  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.
