Reaction of O2 with the boron-terminated TaB2(0 0 0 1) surface

X-ray photoelectron spectroscopy has been used to study the clean TaB2(0 0 0 1) surface and its reaction with O2. In agreement with previous studies, XPS indicates that the clean surface is boron terminated. The topmost boron layer shows a chemically shifted B 1s peak at 187.1 eV compared to a B 1s peak at 188.6 eV for boron layers below the surface. The 187.1–188.6 eV peak intensity ratio and its variation with angle between the crystal normal and the detector is well described by a simple theoretical model based on an independently calculated electron inelastic mean free path of 15.7 Å for TaB2. The dissociative sticking probability of O2 on the boron-terminated TaB2(0 0 0 1) surface is lower by a factor of 104 than for the metal-terminated HfB2(0 0 0 1) surface.