Phase formation of nanolaminated Mo 2 AuC and Mo 2 (Au 1-x Ga x ) 2 C by a substitutional reaction within Au-capped Mo 2 GaC and Mo 2 Ga 2 C thin films.

Au-containing nanolaminated carbides Mo ₂ AuC and Mo ₂ (Au _1-x Ga _x ) ₂ C were synthesized by a thermally induced substitutional reaction in Mo ₂ GaC and Mo ₂ Ga ₂ C, respectively. The Au substitution of the Ga layers in the structures was observed using cross-sectional high-resolution scanning transmission electron microscopy. Expansion of c lattice parameters was also observed in the Au-containing phases compared to the original phases. Energy dispersive spectroscopy detected residual Ga in Au-substituted layers of both phases with a peculiar Ga in-plane ordering for Au : Ga = 9 : 1 ratio along the Au-Ga layers in Mo ₂ (Au _1-x Ga _x ) ₂ C. These results indicate a generalization of the Au substitution reaction for the A elements in MAX phases.