Size dependence of laser driven processes of adsorbates at supported nanoparticulate metal systems

UV-laser induced adsorption site changes of CO at nanoparticulate palladium aggregates have been investigated using laser light at λ=355 nm. Systematic studies on the influence of the size and morphology of the particles to the photochemical process will be presented. The average sizes of the aggregates grown by evaporating palladium atoms onto an epitaxial Al2O3 film on NiAl(1 1 0) were varied between 100 and >10,000 atoms per island. Amorphous aggregates grown at 120 K and crystalline aggregates grown at 300 K have been investigated. As is apparent from Fourier transform infrared reflection absorption spectroscopy and temperature programmed desorption laser induced migration of CO occurs depending on the aggregate size and morphology when irradiating non-equilibrium adsorbate structures of CO. The laser induced adsorption site changes of CO are correlated to the presence of higher local adsorbate densities and substantial population of edge sites. The size and morphology dependence will be discussed on the basis of a photoinduced collective process involving dynamical coupling in connection with local adsorbate density fluctuations.