The different initial oxidation kinetics of Zr(0001) and Zr(10(1)over-bar0) surfaces

The growth kinetics of thin (thickness <10 nm) oxide films on Zr(0001) and Zr(10<(1)over bar>0) single-crystal surfaces were investigated by real-time in situ spectroscopic ellipsometry (RISE) and angle-resolved x-ray photoemission spectroscopy (AR-XPS). To this end, clean crystalline Zr(0001) and Zr(10 (1) over bar0) surfaces were prepared under UHV conditions by a cyclic treatment of alternating ion-sputtering and in vacuo annealing steps. The thus-obtained bare Zr surfaces were then exposed to dry O(2)(g) in the temperature range of 300 450 K (at a partial oxygen pressure of 10(-4) Pa), while monitoring the growth kinetics by RISE. It was found that the less-densely packed Zr(10 (1) over bar0) surface oxidizes more readily than the densely packed Zr(0001) surface. A near-limiting thickness of the oxide film on both surfaces is attained only at oxidation temperatures T<375 K. At T >= 375 K, the oxidation rate becomes controlled by the thermally activated dissolution and diffusion of oxygen in the alpha-Zr substrate. The higher oxidation rate of the Zr(10<(1)over bar>0) surface for T >= 375 K is attributed mainly to the higher oxygen diffusivity in a-Zr along the Zr(10 (1) over bar0) direction than along the Zr(0001) direction. (C) 2011 American Institute of Physics. [doi:10.1063/1.3608044]