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A Novel Approach for True Work Function Determination of Electron-Emissive Materials by Combined Kelvin Probe and Photoelectric Effect Measurements

Published online by Cambridge University Press:  14 March 2011

Bert Lägel ,
Iain D. Baikie ,
Konrad Dirscherl  and
Uwe Petermann
Bert Lägel
Affiliation:
Department of Applied Physics, The Robert Gordon University, Aberdeen, UK
Iain D. Baikie
Affiliation:
Department of Applied Physics, The Robert Gordon University, Aberdeen, UK
Konrad Dirscherl
Affiliation:
Department of Applied Physics, The Robert Gordon University, Aberdeen, UK
Uwe Petermann
Affiliation:
Department of Applied Physics, The Robert Gordon University, Aberdeen, UK
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Abstract

For the development of new electron-emissive materials knowledge of the work function Φ and changes in Φ is of particular interest. Among the various methods, the ultra-high vacuum (UHV) compatible scanning Kelvin Probe has been proven to be a superior technique to measure work function changes due to e.g. UHV cleaning processes, chemical contamination, thermal processing etc. with high accuracy (<1meV).

The Kelvin Probe measures local work function differences between a conducting sample and a reference tip in a non-contact, truly non-invasive way over a wide temperature range. However, it is an inherently relative technique and does not provide an absolute work function if the work function of the tip (Φtip) is unknown.

Here, we present a novel approach to measure Φtip with the Kelvin Probe via the photoelectric effect, where a Gd foil is used as the photoelectron source. This method thus provides the true work function of the sample surface with an accuracy of approx. 50meV. We demonstrate the application of the technique by in situ work function measurements on evaporated layers of the low work function material LaB6 on a Re substrate and follow the changes in Φ of LaB6 due to the surface adsorption of residual gas molecules. Thus, the extended Kelvin Probe method provides an excellent tool to characterise and monitor the stability of low work function surfaces.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 621: Symposia Q/R – Electron-Emissive Materials, Vacuum Microelectronics… , 2000 , R3.5.1
Copyright
Copyright © Materials Research Society 2000

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