Inner Shell Target Ionization by the Impact of N⁶⁺, O⁷⁺ and Ne⁹⁺ on Pt(110)

Abstract

Highly charged ions from the test bench of the 14GHz Electron Cyclotron resonance (ECR) ion source at the Grand Accelerateur National des Ions Lourds (GANIL), Caen, were used to study the ion-induced electron emission (IEE) from a single crystal Pt(110) surface. Mass and charge selected beams of N⁶⁺, O⁷⁺ and Ne⁹⁺ with currents of 150nA, 60nA and 15nA are obtained. The IEE spectra are measured with an electrostatic analyzer with an energy resolution of AE/E = 2.5%. The dependencies of the IEE yields are studied as function of the impact angle and of the electron observation angle, i. e. the analyzer is rotable around the target in the scattering plane. The primary energy of the ions is 10q-keV, where q is the charge of the ion. Projectile velocities are hence 0.4 v₀ (v₀ = Bohr velocity). The energy component perpendicular to the surface E_⊥ = E₀sin²ψ reaches values below 2keV, when lowering the grazing angle of incidence ψ below 10°. The IEE spectra show beside the “δ-electron” background line emission due to Auger processes in the projectile and in the target atoms. We identify KLL and LMM projectile electrons and NNV, NOO, NVV and OVV target Auger electrons. An interesting result is the finding that Ne⁹⁺ does not excite the Pt-NOO and -NNV Auger emission. The analysis of possible vacancy transfer mechanisms for a K-shell projectile vacancy to the target N-shell is based on an atomic structure calculation and on a diabatic potential curve crossing model. The target N-shell ionization is identified as a vacancy transfer of the Landau-Zener type.