Berlin 2018 – scientific programme
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O: Fachverband Oberflächenphysik
O 57: Electronic structure of surfaces: Spectroscopy, surface states II
O 57.2: Talk
Wednesday, March 14, 2018, 11:00–11:15, MA 042
Work function measurements on heterogeneous surfaces: The role of electrostatic potentials for ultraviolet photoelectron spectroscopy (UPS) — •Thorsten Schultz1, Thomas Lenz2, Naresh Kotadiya2, Georg Heimel1, Gunnar Glasser2, Rüdiger Berger2, Paul W. M. Blom2, Patrick Amsalem1, Dago M. de Leeuw2, and Norbert Koch1 — 1Humboldt Universität zu Berlin, 12489 Berlin — 2Max Planck Institute for Polymer Research, 55128 Mainz
UPS is a primary technique to determine the work function of surfaces. According to literature, heterogeneous surfaces are expected to exhibit one secondary electron cut-off (SECO) representing an area-averaged work function. However, several reports show that more than one cut-off can be observed for heterogeneous surfaces. To clarify this discrepancy, heterogeneous model surfaces consisting of bilinear arrays, providing a work function contraast of more than 1 eV, were investigated. With UPS we measure two SECOs, one reflecting the high work function surface fraction and the other an averaged work function. The electrostatic potential away from the surface was measured by Kelvin-probe force microscopy and compared to electrostatic modeling. With this we can quantitatively explain that the high work function areas lead to an additional energy barrier for electrons emitted from the low work function areas.[1] We detail the role of experimental parameters on the appearance of SECOs and how this influences the determination of ionization energy of molecules deposited on heterogeneous surfaces. [1] T. Schultz et. al, Adv. Mat. Interf. 4, 1700324 (2017)