Reliable Work Function Determination of Multicomponent Surfaces and Interfaces

The Role of Electrostatic Potentials in Ultraviolet Photoelectron Spectroscopy

Journal article (2017)

Authors

Thorsten Schultz Humboldt-Universitat zu Berlin
Thomas Lenz Graduate School Materials Science, Max Planck Institute for Polymer Research
Naresh Kotadiya Max Planck Institute for Polymer Research
Georg Heimel Humboldt-Universitat zu Berlin
Gunnar Glasser Max Planck Institute for Polymer Research
Rüdiger Berger Max Planck Institute for Polymer Research
Paul W.M. Blom Max Planck Institute for Polymer Research, Graduate School Materials Science
Patrick Amsalem Humboldt-Universitat zu Berlin
D.M. de Leeuw Novel Aerospace Materials - Aerospace Engineering , Max Planck Institute for Polymer Research
Norbert Koch Humboldt-Universitat zu Berlin
Research Group
Novel Aerospace Materials (Aerospace Engineering) (TU Delft)
Photoelectron spectroscopy Work function Nanostructured materials Electronic materials Microcontact printing
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Published Date

2017

Language

English

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Faculty

Aerospace Engineering

Department

Aerospace Structures & Materials

Research Group

Novel Aerospace Materials

Abstract

Ultraviolet photoelectron spectroscopy (UPS) is a key technique to determine the work function (Φ) of surfaces by measuring the secondary-electron cut-off (SECO). However, the interpretation of SECO spectra as obtained by UPS is not straightforward for multicomponent surfaces, and it is not comprehensively understood to what extent the length scale of inhomogeneity impacts the SECO. Here, this study unravels the physics governing the energy distribution of the SECO by experimentally and theoretically determining the electrostatic landscape above surfaces with defined patterns of Φ. For such samples, the measured SECO spectra exhibit actually two cut-offs, one representing the high Φ surface component and the other one corresponding to an area-averaged Φ value. By combining Kelvin probe force microscopy and electrostatic modeling, it is quantitatively demonstrated that the electrostatic potential of the high Φ areas leads to an additional energy barrier for the electrons emitted from the low Φ areas. Theoretical predictions of the induced energy barrier dependence on the Φ-pattern length scale and sample bias are further experimentally verified. These findings establish a solid base for reliable SECO interpretation of heterogeneous surfaces and improved reliability of interfacial energy-level diagrams from UPS experiments.