Growth of Al-Mn quasi-crystals by vacuum deposition

Abstract

Thin films of Al-Mn quasi-crystals are prepared by a successive deposition technique in vacuum onto air-cleaved sodium chloride surfaces. At a substrate temperature of 280 to 330°C, the growth of the quasi-crystals is found to produce polycrystalline films with a grain size of 20 to 50 nm, the composition ratio of aluminium and manganese being about 5:1. No structure change can be found after a heat treatment of the film at 280°C for 8 h, though a trend of grain growth is detected. For a specimen with a composition ratio above 8:1 grown at 280°C, a diffraction pattern due to aluminium with (111) orientation is recognized in addition to that of quasi-crystals, the lattice relation being that the [110] direction of aluminium is parallel to the two-fold axis of the quasi-crystal. A heat treatment at 330°C for a few hours brings about a transformation from quasi-crystalline films to an alloy phase, Al 6Mn. High resolution electron microscopy is applied to the quasi-crystal films and the edge length of the fundamental hexahedron of the Penrose tiling has been determined to be 0.47 nm from the structure images.