Dependence of characteristics of Hf(M)SiBCN (M = Y, Ho, Ta, Mo) thin films on the M choice: Ab-initio and experimental study

Amorphous HfMSiBCN materials (M = Y, Ho, Ta, Mo or an enhanced Hf content instead of any other M) are investigated by ab-initio calculations and magnetron sputtering. We focus on combining the high-temperature stability and oxidation resistance of these materials with optimised mechanical, optical and electrical properties. First, we predict the corresponding trends by calculating the effect of the M choice and fraction on formation energy (E_form) and mechanical properties of MN and Hf_xM_1–xN crystals. We discuss the dependence of E_form(Hf_xM_1–xN) on the crystal structure and the distribution of Hf and M in the metal sublattice. The mechanical properties calculated for MN correlate with those measured for HfMSiBCN. The driving force towards N incorporation, decreasing with the periodic-table group number of M according to the calculated E_form(MN), correlates with the measured increasing electrical conductivity and extinction coefficient of HfMSiBCN. Second, we model the amorphous HfMSiBCN materials themselves by ab-initio molecular dynamics. The calculated band gap, localisation of electronic states and bonding preferences of M also correspond to the increasing metallicity with respect to the periodic-table group number of M and confirm the possibility of predicting the trends in characteristics of HfMSiBCN using those of MN. Third, we study the measured HfMSiBCN properties as functions of each other and identify sputter target compositions leading to hard films with high electrical conductivity at a relatively low extinction coefficient. The results are important for the design of hard, conductive and/or transparent high-temperature coatings.