THE INTERACTION OF C-60 WITH NOBLE-METAL SURFACES

The interaction of C60 with Ag(111) was studied using UHV-STM, LEED, A ES, and TOF-SIMS and compared with previous results for Au(111). On bo th surfaces, C60 grows in a layer-by-layer manner with nucleation occu rring at steps separating narrow terraces followed by growth from the steps onto larger terraces. However, differences in C60 growth on the two surfaces due to the Au(111) surface reconstruction were observed. Also, on Ag(111), C60 was found to form a 2 square-root 3 X 2 square-r oot 3 R30-degrees structure while on Au(111) a 38 X 38 in-phase struct ure was also observed indicating a stronger driving force for adsorpti on into specific sites on Ag(111). Adsorbed C60 molecules were found t o rotate faster on Au(111) than on Ag(111) also indicating a stronger interaction between C60 and Ag. Annealing studies, however, showed tha t C60 desorbs from both Au(111) and Ag(111) at approximately 500-degre es-C indicating that differences in interaction strength between the t wo surfaces cannot be large. The mobility of first and second layer mo lecules was also studied using STM. The results indicated that individ ual adsorbed molecules are sufficiently mobile for thermodynamic consi derations to be important in determining nucleation and growth on both surfaces. It was also found that small second layer islands rearrange over the time-scale of minutes, but that concerted motion and rearran gement of large first layer domains is not likely at room temperature on both surfaces.