Platinum and gold thin films deposited by filtered vacuum arc: morphological and crystallographic grain sizes

Nanostructured platinum and gold thin films have been fabricated by filtered vacuum arc with thickness between 2 and 430 nm. The morphological and crystallographic grain sizes of these films have been measured as a function of their thickness. The techniques used for the analyses were scanning tunneling microscopy (STM) and X-ray diffraction. We showed that the crystallographic grain sizes saturate for large thickness. For Pt films, the saturation occurs for thickness about 100 nm, with a maximum grain size around 23 nm. For Au films, this saturation occurs for thickness about 140 nm, and maximum grain size around 48 nm. It was also verified that both platinum and gold films grow preferentially in the direction (111). This effect was observed for silicon and glass substrates, showing that the films growing process is self-orientated. The morphological grain sizes, for both platinum and gold films, increase rapidly in the region with thickness lower than 4 nm. In the range of thickness between 4 and 45 nm, the morphological grain sizes become constant, about 13–15 nm. For film thickness higher than 45 nm, the morphological grain sizes increase as the thickness increases. These results show that, for d>45 nm, the morphological grain sizes D(d) increases with d, differently of the crystallographic grain sizes Dc(d) that saturate. Concerning to the early growth of the films studied in this work, they grow in island, but the thinner films analyzed must be conductive enough to allow to obtain the STM images; this implies that the films have already coalesced.