The thermally induced rearrangement of field evaporated rhenium and ruthenium surfaces

Abstract

The thermally induced rearrangement of field evaporated rhenium surfaces has been investigated in the field ion microscope (FIM) in the temperature range 400–2000 K. The atomic processes involved in surface self diffusion have been identified and approximate activation energies determined to provide information on the surface structures exposed by field evaporation. The initial diffusion observed at 475 K on {10 1 0} (dim plane), {10 1 1} (bright plane), {21 1 3}, {31 4 4}, and {20 2 1} is attributed to the displacement of surface atoms with five nearest neighbours, which leads to the formation on {21 3 3} of a well ordered superstructure of different symmetry to that on the field evaporated surface. In contrast, initial rearrangement is observed on ruthenium at {101̄0} (dim plane), {10 1 1} (bright plane), {21 3 3}, {31 4 4}, and {31 4 0}, indicating the presence of five-coordinate surface atoms on the field evaporated surface, in agreement with the results previously reported from low coverage oxygen adsorption experiments. At elevated temperatures, large flat facets are produced at the major close packed poles and, in the case of rhenium, approximate values of relative surface free energy have been obtained from the equilibrium end form.