Phase separation in strained epitaxial InGaN islands

Journal ArticlePhase separation (PS) produces InN composition gradients in InGaN islands, which may be important for light emitting diodes, solar cells, and lasers. Thus, the control of PS is critical, and the kinetic growth process, which is suggested to be important for controlling PS in Stranski-Krastanov islands, becomes a key factor in producing materials for optoelectronic devices. We present atomistic-strain-model Monte Carlo simulations for PS in strained epitaxial InGaN islands. Our simulations illustrate how the PS in InGaN islands depends on the kinetic growth mode and subsurface diffusion, and thus suggest ideas for controlling the microstructure of alloy islands formed during epitaxial growth

Simulation of self-assembled compositional core-shell structures in In xGa 1-xN nanowires

Journal ArticleWe report the simulation of compositional core-shell structure formation in epitaxial InGaN nanowires (NWs) and its dependence on kinetic growth mode and epitaxial relation to substrate, based on atomistic-strain-model Monte Carlo simulations. On a lattice mismatched substrate, the layer-by-layer growth results in self-assembled core-shell structures with the core rich in the unstrained component (relative to the substrate), while the faceted growth mode leads to the strained core component, and both are distinctively different from the equilibrium composition profiles. Our simulation results explain the reason that all the existing core-shell alloy NWs grown by vapor-liquid-solid experiments have cores rich in the unstrained (or less strained) components is because they have been grown via the layer-by-layer mode and, more importantly, suggest a possible route towards controlling the NW core-shell composition by altering growth mode and/or selecting substrate

Three-Leaf Dart-Shaped Single-Crystal BN Formation Promoted by Surface Oxygen

Two-dimensional hexagonal boron nitride (h-BN) single crystals with various shapes have been synthesized by chemical vapor deposition over the past several years. Here we report the formation of three-leaf dart (3LD)-shaped single crystals of h-BN on Cu foil by atmospheric-pressure chemical vapor deposition. The leaves of the 3LD-shaped h-BN are as long as 18 {\mu}m and their edges are smooth armchair on one side and stepped armchair on the other. Careful analysis revealed that surface oxygen plays an important role in the formation of the 3LD shape. Oxygen suppressed h-BN nucleation by passivating Cu surface active sites and lowered the edge attachment energy, which caused the growth kinetics to change to a diffusion-controlled mode.Comment: 7 pages,6 figure

Liquid phase oxidation of p-xylene to terephthalic acid at medium-high temperatures: multiple benefits of CO2-expanded liquids

This is the published version. Copyright 2010 Royal Society of ChemistryThe Co/Mn/Br catalyzed oxidation of p-xylene to terephthalic acid (TPA) is demonstrated in CO2-expanded solvents at temperatures lower than those of the traditional Mid-Century (MC) process. As compared with the traditional air (N2/O2) oxidation system, the reaction with CO2/O2 mixture at 160 °C and using an additional inert gas (N2 or CO2) pressure of 100 bar increases both the yield of TPA and the purity of solid TPA via a more efficient conversion of the intermediates, 4-carboxybenzaldehyde and p-toluic acid. At the same time, the amount of yellow colored by-products in the solid TPA product is also lessened, as determined by spectroscopic analysis. Equally important, the decomposition or burning of the solvent, acetic acid, monitored in terms of the yield of the gaseous products, CO and CO2, is reduced by ca. 20% based on labeled CO2 experiments. These findings broaden the versatility of this new class of reaction media in homogeneous catalytic oxidations by maximizing the utilization of feedstock carbon for desired products while simultaneously reducing carbon emissions

Diffusion Boundary Condition at Surface Steps

This Communication reports a geometrical factor that is necessary in the diffusion boundary condition across surface steps. Specifically, this factor relates adatom concentration to its spatial gradient at a surface step, and it describes the fraction of jump attempts that cross the step. In this Communication, the authors show that the factor is 1/\Pi using theoretical formulation and further verify the formulation using numerical simulations for triangular, square, and hexagonal surface lattices