Ion-Neutralization Spectroscopy of Copper and Nickel

Experimental results concerning the band structure of copper and nickel have been obtained by a new method of electronic spectroscopy of solids. The spectroscopic information comes from deconvolution of the kinetic-energy distribution of electrons ejected in the radiationless, two-electron neutralization of slowly moving noble-gas ions at the solid surface. This leads to a transition density function which includes information about the density of states in the filled conduction band, transition probabilities of the Auger-type neutralization process, and possible many-body effects and final-state interactions. Data are presented for the atomically clean (111), (110), and (100) faces of both Cu and Ni, and for the ions ${\mathrm{He}}^{+}$, ${\mathrm{Ne}}^{+}$, and ${\mathrm{Ar}}^{+}$. Transition probability factors depending on band energy, symmetry character of the band electron's wave function, and crystallographic orientation are evident in the results. The data are entirely consistent with the rigid-band model. Measurements above and below the Curie point for Ni are consistent with a spin-exchange energy of, at most, a few tenths of an eV. The large resonance centered at 4.5 eV below the Fermi level reported by photoelectric emission is not observed in this work. The same statement can be made concerning the resonance reported for Cu at 6 eV below the Fermi level. Detailed comparison is made with the results of band-structure calculations and with the experimental results from photoelectric emission and the soft-x-ray spectroscopy.