Microscopic changes of thin films of directly thiolated fullerenes depending on substrate and number of thiol

Direct thiolation of fullerene is promising for molecular electronics because it enables high electronic conductivity of fullerene-electrode systems through direct adsorption between thiols and electrodes, for example, via Au-S bonds. Microscopic changes of thin films of directly thiolated fullerene (SH-C₆₀) formed on various substrates, such as bare mica, mica treated in MgCl₂ solution, graphite, and gold, have been observed by scanning probe microscopy (SPM). It has been elucidated that the structure of the thin films can be varied from nanodots to self-assembled layers by adjusting three energetic parameters, namely, the type of substrate, surface charge, and the number of -SH groups attached to fullerene. In addition to these energetic parameters, kinetic parameters, for example, supply rate of the molecules to the surfaces, should also be considered in the study of the mechanism underlying the formation of films.