Mechanics and kinetics of platinum heteroepitaxy on gold

A comprehensive study of Pt thin-film heteroepitaxial growth on planar as well as modified Au(111) substrates was conducted. A strain-energy mediated threedimensional growth mode of Pt on pre-roughened Au substrates was discovered, and a descriptive model for this phenomenon was developed.;This dissertation was motivated by the experimental observation that Pt growth on nanoporous gold (NPG) surface occurred in islanding mode, which contrasted with some literature reports on planar Au surfaces that had noted layer-by-layer growth, although yet others reported islanding mode.;In the present work, Pt thin-films were grown on Au surfaces using molecular beam epitaxy (MBE) in ultra-high vacuum (UHV). It was clarified using in-situ and ex-situ analytical techniques that Pt growth on planar Au(111) surface at low deposition flux and at room temperature does indeed occur in a layer-by-layer mode; the lattice mismatch between the film and the substrate is accommodated by misfit dislocations at the interface and the critical film thickness for misfit-dislocations was measured in this work.;Platinum thin-films were then grown on Au surfaces that simulated characteristic features of the nanoporous gold surface, in an effort to identify the cause of Pt/NPG islanding morphology. It was determined by theory and experiment that large surface curvatures and small facet sizes play marginal roles in heteroepitaxial growth. Instead, growth experiments on pre-roughened Au substrates revealed that preferential Pt growth occurred on top of substrate 'islands' compared to the 'pits'. This phenomenon led to an increase in surface roughness and island height during early growth (<4nm Pt thickness), followed by a subsequent smoothening process. These observations were explained in terms of a simple model that accounts for the fact that strain-energy relaxation in a lattice-mismatched film occurs atop islands, but not in pits. A resulting chemical potential gradient on the surface drives adatoms from the pits to the mesas. This model, together with arguments that characterize NPG surface as kinetically 'rough', explains the observed Pt/NPG islanding morphology.;The elastic properties of nanoporous gold thin films were also investigated, and a porosity-length-scale dependence in the effective Young's modulus of NPG was revealed. Further, a remarkably simple and inexpensive method to fabricate large single crystals in thick Au and AuAg alloy foils was discovered and is presented here. The surfaces of these crystals, made by exploiting surface energy driven abnormal grain growth, were examined in detail and were revealed to be of very high quality, comparable to those prepared using traditional approaches such as UHV deposition. Lastly, a self-ordering phenomenon in colloidal particles sitting atop surfaces with very shallow nanoscale corrugations was investigated and explained in terms of capillary effects; this work is discussed in the appendix.