Adsorption of ${\mathrm{C}}_{60}$ onto the Si(111)-$\alpha$-$\sqrt{3}\times \sqrt{3}$-Au surface with a high density of domain walls and its In-induced modification, a domain-wall-free Si(111)$\sqrt{3}\times \sqrt{3}$-(Au,In) surface, has been studied using scanning tunneling microscopy (STM). Adsorbed ${\mathrm{C}}_{60}$ have been found to form close-packed hexagonal arrays displaying specific patterns of ${\mathrm{C}}_{60}$ having different dim-bright STM contrast. On the Si(111)-$\alpha$-$\sqrt{3}\times \sqrt{3}$-Au surface, the dim-bright ${\mathrm{C}}_{60}$ pattern replicates the domain-wall network of the substrate surface and has plausibly an electronic origin. On the homogeneous Si(111)$\sqrt{3}\times \sqrt{3}$-(Au,In) surface, a Moiré pattern of a two-dimensional lattice develops, which indicates periodic occupation of the same regular adsorption sites on the surface. Here, the dim-bright ${\mathrm{C}}_{60}$ contrast is associated plausibly with different topographic heights of the molecules. In the case of the multilayer ${\mathrm{C}}_{60}$ films, the dim-bright ${\mathrm{C}}_{60}$ patterns of the first ${\mathrm{C}}_{60}$ monolayer have been found to be inherited with gradual smearing in the next ${\mathrm{C}}_{60}$ layers.

• Received 26 January 2011

DOI:https://doi.org/10.1103/PhysRevB.83.195421