Thickness Effect on Structural, Electrical, and Optical Properties of Ultrathin Platinum Films.

Owing to the fact that ultrathin platinum films have many practical applications, the information concerning the initial stage of the formation of these films raises considerable interest. The effect of the film thickness on the morphology, as well as on the electrical and optical properties, was experimentally studied by a combination of methods (TEM, SAED, SEM, AFM, optical spectrophotometry, and electrical resistance measurements). The growth mechanisms of the films with an average thickness from 0.2 to 20 nm were determined, which is equivalent to the thickness of 1 to 100 monolayers (ML). The percolation threshold was reached, with the average film thickness being ≈1.0 nm, when electrical conductivity appeared. With an average thickness of ≈2.0 nm, the platinum films became almost continuous. The obtained data were analyzed within the framework of scaling theory. The growth of the platinum films at the initial stage (0.2-2.0 nm) was shown to proceed in the mixed 2D/3D growth mode. Here, 3D nanoislands, having a crystalline structure, were formed simultaneously with the formation of an almost continuous 2D subnanometer layer possessing an amorphous-like structure.