Templated Self-Assembly of Metal Particles: Controlled Dewetting of Thin Films

We are exploring templated self-assembly as a tool for producing ordered arrays of metal nanodots over large areas via dewetting of thin solid films. Such arrays may be interesting in memory or plasmonic applications and for use as catalysts for the growth of carbon nanotube or semiconductor nanowire arrays.

Templated self-assembly (TSA) is an attractive tool for patterning nano-scale materials. By using physical templates to alter the surface environment, self-forming and self-ordering processes can be initiated in materials systems that have little or no inherent order. TSA is particularly attractive if we can obtain sub-lithographic assembly or assembly of objects with sub-lithographic sizes.

As an initial demonstration of templated dewetting, we achieved one-to-one self-assembly of gold particles less than 100 nm in diameter and ordered over large areas. This was done by depositing gold films on di-periodic arrays of pits on oxidized silicon substrates, thereby modulating the curvature of the films. This results in a well-ordered solid-state dewetting process. Compared to dewetting on flat substrates, the templates impose a significant decrease in average particle size as well as ensuring a narrow size and spatial distribution. This templating technique uniquely results in crystallographic ordering (i.e. graphoepitaxy) of the particles, imposing an in-plane texture and changing the out-of-plane texture. Particles formed in topographic features are expected to be stable with respect to agglomeration during tube or wire growth.

Current efforts include investigating the templating phenomena in other metals, particularly those that are known to catalyze nanotube and nanowire growth. We are also exploring methods for further scaling down of the process and seeking topographies that will enable self-assembly on sub-lithographic length scales. In addition, we are developing phase field and numeric models of topographic dewetting in order to fully characterize the mechanism.