I. Beszeda

Kinetics of evaporation of beaded Ag film on sapphire and on alumina scale

Morphological changes of beaded Ag film on sapphire and on alumina scale were investigated by means of scanning electron microscopy and Auger spectroscopy in the temperature range of 822–973 K. It was found that the decrease of the effective thickness and the shift of the boundary of the layer can be attributed to the evaporation of silver into the gas phase. Experimental results were analyzed in terms of the model developed by Kaganovskii and Beke. Our results show that the process is controlled by surface diffusion and temperature dependence of the surface mass transport coefficients is deduced from the experimental data.

Calculation of Surface Self-Diffusion Coefficients from AES Data on Decay of Thin Metal Films

We propose a simple method for calculation of surface self-diffusion coefficients using kinetic data on the decay of thin films – void growth and transformation of the island shape to the equilibrium. Calculations are made taking into account equilibrium wetting angle of the film on a substrate. The kinetic data on the decay of Pd thin films on sapphire and silica substrates were obtained using Auger electron spectroscopy. By in situ monitoring the intensity of the Auger signal from the film, three different stages of the decay could be distinguished. The surface self-diffusion coefficients were calculated for the temperature range 583 – 823 K. The values of the surface diffusion coefficients and the activation energies are discussed compared to those obtained by other methods.

Kinetics of Morphological Changes in Nanoscale Metallic Films Followed by Auger Electron Spectroscopy

Thin metallic films deposited on oxide surfaces are subjected to surface forces which can induce morphological changes. Two cases are considered : (1) Ostwald ripening of particles and (2) beading of continuous films. These processes can be followed in-sit u by Auger electron spectroscopy after an appropriate choice of the experimental condi tions (temperature, thickness of the deposit and nature of the substrate). Examples are given for the gold/alumina system. The kinetics curves are analysed by invoking mass transfer surface di ffusion of gold on alumina for the Ostwald ripening process, and surface self diffusion of gold for the beading proce ss. Symbols t : time, T : temperature , m : atomic mass, M : molar mass, k : Boltzman constant, R : gas constant, Na : Avogadro number h : average thickness of a deposit, r : particle radius (Ostwald ripening), void radius (beading), l : average distance between particles, θ : contact angle Ns : surface density of particles (Ostwald ripening), surface density of holes (be ading) γ : surface energy of the metal, ω : atomic volume of the metal, ν = ω : surface density of sites Dv, Ds : volume, surface diffusion coefficients, λ = (Dt) 1/2 : mean diffusion distance , cs : surface concentration of adatoms, expressed in atomic fraction, or coverage ratio, Ds = Ds.cs : mass transfer surface diffusion coefficient , sv, sx : solubility in a substrate, expressed in number of atoms per unit volume or in atomic fraction, p : equilibrium vapor pressure above a solid ∆Hvap, ∆Svap: enthalpy, entropy of vaporisation (sublimation), ∆Had : enthalpy of adsorption