Deuterium uptake by Sn films on a W substrate

Sn is under consideration as a liquid-metal plasma-facing component for high power load applications in the divertor region of fusion reactors due to potential abilities for self-recovery and heat-flux management. Improved fundamental understanding of deuterium-Sn interactions that occur in Sn films on W substrates will be useful for further evaluating the compatibility of this system with fusion reactors. We report on surface science experiments under UHV conditions exploring the thermal stability and deuterium uptake by Sn films on polycrystalline W substrates using surface diagnostic tools such as AES, XPS, LEIS, and TPD. Our results show that multilayer Sn films start to evaporate near 1170 K, but the Sn monolayer on W is not fully removed until 1800 K. Clustering or diffusion of Sn films was observed above 310 K. Deuterium uptake on Sn films at 310-750 K from irradiation using 700 eV D2$+$ ions showed lower uptake on liquid Sn films compared to solid Sn. Oxidation of solid and liquid Sn films by O2 was studied using XPS, with more extensive oxidation at higher temperature. TPD shows Sn loss from SnO2 films at below the Sn multilayer desorption temperature. Irradiation of these oxidized Sn films by 700 eV D2$+$ caused reduction of the film to metallic Sn.