Influence of different temperatures on morphology and chemical state of the surface-active layer of scandium‑tungsten cathode

Abstract

Scandium‑tungsten (ScW) cathodes have garnered a lot of research attention due to their high emission current density. Herein, the cathode working environment is simulated by heating in a vacuum chamber, and scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) are used to study the surface morphology and chemical oxidation states in the temperature range of 25 °C to 1300 °C. The results reveal that the surface of the tungsten matrix is obviously recrystallized with increasing temperature. Moreover, the scandium oxide becomes globular and clear depressions or holes occur in the aggregation region of the rare-earth oxide at the grain boundaries. The work function is measured by the Richardson method at room temperature, 1000 °C, and 1300 °C and is found to be 2.77, 2.72, and 2.88 eV, respectively. The work function of the cathode initially decreases with increasing temperature, followed by a gradual increase. This is due to the fact that active substances such as scandium oxide are severely lost at high temperatures, destroying the surface structure of the sample. As the Sc/W value decreases, the rate of depletion of active material from the surface is greater than the rate of replenishment of material to the surface.