Senior Research Scientist, Surface Chemistry Laboratory, Discovery Research Institute, RIKEN (The Institute of Physical and Chemical Research)
Formation of atomic scale low-dimensional structures and control of their physical properties
Metals with low-dimensional structures have characteristic phenomena, such as CDW, SDW, spin-charge separation, quantized conductance and ferromagnetism caused by a narrow or a flat band, and their physical properties are completely different from those of ordinary metals. In this study, we have aimed at establishing a universal method for forming artificial low-dimensional nanostructures of various metals. Our goal is to tailor the physical properties by controlling the geometric features on an atomic scale. We assume a simple scenario where dosed metal atoms on a clean solid surface with periodic surface potential diffuse and are trapped resulting in the formation of a low-dimensional nanostructure. As substrates, we employ vicinal surfaces of single crystals on which steps giving potential minima are periodically aligned in a parallel configuration.
On vicinal surfaces of SrTiO3(100), dosed Sr and Cu formed one-dimensional (1D) nanoscale structures along the steps. However, atomic fine structures were not formed because of randomness, such as oxygen deficiency, other defects, such as substitution, and the relatively low surface energy peculiar to oxide materials.
On the other hand, on vicinal Au(111) surfaces, atomically controlled step flow growth of 1D nanostructures was observed for Mn and Cu, which form smooth shapes, and for Fe and Ni, which form undulated shapes with the same periodicity as the surface reconstruction of the Au substrates. Dosed Co formed a regularly arranged array of dots along the steps, and Gd grew as random islands. Angle-resolved photoemission spectroscopy measurements on Fe/Au(788) revealed that Fe monatomic rows formed along the steps have a 3d degenerated band showing a 1D dispersion relation. This localized nature is completely different from that of bulk Fe, and the electronic structure changes as the dimensionality increases with higher Fe coverages. Similar results were obtained for Ni/Au(788) and Co/Au(788).
Novel properties for metals can be obtained by structurally controlling their dimensionality on an atomic scale. However, this work is still the tip of the iceberg. Currently, we are searching for a combination of dosed metal and substrate that will cause an interesting and useful phenomenon and lead to modern alchemy.
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| Fig. 1 Large Image |
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| Left picture: STM image of 0.04 ML Fe/Au(455). Single or double atomic rows formed along the steps are clearly observed. Right picture: STM image of 0.6 ML Co/Au(788). A regular array of nanosize dots have formed along the steps. |
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| Fig. 2 Large Image |
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| Angle-resolved photoemission spectra measured perpendicular to the steps on Au(788), and the band dispersion relations obtained. On the clean surface, two flat bands corresponding to the standing waves are observed. At an Fe coverage of 0.08 ML, one degenerate Fe 3d band appeared with no dispersion, which strongly suggested a 1D electronic structure. |
Relevant papers
- Shiraki, S., Nantoh, M., Wakatsuchi, M. & Kawai, M.
Contrast in friction and its inversion observed on metal deposited SrTiO3(100) surfaces
J. Appl. Phys. 94, 3082-3090 (2003). - Fujisawa, H., Shiraki, S., Nantoh, M. & Kawai, M.
Angle-resolved photoemission study of Fe on a vicinal Au(788) surface
J. Electron Spectrosc. Rela. Phenom. 137-140, 89-95 (2004). - Shiraki, S., Fujisawa, H., Nantoh, M. & Kawai, M.
Confining barriers for surface state electrons tailored by monatomic Fe rows on vicinal Au(111) surfaces
Phys. Rev. Lett. 92, 96102/1-4 (2004).
