Kinematic and thermodynamic effects on liquid lithium sputtering

The lithium-sputtering yield from lithium and tin-lithium surfaces in the liquid state under low-energy, singly charged particles as a function of target temperature is measured by using the IIAX (Ion-surface Interaction Experiment) facility. Total erosion exceeds that expected from conventional physical sputtering after accounting for lithium evaporation for temperatures between 200 and 400 oC. 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-degree incidence. Erosion measurements account for temperature-dependent evaporation. Results show the sputtering yield of lithium is anomalously enhanced to absolute values above unity as the temperature nears ~ 2.0 Tm (where Tm is the melting temperature of the sample). The enhancement of lithium sputtering is measured for all incident particle energies and exceeds sputtering levels predicted by linear cascade theory. Modeling with modified binary collision approximation codes suggests that two mechanisms are responsible for the enhancement: near-surface energy deposition and the nature of the binding between target atoms and the sputtered atom. Comparison to a low-vapor-pressure lithium alloy (0.8 Sn-Li) also results in nonlinear rise of lithium erosion as a function of temperature. Secondary ion-induced sputtered fraction measurements indicate a weak dependence with surface temperature. PACS codes: 34.50.Dy, 52.40.Hf, 61.25.Mv, 69.49.Sf