Epitaxial Growth of Ruby Crystal Films on Sapphire Crystal Substrates and Solubility of Aluminum Oxide in Molybdenum Trioxide Flux

Ruby (Al2O3:Cr) crystal films were, for the first time, epitaxially grown on sapphire (Al2O3) crystal substrates via the evaporation of molybdenum trioxide (MoO3) flux. The crystal films were grown by heating the flux placed on the sapphire crystal substrates at 1100 °C for 1200 min. The films thus obtained exhibited a red color and were approximately 200 μm in thickness. Based on the X-ray diffraction and electron backscatter diffraction analyses data, the crystallographic orientation of the crystal films was found to be the same as that of the substrate crystals. A ruby crystal film with a (0001) face developed on the (0001) substrate face, and a film with a (112̅0) face developed on the (112̅0) substrate face. In addition, the solubility of Al2O3 in the flux at 1100 °C was estimated to be approximately 9.6 mol % by measuring the mass loss of the substrate and the amount of evaporated flux when the crystallization of the ruby crystals occurred.