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

TL;DR

This study examines how keV-energy light ions like protons and helium ions deposit electronic energy in transition metal nitrides, revealing differences in stopping cross sections and excitation mechanisms relevant for material applications.

Contribution

It provides new experimental data on electronic stopping cross sections in transition metal nitrides and compares these with theoretical predictions, highlighting additional excitation mechanisms.

Findings

Protons in light nitrides show stopping cross sections similar to N2 gas at low energies.

He ions exhibit higher electronic energy loss than N2 gas across all nitrides.

Deviations from velocity proportionality suggest additional excitation mechanisms.

Abstract

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 5th and 6th 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.