Optical and Photoemissive Properties of Nickel in the Vacuum-Ultraviolet Spectral Region

Abstract

Measurements of the optical properties of evaporated films of nickel for the spectral region of 4 to 24 eV and of the photoemissive properties of similarly prepared samples for photon energies of 10.2 to 22.4 eV are reported. The optical data were analyzed using a modified form of the Kramers-Kronig method, structure being found in the dielectric functions characteristic of interband transitions of 4.5 and 14.0 eV. The loss function $\ensuremath{-}\mathrm{Im}(\frac{1}{\ensuremath{\epsilon}}+1)$, where $\ensuremath{\epsilon}$ is the dielectric constant, shows structure at 8.0 eV, and the loss function $\ensuremath{-}\mathrm{Im}(\frac{1}{\ensuremath{\epsilon}})$ shows structure at 10 and 20 eV associated with plasma oscillations. The photoelectron energy distribution curves are found to be in reasonable agreement with previously reported data for excitation energies below 11.8 eV, except that the contribution attributed to a peak in the density of electronic states 5 eV below the Fermi level is somewhat smaller for freshly prepared films. This contribution to the photo-electron energy distribution for an incident photon energy of 10.2 eV shows a marked temporal dependence for samples prepared and stored in situ at ${10}^{\ensuremath{-}8}$ Torr. Evidence is given from the data at higher excitation energies for photoelectron excitation of volume plasmons and for the possible photoelectron excitation of an interband transition.