C70 self-assembly on In- and Tl-adsorbed Si(111)[formula omitted]-Au surfaces

Abstract

Behavior of C70 fullerenes adsorbed onto the In- and Tl-modified Si(111)3×3-Au surfaces at room temperature (RT) and 112K has been studied using scanning tunneling microscopy observations and compared with the known results for the C60s on the same surfaces. During island growth at 112K, both C70 and C60 are characterized by the same critical island size i=1. The difference is in an island shape as C70s tend to form chain-like islands built of double or triple molecular rows along the [1¯10] Si(111) substrate directions. At RT, C70s have a lower mobility as compared to C60s. In contrast to the C60 magic islands, the C70 islands do not demonstrate any strong preference for specific shapes or sizes. Extended C70 arrays exhibit a stripe-like 3×1 reconstruction where a single row of bright fullerenes mediated by a double row of dim fullerenes. The reconstruction is due to the different orientations of C70s within the layer which does not relate to the structure of the underlying Au/Si(111) substrate. This is in contrast to the hexagonal reconstructions of C60s where the bright fullerenes occupy the specific adsorption site atop Au trimers. The difference in the behavior of C70 and C60 is plausibly affected by the non-spherical shape of C70 molecule and a greater intermolecular C70-C70 interaction.