Decomposition of the five-fold surface of Al70Pd21Mn9 at elevated temperature

Several surface phases have previously been identified on the five-fold sur face of the Al70Pd21Mn9 quasicrystal. Two of these, the clustered and terra ced phases, have been discovered by scanning tunnelling microscopy (STM) st udies. In this paper, we report STM images showing the existence of a new p hase on this surface. This new topography was obtained by annealing the sam ple close to its melting point for several minutes. A model is presented wh ich exhibits the main features of the structure. The unit-cell dimensions m atch those of the Al3Mn orthorhombic phase. Mechanical polishing followed b y sputtering and annealing restored a pentagonal quasicrystalline surface i ndicating that the decomposition is a near-surface phenomenon. (C) 2000 Els evier Science B.V. All rights reserved.