Temperature threshold for nanorod structuring of metal and oxide films grown by glancing angle deposition

Thin films of tin (Sn), aluminum (Al), gold (Au), ruthenium (Ru), tungsten (W), ruthenium dioxide (RuO2), tin dioxide (SnO2), and tungsten trioxide (WO3) were grown by glancing angle deposition (GLAD) to determine the nanostructuring temperature threshold, Theta(T), above which adatom surface diffusion becomes large enough such that nanorod morphology is no longer formed during growth. The threshold was found to be lower in metals compared to oxides. Films were grown using both dc and pulsed dc magnetron sputtering with continuous substrate rotation over the temperature range from 291 to 866 K. Film morphologies, structures, and compositions were characterized by high resolution scanning electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. Films were also grown in a conventional configuration for comparison. For elemental metals, nanorod structuring occurs for films with melting points higher than that of Al (933 K) when grown at room temperature with a rotation rate of similar to 5 rpm, corresponding to a value of Theta(T) approximate to 0.33 +/- 0.01. For the oxide films, a value of Theta(T)approximate to 0.5 was found, above which GLAD nanorod structuring does not occur. The existence of a nanostructuring temperature threshold in both metal and oxide GLAD films can be attributed to greater adatom mobilities as temperature is increased resulting in nonkinetically limited film nucleation and growth processes. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3525882]