The influence of substrate temperature during ion beam deposition on the diamond-like or graphitic nature of carbon films

Abstract

The structure and properties of pure carbon diamond-like films have aroused great interest in recent years for both scientific purposes and technological applications. The complex mechanisms that lead to the formation of films with properties which can be varied between those of diamond and those of graphite, or can even produce pure “amorphous diamond” (100% sp 3) films, are still unresolved. In the present work, pure carbon (purity greater than 99.9%) films deposited onto silicon from a mass-selected C + beam were studied. Deposition energies were in the range 30–300 eV and substrate temperatures were in the range 25–220°C. A transition from diamond-like to graphitic properties was observed to take place at about 150°C regardless of the ion energy. The changes of properties upon transition include (i) a reduction in density from 3.5 g cm −3 to 2.2–2.8 g cm −3, (ii) a sharp increase in the absorption coefficient in the visible region, and (iii) a clear change in the Raman spectra. The results are in accord with the “subplantation model” which emphasizes the role of carbon atoms trapped in subsurface layers in the evolution of a dense sp 3-rich phase at room temperature. At slightly higher temperatures (above 150°C) diffusion of carbon atoms to the surface of the evolving film releases internal stresses and leads to the formation of a graphitic sp 2 phase.