Microstructure of Cu(x)Mo6S8 Chevrel phase thin films on R-plane sapphire

Cu(x)Mo6S8 Chevrel phase thin films epitaxially grown on R-plane sapphire substrates have been studied using field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HREM). For samples grown in optimal conditions, the SEM images evidence oriented grains of about 100 nm average size; the HREM images of cross-section samples allow to deduce the local epitaxial relations between the substrates and films. HREM also evidences two grain families, previously deduced from X-ray and reflection high-energy electron diffraction studies. No defects have been observed in the films; a higher molybdenum content in the films results in Mo-precipitation at the film-substrate interface.