Principal Investigator Carl Thompson
Templated Self-Assembly for Nanoparticle Organization: Solid State Dewetting
We are exploring solid-state dewetting of thin films as a tool for producing ordered arrays of metal nanodots over large areas. 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. Current investigations focus on two topics: (1) the effects of materials anisotropies on dewetting; and (2) the effects of physical templates to control dewetting.
In the area of materials anisotropies, we seek a material system in which the islands formed by dewetting exhibit spatial order due to anisotropy in the surface energies and diffusivities. As an initial step, we observed significantly different dewetting behaviors of Ni thin films on MgO substrates, depending on the crystallographic orientation of the substrate surface. The future work will involve investigating how micro-faceting of MgO affects the dewetting behaviors of Ni thin films.
In the area of physical templating, we use topographically patterned substrates to modulate the curvature of asdeposited films and thus influence the dewetting behavior of polycrystalline films. We deposit and anneal gold films on di-periodic arrays of pits on oxidized silicon substrates to induce one-to-one self-assembly of ordered arrays of gold particles over large areas. Average particles sizes of less than 50 nm can be achieved. Compared to dewetting on flat substrates, the templates impose a significant decrease in average particle size, as well as ensure 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 growth of tubes or wires. Current efforts include investigating additional techniques for imposing topographic templating on thin films; exploring the templating phenomena in other materials, including those that are known to catalyze carbon nanotubes and those with high surface mobilities; and developing numeric models of topographic dewetting in order to fully characterize the mechanism.