The interaction of oxygen with Rh studied by field electron microscopy

Abstract

The initial process of the oxidation of Rh has been studied with field emission microscopy (FEM). This process is surface-structure-sensitive: the more open and rough the surfaces are, the more easily the oxidation. The most stable Rh-oxygen bond is formed around the (210) orientation. Heating a saturated oxygen layer in vacuum showed that two factors influence the desorption behaviour: (1) the heating rate and (2) the diffusion rate of oxygen into the bulk below 700 K. At high heating rates (12–30 K/s) oxygen dissolves into the near-surface region to create a surface oxide species. This oxide species decomposes and oxygen desorbs between 800 and 1200 K. On the other hand, at low heating rates (< 0.3 K/s) or stepwise heating no oxide in the near-surface region is formed: the oxygen has diffused deeply enough into the bulk of the tip. The applied field disturbs this picture at low heating rates. The oxygen is forced to stay in the near-surface region and an oxide is formed above 700 K.