Quantitative aspects of ultraviolet photoemission of adsorbed xenon—a review

Abstract

Ultraviolet photoelectron spectroscopy (UPS) is usually not considered to be a quantitative technique for the analysis of solid surfaces However, careful examination of the He(1)-induced 5p spectra of adsorbed xenon provides the basis for a quantitative description of non-uniform solid surfaces and/or adsorbed layers of xenon themselves. The shape, intensity and electron binding energy of the Xe 5p emission can be associated with the distribution, concentration and local surface potential of particular adsorption sites, respectively. Structural defects, such as steps, edges of evaporated metal islands and pores, can be characterized in this way. A particularly important application of the photoemission of adsorbed xenon (PAX) is the determination of the coverage and average island size of metal adsorbates. The early stages of film growth and the thermally activated healing of surface roughness of such deposits can be followed quantitatively by PAX. Interesting quantitative information can also be obtained on the structure of the adsorbed xenon layer itself, such as the critical coverage for the two-dimensional 2D Xe gasw2D Xe solid phase transition, the nucleation of three-dimensional Xe clusters at defects and the presence and equilibrium topography of adsorbed Xe multilayers. These analytical possibilities of the PAX method are illustrated with applications to the Ru(001) surface, the epitaxially grown Ag film, the bimetallic Ag/Ru(OUl) system and the trimetallic AgAu/Ru(001) system.

Thin-film metal oxides in organic semiconductor devices: their electronic structures, work functions and interfaces

“…Work function represents the sum of electron chemical potential and surface dipole. Factors such as surface roughness, 204,205 exposed crystal face, 206 radiation exposure 207,208 and adsorbate coverage 209 affect the surface dipole component, whereas electron chemical potential is affected by the chemical identity of a material, the presence of impurities and the stoichiometry of a material. 106 Although there are many factors that can alter work function, it is possible to gain control over many of these factors to tune work function.…”

Interplay of local and global interfacial electronic structure of a strongly coupled dipolar organic semiconductor

“…The work function, measured at the secondary electron cut-off in photoelectron spectroscopy as a global work function [20], exhibits the balance between various forces that increase or decrease the vacuum level of a system upon molecular adsorption [5,21,22]. Molecular dipole moment [23,24], electron transfer from surface to molecule and chemisorption [25,26] as well as push-back effects [27] can all contribute to the work function change upon film growth.…”

Image states at the interface with a dipolar organic semiconductor

“…It is however conceivable that there exist several different local vacuum levels, 56 since the notion of a single vacuum level at submonolayer coverages obtained from the secondary-electron cut-off may be somewhat misleading. It is however conceivable that there exist several different local vacuum levels, 56 since the notion of a single vacuum level at submonolayer coverages obtained from the secondary-electron cut-off may be somewhat misleading.…”