Quintuple-period Si atomic wires with alternative double and triple modulations by metal: Mg/Si(557)

The formation of Mg-induced quasi-one-dimensional atomic wires on a Si(557) surface was studied by low energy electron diffraction (LEED), scanning tunneling microscopy (STM), and first-principles calculations. The atomic wires were produced on the Si(557) surface without faceting when heated to 330 ?C. The atomic wires had a × 5 period along the wires, as observed by LEED. STM images showed the existence of three kinds of atomic wires in a unit cell: an atomic wire located at the step edge and the others on the terrace. Interestingly, alternative double and triple modulations resulting in the × 5 period was observed at the atomic wire located at the step edge. Among the variety of atomic structure models available, the one based on a honeycomb-chain-channel model, which is that of a metal/Si(111)-(3 × 1) surface, reproduced the STM images well and was relatively stable energetically.