Surface structure of VN0.89(100) determined by low-energy electron diffraction.

Abstract

The structure of the (100) surface of substoichiometric vanadium nitride was studied by low-energy electron diffraction on a ${\mathrm{VN}}_{0.89}$(100) sample. A simple 1\ifmmode\times\else\texttimes\fi{}1 (100) diffractogram was observed. To describe the electron scattering in substoichiometric VN we apply the averaged t-matrix approximation to the nitrogen atoms. We find that the best structural model is one having no nitrogen vacancies in the surface region. It turns out that the first layer is rippled with the N atoms displaced 0.17 \AA{} above the subplane of V atoms, that the spacing between this subplane and the second layer is 1.92 \AA{}, and that the spacing between the second and the third layer is 2.08 \AA{}. In relation to the (100) spacing of the bulk, 2.06 \AA{}, these spacings are 6.8% contracted and 1% expanded, respectively. The Debye temperature of VN is found to be 660 K in good agreement with a prediction from entropy data and from neutron diffraction and helium-ion channeling experiments.