Field-emission energy spectroscopy of the platinum-group metals

Energy-distribution functions have been measured for field-emission electron currents from the (100), (110), (210), (211), and (311) faces of field-evaporated rhodium, iridium, and platinum emitters and from the (100) and (111) faces of a field-evaporated palladium emitter. The structures contained in these energy spectra are interpreted in terms of current contributions among overlapping sub-bands of calculated, electronic band structure for the bulk metal. A systematic correlation between the calculated band-edge eigenvalues and the details of the energy spectra is observed. It is concluded that the field-emission spectra for the platinum-group metals contain many of the directional features of the electronic band structure for the bulk material. General predominance of $t_{2g}$ bands relative to the $\Gamma$-centered bands characterizes the normalized field-emission spectra, which are believed to contain directional, local density-of-states information. Adsorption of saturation layers of hydrogen and nitrogen on the (100), (110), (210), and (111) faces of rhodium indicate suppression of the $e_g$ bands relative to the $t_{2g}$ bands for states in the surface-normal direction. Implications with reference to the specific electron structure of the surfaces of platinum-group metals and the effects of chemisorption on the surface electron structure are discussed.