XPS Measurements of Cs and/or Re-doped Silver Powder Surfaces

Abstract

The self-supporting disk surfaces of Cs and/or Re-doped silver powders (500 ppm of each element referred to Ag) were measured by XPS, in order to investigate the electric charges of Cs, Re, and 0, their surface concentrations, and their dynamical behaviors during the operation of O₂-Jet in ultra high vacuum system (UHV).
On the single element-doped silver samples, the binding energies (BE) of Cs 3 d 512a nd Re 4 f_7/2 were 723.9 and 45.7 ev, respectively, after being oxidized by oxygen, whereas they. shifted to 725.6 and 40.8 eV, respectively, after being kept under the most reducing conditions (heating at 483 K in UHV). On the (Cs+Re)-doped sample, BE of Cs 3 d_5/2was 0.2-0.7 eV lower than those on Cs-doped one under every condition, and the lowest value, 724.4eV, was obtained after being oxidized by oxygen; the highest BE, 46.5 eV, of Re 4 fv, was observed during the operation of O₂-Jet at 483 K, but the spectrum at around 45.7 eV indicated above was not detected under any condition. The Re 4 f_7/2, spectra at 46.5, 45.7, and 40.8eV were assigned to Re₇₊, Re₆₊, and Re_O, respectively, whereas the Cs 3 d_5/2 spectrum at 725.6 eV would result from Cs0., species (x<1/2) and the spectrum at 723.9 eV did from CsO₂.0 1 s spectra had large full width at half maximum (FWHM) and could be deconvoluted into four or five core spectra (FWHM-1.7 eV) by curve-fitting method. The spectrum at the lowest BE (528.4-529.0 eV), assignable to oxydic oxygen, was observed only with the (Cs+Re)-doped sample oxidized at 483 K. Surface atomic compositions varied depending on the sample conditions. For the Cs- or Re-doped sample, compositions of Cs, Re, and 0 were in the ranges of 1.0, 3.3, 0-0.4, and 7.6 -27 atom%, respectively, while those for the (Cs+Re)-doped sample were 3.2-7.2, 0-1.1, and 30-38 atom%, respectively. It was noted that the 0 composition was far larger in the last sample. Especially conspicuous responce to Or. Jet were exhibited by the (Cs +Re)-doped sample heated at 483 K; with increasing exposure time, Re 4 f_7/2 spectrum rapidly shifted from 40.8 to 46.5 eV and Cs 3 d_5/2 did from 725.4 to 724.6 eV, whereas 0 1 s gradually did to the low BE side. The O 1 s core spectrum at 528.7eV increased up to 18% of the total area ofO 1 s specrum. From these results, it was estimated that the simultaneous addition of Cs and Re enhanced the sorption of oxygen, increasing the amount of the oxygen species of lower BE, as well as facilitating to keep the Re7+ state and the Cs state surrounded by a large number of oxygen atom.