial siicide layers. CoSi2 layers were grown via the template technique on one-dimensionally patterned Si (100) substrates. These substrates contained mesa stripes, running parallel to Si[011], and exhibited either smoothly varying sinusoidal profiles, or a number of well defined Si Ihkl) facets. Conventional plan view and high resolution cross section transmission electron microscopy were used to analyze the films grown on these substrates. The orientation and morphology of the CoSi2 grains depend on the angle (θ), between the CoSi2 / Si interface normal and Si (100). High quality (100) oriented CoSi2 grew on the tops and bottoms of mesa structures, where θ < 5°, and formed atomically sharp interfaces with the substrate. In contrast, CoSi2 (110) and CoSi2 (221 ) grains nucleated along the sidewalls of the mesa structures. The CoSi2 (110) grains formed rough interfaces with the substrate and were terminated by regions of step bunching at the grain boundary / substrate triple points. CoSi2 (110) grains were most highly concentrated in regions where θ varied from 5° to 12°. Similarly, the CoSi2 (221 ) grains formed faceted (111) b-type silicide / substrate interfaces, and were most highly concentrated in regions where θ > 10°. These data suggest that double height steps, step bunches and facets on the substrate are related to the nucleation of misoriented silicide grains.
New Epitaxially Stabilized Silicide Phases
Authors: Goncalves-Conto S. , Müller E. , Schmidt K. , Von Känel H.
Published: April 2011

A new epitaxial CoSi2 phase has been synthesized on Si(111) by molecular beam epitaxy (MBE) at room temperature (RT). Structural investigations revealed, that films grown onto an ultrathin CoSi2 template crystallize with the CsC1 structure with 50% vacancies on the cation lattice. The same is true for codeposited films nucleating from the amorphous phase at very low annealing temperatures (100–200 °C). Upon annealing a gradual transition to the stable bulk phase with the CaF2 structure takes place. For films grown onto a template, some grains of (CsCl)Co0.5Si remain stable up to at least 550 °C, while the films grown without a template are fully transformed.
Structural Characterization of Ion Beam Synthesized Epitaxial ErSi2-x Layers
Authors: Bender H. , Wu M. F. , Vantomme A. , Pattyn H. , Langouche G.
Published: April 2011

The results are discussed of the characterization by means of TEM, RBS and XRD of ErSi2-x layers prepared by ion beam synthesis on (111) silicon. It will be shown that high quality (buried) layers can be prepared by channelled implantation of the erbium, whereas unchannelled implantation leads to discontinuous polycrystalline surface layers. The epitaxial growth and vacancy ordering in the silicide are discussed.
Rapid Thermal Annealing of Tungsten Silicide Films
Authors: Fabricius A. , Nennewitz O. , Spieβ L. , Cimalla V. , Pezoldt J.
Published: April 2011

Tungsten / silicon multisandwich layers were deposited by DC magnetron sputtering on silicon and silicon oxide substrates. After the deposition the samples were annealed by rapid thermal annealing at different temperatures under H2 atmosphere. X-ray diffraction measurements were carried out to determine the crystal structure of the obtained silicide layers. To estimate the grain size and the relative lattice strain in dependence on the annealing temperature from the X-ray profile the deconvolution method of Lagrange was used. To characterize the electrical properties the specific resistance was measured by a linear four-point method. The best specific resistance measured was approximately 17 μΩcm for the sample on silicon substrate annealed at 1195 °C for 20 seconds. Rutherford Backscattering Spectroscopy measurements were carried out to obtain the stoichiometric depth profile.
Evaluation of Mechanical Properties of Sputtered Ceramic Films from Nanoindentation and Wafer Curvature Techniques
Authors: Inturi Rama B. , Barnard John A.
Published: April 2011

TiB2, MoSi2, Si3N4 and Ta4N ceramic films were magnetron sputtered on oxidized Si and Coming 7059 glass substrates at ambient temperature. X-ray diffraction studies indicate that the structure of the films is very different on the two substrates, even though the surface of both substrates is amorphous. The hardness and elastic modulii of the films on oxidized Si are slightly higher than those of the films deposited on Coming glass substrate, even at indentation depths where substrate effects are considered to be negligible. A substantial increase in hardness (5–10 GPa) was observed for TiB2 films, when compared to the properties of bulk stoichiometric TiB2. Stress- temperature diagrams determined from room temperature to 250 C indicate that all the films prepared in this study display a pure elastic behavior in that temperature range.
Microstructure and Mechanical Properties of Plasma Assisted CVD Ti(C,N) Films as a Function of Carbon Content
Authors: Xu K. W. , Sun H. L. , Hu N. S. , Hendrix B. C.
Published: April 2011

The results show that unlike those made by physical vapour deposition, Ti(C,N) coatings made by plasma assisted chemical vapour deposition are composed of two phases, TiN and TiC. With the formation of two phases, the columnar structure vanishes gradually and the crystal size becomes small. The carbon content is the dominant controlling factor for a linear increase in microhardness of the coatings, but the residual macrostress and the adhesive strength evaluated under cyclic contact conditions are dependent to a great extent on the percentage of the two phases. There is an intermediate carbon content for the present Ti(C,N) coatings which yields a fine mixed microstructure and optimum mechanical properties.
Growth of Polycrystalline Silicon Films at Low Temperature by Plasma Enhanced Chemical Vapor Deposition
Authors: Hatanaka Y. , Jayatissa A. H. , Ishikawa K. , Nakanishi Y.
Published: April 2011

Polycrystalline silicon (poly-Si) films are of great interest in the field of TFT fabrication for active matrix liquid crystal display(AM-LCD) applications. Low temperature depositions below 500 °C are necessary for using a glass substrate for the application to large area devices such as display devices. We investigated poly-Si growth at low temperature by plasma enhanced chemical vapor deposition (PECVD). Cathode deposition is used in which substrates are mounted on the powered electrode and a mesh electrode is attached on the cathode for protecting the growing surface from ion impacts. It is found that poly-Si films can be deposited in the wide range of SiH4 concentration even at 100%, and a high deposition rate of 35nm/min has been realized. This investigation gives highly promising results for poly-Si growth technology at low temperature.
Texture Maps for Orientation Evolution During Grain Growth in Thin Films
Authors: Seel Steven C. , Carel Roland , Thompson Carl V.
Published: April 2011

Orientation selective grain growth in thin films arises due to anisotropy in materials properties. For continuous thin films, there are at least two orientation dependent driving forces for grain growth: (i) surface and interface energy anisotropy; (ii) strain energy anisotropy (both elastic and plastic). In fcc metals, the preferred growth of grains with (111) texture occurs due to their low surface and interface energy. Stresses in thin films arise during deposition and as a result of post-deposition annealing. A texture dependence of strain energy density arises in biaxially strained thin films due to anisotropy of elastic properties and/or orientation-dependent yield stresses. For most fcc metals, the strain energy driving force promotes the growth of (001) grains due to minimization of the combined elastic and plastic strain energy. The magnitudes of the orientation dependent driving forces for grain growth depend on the characteristics and processing conditions of the film and substrate. We have performed grain growth experiments for Ag films on single crystal Ni on MgO; Ag films on plasma-enhanced chemical vapor deposited (PECVD) SiO2 on MgO; Ag films on oxidized Si; and Ni films on oxidized Si. The texture resulting from grain growth in films of different thicknesses and deposited at different temperatures were determined, and the results are presented in the form of texture maps. The texture which dominates as a result of grain growth can be understood through the use of texture maps and compares well with analytic models for texture development during grain growth in thin films.
Microstructural and Magnetotransport (EHE) Properties of Epitaxial τ-MnAl on (100)GaAs Substrates by Pulsed Laser Deposition
Authors: Rosier T. M. , He Y. , El-Masry N. A.
Published: April 2011

We report on the crystal quality and magnetotransport properties (EHE) of epitaxial (001) τ-MnA1/GaAs(100) grown by the laser ablation deposition technique. Films (10–30 nm thick) were grown by two methods: (1) ablating a τ-MnAl target, prepared in-house; (2) alternate deposition of ultra thin layers of Mn and Al (˜6 periods) followed by annealing at different temperatures. For both deposition approaches ultrathin coherent epitaxial τ-MnAl films have been grown at temperatures in the range 250–420°C that is below the ε-phase transformation temperature. Reflection high energy electron diffraction (RHEED) and high resolution transmission electron microscopy (HRTEM) were used to characterize the crystalline quality of the deposited films. The Extraordinary Hall Effect measurements (EHE) indicate that the deposited films are perpendicularly magnetized showing coercivity up to 6 kOe at room temperature. The epitaxial growth of thin film ferromagnetic materials on lattice matching semiconductor substrates offers the possibility of integrating magnetic and semiconducting devices.
Preferred Crystal Orientation and its Effect on the Magnetization Reversal Property of CoCrTa Thin Films
Authors: Yeh T. , Wang G. , Lin J. C. , Sivertsen J. M.
Published: April 2011

CoCrTa thin films with c-axis predominatly oriented perpendicular to the plane of the film were obtained by sputter deposition on thin tantalum nitride underlayers with −75 volts substrate bias applied during the deposition of the film. The relationship between the distribution of c-axes preferred crystal orientation and magnetization reversal properties of the sputtered CoCrTa films was investigated. Higher coercivities are obtained for CoCrTa films having a more random crystal orientation distribution of hcp c-axes in polycrystal films, while lower coercivity is obtained for the highly oriented films. Such behavior may be attributed to the form of the induced local energy fluctuations associated with the crystal orientation distributions.
Using Principle of Virtual Motion and Galerkin Approximation to Analyze Surface Diffusion
Authors: Sun B. , Suo Z. , Cocks A. C. F.
Published: April 2011

This paper outlines the use of the Principle of Virtual Motion and the Galerkin approximation to analyze surface diffusion phenomena. Various ideas are illustrated with an analysis of the evolution of a fiber of bamboo-like grain structure.
Growth and Thermal Stability of Thin Niobium Overlayers on (0001) Sapphire Substrates
Authors: Wagner T. , Lorenz M. , Langjahr P. A. , Ruhle M.
Published: April 2011

Thin Nb films were deposited by MBE on (0001)α-Al2O3 in UHV. At a substrate temperature of 800°C, reflection high energy electron diffraction (RHEED) revealed that the film grew with the orientation relationship (planes of similar symmetry are parallel to each other): (0001)α-Al2O3 ‖ (111)Nb; [2110]α-Al2O3 ‖ [110]Nb. Investigations with conventional transmission electron. microscopy (CTEM) revealed that the film was not perfectly epitaxial after deposition. Small Nb grains with different orientations were embedded in the epitaxial Nb film. During annealing at temperatures well above the deposition temperature, secondary grain growth of the small embedded Nb grains occured, leading to a different epitaxial relationship between the Nb film and the sapphire: (0001)α-Al2O3 ‖ (110)Nb; [0110]α-Al2O3 ‖ [001]Nb.
Features of the Metal Nuclei Spatial Distribution on the Glassy Carbon Surface During the Receipt of Thin Films by Electrolysis
Authors: Arzhanova T. A. , Kovarsky N. Ya. , Radchenkova T. V.
Published: April 2011

The statistics of the distances among the nearest-neighbor nuclei developed at the initial stage of the electrolysis was analyzed using the example of the metal (Cu, Ag, Cd) electrocrystallization on the isotropic glassy carbon. It was confirmed that the most frequently met intemuclei distances tn that follow the progression equation tn = t1 · qn-1 with q≈1.4 form “structural spots” where they are located following each other in a strict sequence ti, t2 …. , tn,. It is found that the form of the “structural spots” is variable and the nuclei's density toward the border of the spot either is decreased or increased. The conditions of electrolysis under which the phenomenon of the nuclei statistically arranged order is not seen are also found.
Mechanisms of Hydrothermal Barium Titanate Thin Film Formation
Authors: Dogan F. , Sarikaya M.
Published: April 2011

Low temperature synthesis of BaTiO3 thin films was performed under hydrothermal conditions below 80°C. Titanium metal, polycrystalline titanium oxide, and polystyrene (coated with a metallo-organic titanium precursor by a sol-gel process) were used as substrate materials. The reactions between the substrates and aqueous Ba(OH)2 solution took place at different time intervals from 10 minutes to 48 hours. The formation mechanisms of BaTiO3 was investigated by electron microscopy techniques during the reaction sequence. It is proposed that the nucleation and growth of crystalline BaTiO3 occur within an amorphous intermediate phase on Ti-metal and polystyrene substrates. However, thin film of BaTiO3 does not form on the surface of the sintered polycrystalline TiO2 under similar reaction conditions.
Linear-Response Calculations of Electron-Phonon Coupling Parameters and Free Energies of Defects
Authors: Quong Andrew A. , Liu Amy Y.
Published: April 2011

Linear-response theory provides an efficient approach for calculating the vibrational properties of solids. Moreover, because the use of supercells is eliminated, points with little or no symmetry in the Brillouin zone can be handled. This allows accurate determinations of quantities such as real-space force constants and electron-phonon coupling parameters. We present highly converged calculations of the spectral function α2F(ω) and the average electron-phonon coupling for Al, Pb, and Li. We also present results for the free energy of vacancy formation in Al calculated within the harmonic approximation.
Phase Stability of the Sigma Phase in Fe-Cr Based Alloys
Authors: F Marcel Il. , Esfurjani Sluiter. Koivan , Kawazoe Yoshiyuki
Published: April 2011

The FeCr sigma phase is a good example of a complex structure: it. has 30 atoms in the unit cell and 5 inequivalent lattice sites, and it belongs to the class of tetrahedrally close packed structures, also known as Frank-Kaspar structures. So far. such structures have riot been treated within a first-principles statistical thermodynamics framework. It will be shown that dtlme to advances in algorithms and hardware important features of the phase stability of complex phases can be computed. The factors which affect the stability of the sigma phase have been studied using carefully selected supercells for electronic total energy calculations. cluster variation calc:ulations in the tet.rahedron approximation were performed to evaluate the effect of partial disorder and of finite temperature. The preferred occupancy of the 5 lattice sites has been investigated and is compared with experimental determinations.
Ab Initio Study of Expitaxial Growth on a Si(100) Surface in the Presence of Steps
Authors: Milman V. , Pennycook S. J. , Jesson D. E.
Published: April 2011

The motion of a Si adatom over the reconstructed Si(100) surface with single-height rebonded (SB) step is studied using the pseudopotential total energy method. The step is shown to act as a good sink for adatoms descending onto the lower ledge. This is due to the presence of deep traps at the rebonded dimer row on the lower terrace and to the negative Ehrlich-Schwoebel barrier (the activation barrier for descent from the edge is 0.23 eV lower than for the motion on a flat surface). The diffusion characteristics of the adatom on both terraces are virtually unaffected by the presence of the step. The dimer buckling sequence on a lower terrace depends strongly on the position of the adatom along the diffusion path.
Electronic Structure and Stability of Ordered Vacancy Phases of NbN
Authors: Ethridge E. C. , Erwin S. C. , Pickett W. E.
Published: April 2011

A recently reported metastable phase of NbN with a superconducting Tc=16.4 K is characterized using full potential electronic structure methods. This new phase, which has Pm3m (cubic) symmetry, can be described as the B1 (rocksalt) structure with 25% ordered vacancies on each sublattice. We compare the equation of state and electronic spectrum of this Pm3m phase with its rocksalt counterpart [1] and with Nb4N3 in the 14/mmm (tetragonal) phase, which allows the characterization of N vacancies without accompanying Nb vacancies. For Pm3m NbN, the calculated lattice constant is 5% smaller than reported and the energy is 1.00 eV/molecule higher than B1 NbN, suggesting that the newly reported phase is something other than a stoichiometric Pm3m phase of NbN. We report on the energy surface for tetragonal distortions of this phase, from which we evaluate its structural stability and obtain Poisson's ratio.
Ab-Initio Calculations of the Electronic Structure and Properties of Titanium Carbosulfide
Authors: Ramalingam Bala , McHenry Michael E. , Garrison Warren M. , MacLaren James M.
Published: April 2011

Titanium carbosulfide (Ti2CS) is frequently found as an inclusion phase in Ti - containing steels. It is of considerable interest because, whenever present in preference to the more common manganese sulfide (MnS), it significantly improves the toughness (a very desirable property) of the steel. Currently, to the best of our knowledge, there is no data, either computational or experimental, regarding the structural properties of Ti2CS. This data is needed to understand the influence of the Ti2CS inclusions on the toughness of the host material.

In this paper, our results from the ab-initio calculations, using the LKKR-ASA (Layer Korringa Kohn Rostoker method in the Atomic Spheres Approximation) on the equilibrium ground state properties of bulk Ti2CS are presented and discussed. In particular, attention is focused upon (a) the Energy – Atomic Volume curve generated to calculate the equilibrium lattice constant and the bulk modulus, and (b) the density of states calculations. The application of these results to the subsequent study of an interface involving the carbosulfide and the host matrix is also illustrated.
O(N) Multiple Scattering Method for Relativistic and Spin Polarized Systems
Authors: Beiden S. V. , Guo G. Y. , Temmerman W. M. , Szotek Z. , Gehring G. A. , Wang Yang , Stocks G. M. , Nicholson D. M. C. , Shelton W. A. , Ebert H.
Published: April 2011

We have implemented the fully relativistic and spin-polarized extension of the O(N) real space locally self-consistent multiple scattering formalism [1]. Here we present preliminary results for the spin and orbital magnetic moments and magneto-crystalline anisotropy in iron metal. The spin and orbital moments are in good agreement with the results of conventional electronic structure methods. In addition we present preliminary results for the magnetocrystalline anisotropy obtained in the frozen potential approximation.
Polarization, Dynamical Charge, and Bonding in Partly Covalent Polar Insulators
Authors: Resta R. , Massidda S. , Posternak M. , Baldereschi A.
Published: April 2011

We have investigated the macroscopic polarization and dynamical charges of some crystalline dielectrics presenting a mixed ionic/covalent character. First principles investigations have been done within the Hartree-Fock, LDA, and model GW approaches. All calculations have been performed on the same footing, using the all-electron FLAPW scheme. Apparently similar oxides have strikingly different behaviors: some (like the ferroelectric perovskites) have giant dynamical charges, while others (like ZnO) are quite normal and display dynamical charges close to the nominal static ones. We find the rationale for such differences.
Dynamics And Morphology Of Cracks In Silicon Nitride Films: A Molecular Dynamics Study On Parallel Computers
Authors: Nakano Aiichiro , Kalia Rajiv K. , Vashishta Priya
Published: April 2011

Multiresolution molecular dynamics approach on parallel computers has been used to investigate fracture in ceramic materials. In microporous silica, critical behavior at fracture is analyzed in terms of pore percolation and kinetic roughening of fracture surfaces. Crack propagation in amorphous silicon nitride films is investigated, and a correlation between the speed of crack propagation and the morphology of fracture surfaces is observed. In crystalline silicon nitride films, temperature-assisted void formation in front of a crack tip slows down crack propagation.
Simulation Of Dislocations In Ordered Ni3Al By Atomic Stiffness Matrix Method
Authors: Hsu Y. E. , Chaki T.K.
Published: April 2011

A simulation of structure and motion of edge dislocations in ordered Ni3Al was performed by atomic stiffness matrix method. In this method the equilibrium positions of the atoms were obtained by solving a set of linear equations formed by a stiffness matrix, whose terms consisted of derivatives of the interaction potential of EAM (embedded atom method) type. The superpartial dislocations, separated by an antiphase boundary (APB) on (111), dissociated into Shockley partials with complex stacking faults (CSF) on (111) plane. The core structure, represented by the Burgers vector density distribution and iso-strain contours, changed under applied stresses as well as upon addition of boron. The separation between the superpartials changed with the addition of B and antisite Ni. As one Shockley partial moved out to the surface, a Shockley partial in the interior moved a large distance to join the lone one near the surface, leaving behind a long CSF strip. The decrease in the width of the APB upon addition of B and antisite Ni has been explained by a reduction of the strength of directional bonding between Ni and Al as well as by the dragging of B atmosphere by the superpartials.
The Composition Of Polymer Composite Fracture Surfaces As Studied By Xps
Authors: Wiegand Donald A. , Pinto James J.
Published: April 2011

The composition of the fracture surfaces of a composite made up of a polycrystalline organic nonpolymeric filler and a binder composed of a copolymer was studied by XPS. Because the binder and the filler of the composite each have at least one element not in common it is possible to easily distinguish between the binder and filler by XPS. A measure of the relative amounts of binder and filler on the fracture surfaces, therefore, could be made as a function of the sample temperature, T, and the strain rate during fracture. The ratio of filler to binder, F/B, increases with decreasing T at constant strain rate and is least sensitive to strain rate at T's below TG, the quasi static glass transition T. At higher T, F/B increases with strain rate at constant T. These results indicate that as the binder becomes stronger and stiffer due to a decrease in T or an increase in strain rate more of the fracture processes take place in the filler whose properties are expected to be less sensitive to T and strain rate. These results are related to the fracture properties as observed by uniaxial compression.
Molecular-Dynamics Simulations Of Fracture: An Overview Of System Size And Other Effects
Authors: Holian B. L. , Zhou S.J. , Lomdahl P.S. , Gronbech-Jensen N. , Beazley D.M. , RAVELO R.
Published: April 2011

We have studied brittle and ductile behavior and their dependence on system size and interaction potentials, using molecular-dynamics (MD) simulations. By carefully embedding a single sharp crack in two- and three-dimensional crystals, and using a variant of the efficient sound-absorbing reservoir of Holian and Ravelo [Phys. Rev. B 51, 11275 (1995)], we have been able to probe both the static and dynamic crack regimes. Our treatment of boundary and initial conditions allows us to elucidate early crack propagation mechanisms under delicate overloading, all the way up to the more extreme dynamic crack-propagation regime, for much longer times than has been possible heretofore (before unwanted boundary effects predominate). For example, we have used graphical display of atomic velocities, forces, and potential energies to expose the presence of localized phonon-like modes near the moving crack tip, just prior to dislocation emission and crack-branching events. We find that our careful MD method is able to reproduce the ZCT brittle-ductile criterion for short-range pair potentials [static lattice Green's function calculations of Zhou, Carlsson, and Thomson, Phys. Rev. Letters 72, 852 (1994)].

We report on progress we have made in large-scale 3D simulations in samples that are thick enough to display realistic behavior at the crack tip, including emission of dislocation loops. Such. calculations, using our careful treatment of boundary and initial conditions - especially important in 3D - have the promise of opening up new vistas in fracture research.
Fracture Surface Fractal Dimension Determined Through An Extensive 3-D Reconstruction
Authors: Ammann J.J. , Nazar A.M.
Published: April 2011

An efficient image processing method is developed to determine the fractal dimension from a high resolution 3-D reconstruction of fracture surface. The third dimension of the fracture surface is obtained from a stereo pair. The elevation is locally determined through a recursive window matching algorithm centered on the cross-correlation operation. The method allows to reach high vertical and horizontal resolutions of the elevation map.

The fractal dimension is obtained by an implementation of the slit-island method. A series of contour lines is extracted from the reconstructed surface. The images of the contour lines are progressively reduced in size and at every step the curve length is estimated. The result is then normalized according to the scale factor to build a Kolmogorov plot.

The performance of this method is demonstrated on a synthetic image generated by a fracture surface mathematical model.
High-Pressure Behavior of Iron Sulfide
Authors: Fei Y. , Prewitt C. T.
Published: April 2011

A high-temperature diamond-anvil cell has been developed for in situ characterization of material properties at high pressure and temperature. Using this technique, we have studied the phase relations and physical properties of iron sulfide, FeS, up to 30 GPa and 900 K. In situ X-ray diffraction measurements revealed five polymorphs of FeS, which are closely related to a simple NiAs-type hexagonal structure. In addition to confirming the previously observed phase transitions, we observed a new hexagonal phase of FeS with axial ratio (c/a ) close to ideal closepacking value of 1.63 at high pressure and high temperature. The compression behavior of this new high P-T phase was studied up to 25 GPa at 500 K, 600 K, and 800 K. There is an abrupt shortening of the c axis at about 6 GPa, which may result from an electronic transition, possibly a spin-pairing transition. The c-axis shortening across the electronic transition means that the high P-T phase has substantially shorter interlayer Fe-Fe distances, which would lead to metallization of FeS at high pressure. Changes in density and chemical bonding of FeS at high pressure and temperature will affect the solution and melting behavior in systems such as Fe-FeS. These changes also have important implications for understanding sulfur-bearing iron-cores of planetary bodies.
Crystal Phases and Lattice Dynamics of Slip-Cast β'-Sialons
Authors: Loong C.-K. , Richardson J. W. , Suzuki S. , Ozawa M.
Published: April 2011

The crystal structures and phonon densities of states (DOS) of β'-Sialon ceramics, Si6-zAlzOzN8-z (0 ≤ z ≤ 6), prepared by a novel slip-cast method were studied by neutron scattering techniques. A Rietveld analysis of the diffraction patterns shows that samples of z < 4 form a single-phase solid solution of Si-A1-O-N isostructural to β-Si3N4 (space group P63/m). Within this structure there is a consistent preferred occupation of 0 on the 2c sites and N on the 6h sites. For z > 4 the materials exhibit multiple-phase structure. The observed phonon DOS of the 0 ≤ z ≤ 4 ceramics displays phonon bands at about 50 and 115 meV. These features are considerably broader than the corresponding ones in β-Si3N4 powder. As z increases, effects due to atomic disorder lead to an overlap of the two phonon bands and a complete fill up of the phonon gap at ˜100 meV.