Special Numerical Analysis and Scientific Computing
Dr. Xiaobin Niu, University of Utah, Material Science Dept.
"Strain Induced Growth Instability and Island Nucleation on Patterned Substrate"
Time: 2:00 PM
Location: Hill 423
Abstract: Strain induced self-assembly provides an attractive route to
nanofabrication of semiconductor quantum dots on surfaces. Recent
experiments have demonstrated that combining the strain induced
self-assembly with surface patterning provides an effective method to
further improve the size uniformity and spatial ordering of quantum
dots. However, the underlying mechanisms responsible for such
improvement remain poorly understood. In this talk, I will present
theoretical analyses of strain induced growth instability and island
nucleation on patterned substrates. We show that the growth of a
strained film is inherently less stable on a wavy substrate than on a
flat substrate. For small surface undulation, the critical wavelength
characterizing the initial instability on a wavy substrate is
effectively half of that on a flat substrate. Furthermore, on patterned
substrates, island nucleation is directed to the preferred sites by a
much lower energy barrier and smaller critical size. Strain relaxation
directs island nucleation to the bottom of a pit rather than the top of
a ridge as commonly perceived, while large surface energy anisotropy
leads to nucleation at both places. Our theory explains some puzzling
experimental results and provides useful guidelines for future
exploration of directing the self-assembly of quantum dots on patterned
substrates.
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