Oxidation of Ir(111): From O-Ir-O trilayer to bulk oxide formation

The oxidation of the Ir(111) surface was studied by in situ surface X-ray diffraction (SXRD) in an oxygen pressure range of 10(-6)-100 mbar at temperatures from 575 to 875 K, in combination with density functional theory calculations. Depending on the partial pressure and temperature, the formation of a series of oxide phases is observed. At a sample. temperature of 575 K, a single O-Ir-O trilayer forms at oxygen pressures of 10(-3) to 1 mbar, which grows into a hexagonal multilayer surface oxide at pressure of 100 mbar. Both surface oxides are only kinetically stabilized structures according to DFT calculations. The multilayer surface oxide is kinetically very stable against decomposition in vacuum and further oxidation at low temperature of 575 K as revealed by SXRD. At higher sample temperatures (775 and 875 K), O-Ir-O trilayers form at pressures around 1 mbar, whereas at a pressure of 100 mbar, bulklike rutile IrO2 grows with predominant orientations of (110) and (100) along the normal of Ir(111).