Surfactant-Mediated Growth of Epitaxial Films on Quasiperiodic Surfaces
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Surfactant-Mediated Growth of Epitaxial Films on Quasiperiodic Surfaces Masahiko Shimoda, Junqing Guo1, Taku J. Sato, and An Pang Tsai National Research Institute for Metals 1-2-1, Sengen, Tsukuba, Ibaraki, 305-0047, Japan 1 CREST, Japan Science and Technology Corporation, Kawaguchi, Saitama, 332-0012, Japan ABSTRACT We have succeeded for the first time in inducing epitaxial growth of metal films on quasiperiodic surfaces. Depositions of Au onto the tenfold surface of a decagonal Al-Ni-Co quasicrystal were originally attempted to create a quasicrystal of a single element as an epitaxial film. Although the desired film was not obtained on the clean surface, a multiply twinned AuAl2 crystalline layer with a (110)-oriented surface was formed with the aid of an In pre-deposition layer. The presence of pre-deposited In also worked as a surfactant for the case of Au-deposition onto the fivefold surface of an icosahedral Al-Pd-Mn quasicrystal and promoted the formation of an ordered film of Au-Al alloy. X-ray photoelectron diffraction images from this ordered film show that the alloy has an icosahedral structure as a long-range order, suggesting the formation of a quasicrystalline film.
INTRODUCTION So far, quasicrystals have been discovered only as alloys with limited combinations of elements under restricted conditions, which suggests that the formation of quasicrystals in a desired combination of elements is thermodynamically impossible with conventional means. Recently, we have found that the depositions of a submonolayer of Au onto the quasiperiodic surface of a decagonal Al-Ni-Co quasicrystal and subsequent annealing give rise to a selective alloying with Al in the substrate and form a layer of multiply twinned AuAl2 crystals [1]. Each domain of the crystalline layer has an (110)-oriented surface and an azimuthal orientation corresponding to the tenfold symmetry of the substrate. These results indicate that epitaxial films can be grown even on a quasiperiodic surfaces and that quasicrystalline phases of various materials, such as semiconductors, oxides, and organic compounds can be expected to form as an epitaxial film. (Note that we stretch the meaning of "epitaxy" to describe the phenomenon in which films grown on a quasiperiodic substrate maintain the directional order of the substrate). In the present paper, we report on the results of depositions of Au onto two different quasiperiodic surfaces, i.e. the tenfold surface of Al-Ni-Co and the five fold surface of Al-Pd-Mn. These experiments were originally attempted to create quasicrystal films with a single element. Although the desired films have not yet been formed, we have found that an epitaxial layer of an Au-based alloy could be formed on both the quasiperiodic surfaces with the assistance of an In pre-deposition layer. This surfactant effect of In is one of the most important findings of this study.
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EXPERIMENTAL The substrates with quasiperiodic surface were prepared as follows. Slices of samples were initially cut from large single-grained Al72N
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