ARUPS investigation of the NiI2band structure

The electronic structure of the layered insulator NiI 2 has been investigated by means of angle-resolved ultraviolet photo-electron spectroscopy. Energy distribution curves have been measured in three different azimuthal directions using He I radiation. it was found that spectral features originating from the I 5p derived bands could be interpreted in terms of the direct-transition model (with some relaxation of the k perpendicular to -conservation) and the three-dimensional nature of these bands was confirmed. A good agreement was found with calculated halogen p bands for the closely related compounds NiCl 2 and NiBr 2 , and a number of critical-point energies could be obtained. Observed strong dependence on the light incidence direction is qualitatively explained as an A.k effect. Structures close to the Fermi level were found to be of Ni 3d origin and were additionally studied using He II radiation. Some evidence for delocalisation due to hybridisation with the I 5p states was found, in line with recent theory.