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Research Activities > Programs > Nonequilibrium Interface and Surface Dynamics 2007

2D Self-Assembling Systems Far from Equilibrium

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2D Self-Assembling Systems Far from Equilibrium

Professor Vivek Shenoy

Brown University

Abstract:   It is well known that long-range elastic, electrostatic, or magnetic interactions can induce the spontaneous formation of 2D periodic patterns in two-phase systems. In many cases, the features have nanoscale dimensions, making them of interest for sub-lithographic surface templating. For self-assembled patterns in equilibrium, the characteristic feature sizes can be directly related to surface thermodynamic parameters, which can then be extracted from experiments in material systems that are easily equilibrated. However, in many cases, interplay of crystalline anisotropy and long-range interactions can give rise to complex energy landscapes that make equilibration practically impossible. Here we study the growth of isolated stress domains far from equilibrium using in situ electron microscopy. While small domains always adopt compact shapes, depending on the growth conditions, large domains either develop serrated edges or evolve into ramified metastable configurations, both of which are not predicted by existing theoretical models. By comparing the recorded shapes with dynamic growth simulations, we gain a quantitative understanding of how the domain shapes fall out of equilibrium and why metastability occurs in this system. We then show that the thermodynamic parameters that govern self assembly can be determined by analyzing shapes that the domains adopt as they grow in size. In addition, we have identified a generic metastable domain configuration that will be adopted by essentially any self-assembling system at large domain size.

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