A systematic study of the characteristic velocities of the negative secondary ion emissions of H, O and matrix species from Sc, Ti, V, Co, Ni and Cu substrates

The negative H, O and matrix secondary ion emissions resulting from Ar +, Cs + and O + 2 bombardment of Sc, Ti, V, Co, Ni and Cu foils were found to exhibit a wide range of energy distribution shapes and intensities. These energy distributions could be reconstructed using two velocity dependent functions. Characteristic velocity values extracted from these velocity dependent functions were found to fall into groups according to the primary and secondary ions studied. Characteristic velocity values from within a particular group were found to correlate with work function and electron affinity arguments consistent with the Auger and resonance charge transfer processes (the Auger process predominating at lower emission energies (< 30 eV) while the resonance process predominates at higher energies (> 40 eV)). All secondary ion groups (H, O and the matrix secondary ion) resulting from a particular primary ion species could then be related on introducing a function relating the covalent radius of the secondary ion-surface atom pair. This, in turn, allowed for an empirical description of the negative secondary ion yield from metal surfaces to be defined.