Abstract: A method for depositing a hard protective coating on at least one part, wherein 10-70% of nitrogen combined with 10-70% of a mixture of helium and argon or 10-70% of neon for strongly exciting and dissociating the nitrogen and hydrogen, is added to a precursor gas, and the energy delivered to each atom of the precursor gas is selected so as to achieve so-called "Lifschitz" conditions which define the energy range in which a maximum number of diamond-like tetrahedral structures are produced instead of graphite structures.