Collisional and thermal effects on liquid lithium sputtering

The lithium sputtering yield from lithium and tin-lithium surfaces in the liquid state under bombardment by low-energy, singly charged particles as a function of target temperature is measured by using the Ion-surface Interaction Experiment facility. Total erosion exceeds that expected from conventional collisional sputtering after accounting for lithium evaporation for temperatures between 200 and 400 deg. C. Lithium surfaces treated with high-fluence D atoms are bombarded by H+, D+, He+, and Li+ at energies between 200 and 1000 eV and 45 deg. incidence. Erosion measurements account for temperature-dependent evaporation. For example, 700 eV He+ particles bombarding the D-treated liquid Li surface at room temperature result in a sputter yield of 0.12 Li/ion and at temperatures ∼2.0Tm (where Tm is the melting temperature of the sample), a yield near and above unity. The enhancement of lithium sputtering is observed to be a strong function of temperature and moderately on particle energy. Bombardment of a low-vapor-pressure lithium alloy (0.8 Sn-Li), used for comparison, also results in nonlinear rise of lithium erosion as a function of temperature. Measurements on both pure liquid Li and the alloy indicate a weak dependence with surface temperature of the secondary ion-induced secondary ion emission. Treatment of liquid Li surfaces with D, yields reduced sputtering under He+ impact by a factor of 5-6 when measured at room temperature due to preferential sputtering effects