Real-time scanning tunneling microscopy observation of Si(111) surface modified by Au⁺ ion irradiation

The real-time scanning tunneling microscopy (STM) observation of Au ⁺ ion irradiation effects on a high-temperature Si surface has been performed using our original ion gun and STM combined system. Sequential STM images of a Si(111)-7×7 surface kept at 500 °C have been obtained before, during, and after Au⁺ ion irradiation with 3 keV. Vacancy islands, which are two-dimensional clusters of surface vacancies, and 5×2-Au structures were formed on the sample surface, and their size were changed during the heat treatment after the ion irradiation. This method enables us to count exact numbers of vacancies and Au atoms on the surface by measuring the sizes of vacancy islands and 5×2-Au reconstructions. The timescale of the growth of the 5×2-Au domain suggests that the implanted Au atoms diffuse to the surface almost without interacting with point defects induced by the ion irradiation.