Scanning tunnelling microscopy with atomic resolution on the twofold surface of the icosahedral AlPdMn quasicrystal
Abstract:We have investigated the 2-fold surface of an icosahedral Al 70 Pd 21 Mn 9 quasicrystal by means of low-temperature scanning tunnelling microscopy (77?K). The sequence of the terrace step edge heights revealed a Fibonacci sequence with S?=?2.40?Å and L?=? t S?=?3.88?Å as fundamental terrace step heights. S and L can be related to the pentagon edge length of the below terrace Bergman polytope and the surface dissected Bergman polytope of the 5-fold surface. The atomic resolution STM images of the 2-fold surface have been compared to the M-model structure of the i-AlPdMn and the experimental STM surface structure of the 5-fold surface by analysis of the FFT spots. We could show that the positions of the FFT spots in the 2-fold surface are related to the FFT spots of the 5-fold surface by projections onto the fivefold axis and are in good correspondence to the model structure. We identified characteristic rectangular features on the 2-fold surface with edge length of 4.8, 7.7 and 12.6?Å corresponding to D 2 , t D 2 and t 2 D 2 with D 2 being the pentagon edge length of the surface dissected Bergman polytope. We interpret our results as being a strong indication for the bulk termination of the 2-fold surface of the i-AlPdMn quasicrystal.
Document Type: Research Article
Affiliations: EMPA, Materials Science and Technology, nanotech@surfaces, Feuerwerkerstrasse 39, CH-3602 Thun
Publication date: February 1, 2006
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