Surface structures of Al-Pd-Mn and Al-Cu-Fe icosahedral quasicrystals

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In this dissertation, the author reports on the surface structure of i-Al-Pd-Mn twofold, threefold, fivefold and i-Al-Cu-Fe fivefold surfaces. The LEED studies indicate the existence of two distinct stages in the regrowth of all four surfaces after Ar{sup +} sputtering. In the first stage, upon annealing at relatively low temperature: 500K--800K (depending on different surfaces), a cubic phase appears. The cubic LEED patterns transform irreversibly to unreconstructed quasicrystalline patterns upon annealing to higher temperatures, indicating that the cubic overlayers are metastable. Based upon the data for three chemically-identical, but symmetrically-inequivalent surfaces, a model is developed for the relation between the ... continued below

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23 p.

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Shen, Z. February 12, 1999.

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  • Ames Laboratory
    Publisher Info: Ames Lab., IA (United States)
    Place of Publication: Iowa

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In this dissertation, the author reports on the surface structure of i-Al-Pd-Mn twofold, threefold, fivefold and i-Al-Cu-Fe fivefold surfaces. The LEED studies indicate the existence of two distinct stages in the regrowth of all four surfaces after Ar{sup +} sputtering. In the first stage, upon annealing at relatively low temperature: 500K--800K (depending on different surfaces), a cubic phase appears. The cubic LEED patterns transform irreversibly to unreconstructed quasicrystalline patterns upon annealing to higher temperatures, indicating that the cubic overlayers are metastable. Based upon the data for three chemically-identical, but symmetrically-inequivalent surfaces, a model is developed for the relation between the cubic overlayers and the quasicrystalline substrate. The model is based upon the related symmetries of cubic close-packed and icosahedral-packed materials. These results may be general among Al-rich, icosahedral materials. STM study of Al-Pd-Mn fivefold surface shows that terrace-step-kink structures start to form on the surface after annealing above 700K. Large, atomic ally-flat terraces were formed after annealing at 900K. Fine structures with fivefold icosahedral symmetry were found on those terraces. Data analysis and comparison of the STM images and structure model of icosahedral Al-Pd-Mn suggest that the fine structures in the STM images may be the pseudo Mackay (PMI) clusters which are the structure units of the structure model. Based upon his results, he can conclude that quasicrystalline structures are the stable structures of quasicrystal surfaces. In other words, quasicrystalline structures extend from the bulk to the surface. As a result of the effort reported in this dissertation, he believes that he has increased his understanding of the surface structure of icosahedral quasicrystals to a new level.

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23 p.

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OSTI as DE99002522

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  • Other Information: DN: Thesis submitted to Iowa State Univ., Ames, IA (US); TH: Thesis (Ph.D.)

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  • Other: DE99002522
  • Report No.: IS-T--1853
  • Grant Number: W-7405-ENG-82
  • Office of Scientific & Technical Information Report Number: 348927
  • Archival Resource Key: ark:/67531/metadc678358

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  • February 12, 1999

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  • July 25, 2015, 2:20 a.m.

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  • Nov. 6, 2015, 9 p.m.

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Shen, Z. Surface structures of Al-Pd-Mn and Al-Cu-Fe icosahedral quasicrystals, thesis or dissertation, February 12, 1999; Iowa. (digital.library.unt.edu/ark:/67531/metadc678358/: accessed September 25, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.