PHOTOELECTRON-DIFFRACTION STUDIES OF NB(001)

Photoelectron-diffraction studies of Nb(001) have been performed to de termine the first-interlayer contraction using Mg K alpha radiation (h nu = 1253.6 eV) as an excitation source. Photoemission intensities of the 3d(5/2) core level were measured as a function of the polar angle along several azimuths on the single-crystal surface. The 202.3-eV (2 05.0-eV) binding energy for the 3d(5/2) (3d(3/2)) core level was well resolved in the photoemission spectra, where the peak intensity could be easily evaluated by curve-fitting processes. Large oscillations of the 3d(5/2) intensity as a function of the polar angle due to forward- focusing were observed. Based on multiple-scattering calculations for several first-interlayer spacings ranging from the bulk value to 16% c ontraction, the best agreement with experiment was obtained for a (13 +/- 5)% contraction of the first-interlayer spacing.