Sputtering of excited-state potassium atoms from electron-bombarded KBr crystals

Sputtering of excited-state potassium atoms from electron-bombarded KBr crystals has been investigated at 300 and 443 K by measuring simultaneously the optical emission, Auger, and mass spectra. The beam current dependences of the intensities of the ground-state and excited-state potassium atoms at 443 K are nearly linear and quadratic, respectively, indicating that excited-state potassium atoms are produced by gas-phase collisions of potassium atoms desorbed from the surface. On the other hand, the room-temperature data show complicated dependences, which can be divided into three current regions. In the low-current region (<13 μA), electronic excitation followed by Auger-induced Coulomb repulsion produces the excited-state potassium atoms. In the high-current region (>25 μA), effects due to sample decomposition, nonstoichiometry, and gas-phase collisions play important roles in the production of excited-state potassium atoms. The nonlinear sputtering yield of excited-state potassium atoms in the intermediate-current region may be due to secondary effects including the formation of defects and cluster ions