Electronic energy-loss mechanisms for H, He, and Ne in TiN

The specific energy loss of medium-energy hydrogen, helium, and neon ions in titanium nitride is studied. Electronic stopping cross sections of ions in the energy range of 3--140 keV/amu were measured in backscattering geometry using time-of-flight medium-energy ion scattering, from the energy loss experienced in TiN thin films on Si. For the lowest energies, data for H show a strong deviation from Bragg's rule. For hydrogen and Ne ions, electronic stopping exhibits velocity proportionality at ion velocities below 1 a.u. Comparison to density functional theory calculations of the stopping power yields very good agreement for H, while for He and Ne, the experimentally observed electronic stopping power is considerably higher than predicted. For He the extrapolation of the stopping power at low energies points to a nonvanishing energy loss at vanishing ion velocity. The present data can thus be taken as an indication of additional energy-loss processes different from direct electron-hole pair excitation. Furthermore, the results provide reference values for ion-beam-based analysis of TiN, a material with huge technological relevance.