Insights into the gas phase oxidation of Ru(0001) on the mesoscopic scale using molecular oxygen

We present an extensive mesoscale study of the initial gas phase oxidation of Ru(0001), employing in situ low-energy electron microscopy (LEEM), micro low-energy electron diffraction (mu-LEED) and scanning tunneling microscopy (STM). The initial oxidation was investigated in a temperature range of 500-800 K at a constant oxygen pressure of p(O-2) = 4 x 10(-5) mbar. Depending to the preparation temperature a dramatic change of the growth morphology of the RuO2 film was observed. At lower temperature (580 K) the RuO2(110) film grows anisotropically oriented along the high symmetry directions of the Ru(0001) substrate. At higher temperature (680 K), new rotational domains of RuO2(110) begin to appear, which are slightly rotated by up to 201 with respect to the high symmetry direction. These rotated RuO2(110) domains grow along slightly rotated step edges and reveal an isotropic growth morphology. Both the growth speed and the nucleation rate differ from that of the oxide growth at lower temperature (580 K).