FIELD-ION MICROSCOPE STUDIES OF SUBMONOLAYER RHODIUM FILMS ON (110)TUNGSTEN AND MOLYBDENUM SURFACES

The behaviour of rhodium adatoms on the (110) surfaces of tungsten and molybdenum has been studied by field ion microscopy. Activation energies for diffusion of single Rh adatoms were found to be 70 ± 5 kJ mol-1 for W(110) and 60 ± 6 kJ mol-1 for Mo(110). For both substrates, small Rh clusters were seen only as linear chains aligned along 〈111〉 directions. Clusters of 2 to 4 Rh adatoms were rather unstable and dissociated at temperatures only 20-50 K higher than for the onset of observable cluster diffusion. On the Mo(110) surface, chains of more than about ten adatoms transformed readily to two-dimensional islands, as found previously for Pd on W(110). In contrast, monolayer growth on W resembles that of Ir, with Rh islands nucleating only at intersections between chains. © 1990.