No abstract

In situ DC resistance measurements were performed on semicontinuous niobium and silver films,which were made on mica and fullerene substrates in an ultra-high-vacuum chamber.Right after the interruption of the deposition,we investigated the changes (relaxation) of the sample resistance on a time scale of about 10 minutes.Resistance increase was observed for Nb/mica and Ag/C60 systems,and decrease for Ag/mica system.The relaxation is sensitive to substrate temperature and film thickness.We suggest that the edge diffusion and mergence of islands due to thermomigration of the metal atoms are responsible for the resistance relaxation.The intensity and direction of the relaxation reflect the interfacial activity of the metal/substrate system.The heterogeneities on substrate may also play an important role during this process.The analysis is presented from the angle of atom-migration and of thermodynamic evolution.

Fullerene （Ｃ６０ and Ｃ7０）films were epitaxially grown on fresh (001) mica fcc closely-packed plane parallel to the substrate surface. Metal-overlayers were deposited onto these fullerene films in an ultra-hight-vacuum(UHV) chamber and in situ resistance measurements were performed. With increasing current, we observed reversible resistance variation and irreversible breakdown. Nera the percolation threshold we find power law scaling behavior Ｉb～Ｒ－α,where Ｉb is breakdown current and R the sample resistance. The exponent α is much smaller than the values given by previous experiments and prediction of conventional Ｎｏｄｅｓ-Ｌｉｎｋｓ-Ｂｌｏｂｓ(NLB) model. Possible explanation of these phenomena based on metal-fullerene interfacial interactions is discussed.