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Introduction Atomically perfect nanowire with bismuth atoms has attracted much interest in recent years [1]. STM analyses revealed that the Bi wire is qualitatively different from other atomic wires that are formed by many group-III and -V elements at the initial stage of growth on Si (001): the Bi wire is free of kinks or defects, a narrow width of 1nm is kept for more than 400 nm, and the wires appear to be embedded in the surface, not as adsorbates. Since the wire formation is a self-assembling process, it might play a role of template for the nanodevice fabrication. Its mechanism also is great interest in surface science, because a precursor Bi monolayer (ML) surface is well known with specific structures [2]. Although Xray photoelectron diffraction and the theoretical analysis were applied to reveal the Bi wire structure in UHV condition [1,3], the wire in the buried interface can be hardly estimated because of the methodological difficulty, despite its importance in application. Only transmission electron microscope suggested a weak interaction of the amorphous Si (a-Si) layer to the Bi nanowire [4]. X-ray standing wave (XSW) method is suitable for this perfect, dilute, and buried system. The three-dimensional site of Bi atoms has been estimated relative to the Si bulk crystal. |
