Element- and charge-state-resolved ion energies in the cathodic arc plasma from composite AlCr cathodes in argon, nitrogen and oxygen atmospheres

TL;DR

This study measures and analyzes the energy distributions and charge states of ions in cathodic arc plasmas from composite AlCr cathodes across various gas atmospheres and pressures, revealing how these factors influence ion energies and compositions.

Contribution

It provides the first comprehensive characterization of element- and charge-state-resolved ion energies in AlCr cathode plasmas under different gases and pressures.

Findings

Al$^{+}$ ions are most abundant regardless of gas.

Cr$^{2+}$ dominates in Ar and N$_2$, Cr$^{+}$ in O$_2$.

Ion energy distributions include high-energy and thermalized components.

Abstract

The energy distribution functions of ions in the cathodic arc plasma using composite AlCr cathodes were measured as a function of the background gas pressure in the range 0.5 to 3.5 Pa for different cathode compositions and gas atmospheres. The most abundant aluminium ions were Al$^{+}$ regardless of the background gas species, whereas Cr$^{2+}$ ions were dominating in Ar and N$_2$ and Cr$^{+}$ in O$_2$ atmospheres. The energy distributions of the aluminium and chromium ions typically consisted of a high-energy fraction due to acceleration in the expanding plasma plume from the cathode spot and thermalised ions that were subjected to collisions in the plasma cloud. The fraction of the latter increased with increasing background gas pressure. Atomic nitrogen and oxygen ions showed similar energy distributions as the aluminium and chromium ions, whereas the argon and molecular nitrogen and oxygen ions were formed at greater distance from the cathode spot and thus less subject to accelerating gradients. In addition to the positively charged metal and gas ions, negatively charged oxygen and oxygen-containing ions were observed in O$_2$ atmosphere. The obtained results are intended to provide a comprehensive overview of the ion energies and charge states in the arc plasma of AlCr composite cathodes in different gas atmospheres as such plasmas are frequently used to deposit thin films and coatings.