Steven T. Christensen

Supported ru-pt bimetallic nanoparticle catalysts prepared by atomic layer deposition.

Atomic layer deposition (ALD) is used to deposit ruthenium-platinum nanostructured catalysts using 2,4-(dimethylpentadienyl)(ethylcyclopentadienyl) ruthenium, trimethyl(methylcyclopentadienyl) platinum, and oxygen as precursors. Transmission electron microscopy shows discrete 1.2 nm nanoparticles decorating the surface of the spherical alumina support. The Ru-Pt particles are crystalline and have a crystal structure similar to pure platinum. X-ray fluorescence measurements show that the nanoparticle composition is controlled by the ratio of metal precursor ALD cycles. X-ray absorption spectroscopy at the Ru K-edge indicates a nearest neighbor Ru-Pt interaction consistent with a bimetallic composition. Methanol decomposition reactions further confirm a Ru-Pt interaction and show enhanced methanol conversion for the bimetallic nanoparticles when compared to catalysts comprised of a mixture of pure Pt and Ru nanoparticles of similar loading. These results demonstrate that ALD is a viable technique for synthesizing mixed-metal nanostructures suitable for catalysis and other applications.

Controlled Growth of Platinum Nanoparticles on Strontium Titanate Nanocubes by Atomic Layer Deposition

With an eye toward using surface morphology to enhance heterogeneous catalysis, Pt nanoparticles are grown by atomic layer deposition (ALD) on the surfaces of SrTiO(3) nanocubes. The size, dispersion, and chemical state of the Pt nanoparticles are controlled by the number of ALD growth cycles. The SrTiO(3) nanocubes average 60 nm on a side with {001} faces. The Pt loading increases linearly with Pt ALD cycles to a value of 1.1 x 10(-6) g cm(-2) after five cycles. Scanning electron microscopy images reveal discrete, well-dispersed Pt nanoparticles. Small- and wide-angle X-ray scattering show that the Pt nanoparticle spacing and size increase as the number of ALD cycles increases. X-ray absorption spectroscopy shows a progression from platinum(II) oxide to metallic platinum and a decrease in Pt--O bonding with an increase in Pt--Pt bonding as the number of ALD cycles increases.

Thermally induced nanoscale structural and morphological changes for atomic-layer-deposited Pt on SrTiO3(001)

Platinum grown by atomic layer deposition (ALD) on SrTiO3(001) surfaces was studied as a function of Pt coverage and post-deposition thermal treatment. The combination of atomic-force microscopy, scanning electron microscopy, x-ray fluorescence, x-ray reflectivity, and grazing-incidence small-angle x-ray scattering reveals significant changes in the nanoscale surface morphology and crystallinity for the differently prepared films. Surfaces with Pt coverages from 1 to 40 monolayers (ML) show different initial morphologies that evolve into different final Pt microstructures after annealing to 800 °C. These distinct nanoscale structural changes are explained by surface diffusion and the surface and interface energies for noble metals on oxides.