Evidence for two growth modes during tungsten oxide vapor deposition on mica substrates.

Abstract: The morphology, the structure and the orientation of tungsten oxide nanorods grown on mica are investigated as a function of the deposition time. The previous results are recalled to point out the changes with the nanorod thickness. The investigations were conducted by Atomic Force Microscopy (AFM) and Reflection High Energy Electron Diffraction (RHEED). The results evidence two successive growth modes. In the first stage thin and long nanorods were formed. They grew layer by layer with a hexagonal tungsten bronze structure and two different (1−10) and (2–10) planes parallel to the mica surface. In the second stage, as the deposition time increased thin nanorods with the (1−10) orientation grew in thickness when the others preserve their morphology and structure. In the discussion the difference between the two growth modes is emphasized. In the first stage the nanorod growth proceeds mainly by the surface diffusion of K x WO3 species. In the second stage the growth is due to the by direct impinging of WO3 molecules on some thin nanorods having already the (1−10) orientation, leading to growth of thick nanorods with a monoclinic structure. [Copyright &y& Elsevier]