Nanoscale pattern formation from laser induced thin film instabilities: Role of internal and external effects

Pulsed laser assisted pattern formation in single and bilayer metal films was investigated in this dissertation. The overall goals were: (1) to overcome limitations in conventional pulsed laser dewetting techniques, (2) to better understand the role of effects such as thermal gradients, dispersion forces, pressure gradients, and electric fields on pattern formation, and (3) to investigate nanostructure morphology and its progression in the dewetting of bilayer metal films. This study was divided into two parts. In the first part, pulsed laser-induced instabilities of single layer metal films was discussed. The spinodal dewetting of Au films, a novel Rayleigh-Taylor instability induced by pressure gradients, and the role of DC electric field on pattern formation is presented. In pulsed laser dewetting of Au, the trend in particle spacing and diameter was consistent with the predictions of classical spinodal dewetting theory. The early stage dewetting morphology changed from bicontinuous structures to hole like, and thermal gradient forces were found to be significantly weaker than dispersive forces in Au. Next, we showed through experiment and theory that nanoscale Rayleigh-Taylor instabilities can be seen in thin metal films. This instability was a result of pressure gradients developed when Au films were melted inside a bulk fluid like glycerol. One of the primary findings in this pattern formation was that the spacing of the nanoparticles was independent of the film thickness and could be tuned by the magnitude of the pressure gradients. Finally, we concluded this part by presenting the discovery of phase array self assembly of metallic nanoparticles under the application of a DC electric (E) field. In the second part, the morphology evolution under pulsed laser dewetting of a bilayer of the immiscible metals Ag and Co was investigated. We found multiple transitions in morphology for bilayers and correlated these transitions with an experimentally constructed dewetting morphology phase diagram. Finally, the role of thermal gradients was assessed in the formation of a variety of bimetal nanostructure. Work by our collaborator using computational non-linear dynamics showed that different nanoscale morphologies such as core-shell, embedded, or stacked cases could be formed in the Co-Ag system.