Photoemission studies of crystalline palladium and the metallic alloy Pd0.775Cu0.06Si0.165 in its glassy and crystalline forms

Abstract

We report x-ray and ultraviolet photoemission measurements of the levels and valence bands of palladium and of the metallic alloy ${\mathrm{Pd}}_{0.775}$ ${\mathrm{Cu}}_{0.06}$ ${\mathrm{Si}}_{0.165}$ in both its glassy and crystalline forms. The x-ray photoemission measurements show that there is little significant difference between the relative peak positions of the various levels, and that only the copper core level widths in the glass alloy are broader than those in the crystal. The anomalously large width of the $4p$ levels, which is often more sensitive to the chemical environment than the chemical shifts, is also the same for all three samples. A large variation with angle was observed in the peak positions of the $3d$ core levels of the crystalline palladium sample. In the valence band the ultraviolet photoemission spectra of both forms of the alloy are quite similar. However, the valence band for the alloy is narrower than that for the pure palladium, and the density of states at the Fermi level is smaller. The results of these measurements are compared with the various theories of metallic glass stability, and it is suggested that chemical bonds do not contribute to the enhanced glass-forming tendency or stability against crystallization of this alloy. The results are consistent with the nearly-free-electron model of metallicglass stability.