RECTANGULAR ARRANGEMENT OF SE-RING CLUSTERS ON GRAPHITE SURFACE AND THEIR STRUCTURAL TRANSFORMATION

Ring-type Se clusters have been deposited on the C-plane of a graphite crystal and examined by STM images which were found to consist of 0.7 2nmx0.85nm rectangular lattices with individual molecules of 0.53nm in diameter. Se ring-type clusters sitting on each lattice point are mos t probably 6-membered. The STM images were taken with the bias voltage V(T) between probe vs. sample as a parameter. For -0.7V < V(T) < +0.7 V the patterns of the rectangular lattice remains similar, but an orde r-disorder transition takes place at -0.065V; whereas V(T) at -0.7V, t he regular arrangement suddenly collapses to a random distribution of larger clusters consisting of their diameter in a range up to 5nm. The process of the structural change in the lattice system is not reversi ble with respect to the bias voltage. These experimental results are w ell explained by first-principles theoretical calculation on the struc ture and electronic properties of Se cluster using the DV-SCM method.