Time-resolved reflectance studies of surface melting during laser-assisted deposition with a modulated laser source

Abstract

Time-resolved reflectance measurements have been used to study the time evolution of the surface reflectance during deposition of gold from dimethylgold hexafluoroacetylacetonate with both modulated and unmodulated laser light. The observed change in reflectivity found during deposition with a modulated laser source is due to surface melting or sintering of the gold deposit. The change in reflectance observed upon undergoing a transition from a rough to a smooth surface is theoretically calculated for a surface with a random distribution of facet shapes and sizes. The observed changes in reflectance are consistent with the rough polycrystalline surface layer becoming smooth in a transient molten state. An impulsive temperature rise due to a rapid exothermic reaction taking place at the leading edge of the laser pulse has been estimated theoretically and is consistent with the observed time-dependent data.