Electronic excitation of transition metal nitrides by light ions with keV energies

We investigated the specific electronic energy deposition by protons and He ions with keV energies in different transition metal nitrides of technological interest. Data were obtained from two different time-of-flight ion scattering setups and show excellent agreement. For protons interacting with light nitrides, i.e. TiN, VN and CrN, very similar stopping cross sections per atom were found, which coincide with literature data of N₂ gas for primary energies ⩽25 keV. In case of the chemically rather similar nitrides with metal constituents from the 5^th and 6^th period, i.e. ZrN and HfN, the electronic stopping cross sections were measured to exceed what has been observed for molecular N₂ gas. For He ions, electronic energy loss in all nitrides was found to be significantly higher compared to the equivalent data of N₂ gas. Additionally, deviations from velocity proportionality of the observed specific electronic energy loss are observed. A comparison with predictions from density functional theory for protons and He ions yields a high apparent efficiency of electronic excitations of the target for the latter projectile. These findings are considered to indicate the contributions of additional mechanisms besides electron hole pair excitations, such as electron capture and loss processes of the projectile or promotion of target electrons in atomic collisions. (paper)