Shape and stability of epitaxial nanostructures evolving under growth or annealing

Nanostructures may become useful components of future electronic devices. In our first study, the growth dynamics of Ge islands on Si(001) and Si(113) surfaces is studied in situ using ultra-violet photoelectron emission microscopy (UV-PEEM) with tunable UV light from the free electron laser at Duke University. In situ Ge deposition and realtime monitoring of the growing islands allowed observation of the evolution of the size, shape and density of the surface structures. AFM measurements were performed on the samples.; Next, narrow and wide nanowires of DYSi2 were formed on a Si (001) substrate through high temperature deposition of few monolayers of dysprosium and annealing at 700°C. The formation, growth and decay of the silicide nanowires were observed by real time imaging using photo electron emission microscopy (PEEM). Narrow nanowires decay only from the ends while wide nanowires may also break in fragments before they eventually disappear.; We also report on the shape transition and migration of TiSi2 nanostructures embedded in a Si matrix. Grown multifaceted TiSi2 were exposed to a Si flux under different growth conditions forming a thick capping layer. AFM and XREM have been used to study the shape, geometry and evolution of the buried structures. We establish that under conditions of epitaxial Si deposition, Ti-silicide nanostructures undergo a shape transition and "migrate" to the surface.; We have also studied the shape evolution of Si/Ge quantum dots (QDs) superlattices. Using a two-temperature procedure, we have grown dense, uniformly sized and distributed QDs. The dome-shaped Ge QDs were capped by a cold Si layer followed by a hot layer of Si before depositing another layer of Ge at high temperature, repeating the process 20 times. The surface morphology was studied by AFM. Cross-sectional TEM was used to analyze the growth sequence and the shape of the buried QDs.; The observed structural changes in these experiments are explained in terms of the interplay between thermodynamics and kinetics, solid state capillarity, and the roughening transition.