Ostwald ripening of Pd particles on the (101̄2̄) surface of sapphire

Morphological changes of small Pd particles on the (101̄2̄) surface of α-Al 2O 3 single crystal were investigated by Auger electron spectroscopy in the temperature range 833–923 K. It was shown that practically there was no decrease of the effective thickness during heat treatments under 6×10 −9 mbar. Supposing that the observed change in the Auger intensities is due to the surface Ostwald ripening, it was established that the process was controlled by surface diffusion. It was shown that in this case, taking into account the dissolution of small particles, the normalised Auger intensity is inversely proportional to the normalised average radius. The surface mass transport diffusion coefficients were determined and they were in the range 10 −15–10 −17 m 2 s −1 in the investigated temperature interval. Their temperature dependence can be given as D s ′= 6 +486 −5.93 ×10 −5 exp{[−(203±30) kJ mol −1]/RT} m 2 s −1 .