The issue of the reproducibility of deposition of superhard nanocomposites with hardness of ≥50 GPa

It is shown that the lack of the reproducibility of the data of Veprek et al. on the deposition of superhard nanocomposites with hardness reaching and even exceeding 50 GPa, that can be found in many recent papers of other groups, is due to either the choice of inappropriate deposition conditions, such as too low deposition temperature and pressure of nitrogen, or impurities. The problem of impurities is particularly difficult to solve when reactive sputtering is used. It is shown that using a sufficiently high deposition temperature of >500 °C, high deposition rates and nitrogen pressure of ≥0.002 mbar, hardness of ≥50 GPa is achieved in the binary nc-TiN/a-Si3N4 system, provided the oxygen impurities are below about 0.2 at.%.