Atomic wires do not interact directly with each other and are therefore ordered by an indirect substrate mediated interaction, whereas molecular structures can be assembled spontaneously by a direct interaction with each other. Such interwire interactions were very short and subsequently an interwire distance of ordered atomic wires were a few Å. Because of the interwire interaction, atomic wires have been described as a quasi 1D system rather than an ideal 1D system. Therefore, an atomic wire with a long interwire distance needs to study an ideal 1D system but, as mentioned before, atomic wires were not ordered with a long interwire distance. Assembly of a long interwire distance atomic wire is thus very challenging and demanded to widen experimental scope of studies on one-dimensional physics. In this study, indium atomic wires with a long interwire distance of 5.7 nm were ordered spontaneously at room temperature on a stepwise nanotemplate, a Si(557) surface. In general, interwire interactions are required to produce ordered nanowires so that other ordered atomic wires have a short interwire distance of a few Å, as described above. The long interwire distance of the ordered indium atomic wires is therefore very unique. Indium atoms were mobile at room temperature and were adsorbed on a only specific step among four steps, one (111) and three (112) steps of the reconstructed Si(557) surface, maintaining the stepwise nanotemplate structure, as observed by scanning tunneling microscopy (STM), despite the fact that the triple steps have similar local atomic structures. The energetic stability of the indium atomic wires was calculated by first-principles calculations. The reconstructed Si(557) structure model was based on the dimer-adatom-stacking fault (DAS) model and adatom-parallel dimer (AD) model of (111) and (112) facets, respectively.[1, 2] Total energy differences between indium atomic wires on the three (112) steps was very small and the most stable atomic structure was located at the second (112) step, which was consistent with STM images. STM simulations also reproduced the x2 periodicity of the In-induced atomic wires along the wire direction.

 

[1] K. Takayanaki, Y. Tanishiro, M. Takahashi, and S. Takahashi, J. Vac. Sci. Technol. A 3, 1502 (1985)

[2] D. Oh, M. Kim, J. Nam, I. Song, C. Park, S. Woo, H. Hwang, C. Hwang, J. Ahn, Phys. Rev. B, 77, 155430 (2008)