SURFACE SELF-DIFFUSION OF Pt ON THE Pt(311) PLANE

Abstract
The surface diffusion of single Pt atoms and Pt clusters on the channeled (311) plane of Pt has been investigated by field ion microscopy. Single atoms were found to migrate within a given channel of the (311) plane at temperatures above 215 K with an activation energy of 0.60 ± 0.03 eV and a diffusivity of 1.9 x 10^-4 cm²/sec. No cross-channel diffusion was observed for single atoms. Two atoms within the same channel associated into a dimer which was immobile and stable up to temperatures of 340 K. Subsequent addition of atoms to the same channel resulted in the formation of chains of atoms along the channel. The motion of two atoms diffusing in adjacent channels were not strongly correlated. However, occasional occurrences of cross-channel processes between adjacent channels to produce the stable dimer configuration were observed. Observations of atoms diffusing in next-adjacent channels suggested a weak attraction at separations from 9.2 to 12.4Å. Small clusters of atoms left on the plane after field evaporation were stable below 370 K, but at 370 K and above, the atoms rearranged to form a long chain within one channel. These results suggest that the mechanism for the formation of missing rows in the (1x2) reconstruction of channeled surfaces of Pt, Ir, and Au involves surface diffusion of atoms which are stabilized by short-ranged atomic interactions.