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The scanning tunnelling microscope has revolutionized the quantitative analysis of epitaxial phenomena. This, in turn, has spawned a huge theoretical effort aimed at analyzing various aspects of the morphology of growing surfaces. One of the most important general approaches to have emerged from this effort is based on the application of scaling concepts to epitaxial island-size distributions in the regime of submonolayer coverage prior to coalescence. We first discuss the analytical basis for scaling solutions to rate equations. In the limit of irreversible aggregation, a solution is obtained in terms of the capture numbers which agrees with previous work. For reversible aggregation, we identify a new quantity that may be regarded as a continuous analogue of a critical island size. We then examine the influence of spatial correlations by introducing a method for modeling epitaxial phenomena in terms of the motion of island boundaries, which is implemented numerically using the level set method. This island dynamics model is continuous in the lateral directions, but retains atomic scale discreteness in the growth direction. Several choices for the island boundary velocity are discussed and computations of the island dynamics model using the level set method are presented.
Sputtering with Ar+ ions induces structural phase transitions at the pentagonal surface of the icosahedral quasicrystal Al70Pd20Mn10. Sputtering at different temperatures changes the surface composition, thereby stabilizing different structures. At room temperature, the structure changes to body-centered cubic but, at elevated temperatures, it displays decagonal symmetry. In both cases, annealing the sample restores both the bulk composition and the icosahedral symmetry of the original surface.
We investigate growth of GaAs(001) using kinetic Monte Carlo simulations of a very simple atomistic solid-on-solid model. The key features of this model are a short-range incorporation process of freshly deposited atoms and additional activation barriers to interlayer transport. Both are required to obtain close agreement between measured electron-diffraction intensities and simulated surface step densities during growth and post-growth equilibration on vicinal surfaces. This model is used to study long-time evolution of the surface morphology. Large pyramid-like features develop during growth on a singular surface which coarsen in time while maintaining an approximately constant slope. Growth on a vicinal surface is also found to be unstable. Simulated surface morphologies are compared with recent work using atomic-force microscopy. Finally, we show how a suitably modified version of this model helps to explain the recently observed phenomenon of re-entrant layer-by-layer chemical-beam etching of a singular GaAs(001) surface. The central features responsible for this behavior are the site selectivity of the etching process combined with step-edge barriers to interlayer adatom migration.
A detailed understanding of planar defects plays an important role in the search for a comprehensive description of the mechanical behaviour of metals and alloys. We present calculations for isolated stacking faults and grain boundaries using the layer Korringa-Kohn-Rostoker method including an assessment of the force theorem, which has already proven itself in evaluating defect energies for elemental close-packed metals. These ab initio total energy calculations will be supplemented by a study of the changes in bonding and local magnetic properties near a symmetric Σ5 (310) grain boundary in Fe
Through application of a lattice model of the Si(001) surface, implemented in a Monte Carlo growth simulation we investigate the structural evolution of the Si(001) surface during molecular beam epitaxy. Particular emphasis is placed upon identifying the role of both enhanced diffusion and directional bonding.
Molecular-beam epitaxy of quantum-well wires on vicinal surfaces is studied by application of Monte Carlo simulations of a solid-on-solid model. Characterization of simulated quantum-well wires indicates an optimum regime within which the quality of the quantum-well wire is maximized. The model is extended to include observed anisotropies in GaAs growth on vicinal surfaces, and the conclusion is reached that better quality quantum-well wires may be grown on substrates misoriented from the (001) towards , rather than , due to relative step edge stability on the two misoriented surfaces.
Stacking faults in close-packed metals are known to play a crucial role in determining mechanical behaviour. Extending recent layer Korringa-Kohn-Rostoker calculations on twin faults in a variety of FCC crystals, we study in detail the aluminium defect and develop an atomistic understanding of the modifying behaviour of small concentrations of impurity atoms.
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