Electron spectroscopy and temperature programmed desorption of potassium on Ag(111)

Abstract

The adsorption of K on Ag(111) has been studied with ultra-violet photoelectron spectroscopy (UPS), low resolution electron energy loss spectroscopy (ELS), work function measurements (φ and Δφ), temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), Auger spectroscopy (AES). The Δφ is characterized as a function of coverage and correlated with TPD and ELS. ELS shows a signal which is derived from the K(4s) electron density and has a coverage dependent loss energy at submonolayer coverages. Plasmons appear in ELS, UPS and XPS at coverages corresponding to the transformation of the K overlayer from ionic to metallic. The K(3p) UPS intensity grows, and its peak position shifts to higher binding energies (BE), with increasing coverage. Ag(111) is typical of transition metals in general; as the potassium coverage increases, the value of φ drops sharply from the clean substrate value (4.68 eV) to a local minimum (1.26 eV) and then rises to the bulk K value (2.04 eV), and the TPD spectra broaden systematically from high temperatures down to ~ 325 K. Desorption temperatures observed at low coverages are lower than on most transition metals. The work function versus coverage curve is characterized by an initial dipole of μ = 7.94 D and a polarizability of α = 37.1 Å 3.