SURFACE CHARACTERIZATION STUDY OF THE THERMAL-DECOMPOSITION OF AGO

In this study the thermal decomposition of AgO was examined by collecting XPS data from a pressed powder AgO sample before and after annealing at 100, 200, 300, and 400 degrees C. Comparative data were also collected from a polycrystalline Ag foil that had been extensively cleaned by annealing at 500 degrees C and sputtering with 2 keV Ar+. However, a mixture of dissolved atomic oxygen and hydroxyl groups characterized by a broad peak in the O 1s spectrum and centered at a binding energy (BE) of 531.0 eV remain on the foil after cleaning. The compositional and chemical-state changes that occur on the AgO surface during an anneal are characterized according to the peak intensity and shape changes and BE shifts in the XPS spectra. The results show that the BE shifts of the Ag 3d peaks from AgO and Ag2O are -0.7 and -0.3 eV relative to the metallic state. The predominant form of contamination on the AgO sample is a carbonate or bicarbonate species. The removal of more than 50% of the carbonate contamination during the 100 degrees C anneal results in a fwhm decrease of 0.15 eV in the Ag 3d peaks and narrowing of the Ag MNN and valence-band peaks. These peak shapes and BEs are believed to be characteristic of AgO features. Annealing at 200 degrees C results in decomposition of the AgO to Ag2O and complete decomposition of the carbonate species. Incomplete dissociation of Ag2O at 300 degrees C produces a mixture of Ag2O and Ag metal on the surface which yields XPS features characteristic of a combination of both Ag states. The Ag 3d(5/2) peak is centered at a BE of 367.7 eV, as reported for Ag2O, but is broadened (fwhm = 2.1 eV) compared to either the Ag2O or Ag metal feature. Peak broadening also occurs in both the Ag MNN and valence-band spectra, and the splitting in the Ag MNN peaks decreases relative to the spectra obtained from Ag2O. Annealing at 400 degrees C for 30 min results in nearly complete decomposition of the remaining silver oxide. The XPS spectra closely resemble those obtained from the Ag foil. Some oxygen remains in the near-surface region as dissolved O or OH, Ag2O, and atomically adsorbed O.