Temperature dependence of secondary ion emission from tantalum produced by atomic and polyatomic gold projectiles

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Temperature dependencies have been measured within a wide range of target temperatures of 300 K ≤ T ≤ 2400 K for secondary ion yields of Ta n +, Ta n O m +, Ta n Nb + and Ta n Au + ( n = 1–14, m = 1–3) under the bombardment of tantalum target with 12 keV atomic Au − and 18 keV polyatomic Au 3 − projectiles. It is demonstrated that yields of Ta n + ( n = 2–14) and Ta n Nb + ions increase with temperature for T ≤ 1700 K and then tend to become temperature independent. On the contrary, the yields of Ta n O m + and Ta n Au + ions slightly increase with temperature reaching their maxima in the range of 1000 K ≤ T ≤ 1500 K and then sharply decrease to zero at T ≈ 1700 and 2100 K, respectively. These trends are interpreted to indicate the redistribution of the sputtered flux between these different emission channels while sputtering conditions change with the target temperature. Oxygen presence on the surface at lower temperatures limits the yield of Ta n + clusters and stimulates that of Ta n O m +. Removing oxygen from the surface enhances the yield of Ta n + clusters and the disappearance of Ta n O m +. After clean surfaces are established in the range of 1700 K ≤ T ≤ 2400 K, the yield of the Ta n + and Ta n Nb + cluster ions becomes constant thus indicating that their ionization probability does not depend on the target temperature in this range. Some differences in the temperature dependencies obtained under the atomic and polyatomic ion bombardment are observed and interpreted as the indication of different efficiencies of the sputtering process since polyatomic projectiles sputter more material than atomic ones. This, in addition to better surface cleaning, enhances yields of cluster ions. For atomic ions Ta +, an additional emission channel, thermal evaporation/surface ionization, is identified at target temperatures T > 2300 K. No evaporated cluster ions are observed.