Sandia National Laboratories

About: Sandia National Laboratories is a facility organization based out in Livermore, California, United States. It is known for research contribution in the topics: Laser & Thin film. The organization has 21501 authors who have published 46724 publications receiving 1484388 citations. The organization is also known as: SNL & Sandia National Labs.

Anomalous exchange interactions in III-V dilute magnetic semiconductors

Abstract: Based on local-density functional calculations, we study the exchange interactions between magnetic dopants Cr, Mn, and Fe in the III-V compounds GaAs, GaN, and AlN. We show the magnetic exchange interactions deviate strongly in behavior expected from simple models, and may explain the observed maximum in critical temperature with impurity concentration. Additionally the magnetism is responsible for a strong, short-range attraction between the magnetic dopants, thus creating an anomalous effective alloy hamiltonian. This suggests that the impurities may aggregate into small nanoclusters of a few magnetic atoms.

Transparent boundary condition for beam propagation

Abstract: A new boundary condition algorithm is presented that passes outgoing radiation freely with a minimum reflection coefficient (typically 10−5) while inhibiting the flux of incoming radiation. In contrast to the commonly used absorber method, this algorithm contains no adjustable parameters and is thus problem independent. It adapts naturally to a standard Crank–Nicholson difference scheme and is shown to be accurate and robust for both two-and three-dimensional problems.

Automated analysis of SEM X-ray spectral images: a powerful new microanalysis tool.

Abstract: Spectral imaging in the scanning electron microscope (SEM) equipped with an energy-dispersive X-ray (EDX) analyzer has the potential to be a powerful tool for chemical phase identification, but the large data sets have, in the past, proved too large to efficiently analyze. In the present work, we describe the application of a new automated, unbiased, multivariate statistical analysis technique to very large X-ray spectral image data sets. The method, based in part on principal components analysis, returns physically accurate (all positive) component spectra and images in a few minutes on a standard personal computer. The efficacy of the technique for microanalysis is illustrated by the analysis of complex multi-phase materials, particulates, a diffusion couple, and a single-pixel-detection problem.

Deformation of FCC nanowires by twinning and slip

Abstract: We present atomistic simulations of the tensile and compressive loading of single crystal face-centered cubic (FCC) nanowires with 〈 1 0 0 〉 and 〈 1 1 0 〉 orientations to study the propensity of the nanowires to deform via twinning or slip. By studying the deformation characteristics of three FCC materials with disparate stacking fault energies (gold, copper and nickel), we find that the deformation mechanisms in the nanowires are a function of the intrinsic material properties, applied stress state, axial crystallographic orientation and exposed transverse surfaces. The key finding of this work is the first order effect that side surface orientation has on the operant mode of inelastic deformation in both 〈 1 0 0 〉 and 〈 1 1 0 〉 nanowires. Comparisons to expected deformation modes, as calculated using crystallographic Schmid factors for tension and compression, are provided to illustrate how transverse surface orientations can directly alter the deformation mechanisms in materials with nanometer scale dimensions.