Growth of silver on MgO(001) and infrared optical properties

Silver-film growth on MgO(001) was systematically studied with infrared spectroscopy in ultra-high vacuum for different substrate temperatures from 60 K to 500 K at a similar deposition rate. In all cases the spectral development clearly indicated the formation of islands. For 300 K the coalesced islands further developed to a film that reached bulk conductivity already at about 9 nm. The conductivity of the films beyond percolation was obtained from spectral fits to the Drude model of the dielectric function. Additionally to transmittance studies, infrared reflection spectra at oblique incidence of p-polarized light were measured during Ag film growth on MgO(001) at 300 K. Interestingly, a minimum reflectance (relative to the substrate reflectance) was observed at a thickness corresponding to the percolation threshold, which is a new experimental result. The island-like film morphology was directly proved with atomic force microscopy. Pictures taken immediately after film growth proved that particle size and coalescence strongly depend not only on average film thickness but also on the substrate temperature during deposition, which is related to temperature dependent diffusion. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.