The growth of oxide on field-ion specimens of iridium

Abstract

The ability of the field-ion microscope to obtain images, with atomic resolution, of a compound—iridium oxide—is proved and applied to a study of the oxidation of previously examined field-ion specimens. Field evaporation of the oxide layers allows the observation of the metal-oxide interface and also the three-dimensional structure of the oxide layer. From considerations of image contrast it is deduced that only the iridium ions in the oxide are imaged, but the oxygen ions do contribute to the image by modifying the nature of image points obtained from neighbouring iridium ions. The oxide films examined were always polycrystalline and the nature of grain boundaries in the oxide and the extent of overgrowth deduced. The original stages of oxidation were studied and it is concluded that nucleation occurs at particular crystallographic facets of the original tip (probably {102}). The texture of the oxide layer is seen to depend on the rate of increase of temperature.