C60 layer growth on intact and Tl-modified Si(1 1 1)5 × 2-Au surfaces

The Si(1 1 1)5 × 2-Au surface comprises a quasi-one-dimensional surface reconstruction consisting of Au stripes mediated by honeycomb Si chains. In the present study, using STM observations we explored adsorption of thallium (Tl) onto Si(1 1 1)5 × 2-Au surface as well as growth of C₆₀ layers on Tl-modified and intact Si(1 1 1)5 × 2-Au surfaces. Analysis of the results was based on the recently proposed KK model of Si(1 1 1)5 × 2-Au surface [Kwon and Kang, PRL 113 (2014) 086101]. It was found that intact Si(1 1 1)5 × 2-Au surface produces a poor template effect on the overgrown C₆₀ layers which have a close-packed-like structure without distinct ordering. In contrast, the C₆₀ layers grown on the Tl-adsorbed Si(1 1 1)5 × 2-Au surface where Tl atoms occupy various adsorption sites on the honeycomb Si chains have a well-ordered quasi-one-dimensional structure consisting of straight C₆₀ chains. Ordering of the C₆₀ molecules is a result of an intricate interplay between adsorbed C₆₀ molecules with each other and with a substrate surface. Separation between neighboring C₆₀ chains is dictated by the periodicity of the underlying Si(1 1 1)5 × 2-Au template, while the C₆₀-C₆₀ spacing within the chains of ∼ 12 Å that is ∼ 3.2a₀ reflects the peculiarity of the C₆₀-C₆₀ intermolecular interaction on the Tl-adsorbed Si(1 1 1)5 × 2-Au surface. Structural information on (Au, Tl)/Si(1 1 1) and C₆₀/(Au, Tl)/Si(1 1 1) systems gained in the present study can be useful for the prospective works on elucidating the ways to control electronic properties of the Si(1 1 1)5 × 2-Au surface using atomic and molecular adsorbates.