Temperature dependence of sputtering behavior of Cu-Li alloys

Three different Cu-Li alloys (4, 10, and 16% Li) have been sputtered by 1 keV and 100 eV D⁺ ions. The Cu sputtering yield and the total weight loss was measured as a function of the target temperature between 25 and 700°C. The yield was measured by the catcher foil technique and by the weight loss method in order to differentiate between the total weight loss and the Cu sputtering yield (i.e., Rutherford backscattering analysis (RBS) of the catcher foil). Targets with lower Li concentration (4 and 10%) did not show a significant change of the Cu sputtering yield [1] as found by other authors [2] and this is probably due to the higher current density (10¹⁵ cm⁻² s⁻¹) in this experiment. An increase in weight loss at temepratures above 550°C was caused by Li evaporation. The target with high Li concentration (16% Li) showed a reduction of the Cu sputtering yield by more than a factor of 50 for both the 1 keV and the 100 eV D⁺ ions. This reduction occurs in a small temperature range around 550°C, which coincides with the transition on the Cu-Li phase diagram from the a-phase to α + liquid. For temperatures above 550°C the sputtering yield increases again, most probaby due to an enhanced evaporation of Li. At optimum temperature conditions, the evaporation rate of Li for the Cu-Li alloy is many orders of magnitude lower than the rate for pure Li. According to the phase diagram, the Cu-Li alloy with even higher Li concentration could reach optimum conditions at lower temperatures and, therefore, would be a promising first-wall candidate.