Strain and surface phenomena in SiGe structures

Atomic Reconstruction of Au Thin Films through Interfacial Strains

Interfaces play a critical thermodynamic role in the existence of multilayer systems. Due to their utility in bridging energetic and compositional differences between distinct species, the formation of interfaces inherently creates internal strain in the bulk due to the reorganization needed to accommodate such a change. We report the effect of scaling interfacial stress by deposition of different adlayers on a host thin metal film. Intrinsic property differences between host and deposited metal atoms result in varying degree of composition and energy gradient within the interface. Interfacial stress can increase defects in the host leading to (i) energy dissipation and reorganization to minimize surface energy, and (ii) increased material strength. We infer that dissipation of interfacial stress induces defect migration, hence bulk and surface atomic reconstruction as captured by the surface roughness and grain size reduction coupled with a concomitant increase in material strength.

Anisotropic extended misfit dislocations in overcritical SiGe films by local substrate patterning

In this work we will show how local substrate patterning leads to a long range controlled propagation of dislocations in SiGe films grown on Si(001) substrates. Dislocations preferentially nucleate in the inhomogeneous strain field associated with the patterned pits, and then partialize on the local (111) surfaces which form the pit sidewalls. The resulting V-shaped defects extend for several microns and effectively block the propagation of randomly nucleated dislocations which propagate in the perpendicular direction. The surface morphology and strain fields associated with the extended defects have been characterized by atomic force microscopy and μRaman spectroscopy, and the defects have been directly observed with high resolution transmission electron microscopy.

Modeling elastic and plastic deformations in nonequilibrium processing using phase field crystals

A continuum field theory approach is presented for modeling elastic and plastic deformation, free surfaces, and multiple crystal orientations in nonequilibrium processing phenomena. Many basic properties of the model are calculated analytically, and numerical simulations are presented for a number of important applications including, epitaxial growth, material hardness, grain growth, reconstructive phase transitions, and crack propagation.