Forces that Drive Nanoscale Self-assembly on Solid Surfaces |
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Authors: | Suo Z Lu W |
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Institution: | (1) Department of Mechanical and Aerospace Engineering, Princeton Materials Institute, Princeton University, Suite D40410, Eng. Qudrangle, Princeton, NJ 08544, USA;(2) Department of Mechanical and Aerospace Engineering, Princeton Materials Institute, Princeton University, Suite D40410, Eng. Qudrangle, Princeton, NJ 08544, USA |
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Abstract: | Experimental evidence has accumulated in the recent decade that nanoscale patterns can self-assemble on solid surfaces. A two-component monolayer grown on a solid surface may separate into distinct phases. Sometimes the phases select sizes about 10 nm, and order into an array of stripes or disks. This paper reviews a model that accounts for these behaviors. Attention is focused on thermodynamic forces that drive the self-assembly. A double-welled, composition-dependent free energy drives phase separation. The phase boundary energy drives phase coarsening. The concentration-dependent surface stress drives phase refining. It is the competition between the coarsening and the refining that leads to size selection and spatial ordering. These thermodynamic forces are embodied in a nonlinear diffusion equation. Numerical simulations reveal rich dynamics of the pattern formation process. It is relatively fast for the phases to separate and select a uniform size, but exceedingly slow to order over a long distance, unless the symmetry is suitably broken. |
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Keywords: | nanostructure epitaxtial film self-assembly surface stress phase separation |
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