Low-temperature one-atom-layer √7 × √7 -In phase on Si(111)

The Si(111)-hex-7×3-In reconstruction has been attracted considerable attention due to its superconducting properties occurring in the one-atom-layer metal film. However, the 7×3 periodicity is a characteristic feature of this surface only at room temperature. Upon cooling to low temperatures the 7×3 structure transforms reversibly to the 7×7 one that should not be ignored while considering superconductivity in this system. In the present study, atomic structure of the low-temperature one-atom-layer Si(111)7×7-In phase has been evaluated using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED) and ab initio random structure searching (AIRSS) technique. Basing on the LEED observations, it has been found that the 7×7-In surface incorporates plausibly eight In atoms per 7×7 unit cell (i.e., ~ 1.14 ML In). AIRSS demonstrates occurrence of a set of various surface structures with very close formation energies. Some of their counterparts can be found in the experimental STM images.