Instabilities and Kinetic Anisotropies as Determining Factors of Island Growth-Shapes
A variety of submonolayer island shapes obtained by molecular beam epitaxy under different deposition conditions has been imaged by scanning tunneling microscopy. The observed shapes are analyzed mainly in connection with the stability criteria for straight steps. The analysis evidences the determining influence of anisotropic kinetic processes. The triangular island shapes with sharp corners growing under given conditions due to these processes deform the diffusional field surrounding the islands. This leads to an incessant and enhanced material supply at these corners and thus eventually to an instability well before the instability of straight steps sets in. The consequence is the rampant growth of dentritic-skeletal islands in a wide range of deposition conditions. The analysis shows also the necessity for a proper consideration of the diffusional field in kinetic Monte-Carlo simulations.
KeywordsDeposition Flux Step Edge Diffusion Field Island Size Island Shape
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