High-resolution scanning tunneling microscopy investigation of the (12110) and (10000) two-fold symmetricd-Al-Ni-Co quasicrystalline surfaces

Abstract

The d-Al-Ni-Co quasicrystal exhibits two crystallographically inequivalent twofold symmetric planes: the ͕10000͖ and ͕12110͖ surface planes. In particular the twofold symmetric surfaces are very interesting since they are spanned by perpendicular periodic and aperiodic axes. We investigated the ͑12110͒ surface of two different compositions d-Al 70 Ni 15 Co 15 and d-Al 72.9 Ni 10.4 Co 16.7 and the ͑10000͒ d-Al 72.9 Ni 10.4 Co 16.7 surface by means of low-temperature ͑5 K͒ scanning tunneling microscopy ͑STM͒ in ultrahigh vacuum. All three surfaces are characterized with atomic resolution and display large and flat terraces with a columnar structure along the periodic axis. Both compositions of the ͑12110͒ d-Al-Ni-Co STM investigations revealed that the surface is faceted into ͕12110͖ and ͕10000͖ facets with a 1:1 area ratio. The ͑12110͒ facets represent the bulk periodicity of 0.4 nm within the prominent columnar structure which is attributed to a stacking of Al dimers. The sequence of the columnar structure along the aperiodic axis as well as the step heights between the ͑12110͒ surfaces could be attributed to the pentagonal tiling edge length of the bulk model. Furthermore, the ͑12110͒ surface is identified as one of the densest planes in the bulk model possessing a slightly lower Al concentration as the nominal bulk composition. However, a difference in the fine structure within the columns is observed between the two investigated compositions. The ͑10000͒ facet presents an identical surface structure as the unfaceted ͑10000͒ surface of the quasicrystal. At the ͑10000͒ surface two terraces with different surface structures are identified and compared to the bulk model. One of them shows a bias voltage depending structure. In contrast to the bulk model the minimal observed periodicity on the ͑10000͒ surface is doubled to 0.8 nm. On the other hand the aperiodic step height sequence and the order of the columnar motifs along the aperiodic axis are in agreement with the bulk model. The height distribution analysis of the ͑10000͒ surfaces exhibits that the surface topmost layer consists of planes which are less dense than the ͑12110͒ surface planes.

Surfaces of Al-based complex metallic alloys: atomic structure, thin film growth and reactivity

“…Additional phenomena have been observed mainly for twofold surfaces of decagonal quasicrystals where facetting of the (12110) surface and variation of the surface periodicity along the [10000] have been reported for decagonal phases of various compositions [40–42] (see section 2.5). The Y-Al-Ni-Co(100) surface (related to a twofold decagonal surface) is also a system where local reconstructions have been identified [39].…”

“…the (12110) and (10000) surfaces) of the d -Al-Ni-Co quasicrystal; facetting of the (12110) surface has been reported and the surface periodicity along [10000] direction varies depending on the composition of the decagonal phase considered [20, 40–42]. The periodicity reported (0.4 nm [20] and 0.8 nm [42]) also diverges between experiments carried out on quasicrystal surfaces of almost similar composition and for comparable surface preparation. It is likely that a small change in the sample composition would have a drastic effect on the final surface structure as discussed in the following section 2.6.…”

Weak bonding of Zn in an Al-based approximant based on surface measurements

“…An exception to the generality of bulk-termination may be decagonal Al-Ni-Co. There, preferential segregation of Al has been reported by one group [5], but other reports in the literature seem contradictory [6][7][8][9]. In the present work, we study a newly discovered Al 57 Pd 30 Zn 13 approximant to a decagonal phase [10].…”

Leaching Effect on Multiple Surfaces of a Single Grain Decagonal Al-Ni-Co Quasicrystal

“…Surprisingly, compared to the previous twofold surface, there is the creation of ordered rows of leached grooves that stretch for long distances across the crystal and examples from two dierent parts of the surface can be seen surface was characterised by a columnar structure perpendicular to the tenfold surface [10]. The terminations of these columns were observed to be parallel to the tenfold surface.…”