INFLUENCE OF CU, AG, IR AND PT ON THE WORK FUNCTION AND NEAR-SURFACE ELECTRON-DENSITY OF RE MASS-SPECTROMETER FILAMENTS

The influence of metal overlayers on the properties of polycrystalline Re mass spectrometer filaments has been examined using contact potential difference (CPD) measurements of the work function, x-ray photoelectron spectroscopy (XPS) measurements of overlayer binding energy (BE) and ultraviolet photoelectron spectroscopy (UPS) measurements of electron energy distribution curves (EDCs). Work function data for Cu-Re, Ag-Re and Ir-Re are compared to earlier results for Au-Re, Pd-Re and Pt-Re as part of the effort to understand the influence of surface additions to the work functions of ionization sources. The changes in work function owing to the addition of a metal overlayer do not always follow predictions of bulk electron transfer, such as the Miedema electronegativity. However, the observed changes in work function are consistent with a simple initial-state understanding of the XPS core-level data involving charge flow toward and away from the surface. The XPS binding energy shifts are consistent with shifts observed in the valence bands for Cu and Ag on Re.