Metallic work function measurement in the range 2–3.3 eV using a blue light-emitting diode source

Abstract

A new photoelectric method to monitor the work function of contaminated metallic surfaces in the range 2–3.3 eV using blue light-emitting diodes (LEDs) is presented. This method was specifically developed for an application onboard a spacecraft, where the simplicity of a system is a great asset. This technique makes it possible to follow the work function of a calibrated surface LED combination with a reproducibility of ∼2% with only one blue LED and a device to count photoelectrons. The surface described in this paper is Cs/W(110). The work function changes with time due to adsorption of residual gas in the moderate vacuum environment (in the mid 10−8 mbar range). Determination of the work function with a standard photoelectric technique is used to calibrate the system. We then derive calibration curves for this specific surface LED combination which reduce the workfunction measurement to a simple current measurement.