Temperature, photon energy and thickness dependent studies of cesium 5p core-levels on copper(100), development of photoemission equipment and the 6m-TGM at CAMD

Temperature and coverage dependent photoemission lineshapes yield insight into many-electron dynamics. The coverage dependence of Cs on Cu(100) was studied. The motivation was to probe for screening environment dependencies in the 5p core-level at low coverage, comparing results to prior studies of Cs on W(110), and to study the role of phonons in the screening dynamics. The temperature variation range investigated extends from approximately the Debye temperature (ca. 40K) to room temperature, and Cs film thicknesses ranged from sub-monolayer through essentially bulk-like films. The low coverage work is supported by coverage dependent work function measurements. The research advances photoelectron spectroscopy by developing new high energy resolution instrumentation and applies the new capabilities to temperature, photon energy and thickness dependent studies of shallow alkali metal core-levels of thin films on noble metal surfaces with possibility for future studies on transition metal surfaces. Technical advances include significant upgrades of a commercial electron spectrometer that improve energy resolution (from about 50 meV to ca. 15 meV) and enhanced sensitivity by adapting multiple channel detection, and improvements in alignment and characterization of a synchrotron radiation beamline resulting in documented improvements in energy resolution. Core electron lineshapes measured at high energy resolution contain information related to electronic screening associated with the photoemission process. Careful analysis of the results from these studies include the following: (1) lineshape analysis of thick film (bulk) Cs 5p core-level lineshapes which confirm the binding energies, spin-orbit energies and total gaussian widths of the bulk and surface components determined by earlier lower resolution measurements of Cs on Cu(111) and W(110); there is some indication that differences in the singularity index (electron-electron interactions) can be resolved; (2) a significant difference in the zero-temperature phonon broadening exists between the bulk and surface atoms as measured by the gaussian broadening vs temperature, which is consistent with recent results for Li; (3) the low coverage dependence of Cs 5p binding energies on Cu(100) is similar to that observed for Cs on W(110) suggesting that the alkali atom-substrate iteration is not well described by the standard charge transfer model.