Secondary emission of MCsn+ molecular ions under the joint influence of electropositive and electronegative elements

Emission of MCsn+ (n = 1, 2, … etc.) molecular ions has been studied under the joint influence of electropositive (cesium) and electronegative (oxygen) elements in the secondary ion mass spectrometry (SIMS) process. The kinetic energy distributions, measured for Cs+, Cs2+, AgCs+ and AgCs2+ ions at different oxygen pressures exhibited changing slopes in their leading parts that hinted at appreciable change in the surface work function. The maximum observed change in the surface work function Δϕmax was ∼0.44 eV. The measured integrated counts of all ionic species showed a strong variation with the changing oxygen environment. The observations are explained in the light of surface work function changes at the sputtering site. Formation mechanisms of Cs2+, AgCs+ and AgCs2+ ions are explained in the framework of sputter-ion emission models.