Evidence that LVV Auger transitions in oxygen can result in low-energy electron emission.

In this paper, we present evidence of low-energy electron emission resulting from the LVV Auger decay of oxygen 2s holes. Low-energy Auger electron emission is difficult to observe principally because of the large, primary beam-induced secondary electron beam. We have overcome this background limitation by using positron-electron annihilation to initiate the Auger process. We present time-of-flight positron annihilation-induced Auger electron spectroscopy measurements of Cu, Si and TiO$_{2}$ surfaces using positrons with kinetic energies less than 1.5 eV. These experiments demonstrate that the majority of spectral weight in the annihilation-induced Auger electron spectra in the energy range of 0-15 eV is associated with the presence of oxygen at the surface. Using an empirically derived lineshape model that takes into account final state effects and the oxygen 2s photoemission line width, we argue that the low-energy intensity is consistent with the Auger decay of annihilation-induced 2s holes in oxygen (O LVV). In addition, we have calculated theoretically the electron kinetic energy distribution of O LVV Auger electrons emitted from a TiO$_{2}$(110) surface. The calculated lineshape is in excellent agreement with our experimental results. Finally, using the measured Auger intensities and the calculated O LVV lineshape, we estimate that the positron annihilation probability for O 2s electrons on a TiO$_2$ surface is 5.86%.