7 - Work function techniques

Summary

Introduction

The measurement of work functions or, more precisely, work function changes (surface potentials) has been widely used in the study of adsorption processes on metal surfaces. The technique has been used both on its own and in conjunction with other techniques such as LEED, infrared spectroscopy or flash desorption to elucidate the mechanism of surface reactions.

The measurement of the work function change or surface potential is useful in that it provides a relatively simple method of monitoring the state of the surface. Any adsorption on the surface will, in general, produce a change in the work function of the surface as will any further change in the state of the adsorbate and/or adsorbent. The method is very sensitive, since adsorption of a monolayer on a surface produces surface potentials which are usually in the range 0.1–1.5 V and, since surface potentials can be measured to within ±0.001 V, very small amounts of adsorption can be measured in a way which causes little or no disturbance to the surface.

A number of techniques are available for measuring surface potentials. In principle, any method which will measure work functions or Contact Potential Difference (CPD) may be used for measuring surface potentials, although some techniques may interfere with the adsorption process to a limited extent.