Using scanning transmission electron microscopy it was possible, by directly imaging single atoms, to investigate the motion of heavy atoms deposited onto the surfaces of thin films. Here, U, Pt, Au, In, Cd, Ag and Pd were deposited onto 15Å-thick amorphous carbon substrates. It is found that adatom motion was strongly dependent upon the local substrate structure and adatom specie (table 1). Diffusion coefficients and activation energies for single atoms, as well as dimers, trimers, etc., were obtained by directly measuring the motion of atoms. Pair-density and nearest-neighbor distributions were measured and used to derive the interatomic potential and the rate of adatom nucleation. It was found that the interatomic potential was very weak and long-ranged.

Direct Observation of the Behavior of Heavy Single Atoms on Amorphous Carbon Substrates. Utlaut, M.: Physical Review B, 1980, 22[10], 4650–60

Table 1

Surface diffusion of various

species on amorphous C film