Experimental Determination of the Density of States in Nickel

Energy distributions of photoemitted electrons and the spectral distribution of quantum yield from nickel in the range of photon energy 4.8-11.6 eV are presented and used in conjunction with the optical data of Ehrenreich, Philipp, and Olechna to deduce the electronic structure and optical selection rules of Ni. No evidence is found in these data consistent with the assumption that conservation of k is an important selection rule. Rather, it is found that first-order agreement is obtained between both the optical and the photoemission data if the optical transition probability is assumed to depend only on the initial and final densities of states. The density of states in the energy regions $-6.0\mathrm{}\le (E-E_F)\le 0$ and $5.0\le (E-E_F)\le 11.6$ eV ($E_F$ is the Fermi level) is determined directly from the photoemission data. The density of states in the region $0\le (E-E_F)\le 5.0$ eV is determined using the photoemission results in conjunction with optical data. The most notable feature of the experimentally determined density of states is a strong maximum at 4.6 eV below the Fermi level. Weaker maxima are found at 0.3 and 2.2 eV below $E_F$. A relatively high density of empty states is found in the conduction band within 0.5 eV of the Fermi level (empty $d$-like states), and the density of states is approximately constant in the region $0.5\le (E-E_F)\le 11.6$ eV (low-density $s$- and $p$-like states). It is shown that the experimentally determined Ni density of states cannot be reproduced from that of Cu via the rigid-band model no matter what value of exchange splitting is chosen.