Pattern Formation in Nanoscopic Metal Films

The talk will begin with a brief overview of some current research problems being investigated in our group, including thin film microstructure control and nanophotonics. Following this, the topic of pattern formation in ultrathin metal films will be discussed. We have observed that when nanoscopic metal films (thickness of 1-10 nm) undergo multiple instances of phase change (i.e. melting and resolidification) by ns laser pulses, robust pattern formation exhibiting spatial order results. We performed detailed experiments and analytical modeling studies of the Co/SiO2 system to understand the length and time scales of this ordering. Using a thin film nonlinear hydrodynamic model (Vrij, Disc. Farad. Soc. 1966) that includes surface tension and long range dispersion forces we determined that pattern formation occurs via a dewetting instability of the spinodal-type. In this problem the length and time scales were dictated only by material parameters and film thickness. A second result to be presented involves accessing additional length and time scales through different instabilities, including the Marangoni- and Rayleigh-type, under non-uniform laser melting. These results demonstrate new opportunities in the investigation of metal thin film phase segregation leading to novel pattern formation. (Seminar joint with Condensed Matter series)