bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mirror Electron Microscope-Low Energy Electron Diffraction for Studies of Surface Ordering and Melting
Authors: Unertl W. N. , Shern C. S. 
Published: March 2011

ABSTRACTMirror Electron Microscopy – Low Energy Electron Diffraction (MEMLEED) combines a LEED with MEM in a single simple instrument for studies of surface processes such as phase transitions and premelting under ultra-high vacuum (uhv) conditions. In MEMLEED, 5–20 keV primary electrons are decelerated by an electrostatic mirror-objective lens in which the sample is the mirror element. In the MEN mode, electrons are reflected just above the surface, reaccelerated through the objective lens and imaged. Contrast is due to variations in both surface potential and topography. Current uhv instruments have lateral resolution of about 1 μm. In the LEED mode, 0-100 eV electrons strike the sample at near normal incidence. Diffracted electrons are accelerated through the objective lens. Beam spacings in the imaged diffraction pattern are proportional to k11 and beams do not move as the incident energy is varied. MEMLEED has intrinsically higher transfer width and is less sensitive to magnetic fields near the sample than conventional LEED. Design considerations for uhv instruments are discussed. Applications to the study of order-disorder transitions, premelting phenomena, and to measurements of changes in surface potential are described.
Double Axis X-Ray Diffractometry Analysis of the Homoepitaxial Interface Between Substrate and Buffer Layer
Authors: Green G. Stephan , Tanner Brian K. , Kightley Philip 
Published: March 2011

ABSTRACTHigh resolution double axis X-ray diffractometry has been undertaken on InGaAs/AlGaAs strained layer epitaxial systems on (001) GaAs substrates. A clear set of fringes has been identified which arises due to the presence of an imperfect layer at the interface between the GaAs substrate and the undoped GaAs epitaxial buffer layer. The period corresponds to the Pendellosung period for the whole epitaxial layer stack. These fringes have very low contrast and are not present in all specimens studied. Detailed simulations have been undertaken assuming a thin interfacial layer of GaAs with a different lattice parameter to the substrate. The system is equivalent to a Bragg case X-ray interferometer. Fringe amplitude is found to vary linearly with interface layer thickness and increases with mismatch of this layer. A good match between experiment and simulation was obtained for a 1 nm layer mismatched by 3000 ppm. The presence of such a layer, probably GaCxAsl-x has been confirmed by transmission electron microscopy. We show that highly sh'rained layers of this thickness between layers over 1 micron in thickness can lead to splitting of high intensity layer peaks, giving rise to possible misinterpretation of data.
Characterization of GaAs/Si Interface Structure by X-Ray Diffraction
Authors: Specht E. D. , Ice G. E. , Peters C. J. , Sparks C. J. , Lucas N. , Zhu X.-M. , Moret R. , Morkoc H. 
Published: March 2011

ABSTRACTBy measuring the intensity profiles along the crystal truncation rods of a Si(001) substrate, we obtain the depth sensitivity necessary for x-ray diffraction measurements of the structure of its interface with a thick GaAs overlayer which is epitaxial to, but not in registry with the substrate. By comparing the diffraction with a model based on a grid of misfit dislocations, we find that the atoms at the interface have a root mean square displacement of 1.09±0.1Å from this ideal structure, and that the interface has a roughness of 2.9±1 Å. The diffraction indicates an anomalously small strain perpendicular to the interface in the GaAs near the interface.
X-Ray Reflectivity Study of Single- and Bicrystals of Gold
Authors: Fitzsimmons M. R. , Burkel E. , Peisl J. 
Published: March 2011

ABSTRACTX-ray reflectivity techniques have been used to characterize the surfaces of 0.4µm thick Au films epitaxially grown on single-crystals of NaCl. Measurements of both the specular and non-specular reflectivity suggest that the Au surface is very rough. The nonspecular reflectivity provides valuable information about the correlation of the heights at different points on the surface. The first in situ reflectivity study of the formation and destruction of a grain boundary shows direct evidence for the existence of diffuse scattering from the grain boundary. Measurements of several [0011 twist grain boundaries suggest that the roughness and texture of an interface depends upon the geometrical orientation of the surrounding substrates.
X-Ray Reflectometry from Semiconductor Surfaces and Interfaces
Authors: Tanner Brian K , Miles Simon J , Bowen D Keith , Hart Linda , Loxley Neil 
Published: March 2011

ABSTRACTX-ray reflectance measurements at grazing incidence provide non-destructively a measure of the thickness of thin layers, the electron density as a function of depth, and interface and surface roughness. We show that the effect of roughness at a buried interface is only to reduce the visibility of the interference fringes, whereas roughness at the top surface leads also to an overall increase in the rate of fall of intensity with angle (or energy). These two contributions can then be readily distinguished.Most work has been performed in monochromatic angular dispersive mode. We present here a preliminary study of the application of the high-energy, fixed-angle, energy dispersive mode for the study of thin epitaxial layers, Langmuir-Blodgett films, surface damage on silicon chemi-sol polished wafers and ion implanted silicon and aluminium. Data has been analysed using the theory of Parratt, which we have adapted for use in the energy dispersive method.
X-Ray Reflectivity Measurements of Surface Roughness Using Energy Dispersive Detection
Authors: Chason E. , Warwick D. T. 
Published: March 2011

ABSTRACTWe describe a new technique for measuring X-ray reflectivity using energy dispersive X-ray detection. The benefits of this method are the use of a fixed scattering angle and parallel detection of all energies simultaneously. These advantages make the technique more compatible with growth chambers and useable with laboratory X-ray sources. We find excellent agreement between the calculated Fresnel reflectivity and the reflectivity obtained from a smooth Ge (001) surface. Reflectivities obtained during 500 eV Xe ion bombardment of Ge surfaces demonstrate the sensitivity of the technique to be better than 1 Å.
A Morphological Approach to Constructing Interatomic Potentials: An Application to Silicon.
Authors: Dallot P. , Bristowe P. D. 
Published: March 2011

ABSTRACTA framework for constructing interatomic potentials is proposed and applied to the case of silicon. The construction relies on a geometrical approach in which we try to reproduce the morphology of the Born-Oppenheimer surface. In particular, we develop a new technique for constructing four body terms. It consists of building invariant coordinate systems on the configuration space of four atoms, thus allowing the choice of the four body term morphology. The potential that we develop has a two and a four body part. It is adjusted to match the only geometrical information known from the Born-Oppenheimer surface which is the position of its minimum of energy and its curvature at that point, as given by the dynamical matrix. The potential is then tested on point defects and surface structures in silicon.
Anisotropic Displacement Threshold Energies in Silicon by Molecular Dynamics Simulations
Authors: Miller LeAnn A. , Brice David K. , Prinja Anil K. , Thomas Picraux S. 
Published: March 2011

AbstractA combination of molecular dynamics simulations and theoretical modeling was used to examine the orientation dependent threshold energies for displacement of silicon atoms from their lattice site due to energetic particle collisions. These results are important for a detailed understanding of both radiation effects in silicon devices and beam-enhanced stimulation of molecular beam epitaxial growth.The molecular dynamics code developed for this study, which employs a Tersoff interaction potential, as well as the theoretical model that incorporates the symmetry of the crystal are described.Bulk displacement threshold energies were determined by the molecular dynamics code for four directions through the open face in the <111>. These values were then incorporated into the theoretical model for the average bulk displacement threshold energy. The average bulk displacement threshold energy was found to be 14.8 eV in 30° about <111> and 11.1 eV in 20° about <100>.
Dislocation Mobilities in NiAl From Molecular Dynamics Simulations
Authors: Moncevicz A. , Clapp P. C. , Rifkin J. A. 
Published: March 2011

ABSTRACTUsing the Voter-Chen Embedded Atom Method (EAM) potentials for the Ni-Al alloy system,the Peierls stress (σp) and velocity of edge dislocations (b=[100]) have been estimated in stoichiometric perfectly ordered B2 NiAIat a temperature of 10 K, by the use of molecular dynamics simulations employing approximately 4000 atoms. σp was determined to be about 3×1010 dynes/cm2, or about 2%of the shear modulus, C44. The steady state velocity was found to be about 1.6×105 cm/s (or 65% of the (001) shear velocity) under an applied shear stress of 3.9×1010 dynes/cm2. Stress induced martensite (SIM) was nucleated in some of the simulations after the dislocation had begun to move, and in all cases when the SIM reached the immediate neighborhood of the dislocation core the motion of the dislocation was arrested.
Atomic-Scale Simulation of Adhesion Between Metallic Surfaces
Authors: Taylor Paul A. 
Published: March 2011

ABSTRACTWe have performed MD simulations of adhesive phenomena, on an atomic scale, between metals possessing both smooth and stepped-surfaces. Studies of adhesion between identical metals, consisting of either Au, Cu, or Ni, with (001) or (111) orientations, reveal the existence of adhesive avalanches as the bodies are brought to within a critical separation (˜2Å). That is, as the surfaces approach one another, one or both surface layers becomes unstable, and abruptly moves towards the other. This signals a transition from an initial system with two distinct surfaces to one possessing no identifiable surfaces. Th presence of adhesive avalanches will pose difficulties in determining adhesive forces and energies by means of atomic forcemicroscopy at sub-nanometer separations of probe tip and sample surface.
Hot Electrons Relaxation
Authors: Mazzone A.M. 
Published: March 2011

ABSTRACTThis work represents the first attempt of a direct simulation of the processes of electron-phonon interaction and lattice excitation which follow the formation of an excited electron gas such as, for instance, is the one produced by high-energy implants. The simulation method is of the type molecular dynamics and is based on a quantum mechanical representation. The results suggest a lattice disorder similar to the one of a thermal spike.
Defect Dynamics of a Nematic Polymer in a Magnetic Field
Authors: Rey Alejandro D. 
Published: March 2011

ABSTRACTAnalysis of the nonlinear dynamical response of a rod-like nematic liquid crystalline polymer, between parallel untreate plates, in a magnetic field is presented. Numerical solutions to the torque balance equations showthat when a uniformly aligned polymer is acted by a magnetic field normal to the initial polymer orientation an array of inversion walls develops. Stability analysis shows that the inversion walls are unstable to localized perturbations. The nonlinear resolution ofthe instability leads to the nucleation of an array of disclination line pairs of strength ±1/2. A perturbation analysis is used to obtain the evolution of the polymer structure towards equilibrium
Dislocation Dynamics In B.C.C. Metals: A Nuclear Magnetic Resonance and Transmission Electron Microscopic Study
Authors: De Hosson J. Th. M. , Kanert O. 
Published: March 2011

ABSTRACTPulsed nuclear magnetic resonance proved to be a complementary new technique for the study of moving dislocations in b.c.c. metals. From the motion induced part of the spin-lattice relaxation rate the mean jump distance of mobile dislocationshas been measured in Vanadium as a function of temperature. The NMR experiments are combined with transmission electron microscopic investigations to reveal the static structure of defects in the samples. The NMR experiments show that the mean jump distance is nearly constant below 230 K whereas it decreases substantially above 230 K to 300 K indicating a transition that marks two different mechanisms. NMR observations in combination with TEM support the physical picture that above that transition temperature dislocation segments are stopped between localized obstacles whereas below Tcthe latticefriction controls the plastic behaviour.
Dislocation Density Determination in Polycrystalline Copper by Neutron Diffraction Extinction Measurements.
Authors: Palacios Gomez. J. 
Published: March 2011

ABSTRACT:(200), (111) AND (311) neutron diffraction peaks were measured on polycrystalline Cu samples with varying degrees of deformation by compression: O%. 0.8%. 1.2%,, 1.5% and 2%. The first two reflections were measured with wavelength 2.358Å and the third one with wavelength 1.55Å.Integrated intensities vary more less monotonically and they tend to reach the kinematical value. This limit was estimated by extrapolation and used to evaluate extinction. To obtain dislocation densities a simple model was proposed which divides the crystal in regions of perfect periodicity and regions perturbed by dislocations, and evaluates the integratedintensity from perfect regions by the general theory of X-Ray diffraction of Zachariasen (1967).Dislocation densities result between 1.2×1O7 cm−2 for the sample without deformation, and approximately 5.0×1O7 cm−2 for the 2%. deformed sample. These results are in the expected range.
Extrinsic Gettering of Copper in Silicon: Heterogeneous Precipitation on Near-Surface Dislocations
Authors: Rice P.M. , Kim M.J. , Carpenter R.W. 
Published: March 2011

ABSTRACTCopper was precipitated on extrinsic near-surface dislocations in {100} Si wafers. Several types of precipitates were heterogeneously nucleated on low index planar arrays. Large crystalline precipitates with visible strain fields proved to bea silicide. Large weakly diffracting precipitates without strain fields proved to be voids. Small, thin, partially crystalline particles of unknown composition also precipitated on the arrays. Point defects played an important role in the precipitation reaction.
Majority Carrier Transport Across Semiconductor Grain Boundaries
Authors: Nelson S.F. , Evans P.V. , Sass S.L. , Smith D.A. 
Published: March 2011

AbstractMajority carrier transport measurements were made across the potential barriers at (100) twist boundaries in silicon. The bicrystals were prepared by hot-pressing single crystals of lightly doped float-zone material, under ultra-high vacuum conditions. The current - voltage measurements were analyzed using combined drift-diffusion and thermionic emission transport mechanisms, and incorporating some inhomogeneity in the charge distribution at the boundary. Evidence has been found for a small, Nd = 3 × 1010 cm−2, density of mono-energetic defect states near midgap, in bicrystals characterized by a variety of misorientation angles. This density is too small to result from the intrinsic structure of the boundary. In addition, no dependence was found on misorientation angle.
X-Ray Topography Studies of Oxygen Precipitates in MCZ Silicon
Authors: Holland Anthony J. , Green G. Stephan , Tanner Brian K. , Zhenhong Mai 
Published: March 2011

ABSTRACTX-ray section topography has been used to study the distribution and size of precipitates resulting from heat treatment of MCZ silicon. A low density of precipitates was found, enabling individual precipitate images to be studied. Images have been simulated by numerical solution of Takagi's equations and the magnitude of the strain field deduced by comparison with experiment. Excellent agreement has been found in the details of simulated and experimental images. The effective defect volume increased monotonically with annealing temperature. The effect of surface relaxation and long range curvature on the accuracy of determining the microscopic strain field by matching simulated and experimental images has been investigated.
Analysis for the Characterization of Oxygen Implanted Silicon (SIMOX) by Spectroscopic Ellipsometry
Authors: Doss M.G. , Chandler-Horowitz D. , Marchiando J. F. , Krause S. , Seraphin S. 
Published: March 2011

ABSTRACTSamples of SIMOX have been prepared by implantation in a high-current implanter (density ≍ 1 mA/cm2) and by annealing at 1300°C for 6 hours. Transmission electron microscopy reveals unusual structure in these samples. Spectroscopic ellipsometry has been used to analyze these structures. Ellipsometric measurements were collected at an angle of incidence of 75. deg, with photon energies from 1.5 to 5.0 eV, and using a rotating polarizer configuration. The measurements were analyzed with three models: a three-layer model, a four-layer model, and a five-layer model. The five-layer model provided the best fit of the three. This model identified a layer of crystalline Si inclusions (“islands”) within the SiO2 layer. A method is presented that provides initial estimates for the thicknesses of the top three layers to help start the regression analysis.
Structural Defects in Laser Annealed Arsenic Implanted Silicon
Authors: Tonnerre J. M. , Matsuura M. , Cargill III G. S. , Hobbs L. W. 
Published: March 2011

ABSTRACTLaser annealed arsenic implanted silicon specimens with doses ranging from 6×1015 to 7×1016 As/cm 2 have been investigated by transmission electron microscopy (TEM) and double crystal xray diffractometry (DCD). For the highest implant dose, laser powers ranging from 1.1 to 2.2 J/cm 2 have been used. Experimental observations show two new features for this kind of specimen. First, in some cases, TEM micrographs evidence small (˜50Å diameter) precipitate-like defects and/or dislocation loops confined within the heavily doped region. Second, in some cases, DCD shows a positive strain in addition to the negative strain attributed to 90% As in substitutional sites. X-ray rocking-curve simulations reveal that the negative strain drops to zero around 1000Å before the end of the As distribution. This might be related to the presence of Si interstitials in the deepest region of the As distribution.
Synchrotron Topographic Studies of the Influence of Rapid Thermal Processing on Defect Structures in Single Crystal Silicon.
Authors: Dudley Michael , Wang Franklin F.Y. , Fanning Thomas , Tolis Georgios , Wu Jun , Hodul David T. 
Published: March 2011

ABSTRACTSynchrotron white beam X-ray diffraction topography in transmission geometry has been used to non-destructively investigate defect structures in silicon single crystal wafers, both prior and subsequent to a 60 second rapid thermal processing (RTP) treatment at 1050°C. Prior to RTP dislocations, precipitates and swirl defects were observed and characterized. Following RTP the following effects were observed: glide of individual dislocations and dislocation multiplication; and the enhancement of the strain field associated with the swirl defects. Precipitates appeared unaffected by RTP. This work shows that synchrotron topography is capable of non-destructively revealing significant dislocation motion induced by RTP under conditions were such motion is not thought to occur. This dislocation motion is likely to be detrimental to device performance. The technique enables determination of the conditions required to avoid such dislocation motion.
Modifications in Gap State Distribution Upon High Energy Electron Bombardment in n Type Hydrogenated Amorphous Silicon
Authors: Babras Suvarna , Bhoraskar S.V. , Bhide V.G. 
Published: March 2011

ABSTRACTModifications in the structural parameters of n type a-Si:H due to bombardment of different doses of 10 keV and 1 MeV electrons and the consequent changes in the gap state distribution are studied. A systematic dependance of the changes on the energy and dosage of electrons is observed. The Deep Level Transient Spectroscopy results reveal that apart from increasing the gap state density over a broad energy range, the electron bombardment also modifies the charge state of the defect, which is conclusively brought out by the result of C-V measurements. An understanding of the reason behind such modifications is sought by studying the structural parameters of the bombarded films directly with the help of Laser Raman Spectroscopy.
A Scanning Tunneling Microscopy Study of the Reduced Tio2(110)Surface
Authors: Rohrer Gregory S. , Henrich Victor E. , Bonnell Dawn A. 
Published: March 2011

ABSTRACTThe scanning tunneling microscope has been used to image a reduced TiO2(110) surface in ultrahigh vacuum. Structural units with periodicities ranging from 21Å to 3.4Å have been clearly imaged and the observed surface structures can be explained by a model involving ordered arrangements of two dimensional defects known as crystallographic shear planes. An electronic state 0.5 eV below the conduction band edge, detected in tunneling spectra, has been assigned to reduced Ti cations which reside along the crystallographic shear planes. This state appears to be empty at the surface, possibly due to asmall amount of band bending. The results indicate that the topography of nonstoichiometric oxide surfaces can be rather complex and that the tunneling microscope provides an effective tool for studying the tomic scale surface features of wide band gap semiconductors.
HREm Study of Al-Si Interfaces
Authors: Shamsuzzoha Mohammad , Deymier Pierre A. , Smith David J. 
Published: March 2011

ABSTRACTInterfaces between aluminum and silicon in samples prepared by solidification of an Al-Si eutectic liquid have been studied by high-resolution electron microscopy. The Al and Si grains have a common [110] axis with a misorientation between grains of 70.5°, thus aligning the (lll)si plane with the (111)ALplane. In general, theinterfaces have a complex structurewith numerous interfacial dislocations and considerable facetting. The core structurescan be characterized in terms of structural unit models. The nature of the facetting has also been investigated, in particular one facet which lies approximately along the (111)AL, and (l15)si planes and another which lies approximately along the (110)AL and (l14)si planes.
Tilt Boundaries In BCC Metals:Comparison of Results Using Different Interatomic Interactions
Authors: Foiles S. M. , Daw M. S. , Phillips R. B. 
Published: March 2011

ABSTRACTTwo classes of interatomic interactions, the embedded atom method and the model generalized pseudopotential theory are used to calculate the structure of tilt boundaries in bcc metals.These interactions differ in the inclusion of explicitlyangular dependent interactions. The results show that these different models of the interactions can lead to qualitatively different predictions for the atomic structure of the boundary. The applicability of the embedded atom method to bcc transition metals is also discussed.
Threading Dislocation Densities in Mismatched Heteroepitaxial (001) Semiconductors
Authors: Ayers J. E. , Ghandhi S.K. , Schowalter L. J. 
Published: March 2011

ABSTRACTIn this paper we propose a theory which accounts for the thickness dependence of threading dislocation densities in mismatched heteroepitaxial (001) semiconductors. This theory predicts that, for thick, planar, highly-mismatched heteroepitaxial layers with equilibrium strain, the threading dislocation density should be proportional to f/h, where f is thelattice mismatch and h is the film thickness. These predictions are in good agreement with experimental resultsin the GaAs on Si(001) system.