Atomic force microscopic observation of molybdenum trioxide surface

Surface morphology of MoO₃ was observed with an atomic force microscope. The array of (MoO₆)^6- octahedra was clearly observable for the oxidized surface of a thin crystal prepared by the evaporation-condensation process. Similar high resolution AFM image was also obtained for the powder sample which was coated and dried on the substrate using an ethanol suspension. The high resolution image of the (MoO₆)^6- array disappeared after heating the thin crystal in reducing atmosphere at 350°C, but restored after reoxidation in air at 500°C. Vacuum deposited MoO₃ film on silica glass was amorphous and its surface was smooth and flat after heating at or below 300°C. The film crystallized on heating at 400°C accompanying a slight microstructural change at the film surface. This film exhibited sharp diffraction lines from (0k0) planes. The thin film morphology was destroyed and changed into randomly oriented particles after heating at 500°C.