bluuebunny/crossref_metadata_2025 huggingface dataset:
Dopant Loss Origins of Low Energy Implanted Arsenic and Antimony for Ultra Shallow Junction Formation
Authors: Shibahara Kentaro , Furumoto Hiroaki , Egusa Kazuhiko , Koh Meishoku , Yokoyama Shin
Published: April 2011

We have investigated the origins of sheet resistance increase in ultra shallow junctions formed by low energy As or Sb implantation. The increase is mainly attributed to dopant loss during annealing due to pileup of dopant at Si02/Si interface. This problem is common to As and Sb and will become more significant as the implantation energies are decreased. We found that the pileup can be classified into two stages from the time dependence of Sb SIMS depth profile .In the early stage of annealing the pileup is very fast and is probably related to the transport of the dopants due to solid phase epitaxial growth of an amorphized layer formed by the implantation. In the later stage the pileup is much slower and is considered to be governed by dopant diffusion.
Transient Enhanced Diffusion for Ultra Low Energy Boron, Phosphorus, and Arsenic Implantation in Silicon
Authors: Yu Ning , Jain Amitabh , Mercer Doug
Published: April 2011

The SIA roadmap predicts that junction depths of 500 angstroms are required for CMOS technology nodes of 0.18 μm or beyond by the year 2001. There are several ultra-shallow junction doping techniques currently under investigation. These include beamline ion implantation, plasma immersion ion implantation, and gas immersion laser doping. This study was based on beamline ion implantation of B, P, and As into single-crystal Si wafers at 0.25-2 keV to doses of (2- 10)×1014 at./cm2 with minimized beam energy contamination. Rapid thermal annealing was applied to the implanted wafers at 1000-1050 °C for 10-15 sec at ramp rates of 35- 50 °C/s in a N2 ambient. Transient enhanced diffusion was observed for all three implant species. For example, the depth of 0.25 keV B measured by SIMS increases from 250 to 520 A at a concentration level of l×1017 at./cm3 upon RTA. To minimize the TED, several schemes of defect engineering were applied prior to low energy implantation, including pre-amorphization and implantation of other species. A comparison of TED for different implantation conditions is given with the aim of process development for minimizing TED. The impact of energy contamination on ultra shallow junctions is also addressed.
Atomistic Modeling of Point and Extended Defects in Crystalline Materials
Authors: Jaraiz Martin , Pelaz Lourdes , Rubio Emiliano , Barbolla Juan , Gilmer George H. , Eaglesham David J. , Gossmann Hans J. , Poate John M.
Published: April 2011

Atomistic process modeling, a kinetic Monte Carlo simulation technique, has the interest of being both conceptually simple and extremely powerful. Instead of reaction equations it is based on the definition of the interactions between individual atoms and defects. Those interactions can be derived either directly from molecular dynamics or first principles calculations, or from experiments. The limit to its use is set by the size dimensions it can handle, but the level of performance achieved by even workstations and PC's, together with the design of efficient simulation schemes, has revealed it as a good candidate for building the next generation of process simulators, as an extension of existing continuum modeling codes into the deep submicron size regime. Over the last few years it has provided a unique insight into the atomistic mechanisms of defect formation and dopant diffusion during ion implantation and annealing in silicon. Object-oriented programming can be very helpful in cutting software development time, but care has to be taken not to degrade performance in the critical inner calculation loops. We discuss these techniques and results with the help of a fast object-oriented atomistic simulator recently developed.
Boron Ted in Pre-Amorphised SI: Role of the A/C Interface
Authors: Mathiot D. , Bonafos C. , OMRI M. , Alquier D. , Martinez A. , Claverie A.
Published: April 2011

In this paper we first review the main experimental results concerning boron diffusion in preamorphised silicon, focusing on the role played by the End Of Range defects. It is then shown that the application of the Ostwald ripening theory to the particular geometry of these defects permits to understand why and how they affect dopant diffusion. Contradictory experimental results can be reconciled if one considers that most of the diffusion enhancement occurs during the nucleation stage of the extended defects, and that the amorphous / crystalline interface is a perfect screen for the diffusion of the self-interstitials.
Wet And Dry Oxidation of Polycrystalline SixGe1-x Films
Authors: Hellberg P.-E. , Zhang S.-L. , d'Heurle F. M. , Petersson C. S.
Published: April 2011

Wet and dry oxidations of polycrystalline SixGe1-x, with various compositions have been studied at different temperatures. The growth rate of SiO2 is found to be enhanced by Ge, and the enhancement effect is more pronounced in H2O than in O2. A mathematical model, which assumes simultaneous oxidation of Si and Ge and reduction of GeO2 by free Si available at the growing-oxide/SixGe1-x interface, is found to give a quantitative description of the SiO2 growth during thermal oxidation of SixGe1-x. Kinetic parameters are extracted by comparing the model with experiments. The linear and parabolic rate constants for Si oxidation are determined on control Si (100) wafers and polycrystalline Si films. Simple expressions are used for the interdiffusion of Si and Ge in SixGe1-x. For wet oxidation, the activation energy for the reaction rate constant of Ge oxidation is found to be smaller than that of Si oxidation.
Evidence For Heterojunction Effects in Polycrystalline Si1-xGex Thin Film Transistors With Si Caps
Authors: Wang Albert W. , Saraswat Krishna C.
Published: April 2011

Polycrystalline silicon-germanium (poly-Si1-xGex) thin film transistors (TFTs) werefabricated with and without Si interlayers (caps) to buffer the SiO2 gate dielectric and theSi1-xGex channel. Both low temperature processes (≤ 550 °C) compatible with glass for flat panel displays and high temperature processes were used. NMOS TFTs show dramatic performanceimprovements up to moderate (5 to 10 nm) interlayer thicknesses. In contrast, PMOS TFTs showonly small improvements at low interlayer thicknesses (< 5 nm), after which performancedeclines. Computer simulations using an effective medium model for polycrystalline materialssuggest that in addition to interface improvement, a pseudomorphic heterojunction is formedfrom the strained Si cap and unstrained poly-Si1-xGex channel with both conduction and valenceband offsets. These offsets play a significant role in inversion layer formation.
Photonic Crystals Based onMacroporous Silicon
Authors: Lehmann V. , Grüning U. , Birner A.
Published: April 2011

The formation of macropore arrays with high aspect ratios by electrochemical etching of n-type silicon in hydrofluoric acid is a well established technique. By using standard photolithograpy the geometry of the array can be controlled with high precision. This enables us to fabricate twodimensional photonic crystals for the infrared regime. The calculated photonic band structure of the crystal corresponds well with the transmission observed experimentally. Furthermore first defect structures like waveguides and cavities have been realized.
Fabrication Of Sub 30 Nanometer Sheets Of Single Crystalline Silicon
Authors: Flemitng J. G.
Published: April 2011

A relatively simple technique for the fabrication of sub 30 rim thick sheets of perfect single crystalline silicon is described. The thinnest sheets formed were 15 nim thick. The width of the sheets is 300–1000 nmn and the length of the sheets can be tens of microns. The sheets are crystallographically well defined with the thin dimension being bound by atomically smooth {111} planes. The sheets are fabricated using a combination of reactive ion etching and wet KOH etching steps.
Band Alignment of Si1-xGex And Si1-x-y.GexCy Quantum Wells On Si (001)
Authors: Rowell N. L. , Williams R. L. , Aers G. C. , Lafontaine H. , Houghton D. C. , Brunner K. , Eberl K. , Schmidt O. , Winter W.
Published: April 2011

Recent low-temperature photoluminescence (PL) studies will be discussed for coherent Si1-xGex. and Si1-xGexCy alloy multiple quantum wells on Si (001) substrates grown by either ultra-high vacuum chemical vapour deposition or solid source molecular beam epitaxy. An in-plane applied-stress technique will be described which removes systematically band edge degeneracies revealing the lower, PL-active CB. Applied-stress data taken with this technique at ultra-low excitation intensity proved intrinsic type II CB alignment in SiGe on Si (001). Apparent type I alignment observed at higher intensity will also be discussed. New applied stress PL results are presented for Si1-x-yGexCy quantum wells under various grown-in stress condition
Strong Deviation Of The Lattice Parameter In Si1-x-yGexCy Epilayers From Vegard's Rule
Authors: Stangl J. , Zerlauth S. , Schäffler F. , Bauer G. , Berti M. , Salvador D. De , Drigo A. V. , Romanato F.
Published: April 2011

From the comparison of precise determinations of the Ge and C contents of a series of Si1-x-yGexCy epilayer samples (x < 0.18, y < 0.02) by Rutherford and resonant backscattering experiments and x-ray diffraction, the variation of the Si1-x-yGexCy lattice spacing as a function of C content is determined. A significant negative deviation from Vegard's rule is observed, in agreement with theoretical predictions by Kelires.
Evidence for Substitutional C, Ordering Effects and Interdiffusion in Epitaxial GE-C and GE-RICH GE-SI-C Alloys
Authors: Yang Bi-Ke , Weber W. H. , Krishnamurthy M.
Published: April 2011

We report on the epitaxial growth of Ge-C and Ge-Si-C alloys (C<10%) grown on Si(100) and Ge(100) substrates using low temperature (∼200°C) molecular beam epitaxy. Thin films (50–70 nm) were characterized in-situ by RHEED and ex-situ by transmission electron microscopy, xray diffraction, and Raman spectroscopy. The films were annealed at 750°C and 850°C in an Ar atmosphere to study interdiffusion effects.

Raman spectroscopy of Ge-C on Ge indicates the existence of a Ge-C local mode at 530cm−1 and is direct evidence for the presence of substitutional C in Ge. The GeSiC alloys grown on Ge do not show the Ge-C local mode, consistent with preferential Si-C bonding. There is evidence for strain enhanced solubility of C based on a comparison of the substitutional C content in Ge-C films on Si (∼1 at %) and on Ge substrates (∼0.1 at %). Silicon interdiffusion in annealed Ge-C samples is strongly suppressed by the presence of C. A simple diffusion model is used to illustrate Si indiffusion in Ge.
Device And Fabrication Issues of High Performance Si/Sige Fets
Authors: Arafa M. , Adesida I. , Ismail K.
Published: April 2011

A review of the latest results on high performance Si/SiGe FETs grown on relaxed buffer is presented. A discussion of the fabrication issues facing the achievement of these devices is also included.
Growth of GaN on Thin SI {111} Layers Bonded to SI {100} Substrates
Authors: Fleming J. G. , Han Jung
Published: April 2011

We have demonstrated the ability to bond thin layers of Si {111} onto either silicon dioxide or silicon nitride coated Si {100}. This was achieved using a “Smart-Cut” process. The integration of SiN required chemical mechanical polishing. The growth of GaN on a thin Si {111} on oxide on Si {100} stack was demonstrated.
Effect of Microstructure and Chemical Bonding on the Adhesion Strength of a Silicon/Polymer Interface for Microelectronic Packaging Applications
Authors: Pantelidis Dimitrios , Lee Hoo-Jeong , Bravman John C.
Published: April 2011

Interface reinforcement brought about by addition of a γ-amino-propyl-triethoxy-silane (γ-APS) adhesion promoter layer between a silicon wafer and a spun-on benzocyclobutene polymer (BCB) is investigated. Combining cross-sectional TEM and XPS, crack growth is shown to occur along the γ-APS/BCB interface. Ion etching and in-situ XPS are further employed to study chain orientation and chemical bonding variations through the silane layer. A tendency of the amide group to orient away from the wafer is documented and Si-O-Si siloxane bonding at the γ- APS/SiO2 interface is hypothesized as an important mechanism for adhesion strength enhancement.
Mocvd-Preparation And In-Situ/Uhvanalysis Of Epitaxial Inp-Films
Authors: Hannappel T. , Visbeck S. , Knorr K. , Zorn M. , Willig F.
Published: April 2011

Surface science analysis can be utilized for improving the preparation of hetero-interfaces. Epitaxial InP(100)-films were prepared with TBP (tertiarybutylphosphine) and TMin (trimethylindium) as precursors in a commercial MOCVD apparatus. With a new type of transfer system the sample is shifted from the MOCVD apparatus to a UHV chamber within 20 s. A description of the new transfer system is given. RAS (reflection anisotropy spectroscopy) is carried out in the MOCVD and UHV environments. It shows whether the InP(100) surface corresponds to the (2×1) or (2×4) reconstruction or whether it is oxidized. For the first time contamination-free transfer of the (2×1) reconstructed, P-rich InP(100) surface is achieved.
Growth And Characterization Of Amorphous Ain Thin Films By Reactive Magnetron Sputtering At Low Temperature
Authors: Gurumurugan K. , Chen Hong , Harp G. R.
Published: April 2011

We present the first report of the preparation and characterization of α-AIN films using reactive magnetron sputtering at cryogenic temperature. By comparison, analogous films grown at room temperature were polycrystalline. The films were characterized using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Rutherford Backscattering Spectrometry (RBS), Infrared (IR) Spectroscopy and optical transmission. XRD studies on films grown at room temperature showed diffraction peaks corresponding to (100), (101), (102) and (210) planes. In contrast, no peaks were observed for AIN films formed at liquid nitrogen temperature confirming the amorphous nature of the films. Composition analysis using RBS showed the presence of Al and N in ˜1:1 stoichiometry. The films were highly transparent and the computed bandgaps of αand c-AIN films were 5.90 and 5.89 eV respectively. We also consider the possibilities of wet etching the AIN films in diluted KOH solution and the results are discussed.
Effects of CF4, Reactive ion Etching on Si-Doped Al0.2Ga0.8As
Authors: Ito Akira , Sakai Atsuyoshi , Tokuda Yutaka
Published: April 2011

Effects of CF4 reactive ion etching on electrical characteristics of Si-doped Al0.2Ga0.8As layers were studied with capacitance-voltage and deep level transient spectroscopy measurements. Plasma exposure for about 30 s drastically degrades the electrical characteristics. Post-annealing at 360 °C for 20 s partially recovers the carrier concentrations. After the post-annealing, some electron traps were observed. Two of the traps show bi-stability. The concentrations of the two traps increase with forward bias temperature annealing and decrease with reverse bias temperature annealing.
Study of SI1−xGEx / SI / SI1−xGEx Heterostructures with abrupt interfaces for ultrahigh mobility FETS
Authors: Sugii N. , Nakagawa K. , Yamaguchi S. , Miyao M.
Published: April 2011

We grew Si1−x, Gex / Si / Si1−xGex heterostructures with abrupt interfaces for a high-speed device application. In order to eliminate the interface and the impurity scatterings, a two-stepsolid-phase epitaxy (SPE) was developed newly. This SPE can obtain an abrupt interface between the upper Si1−xGex. and the Si-channel layers as well as a sharp Sb-doping profile in the upper Si1−xGex layer. Single-step SPE growth of the Si1−xGex. layer including the Sb-doped layer caused solid state diffusion of Sb and made the doping-profile difficult to control. A two-step SPE, (that is, two independent SPE processes forming the Si1−xGex. and the Sb-doped layers), obtained a sharp Sb depth profile and high electrical activation in the Sb-doped Si1−xGex. layer. However, the number of modulation-doped carriers in the Si channel layer was small. Calculation of the carrier distribution between the channel and the doped layer suggests that the carrier density in the channel is low when the Sb-doping profile is extremely sharp; thus, precise control of the modulation-doped-carrier density by optimizing the thickness of the Sb-doped layer is crucial for operating modulation-doped field-effect transistors (MODFETs).
Surface Termination of the Ge(100) and Si(100) Surfaces by Using DHF Solution Dipping
Authors: Sakuraba M. , Matsuura T. , Murota J.
Published: April 2011

Surface termination of Ge(100) and Si(100) was investigated after diluted HF (DHF) solution dipping. On the Ge(100) surface as picked up from DHF, Ge-hydride was observed only in the HF concentration (CHF) region above 10%. The adsorbed fluorine increased with increasing CHF, and the concentration reached around 1014 cm−2 at the CHF of 40-50%. In the case of the DHF dipped Si(100) surface, Si-hydride and hydrophobicity against both DHF and deionized water (DIW) were observed for all the conditions studied, while the fluorine concentration increased and saturated to about 1014 cm−2 in the CHF region above 15%. Hydrophobicity against DHF was observed in the CHF region of 10-30%, but degraded below 5% and above 30%. By transferring the DHF dipped Ge(100) into DIW, hydrophobicity appeared within a few seconds and then was degraded with increase of DIW dipping time. The degradation proceeded slower after dipped in higher concentration DHF. Corresponding to the degradation, it was observed that the total amount of the adsorbed fluoride was gradually decreasing, while the Ge-hydride coverage scarcely decreased. From these results, hydrophobicity of Ge(100) seems to be attributed not only to the hydrogen termination but also to the fluoride adsorption, which is much different from the case of Si(100).
First–Principles Investigation of the Ordered Si 4c compound
Authors: WINDL W. , SANKEY O. F.
Published: April 2011

We have performed intensive theoretical studies on the ordered Si 4C phase which has been proposed first by Riicker et al. [Phys. Rev. Lett.72, 3578 (1994)] and which recently has been reportedly synthesized by Kouvetakis et al. [Appl. Phys. Lett.72, 930(1998). We calculate structural parameters which are significantly different from experimental values, and an IR spectrum with a peak position very similar to their experiment but a much narrower width. We suggest that the experimental findings might be consistent with the assumption of a system of Si4C sections/crystallites and other Si–C structures embedded in a Si matrix.
Image Forces on 3D Dislocation Structures in Crystals of Finite Volume
Authors: El-Azab A.
Published: April 2011

The present work aims at studying the image stress and image Peach-Koehler force fields for three-dimensional dislocation configurations in a single crystal of finite volume. It is shown that the image stress field is significant within the entire crystal volume, and that the image Peach-Koehler force can be of the same order of magnitude as the direct interaction force calculated from the infinite domain solution. The results demonstrate that image stress gives rise to long-range interaction forces that are important in meso-scale dynamics of dislocation structures.
Characterizing and Modeling Plastic Strain Inhomogeneity in Thin Metallic Sheets
Authors: Li X. , Tong W.
Published: April 2011

Using a newly developed plastic strain measurement technique based on digital image correlation, surface plastic deformation of polycrystalline aluminum alloys in a thin sheet form has been experimentally characterized at a length scale comparable to that of the thickness of the aluminum sheets but much larger than the average size of individual grains. Both static and dynamic local straining patterns in these aluminum alloys have been observed and these strain patterns can not be simulated using the conventional plasticity models. The texture clustering of grains may contribute to the static local plastic strain patterns detected in an Al-Mg alloy. Two distinctive dynamic straining behaviors resulted from the dynamic strain aging of dislocations due to the alloying elements have been experimentally established for 5XXX and 6XXX alloys, respectively. First observation of dynamic strain inhomogeneity is also made in a sheet metal specimen deforming predominately in a plane strain state.
Characterization of Cast Metals with Probability Distribution Functions
Authors: Steinzig M. , Harlow F. H.
Published: April 2011

Characterization of microstructure using a probability distribution function (PDF) provides a means for extracting useful information about material properties. In the extension of classical PDF methods developed in our research, material characteristics are evolved by propagating an initial PDF through time, using growth laws derived from consideration of heat flow and species diffusion, constrained by the Gibbs-Thomson law. A model is described here that allows for nucleation, followed by growth of nominally spherical grains according to a stable or unstable growth law. Results are presented for the final average grain size as a function of cooling rate for various nucleation parameters. In particular we show that the model describes linear variation of final grain size with the inverse cube root of cooling rate. Within a subset of casting parameters, the stable-to-unstable manifests itself as a bimodal distribution of final grain size. Calculations with the model are described for the liquid to epsilon phase transition in a plutonium I weight percent gallium alloy.
Large Scale Molecular Dynamics Simulations of a Liquid Crystalline Droplet with Fast Multipole Implementations
Authors: Wang Zhiqiang , Lupo James , Patnaik Soumya S. , McKenney Alan , Pachter Ruth
Published: April 2011

The Fast Multipole Method (FMM) offers an efficient way (order O(N)) to handle long range electrostatic interactions, thus enabling more realistic molecular dynamics simulations of large molecular systems. The performance of the fast molecular dynamics (FMD) code, a parallel MD code being developed in our group, using the three-dimensional fast multipole method, shows a good speedup. The application to the full atomic-scale molecular dynamics simulation of a liquid crystalline droplet of 4-n-pentyl-4'-cyanobiphenyl (5CB) molecules, of size 35,872 atoms, shows strong surface effects on various orientational order parameters.
The Role of Cluster Size and Topology on the Ripening of Defect Aggregates in Crystalline Si
Authors: Magna Antonino La , Coffa Salvatore , Colombo Luciano
Published: April 2011

We present an ‘on lattice’ Monte Carlo study of defect clustering in a Si matrix. The simulations are based on local interaction models, which allows us to reliably include the energetics of defects obtained by tight binding molecular dynamic calculations. In particular the dependence of cluster stability and reactivity on cluster size and geometrical configuration is considered. Proper accelerated algorithms have been implemented in order to extend simulations to macroscopic time scales. Our simulations show that the stability of specific cluster configurations strongly affects the kinetic evolution of the defect ensemble.
Simulation of Dislocation Dynamics in the Continuum Limit
Authors: Schwarz K. W.
Published: April 2011

Peach-Koehler theory is implemented to simulate the motion of three-dimensionally interacting dislocations, located on various glide planes and having any allowed Burgers vector. The self-interaction is regularized by a modified Brown procedure, which remains stable and loses accuracy in a well-controlled manner as atomic dimensions are approached. The method is illustrated by applying it to several problems involving interacting dislocations in an fcc slip system. The strong interaction of two dislocations on intersecting glide planes is investigated with a view towards developing a set of rules to describe the outcome of such interactions. The effect of Frank-Read sources in relaxing a strained layer are illustrated, both for sources on parallel and on intersecting glide planes.
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

The 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

Nanocrystalline 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

The 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

A 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

Small 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

A 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

We 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

New 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

A 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

Aluminum 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

Proton 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

In 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

Significant 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

Single 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

Annealing 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

Metastable 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

By 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

Studies 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

Damage 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

Nd: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

The 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

A 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

I 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.