The electronic structure of ultrathin NiO films on Ag(1 0 0) surfaces studied by high resolution angle-resolved photoemission spectroscopy

Abstract

We have performed a high resolution angle-resolved photoemission study on ultrathin NiO films on Ag(1 0 0) surfaces. The NiO thin films were prepared on Ag(1 0 0) at room temperature by Ni deposition in O 2 atmosphere. The thickness of NiO thin films were determined by a quartz monitor and reflection high energy electron diffraction (RHEED). The low-energy electron diffraction (LEED) result shows a two-domain ( 2 × 1 ) pattern for the 0.9 monolayer (ML) NiO thin film at the optimum O 2 pressure of 7.5 × 10 - 7 Torr at room temperature with subsequent annealing to 450 K. The ( 2 × 1 ) pattern evolves to a ( 1 × 1 ) pattern upon further annealing to 620 K in the presence of O 2 or upon increasing film thickness. Photoemission spectra show finite density of states at Fermi level for 0.9 ML ( 2 × 1 ) NiO and 2 ML ( 1 × 1 ) NiO on Ag(1 0 0). Angle-resolved photoemission spectroscopy was used to measure the band dispersion of the 0.9 and 2 ML NiO thin films on Ag(1 0 0), as well as of a 10 ML film. The band dispersion of the 10 ML thick film was similar to that of the bulk crystals. Weak dispersion of valence bands was observed on the ( 2 × 1 ) NiO thin film, and it was very different from that on the ( 1 × 1 ) for 0.9 ML and 2 ML NiO thin films. The interpretation of the electronic structure of these thin films is presented.