bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface Chemistry of CVD Diamond: Linking the Nanoscale and Mesoscale Modelling Hierarchies
Authors: Oleinik I.I. , Pettifor D.G. , Sutton A.P. , Battaile C.C. , Srolovitz D.J. , Butler J.E. 
Published: April 2011

AbstractThe β-scission growth mechanism at the diamond (100) (2×1) surface is studied by a combination of nanoscale ab-initio LDA/GGA and semiempirical tight-binding techniques to provide the necessary input into the mesoscale variable time step Kinetic Monte-Carlo (KMC) simulations of CVD diamond growth. The reaction path of the beta-scission reaction is critically examined and the activation barrier of the reverse etching of the methylene adsorbate is deduced. Our quantum mechanical calculations support a previous semiempirical PM3 study confirming that the molecular mechanics values for the entalphy of the reaction are a factor of 2 wrong. This conclusion provides strong support for the preferential etching mechanism introduced into KMC to predict experimentally measured growth rates.
Atomic-Scale Modeling of the Deformation of Nanocrystalline Metals
Authors: Schiotz J. , Vegge T. , Jacobsen K. W. 
Published: April 2011

AbstractNanocrystalline metals, i.e. metals with grain sizes from 5 to 50 nm, display technologically interesting properties, such as dramatically increased hardness, increasing with decreasing grain size. Due to the small grain size, direct atomic-scale simulations of plastic deformation of these materials are possible, as such a polycrystalline system can be modeled with the computational resources available today.We present molecular dynamics simulations of nanocrystalline copper with grain sizes up to 13 nm. Two different deformation mechanisms are active, one is deformation through the motion of dislocations, the other is sliding in the grain boundaries. At the grain sizes studied here the latter dominates, leading to a softening as the grain size is reduced. This implies that there is an “optimal” grain size, where the hardness is maximal.Since the grain boundaries participate actively in the deformation, it is interesting to study the effects of introducing impurity atoms in the grain boundaries. We study how silver atoms in the grain boundaries influence the mechanical properties of nanocrystalline copper.
Multiscale Simulations of the RF Diode Sputtering of Copper
Authors: Wadley H. N. G. , Zou W. , Zhou X. W. , Groves J. F. , Desa S. , Kosut R. , Abrahamson E. , Ghosal S. , Kozak A. , Wang D. X. 
Published: April 2011

AbstractThe morphology and microstructure of RF diode sputter deposited materials is a complicated function of many parameters of the reactor operating conditions. Using a combination of computational fluid dynamics (CFD), RF plasma, molecular dynamics (MD) sputter, and direct simulation Monte Carlo (DSMC) transport models, a multiscale approach has been used to analyze the RF diode sputtering of copper. The CFD model predicts the velocity and pressure distribution of the working gas flows in the deposition chamber. The plasma model uses these CFD results to compute ion energies and fluxes at the target and substrate. The MD model of sputtering is used to determine the initial energy distribution of sputtered atoms and reflected neutral working gas atoms and both of their angular distributions. A DSMC transport model then deduces the target atom deposition efficiency, the spatial distribution of the film thickness, the target and reflected neutral atoms energy and impact angle distributions given reactor operating input conditions such as background pressure, temperature, gas type, together with the reactor geometry. These results can then be used in atomistic growth models to begin a systematic evaluation of surface morphology, nanoscale structure, and defects dependences upon the reactor design and its operating conditions.
Multiscale Analysis of Interfacial Stability and Misfit Dislocation Formation in Layer-By-Layer Semiconductor Heteroepitaxy
Authors: Zepeda-Ruiz L. A. , Maroudas D. , Weinberg W. H. 
Published: April 2011

AbstractA theoretical analysis based on continuum elasticity theory and atomistic simulations is presented of the interfacial stability with respect to misfit dislocation formation, the strain fields, and the film surface morphology during layer-by-layer semiconductor heteroepitaxy. The energetics of the transition from a coherent to a semicoherent interface consisting of a misfit dislocation network, the structure of this semicoherent interface, the resulting strain fields and the morphological characteristics of the epitaxial film surfaces are calculated for InAs/GaAs(111)A. Continuum elasticity is found to describe the atomistic simulation results very well. Our theoretical results are discussed in the context of recent experimental data.
Discrete Dislocations Interacting with a Mode I Crack
Authors: Cleveringa H.H.M. , Giessen E. Van Der , Needleman A. 
Published: April 2011

AbstractSmall scale yielding around a plane strain mode I crack is analyzed using discrete dislocation dynamics. The dislocations are all of edge character, and are modeled as line singularities in an elastic material. At each stage of loading, superposition is used to represent the solution in terms of solutions for edge dislocations in a half-space and a complementary solution that enforces the boundary conditions. The latter is non-singular and obtained from a linear elastic, finite element solution. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and dislocation annihilation are incorporated into the formulation through a set of constitutive rules. A relation between the opening traction and the displacement jumps across a cohesive surface ahead of the initial crack tip is also specified, so that crack initiation and crack growth emerge naturally. Material parameters representative of aluminum are employed. Two cases are considered that differ in the strength and density of dislocation obstacles. Results are presented for the evolution of the dislocation structure and the near-tip stress field during the early stages of crack growth.
Silicon Self-Interstitial Clusters
Authors: Colombo L. , Bongiorno A. , ROSATI M. 
Published: April 2011

AbstractA tight-binding molecular dynamics investigation on the structure and energetics of self-interstitial clusters in silicon is presented. We discuss how a small number of self-interstitial atoms give rise to the formation of tedrahedally-shaped clusters, while a larger number of defects exhibit a self-organization mechanism driving the system to form rod-like defects.
Quantitative Calculation of Dislocation Mobility
Authors: Swaminarayan S. , Preston D. L. 
Published: April 2011

AbstractWe present a new method to calculate the response of dislocations to applied stress. This new method, called the dislocation treadmill, can be used to study the effect of vacancies, interstitials, stresses, strain rate, temperature etc., on the steady state velocity of the dislocation. We demonstrate the use of the method by calculating the response of a dislocation to a constant applied shear stress.
Interatomic Potentials for Al and Ni From Experimental Data and AB Initio Calculations
Authors: Mishin Y. , Farkas D. , Mehl M. J. , Papaconstantopoulos D. A. 
Published: April 2011

AbstractNew embedded-atom potentials for Al and Ni have been developed by fitting to both experimental data and the results of ab initio calculations. The ab initio data were obtained in the form of energies of different alternative computer-generated crystalline structures of these metals. The potentials accurately reproduce basic equilibrium properties of Al and Ni such as the elastic constants, phonon dispersion curves, vacancy formation and migration energies, stacking fault energies, and surface energies. The equilibrium energies of various alternative structures not included in the fitting database are calculated with these potentials. The results are compared with predictions of total-energy tight-binding calculations for the same structures. The embedded-atom potentials correctly reproduce the structural stability trends, which suggests that they are transferable to different local environments encountered in atomistic simulations of lattice defects.
A Model of Strain Distribution in Nanocrystalline SiC and Diamond at Very High Pressures; In-Situ X-RAY Diffraction Study and Computer Modelling
Authors: Pielaszek R. , Palosz B. , Gierlotka S. , Stel'Makh S. , Bismayer U. 
Published: April 2011

AbstractA modeling of nanoparticles and ab initio simulation of the scattered intensity from the Debye functions is used as a tool for an examination of the strain induced under high pressure in nanocrystalline silicon carbide and diamond. The analysis of the experimental intensity profiles includes a determination of the atomic structure and microstructure of the materials. The advantages of modeling over conventional methods of the analysis of powder diffraction data are discussed. Examples of using the modeling for determination of the shape and size and of one dimensional disordering in very small particles (2-4 nm), and development of internal strains in 10 nm SiC nanocrystals subjected to high pressures are given.
Structural Characterization of AION by27 Al Mas NMR and Quantum Chemistry Method
Authors: Dai Ying , Min Xin-Min , Nan Ce-Wen , Pei Xin-Mei , Ren Hai-Lan 
Published: April 2011

AbstractAluminum oxynitride (AlON) is a nitrogen-stabilized defective spinel phase of alumina (y-Al2O3). Its structure has not been well understood so far. Solid-state27 Al magic-angle spinning nuclear magnetic resonance and quantum chemistry calculation are used to characterize y-Al2O3 and AMON ceramics in the present study. The resonance spectra clearly show different units (e.g. [AlN4], [AlO4] and [AlO6]) and vary with composition. The calculation shows that the vacancy located at octahedral site is more stable than that located at the tetrahedral site, and nitrogen atoms preferentially replace oxygen atoms in the tetrahedral site, which is in agreement with the experimental analysis by nuclear magnetic resonance.
Flux Dependent Generation Rates of Radiation-Induced Defect Clustering in n-Si Under 17 MeV Proton Irradiation
Authors: Kono K. , Amekura H. , Kishimoto N. 
Published: April 2011

AbstractProton flux and temperature dependent generation rates of radiation-induced defect clusters under 17 MeV proton irradiation have been studied by in-situ Deep Level Transient Spectroscopy (DLTS) measurement, to obtain information on clustering processes. The proton flux was ranged from 2.51×10up to 1.6×1012ions/cm2s with irradiation temperature 200 K or 300 K. Flux dependence is related to the ratio of impurity and primary defect concentrations created during irradiation. Change in temperature mainly modifies the diffusion constants of defects which determine the reaction rates. Rate equations of the defect reactions based on the Oerlein model [1] were solved numerically and compared to the experimental results. The numerical calculation successfully explained temperature and flux dependence except in the higher flux region.
Radiation Induced Nucleation of Nanoparticles in Silica
Authors: Ila D. , Williams E. K. , Poker D. B. , Hensley D. K. , Klatt C. , Kalbitzer S. 
Published: April 2011

AbstractIn this paper, we present the results of our investigation of producing nanoclusters of gold in silica at fluences of two orders of magnitude less than what is traditionally used This is accomplished by implanting 2.0 MeV Au into silica followed by MeV bombardment by MeV Si ions. The size of the nanoclusters, ranging from one to 10 nanometers, is controlled by the implantation dose and by the total electronic energy deposited by each post bombarding ion in the implanted layer. By both indirect measurement methods, such as optical absorption spectrophotometry (non-destructive), and direct methods, such as transmission electron microscopy (destructive) we show how and at what concentrations gold nucleates to form nanoparticles by radiation-enhanced nucleation at a dose below that needed for spontaneous nanoparticle formation.
Selective Intermixing of Ion Irradiated Semiconductor Heterostructures
Authors: Goldberg R. D. , Mitchell I. V , Piva P. G. , Tan H. H. , Jagadish C. , Poole P. J. , Aers G. C. , Charbonneau S. , Weatherly G. C. , Johnson M. B. , Gal M. , Springthorpe A. J. , Chen H. , Feenstra R. M. 
Published: April 2011

AbstractSignificant progress has been realized in the use of quantum well intermixing (QWI) as a method for tailoring the bandgap energies of optoelectronic devices. Intermixing can be driven by an ion implantation process, an approach that appeals because of its simplicity, its planarity and its adaptability to selective area processing. Despite its success, the advantages of irradiation induced QWI need to be tested further and we report here current results of three research activities which address a) the existence or not of a simple scaling relationship which connects intermixing in a given QW structure for any ion species; b) reproducibility of intermixing in identical QW structures which have been obtained from different growth systems; and c) intermixing for above the well versus through the well implantation.
Accumulation and Recovery of Irradiation Effects in Silicon Carbide
Authors: Weber W.J. , Jiang W. , Thevuthasan S. , Mecready D.E. 
Published: April 2011

AbstractSingle crystals of 6H-SiC have been irradiated with a variety of ions over a wide range of fluences and temperatures. The temperature and dose dependence of damage accumulation has been investigated using in-situ Rutherford Backscattering Spectrometry in channeling geometry. At low temperatures, the accumulation of structural disorder exhibits a sigmoidal dependence on dose. At room temperature and higher, simultaneous recovery processes during irradiation significantly reduce the damage accumulation rates by up to a factor of five. Isochronal and isothermal annealing studies have been used to study the damage recovery behavior. For low defect concentrations introduced by 550 keV Si+ irradiation at 160 K, complete recovery is observed at 300 K. However, defects introduced by He+ irradiation on the Si sublattice are more difficult to anneal at room temperature, which suggests trapping of the implanted helium may inhibit defect recombination. Below room temperature, the thermal recovery of defects on the Si sublattice has an activation energy on the order of 0.3 ± 0.1 eV. Defect recovery above 570 K has an activation energy on the order of 1.5 ± 0.3 eV.
Proton Irradiation Induced Defects in 611- and 4H-SiC
Authors: Puff Werner , Balogh Adam G. , Mascher Peter 
Published: April 2011

AbstractAnnealing of defects in proton irradiated bulk n-type 6H- and semi-insulating 4H-SiC has been investigated by positron lifetime spectroscopy and Doppler-broadening measurements. For the n-type sample radiation induced defects in dependence of the proton fluence were studied. Three or four annealing stages were found, during which the formation of larger defect complexes could be observed.
Heavy-Ion Irradiation Induced Diamond Formation in Carbonaceous Materials
Authors: Daulton T. L. , Lewis R. S. , Rehn L. E. , Kirk M. A. 
Published: April 2011

AbstractMetastable phase formation under highly non-equilibrium thermodynamic conditions within high-energy particle tracks are investigated. In particular, the possible formation of diamond by heavy-ion irradiation of graphite at ambient temperature is examined. This work was motivated, in part, by an earlier study which discovered nanometer-grain polycrystalline diamond aggregates of submicron-size in uranium-rich carbonaceous mineral assemblages of Precambrian age. It was proposed that these diamonds were formed within the particle tracks produced in the carbonaceous minerals by the radioactive decay of uranium. To test the hypothesis that nanodiamonds can form by ion irradiation, fine-grain polycrystalline graphite sheets were irradiated with 400 MeV Kr ions to low fluence (6 × 1012 ions-cm−2). The ion-irradiated (and unirradiated control) graphite were then subjected to acid dissolution treatments to remove the graphite and isolate any diamonds that were produced. These acid residues were characterized by transmission electron microscopy. The acid residue of the ion-irradiated graphite was found to contain nanodiamonds (at several ppm of bulk), demonstrating that ion irradiation of graphite at ambient temperature can produce diamond.
Influence of Electron Beam Irradiation on The Nucleation of Fine Water Drops on Misted Silicate (SiO2) Glass
Authors: Oguri K. , Sato K. , Izumi T. , Tonegawa A. , Takayama K. , Nishi Y. 
Published: April 2011

AbstractBy using an electron beam irradiation, reproducible active surface condition of misting can be obtained on the silicate glass. Since an electron beam irradiation activates the SiO2 surface, it controls and enhances the nucleation frequency of fine water drops. The dangling bond is one of reasons to activate the surface condition. Based on the results of electron spin resonance (ESR) spectra, the electron beam irradiation increases the density of E'-center on the surface.
Measurement of Oxygen Disorder and Nano-Twin Microstructure Associated with Columnar Defects In Ybco
Authors: Yan Y. , Walther T. , Kirk M.A. 
Published: April 2011

AbstractStudies of defects generated by high energy (>1 GeV) heavy ion irradiation in high-Tc superconductors have been performed by transmission electron microscopy (TEM). Our study shows that high dose irradiation leads to the formation of nano-twins, by which the columnar defects are connected. An analysis of the local Fourier components of the image intensity in [001] lattice images indicates that these new "twin" boundaries are much more diffuse than preexisting twin boundaries in YBCO. The mechanism of the formation of nano-twin boundaries on {110} planes and their possible relation to superconducting properties are discussed.
Damage Accumulation and Thermal Recovery in SrTiO3 Implanted with Au2+ Ions
Authors: Thevuthasan S. , Jiang W. , Weber W.J. , McCready D.E. 
Published: April 2011

AbstractDamage accumulation and recovery process have been investigated in single crystal SrTiO3 irradiated with 1.0 MeV Au2+ using in-situ Rutherford Backscattering Spectrometry (RBS) in Channeling geometry. Samples were irradiated at a temperature of 200 K with ion fluences ranging from 5.0×1013 2.5×1014Au2+/cm2 (0.22 – 1.10 dpa at damage peak). Subsequent isochronal annealing experiments were performed to study damage recovery processes up to a maximum temperature of 870 K. At an ion fluence between 2.0–2.5×1014Au2+/cm2 (0.88 – 1.10 dpa), the implanted region, which is just below the surface, becomes amorphous. The recovery processes occur over a broad temperature range, and the damage created by low ion fluences, 5.0×1013 − 1.0×1014 Au2+/cm2, is almost completely recovered after annealing at 870 K.
Phase Transformations Induced in Metallic Glasses by Pulsed Laser and Alpha Particle Beam Irradiation
Authors: Sorescu M. 
Published: April 2011

AbstractNd:YAG laser (λ,=532 nm, τ=8 ns, Φ =30 J/cm2, v=10 Hz) induced transformations in Fe81B135Si35C2metallic glass were characterized by transmission and conversion electron Mossbauer spectroscopy, hysteresis loops and ac susceptibility measurements. The radiation-driven changes were further compared with alpha particle beam irradiation effects (W=2.8 MeV, Φ=1016and 1017 cm−2) in the same amorphous material. Pulsed laser irradiation of Fe81B135Si3.5C2 metallic glass was found to induce magnetic anisotropy, surface oxidation, onset of crystallization, slight increase in the saturation magnetic moment and changes in the imaginary susceptibility component. Alpha particle beam irradiation of Fe81B13.5Si3.5C2 metallic glass caused partial crystallization of the bulk of the specimen, total crystallization of the surface, as well as dose-dependent changes in the saturation magnetic moment, hysteresis and real susceptibility component.
Post-Irradiation Annealing and Intergranular Segregation and Desegregation
Authors: Kameda J. , Bloomer T. E. 
Published: April 2011

AbstractThe effect of post-irradiation annealing (PIA: at 573-958 K for 0.1-1000 h) on the intergranular S and P segregation has been examined in ferritic alloys doped with Cu and/or P, all containing residual S. In a Cu-doped alloy showing no P segregation, the rate and amount of segregated S were promoted more by PIA than thermal annealing. Intergranular P enrichment was observed during an early PIA stage at lower temperatures in P-containing alloys. The intergranular P desegregation and S segregation concurrently occurred at higher PIA temperatures. By applying a modified McLean theory, it is shown that the S segregation in the post-irradiation annealed Cu-doped alloy is controlled by vacancy-enhanced diffusion while the P segregation in P-containing alloys subjected to lower temperature PIA proceeds via mobile P-interstitial complexes. Based on a Gaussian relaxation model, the P desegregation during prolonged PIA at higher temperatures is assisted by the formation and migration of vacancies.
Effect of Radiation Damage on Bwr Core-Shroud Cracking
Authors: Kwon Jun , Motta Arthur T. 
Published: April 2011

AbstractA model is presented that estimates the effect of radiation damage on stress corrosion cracking (SCC), resulting from microstructural evolution induced by irradiation. The model is based on the Ford-Andresen film-rupture and slip-dissolution model and on the observation that the crack propagation rate increases as the material hardens. The model relates the neutron and gamma exposure to the irradiation hardening and consequent increase in the crack tip strain rate. A chemical rate theory model was employed to describe the evolution of microstructure in stainless steel leading to radiation hardening. The increase in yield stress can be correlated to an increase in the crack tip strain rate, and thus to SCC behavior. This approach was used to evaluate the effects of irradiation hardening on core shroud cracking. The results show that hardening can have a substantial effect on core shroud cracking.
Effects of Pre-Existing Thermal Sensitization on the Radiation Induced Sensitization in Type 304 Stainless Steels
Authors: Wang L.H. , Tsai C.H. , Kai J.J. , Duh T.S. 
Published: April 2011

AbstractI is generally recognized that radiation induced sensitization plays an important role in initiating irradiation assisted stress corrosion cracking (IASCC) of austenitic stainless steels in reactor core internal of light water reactor. However, the synergism between radiation sensitization and prior thermal sensitization is unclear. This situation is likely to occur in most welded core internal structures subjected to neutron irradiation. In this study, the effect of prior thermal treatment on radiation sensitization were investigated on proton irradiated Type 304 stainless steel (SS) of initially as-received (AR) and thermal-sensitized (SEN) conditions. The Cr depletion profiles were measured by field emission gun transmission electron microscopy/ energy dispersive spectroscopy (FEGTEM / EDS), and were calculated by a radiation induced segregation (RIS) model.The different initial conditions were input in the RIS model calculations. For the asreceived condition, the initial Cr profile was modeled by a uniform concentration distribution. For the initially thermal-sensitized condition, the wider Cr depletion profile measured by FEGTEM / EDS was input as the initial condition. The results showed that radiation sensitization is characterized by a very narrow Cr depleted zone. The Cr content at grain boundary tends to be lower as radiation dose increases. Comparing with the non-sensitized (asreceived) specimens with the same dosage, the grain boundary Cr content without prior sensitization is higher than that with sensitization pre-treatment. The deeper grain boundary Cr concentration of irradiated thermally sensitized sample is induced not only from proton irradiation effect, but also resulted from the pre-existing Cr depletion.