Increase in the work function of W/WO3 by helium plasma irradiation

Abstract

Helium plasma irradiation to tungsten leads to formation of helium clusters, helium bubbles, and fiberform nanostructures near the surface. In this study, tungsten samples exposed to helium plasmas are analyzed by X-ray photoelectron spectroscopy in detail. The W 4f spectra and valence band spectra show chemical composition and electronic state of the surface. It was found that significant differences were not identified on the electronic state between the helium plasma irradiated and pristine samples when the degree of oxidization was the same level. From a low kinetic energy cut-off of X-ray photoelectron spectrum, the work function of the samples was measured. It was found that helium plasma irradiation increased the work function by approximately 0.5 eV when WO3/W was higher than unity. The possible mechanism to arise the difference in the work function is discussed.