Title: Use of energy-filtered photoelectron emission microscopy and Kelvin probe force microscopy to visualise work function changes on diamond thin films terminated with oxygen and lithium mono-layers for thermionic energy conversion

Authors: H.D. Andrade; M.Z. Othman; K.M. O'Donnell; J.H. Lay; P.W. May; N.A. Fox; J. Morin; O. Renault

Addresses: School of Physics, Micro- and Nanostructured Materials Group, University of Bristol, Bristol BS8 1TL, UK ' School of Chemistry, CVD Diamond Group, University of Bristol, Bristol BS8 1TL, UK ' Department of Imaging and Applied Physics, Curtin University, Bentley, WA 6102, Australia ' Bristol Centre for Functional Nanomaterials, University of Bristol, Bristol BS8 1FD, UK ' School of Chemistry, CVD Diamond Group, University of Bristol, Bristol BS8 1TL, UK ' School of Chemistry, CVD Diamond Group, University of Bristol, Bristol BS8 1TL, UK ' CEA, LETI, Minatec Campus, F-38054 Grenoble Cedex 9, France ' CEA, LETI, Minatec Campus, F-38054 Grenoble Cedex 9, France

Abstract: Kelvin probe force microscopy (KPFM) and energy-filtered photoelectron emission microscopy (EF-PEEM) with vacuum UV (VUV) excitation have been used to study the work function of p-type diamond films treated to exhibit a negative electron affinity (NEA) surface. NEA was generated by a lithium-oxygen monolayer termination. This monolayer was achieved in two different ways: thermally evaporated films 50 nm thick were either treated by in situ vacuum annealing or by a subsequent water wash. The work function values obtained from these samples by EF-PEEM were compared with KPFM measurements to establish which of the two fabrication techniques was most effective in activating a NEA surface. The washing method was shown to be more effective and the work function values obtained by the two techniques were comparable, as they showed the same work function peaks at 4.54 eV in their respective histograms. It was found that neighbouring polycrystalline facets could show a large variation in work function of up to 400 meV.

Keywords: diamond thin films; chemical vapour deposition; CVD; negative electron affinity; Kelvin probe force microscopy; KPFM; energy-filtered PEEM; photoelectron emission microscopy; work function; energy conversion; thermionic emissions; nanotechnology; surface functionalisation; visualisation; oxygen; lithium.

DOI: 10.1504/IJNT.2014.063789

International Journal of Nanotechnology, 2014 Vol.11 No.9/10/11, pp.796 - 807

Published online: 19 Jul 2014 *

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