Formation and Structural Characterization of Large Area Thin Films of Elemental Pt Prepared at the Interface of Two Immiscible Fluids*

Single and multilayered films of 5-6 nm diameter Pt nanoparticles self-assembled into 30-40 nm diameter aggregates have been prepared at the planar interface between an aqueous Pt colloidal solution and an immiscible fluid such as hexane. In order to achieve dense and essentially defect free films the zeta potential of the colloidal Pt must be adjusted to about -30 mV; more negative zeta potentials result in less uniform films while less negative zeta potentials lead to the precipitation of the nanoparticles. Interfacial Pt films with areas in excess of 40 cm² can be easily transferred to a glass substrate for further study by evaporating and/or draining the two immiscible fluids. X-ray diffraction measurements on newly prepared single layer films reveal a significantly contracted Pt lattice parameter due to a surface stress induced Laplace pressure which slowly relaxes over time as the Pt surface oxidizes.