Stagnation Mechanism Revealed in Simulations of Grain-Boundary Roughening in Nickel at High Temperatures
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among the smallest Cu 2-x Se nano materials yet synthesized. According to the researchers, cubic phase two-dimensional nanomaterials are uncommon, though a significant number occur in wet chemical syntheses. It is thought that these phases are the result of growth kinetics being controlled by ligand interactions with certain crystal planes of the materials as they grow in solution. The researchers said that the NHC products generated after selenium is removed from the precursor molecule play a significant role in forming the discshaped materials, particularly by coordi-
nating copper species on one particular plane forcing continued growth to occur preferentially in the radial direction rather than equally in all directions. Changing the selenium precursor concentration relative to the copper source altered the particle shapes, which varied from a mixture of discs and tetragonal particles to irregular morphology. Using selenium powder instead of the NHC-based precursor formed irregular particles. Cu2-xSe is a p-type semiconductor with a 1.0–1.4 eV indirect bandgap, a range suitable for use as an absorbing layer in photovoltaic devices. Based on UV-vis
ship between NW size and resonant light scattering. The researchers observed a continuous change in SiNW color across the entire visible spectrum under ran-
domly polarized white light illumination, with color shifting linearly from blue to red with increasing wire diameter. Similarly, they observed size-dependent color in large-scale, sub-wavelength SiNW and SiNP arrays (Figure 1) which were generated with carefully selected physical dimensions using standard polycrystalline Si thin-film deposition, lithographic patterning, and dry etching. The Stanford team noted that color also varied with the polarization state of the illumination source and related this polarization dependence, as well as the size dependence, to the well-known Lorentz-Mie theory of light scattering. They also described the sensitivity of SiNW light scattering to their surrounding dielectric environment, which is related to the “leaky” nature of NW modes whose fields extend outside of the NWs. The ability to engineer color in Si nanostructures by strategic selection of size, dielectric environment, and illumination conditions greatly increases its potential application for information, display, camouflage, ornamental, and biotechnologies. “Si is expected to further solidify its dominance in an increasing number of high-volume technologies,” said Cao, when considering these new findings in conjunction with Si’s excellent electrical, mechanical, and biochemical properties. “This puts this material in a new light.” SAMESHA R. BARNES
grain boundaries and pinning of grain boundaries by second phase particles. However, grain-growth stagnation is also observed in materials where such mechanisms are not applicable, as in high purity materials, and materials with high solute diffusivity. In order to expand understanding of the mechanisms hindering grain growth, E.A. Holm and S.M. Foiles from
Sandia Na
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