Characterization of Sc-O/W(100) surface as Schottky emitter: Work function change for activation processing

To elucidate the electron emissivity of the Sc-O/W(100) Schottky emitter, the Sc-O/W(100) surface, prepared by scandium deposition onto the W(100) surface followed by oxygen exposure and heating at an operating temperature of similar to 1400 K, was studied by ion scattering spectroscopy (ISS), Auger electron spectroscopy (AES) and measurement of the relative work function change. The results have revealed that heating of the oxygen adsorbed Sc/W(100) surface leads to the diffusion of the oxygen atoms into the substrate to locate very probably beneath the topmost scandium atoms. This relocation of the oxygen atoms forms an electric double layer, resulting in a significant decrease of the work function. The topmost surface composition of the Sc-O/W(100) system observed by ISS did not change during cooling the sample from similar to 1400 K to room temperature under the present conditions. The results of the present work strongly suggest that the surface properties of the Sc-O/W(100) system are very similar to those of the Zr-O/W(100) system at the operating temperature.