Untersuchung der physikalischen Einflüsse auf die geometrische Sturktur und chemische Zusammensetzung von Quasikristalloberflächen
Untersuchung der physikalischen Einflüsse auf die geometrische Sturktur und chemische Zusammensetzung von Quasikristalloberflächen
The structure and composition of surfaces of Czochalski-grown icosahedral Al-Pd-Mn anddecagonal Al-Ni-Co single quasicrystals produced by in-situ cleavage fracture in UHV wereinvestigated by STM, SEM and calibrated AES at room temperature and alter heat treatment.The experiments of fivefold i-Al$_{7...
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Personal Name(s): | Kluge, Fanying (Corresponding author) |
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Contributing Institute: |
Publikationen vor 2000; PRE-2000; Retrocat |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2001
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Physical Description: |
119 p. |
Document Type: |
Report Book |
Research Program: |
Addenda |
Series Title: |
Berichte des Forschungszentrums Jülich
3910 |
Link: |
OpenAccess OpenAccess |
Publikationsportal JuSER |
The structure and composition of surfaces of Czochalski-grown icosahedral Al-Pd-Mn anddecagonal Al-Ni-Co single quasicrystals produced by in-situ cleavage fracture in UHV wereinvestigated by STM, SEM and calibrated AES at room temperature and alter heat treatment.The experiments of fivefold i-Al$_{75}$-Pd$_{21}$-Mn$_{8.5}$ quasicrystal surfaces were carried out on the$\textit{as-grown}$ and $\textit{extended longtime annealed}$ (800°C for 2445h) samples. A big differencebetween these two types of samples was observed in the macroscopic scale: the $\textit{extendedlongtime annealed}$ samples showed a large number of big well faceted voids with diametersof several hundreds of $\mu$m, while $\textit{as-grown}$ samples had only a few voids, which were someorders of magnitude smaller. Directly after cleavage all Al-Pd-Mn samples exhibited the samesurface structure and surface composition. After heat treatment pronounced differences insurface structure and composition were found between the two types of samples. Surfaces of$\textit{as-grown}$ samples became optically matt. Large variation of surface composition was alsodetected by AES. In contrast the surfaces of $\textit{extended longtime annealed}$ samples underwentno visible change of structure and almost no variation of composition. This result can beexplained by the model of migration of atomic vacancies between the surface and the nearsurface area and its influence an the surface morphology and composition. This model alsoexplained the smooth denuded zone closed to the grown in voids of as-grown samples afterheat treatment. The data analysis based on this model also showed some information of thechemical nature of the bulk vacancies. The influence of vacancies an the stability of clusterstructure an the surfaces was discussed.The experiments of two dimensional decagonal Al-Ni-Co quasicrystals were performed anthe tenfold cleavage surfaces. At room temperature the STM images showed a kind of cluster-subclusterstructure an the surfaces. The smallest features observed were 1 to 2 nm indiameter. This can be well explained by the current Al-Ni-Co structure models which predictthe columnar atom arrangement extending perpendicular to the cleavage plane. The heightprofile shows that the average roughness of d-Al-Ni-Co surfaces was 0.4 nm, much less thanthe roughness of previously investigated i-Al-Pd-Mn surfaces. $\textit{As-grown}$ Al-Ni-Co surfacesshowed behavior similar to that of the $\textit{extended annealed}$ Al-Pd-Mn surfaces after heattreatment. No significant changes of structure and composition were observed. This indicateda lower vacancy concentration compared to as-grown i-Al-Pd-Mn samples.Furthermore, for the purpose of direct observation of equilibrium surfaces of quasicrystals,the faceted surfaces of grown-in voids exposed by cleavage of a large set of different i-Al-Pd-Mn samples were investigated. Finally experiments of oxidation an the surfaces of i-Al-PdMn quasicrystals were carried out. The results showed that Pd is able to prevent the oxidation. |