bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Kinetics of Ordering in Gadolinium Zirconate: an Unusual Oxygen Ion Conductor
Authors: Haile Sossina M. , Meilicke Scott 
Published: April 2011

ABSTRACTGadolinium zirconate, Gd2Zr2O7, undergoes an order-disorder transition at ∼1550°C, transforming from a defect fluorite structure (Fm3m) to a pyrochlore structure (Fd3m). Both cations and anions are ordered in the low-temperature, pyrochlore structure. In order to understand the interplay between anion and cation order parameters and ordering rates, the transformation kinetics of Gd2Zr2O7 have been examined via X-ray diffraction. Gadolinium zirconate is of particular interest because the oxygen ion conductivity of the ordered phase is significantly greatly than that of the disordered phase, in contrast to virtually every other known solid electrolyte. This difference in conductivity has provided a second technique for characterizing the transformation kinetics: in situ A.C. impedance spectroscopy. Results of the X-ray diffraction showed the growth of superstructure peak intensity to follow an apparent (time)½ dependence, rather than that expected from a nucleation and growth model. The impedance spectroscopy measurements, on the other hand, showed the conductivity to increase linearly with time. These results suggest the transition is second order in nature.
The Effect of Strain on Intra- and Interlayer Mass Transport in Metal Epitaxy
Authors: Brune H. , Bromann K. , Kern K. 
Published: April 2011

ABSTRACTA general concept is shown how to measure both the barriers for terrace and step-down diffusion for an epitaxial system. It is based on the application of mean-field nucleation theory to variable temperature STM data. With this approach we studied the influence of strain on intra- and interlayer diffusion for Ag self diffusion on strained and unstrained Ag(111) surfaces. The strained surface was the first Ag layer that grows pseudomorphically on Pt(111) and is thus under 4.2% compressive strain. The barrier for terrace diffusion is observed to be substantially lower on the strained, compared to the unstrained Ag/Ag(111) case, 60±10 meV and 97±10 meV, respectively. The additional barrier for interlayer diffusion decreases from 120±15 meV for Ag(111) homoepitaxy to only 30±5 meV for diffusion from the strained Ag layer down to the Pt(111) substrate. These examples illustrate the considerable effect of strain on the intra- and interlayer mass transport. They require a new concept of layer dependent nucleation kinetics for heteroepitaxial systems in general.
Pyramid Formation and Coarsening During Homoepitaxial Growth
Authors: Siegert Martin 
Published: April 2011

ABSTRACTOne of the generic scenarios in molecular beam epitaxy is the growth of large scale pyramid-like three-dimensional structures. These structures are a consequence of non-equilibrium surface diffusion currents that result from a transport of adatoms in the uphill direction in regions of the surfaces that are tilted away from a high symmetry orientation. The microscopic origin of these currents are, e.g., diffusion barriers at step edges that suppress the diffusion of adatoms to lower terraces. The temporal evolution of the resulting instabilities can be described by simple continuum equations that display slope-selection, pyramid-like structures, and coarsening. We show that similar scenarios can be found in microscopic models investigated by Monte-Carlo simulations. However, crossover phenomena can complicate the comparison of the asymptotic theory with computer simulations or experiments. We therefore discuss criteria that allow to distinguish experimentally between kinetic roughening with exponents ζ ≃ 1 and unstable pyramid-like growth.
X-Ray Diffraction Analysis of the Strain of SiGeC/(100)Si Alloys
Authors: Bair A.E. , Alford T.L. , Sego S. , Atzmon Z. , Culbertson R.J. 
Published: April 2011

ABSTRACTSamples of Si1-x-YGexCy were analyzed with a triple axis high resolution x-ray diffractometer to produce reciprocal space maps. Films with compositions of approximately Si0.77Ge0.20C0.01 vvith thicknesses ranging from 120 nm to 750 nm were found to be pseudomorphic with a tetragonal distortion, εT, near 1%. The tetragonal distortion in pseudomorphic samples with compositions near Si0.47Ge0.50C0.03 with thicknesses ranging from 61 nm to 115 nm was found to be near 2%. The strain increased linearly with Ge concentration even though the Ge:C ratio remained nearly constant. The strain in samples with similar compositions was not a function of thickness. These strain measurements correlated well with results from ion channeling analysis.
Tem Study of Stacking Faults Formed in Pairs in a ZnSe Epitaxial Layer on a GaAs(00l) Buffer Layer
Authors: Tanimura J. , Wada O. , Endoh Y. , Imaizumi M. , Ogama T. 
Published: April 2011

ABSTRACTStructure of stacking faults in a ZnSe epitaxial layer grown on a GaAs(001) buffer layer was determined with transmission electron microscopy. Two stacking faults were formed in pairs on (111) and (111) planes with the same polarity and met at a point which is a few atomic layers away from the interface between ZnSe and GaAs. Partial dislocations were found to be the Shockley type ones with a Burgers vector of 1/6<211>. Atomic force microscopy showed that hillocks were formed in pairs at a surface where the pair of stacking faults existed in the layer. Moreover, it was observed that the pair of stacking faults elongated along the <110> direction by gliding on the {111} faulted planes under annealing at 200°C for 30min. Formation mechanisms of the pair of stacking faults have been discussed.
Atomistic Simulation and Elastic Theory of Surface Steps
Authors: Shilkrot L. E. , Srolovitz D. J. 
Published: April 2011

ABSTRACTAtomistic computer simulations and anisotropic elastic theory are employed to determine the elastic fields of surface steps and vicinal surfaces. The displacement field of and interaction energies between <100> steps on an {001} Ni surface are determined using atomistic simulations and EAM potentials. The step-step interaction energy found from the simulations is consistent with a surface line force dipole elastic model of a step. We derive an anisotropic form for the elastic field associated with a surface line force dipole using a two dimensional surface Green tensor for a cubic elastic half-space. Both the displacement fields and step-step interaction energy predicted by the theory are shown to be in excellent agreement with the simulations.
Interdiffusion and Stress Evolution During Solid-State Amorphization in Ni-Hf Thin-Film Diffusion Couples
Authors: Atzmon M. , Boyer W. S. L. 
Published: April 2011

AbstractUsing a combination of x-ray diffraction and curvature measurements, the stress evolution during solid-state amorphization in a Ni-Hf diffusion couple has been monitored. In contrast to the Co-Hf system, no dissolution of Ni in Hf is observed. During interdiffusion, the growing amorphous layer develops a large tensile stress, which subsequently relaxes by creep. Irradiation of the diffusion couple leads to an increase in tensile stress, and a further increase following a subsequent anneal. Composition measurements by Rutherford backscattering spectrometry indicate absence of an effect of the stress variations on the effective interdiffusion coefficient.
Thickness Dependent Phase Formation in Fe Thin Film and Si Substrate Solid Phase Reaction
Authors: Molnár G Y. , Pető G. , Zsoldos E. , Horváth Z. E. , Khánh N. Q. 
Published: April 2011

AbstractThe solid phase reaction of Fe thin films with (111) Si substrate was investigated at constant annealing temperature and time (700°C, 7 minutes) as a function of the initial iron film thickness (from 5 nm to 27.5 um in 2.5 nm steps). The formed phases were analysed by X-ray diffraction, Rutherford backscattering and transmission electron microscopy and optical microscopy.After annealing FeSi phase was detected in the thinner samples. Samples with Fe layers thicker than 12.5 nm contained a β-FeSi2 phase. This special phase sequence was explained with the help of a nucleation controlled phase formation model, taking into consideration the critical radius of nuclei of the new phase. The advantages of using the film thickness as a variable during investigation of solid phase thin film reactions and the probable substrate effects are also discussed.
Controlled Nucleation and Growth in the Hydrothermal-Electrochemical Formation of BaTiO3 Films
Authors: Escobar I. , Silva C. , Lorca J. , Fuenzalida V. M. , Lisoni Judit. G. , Vargas T. 
Published: April 2011

AbstractThe influence of controlled potential conditions on the structure and phases of BaTiO3 films grown on titanium by the hydrothermal-electrochemical method was studied. The experiments were conducted using a three electrode high pressure electrochemical cell in a 0.2 M Ba(OH)2 electrolyte at 150 °C. The spontaneous initial nucleation linked to pure hydrothermal BaTiO3 formation was inhibited by cathodically protecting the titanium electrode since its immersion in the electrolyte. The application of initial nucleation pulses of varying cathodic potentials affected the grain size of the deposit. The growth of tetragonal BaTiO3 was achieved combining the initial inhibition of the pure hydrothermal growth, followed by nucleation under controlled potentiostatic conditions.
Effect of Thickness and Substrates on the Mechanical Properties of Tantalum and Tantalum Nitride Thin Films
Authors: Saha Ranjana , Inturi Rama B. , Barnard John A. 
Published: April 2011

AbstractDetermining the intrinsic mechanical properties of films by nanoindentation is complicated by the presence of the substrate. Generally, for very thin films (<100 nm) one unavoidably observes the properties of the film/substrate composite system. In order to determine the extent of the effect of the substrate on the mechanical properties of Ta and Ta-N thin films, we have grown these films in four different thicknesses (50, 250, 400 and 500 nm) and on three different substrates (glass, oxidized Si, and sapphire). The structure of the films was evaluated by x-ray diffraction and the mechanical properties (hardness and elastic modulus) were determined by nanoindentation.
Microstructural Characterization of Platinum Films Grown by Mocvd
Authors: Vellaikal M. , Streiffer S. K. , Woolcott R. R. , Kingon A. I. 
Published: April 2011

AbstractPlatinum thin films were deposited on SiO2/Si(100) by metalorganic chemical vapor deposition using Pt(acetylacetonate) and Pt(hexaflouroacetylacetonate) as precursors. The films were characterized in terms of orientation, surface roughness and morphology. As expected, Pt(111) was the preferred orientation. Higher substrate temperatures led to higher growth rates and increased surface roughness. The presence of oxygen during deposition decreased the minimum substrate temperature required for platinum deposition, indicating that oxygen played a role in the decomposition of these metalorganic compounds. Annealing platinum films at 550°C in an oxygen ambient resulted in hillock formation. Resistivity measurements showed that films deposited without oxygen were more resistive. Conformal coverage of platinum on patterned SiO2/Si substrates was investigated, and a side wall film thickness to top film thickness ratio of 0.6 for growth at 400°C was obtained. These Pt films produced by MOCVD displayed greater surface roughnesses than films grown by evaporation or sputtering.
Boron Induced Changes in the Structural Properties of Amorphous Silicon Boron Alloys
Authors: Yang G-R. , Abburi M. , Tong B. Y. 
Published: April 2011

AbstractThin films of an amorphous Si-B alloy with B contents 1–50% were deposited by low pressure chemical vapor deposition (LPCVD) from diborane (B2H6) and silane (SilH4) gases. XRD patterns of the as deposited films showed them to be completely amorphous. The films were annealed in N2 at 600–800°C for 30 minutes and characterized by Raman spectroscopy. Wet oxidation of the film was carried out 700°C for 30 minutes, and the films examined by XRD. The structural changes induced by B in the a-Si network discussed in the conceptual framework of the continuous random network (CRN) model. We conclude that the boron incorporation enhances the structural disorder and induces topological changes in the amorphous network.
Resistance Decrease of Phosphorus Ion Implanted Poly-Si Thin Films During Low Temperature Annealing
Authors: Tokioka H. , Masutani Y. , Goto Y. , Nagao S. , Kurokawa H. 
Published: April 2011

AbstractDuring low temperature (below 450°C) annealing, the sheet resistance of phosphorus implanted poly-Si thin films (film thickness : 50nm) decreased to lE+3Ω/square. The sheet resistance after annealing decreased with annealing time and became lower when the dosing level was high enough. At the dose of 8E+14 ions/cm2 we obtained a sheet resistance of 1E+3Q/square by annealing at 450°C for 180min. We analyzed ellipsometry data assuming a two-layer model where the surface layer consists of a-Si and the lower layer of poly-Si. This analysis indicated that the surface of implanted films was amorphized by ion implantation and the amorphized layer thickness increased with dosing level. Also, it turned out that the lower poly-Si layer thickness increased from 30nm to 50nm after annealing accompanied by the conversion of a-Si layer to poly-Si layer. During annealing at low temperature, activation of phosphorus ions implanted into poly-Si and recrystallization of a-Si took place simultaneously and the sheet resistance after annealing decreased with the increase in thickness of the recrystallized region.
Stress-Temperature Behavior and Stress Relaxation in Ti/Al-0.5%Cu/TiN and TiN/W Thin Films
Authors: Doucet L. , Brun A. , Jaouen H. , Dupeux M. , Ignat M. 
Published: April 2011

AbstractThe stress behavior of two structures (Ti/Al-0.5%Cu/TiN and TiN/W) has been analyzed versus temperature up to 400 °C using the Flexus measurement system. Microstructure modifications induce stress variations with temperature. Furthermore, stress relaxation after annealing has been investigated. Al-based metallization stress is essentially due to thermal issues and reaches rapidly its yield strength whereas the W film exhibits high intrinsic stress. Microstructural observations afte deposition and after annealing have been conducted using a non destructive technique, the Thermal Wave Imager.
Structural and Magnetic Features of Fe-Based Multilayers with Thick Non-Magnetic Layers
Authors: Hage Y. , Nittono O. 
Published: April 2011

AbstractCoercivity and microstructure were investigated in Fe-based multilayers. Coercivity of the Fe layer near the film surface differs slightly from that of the layer near the substrate. The coercivity of a given Fe layer in the multilayer is related to the thickness of the given layer and to the total thickness of the layers between the given layer and the substrate. In addition, coercivity and microstructure are influenced when various metals are combined with Fe.
Temperature and Strain Rate Effects in Grain Boundary Sliding
Authors: Molteni C. , Francis G. P. , Payne M. C. , Heine V. 
Published: April 2011

AbstractWe have performed total energy density functional theory calculations to investigate the sliding process at the ∑ = 5 (001) twist grain boundary in germanium. The accurate quantum mechanical description of the interatomic bonding provides valuable insights into the mechanisms of bond breaking and remaking that occur during the sliding.In this paper we show how total energy calculations can be used to describe finite
temperature and strain rate effects in this grain boundary.
First-Principles Calculations of Heusler Phase Precursors in the Atomic Short-Range Order of Disordered BCC Ternary Alloys
Authors: Althoff Jeffrey D. , Johnson Duane D. 
Published: April 2011

AbstractWe apply our recently developed first-principles theory of atomic short-range order in disordered multicomponent alloys to CuAuZn2 and AgAuZn2, two alloys which display partially-ordered B2 phases as well as fully-ordered Heusler structures. The calculated Warren-Cowley pair correlation functions for both alloys peak at the special points 〈½ ½ ½〉 and 〈100〉, with the peak at 〈100〉 dominant. This is indicative of a tendency to B2 order at high temperatures, and a subsequent tendency to Heusler-type order at lower temperatures. An analysis in terms of effective interactions shows that the Au Zn interaction drives the 〈100〉 ordering tendency, while the Ag Au and Cu Au interactions contribute more to the 〈 ½ ½ ½〉ordering tendency - this effect is larger in CuAuZn2 and should lead to a slightly higher transition temperature for the B2 to Heusler transition in CuAuZn2 as compared to AgAuZn2.
Dissociative Adsorption and Desorption Processes of Cl2/GaAs(001) Surfaces
Authors: ohno Takahisa 
Published: April 2011

AbstractThe energetics of both dissociative adsorption of C12 molecules on reconstructed GaAs(001) surfaces and desorption of chlorides from the chlorinated GaAs(001) surfaces is theoretically investigated, employing the first-principles pseudopotential density-functional approach within the generalized gradient approximation. On the Ga-rich GaAs(001)-(4x2) surface a C12 molecule is found to dissociate with no potential barrier over a Ga dimer and the Ga dimer is also simultaneously broken upon chlorination, resulting in formation of GaC1 with two backbonds to the As layer below. The desorption energy of a GaCl molecule is smaller than that of a Cl atom, although the former involves breaking two Ga-As backbonds and the latter involves the breakup of one Ga-Cl bond. On the As-rich (2x4) surface, the dissociation of a C12 molecule over an As dimer is an activated process and the As dimer is not broken by the Cl adsorption. The desorption energy of a AsCI molecule is larger than that of a Cl atom. The obtained results are consistent with recent experiments such as temperature-programmed desorption measurements.
Hydrogenation Effects on Structures of Silicon Clusters
Authors: Miyazaki Takehide , Stich Ivan , Uda Tsuyoshi , Terakura Kiyoyuki 
Published: April 2011

AbstractWe have performed anab initiogeometry optimization of hydrogenated silicon clusters Si6Hx,(O ≤x≤ 12), within the generalized gradient approximation (GGA-PW91) in the density-functional theory. We have found that hydrogenation of Si6clusters provides contrasting effects on their stable structures depending onx. From calculation of zeropoint corrected formation energies, we also foundbistabilityof silicon clusters in the existence of hydrogen.
Small-Scale Simulations Of Lattice Fracture
Authors: Marder M. 
Published: April 2011

AbstractMany properties of rapid fracture may profitably be studied in atomic scale computer simulations involving relatively small numbers of atoms. A first result of such a study is that qualitative properties of Mode III fracture change little when one explores various shapes of the interparticle potential, introduction of randomness, and elevated temperatures. A second result is that Mode I fracture is considerably more susceptible to instability than had previously been understood, and that to obtain stable Mode I fracture may require non-central forces between atoms.
Stability Analysis Of Cracks Propagating In Three Dimensional Solids
Authors: Larralde H. , Al-Falou A. A. , Ball R. C. 
Published: April 2011

AbstractWe present a theory for the morphology of the fracture surface left behind by slowly propagating cracks in linear, isotropic and homogeneous three dimensional solids. Our results are based on first order perturbation theory of the equations of elasticity for cracks whose shape is slightly perturbed from planar. For cracks propagating under pure type I loading we find that all perturbation modes are linearly stable, from which we can predict the roughness of the fracture surface induced by fluctuations in the material. We compare our results with the classical results for cracks propagating in two dimensional systems, and discuss the effects in the three dimensional analysis which result from taking into account contributions from non-singular terms of the stress field, as well as the effects arising from finite speeds of crack propagation.
Modeling Acoustic Emission In Microfracturing Phenomena
Authors: Zapperi S. , Vespignani A. , Stanley H.E. 
Published: April 2011

AbstractIt has been recently observed that synthetic materials subjected to an external elastic stress give rise to scaling phenomena in the acoustic emission signal. Motivated by this experimental finding we develop a mesoscopic model in order to clarify the nature of this phenomenon. We model the synthetic material by an array of resistors with random failure thresholds. The failure of a resistor produces an decrease in the conductivity and a redistribution of the disorder. By increasing the applied voltage the system organizes itself in a stationary state. The acoustic emission signal is associated with the failure events. We find scaling behavior in the amplitude of these events and in the times between different events. The model allows us to study the geometrical and topological properties of the micro-fracturing process that drives the system to the self-organized stationary state.
Fractography Of Glass At The Nanometer Scale
Authors: Guilloteau E. , Arribart H. , Creuzet F. 
Published: April 2011

AbstractWe present a nanometer scale description of the fracture surface of soda-lime glass. This is achieved by the use of Atomic Force Microscopy. The mirror zone is shown to be built with elementary entities, the density of which increases continuously while the mist and hackle zones are approached. Moreover, the overall picture leads to some kind of self-similarity, in the sense that small regions of the hackle zone exhibit the full set of mirror, mist and hackle areas.
Growth and Structure of Carbide Nanorods
Authors: Lieber Charles M. , Wong Eric W. , Dai Hongjie , Maynor Benjamin W. , Burns Luke D. 
Published: April 2011

ABSTRACTRecent research on the growth and structure of carbide nanorods is reviewed. Carbide nanorods have been prepared by reacting carbon nanotubes with volatile transition metal and main group oxides and halides. Using this approach it has been possible to obtain solid carbide nanorods of TiC, SiC, NbC, Fe3C, and BCx having diameters between 2 and 30 nm and lengths up to 20 µm. Structural studies of single crystal TiC nanorods obtained through reactions of TiO with carbon nanotubes show that the nanorods grow along both [110] and [111] directions, and that the rods can exhibit either smooth or saw-tooth morphologies. Crystalline SiC nanorods have been produced from reactions of carbon nanotubes with SiO and Si-iodine reactants. The preferred growth direction of these nanorods is [111], although at low reaction temperatures rods with [100] growth axes are also observed. The growth mechanisms leading to these novel nanomaterials have also been addressed. Temperature dependent growth studies of TiC nanorods produced using a Ti-iodine reactant have provided definitive proof for a template or topotactic growth mechanism, and furthermore, have yielded new TiC nanotube materials. Investigations of the growth of SiC nanorods show that in some cases a catalytic mechanism may also be operable. Future research directions and applications of these new carbide nanorod materials are discussed.