Sputtering of Mo and Al in D2/N2 plasma cleaning discharge

•The N2 addition of the D2 plasma accompanied by the synthesis of ND3.•The sputtering rate of Al and Mo increased with the N2 fraction up to 15%.•The Be sputtering rate was practically unchanged.•A further increase in N2 fraction led to a decrease in metal sputtering rate.•Plasma cleaning of Mo mirrors don't cause the deterioration of optical properties. Sputtering of Mo and Al (as Be proxy) in mixed D2/N2 DC glow discharge was studied in view of the first mirror performance. The composition of the working gas was varied from 100% D2 to 100% N2, while keeping a total pressure of 15Pa. The ion energies striking the sample surface were defined by its 100V biasing negative to a floating potential. It has been obtained that the sputtering yield of Mo and Al increases gradually with N2 concentration up to 4‒16mol% and decreases with further N2 addition. In contrast, the sputtering yield of Be remains unchanged up to 10mol% of N2. Adding 16mol% leads to three-fold decrease in the sputtering rate. The sputtering behavior is discussed in context of surface data analysis and mass spectroscopy of the discharge gas exhaust. Variation in reflectivity of a single crystalline Mo due to plasma exposure under similar conditions is also presented and discussed.