Surface core level shift of Hf 4fin HfN and HfC

Photoelectron spectra of the Hf 4 f core levels from a HfN(100) single crystal and a polycrystalline HfC sample have been measured and analysed. Surface-shifted 4 f levels could be identified for both compounds, at a smaller binding energy than the bulk 4 f levels in HfN and at a larger binding energy in HfC. The surface core level shifts were extracted by a curve fitting procedure and found to be −0.65 eV and +0.41 eV in HfN(100) and HfC. For HfC the shift is very similar to the previously published surface core level shift of +0.42 eV in polycrystalline Hf metal which agreed with theoretical calculations. For HfN however the results cannot be explained in terms of d -band narrowing effects, or by a simple electrostatic picture.