Determination of surface diffusion parameters of Pd on sapphire from SEM measurements of morphological changes of beaded films

Abstract.

Changes of the effective thickness and shift of the boundary of Pd discontinuous films on the (10< ![IGNORE[$\bar\Box1\Box$]] ) surface of α-Al₂O₃ were investigated by scanning electron microscopy between 1313–1423 K and under 1.5×10^-6 mbar. The morphological changes were caused by the evaporation of Pd from the surface of sapphire. From the shift of the boundary as well as from the decrease of the effective thickness, the temperature dependence of the surface diffusion length, λ_s, and mass transport diffusion coefficient, D^′ _s, has been determined as: λ_s=(3.6⁺²⁷ _-3.19)×10^-10exp{([(±) 8725kJ mol^-1])/(RT)}m , D^′ _s=(7.9⁺¹³² _-7.46)  ×10^-9exp{([-(±) 20433kJ mol^-1])/(RT)}m² s^-1 . These activation energies are consistent with our previous results determined by Auger electron spectroscopy of diminution (caused by evaporation) and Ostwald ripening of a Pd discontinuous film, containing smaller Pd particles.