Cyclic transformation of one-dimensional structures during homoepitaxy of Si(5 5 12)-2 × 1

In the homoepitaxy of Si(5 5 12) at a finite temperature, 500 °C, it has been found that one-dimensional elements composing of Si(5 5 12)-2 × 1, such as honeycomb (H) chain, tetramer (T) row, and dimer-facing-adatom (D/A) row, transform for themselves with adding Si atoms. It turns out that a Si dimer is a basic building block, and selectively adsorbs on D/A sites of Si(5 5 12)-2 × 1. Dimer-adsorption on a D/A row induces a tensile stress to the neighboring T row to be split to a new D/A row, which can also host Si dimers. The additional Si-dimers arriving at a saturated D/A row transform it to a new H chain. Such a conversion generates a compressive stress causing the neighboring and pre-existed H chain to be broken to a new T row, which can also be split to a D/A row by the external tensile-stress. Under such cyclic transformation among D/A row, H chain, and T row, (1 1 3) facet initially starts to grow from a (1 1 3) seed in Si(5 5 12)-2 × 1 and saturates at the width of four periodicities. Then, a (1 1 2) facet of three periodicities is formed from the opposite side to complete one sawtooth-like facet in one unit-cell of Si(5 5 12). Finally, the valley of sawtooth-like facet is filled and a uniform Si(5 5 12)-2 × 1 terrace is recovered. After one-cycle of such homoepitaxy, the unit-cell of recovered Si(5 5 12)-2 × 1 shifts horizontally by 3.04 Å toward [6¯6¯5] direction relative to the original one and the effective height increases by 1.36 Å, which costs only 28 atoms per unit cell of Si(5 5 12)-2 × 1. These results imply that the exact growth-direction for an identical reconstruction is toward [1¯1¯2] and a new layer is formed in the fashion of adding a cell-unit composed of two dimers from [1¯1¯2] to each of seven (1 1 1)-bilayer step-edges existing in the (5 5 12) surface.