Surface confined self-assembled fullerene nanoclusters: a microscopic study

The structure of the C60-fullerene terminated aminothiol self-assembled monolayers (SAM) generated by tethering the fullerene molecules to the surface of 11-amino-1-undecane thiol (11-AUT) SAM on gold surface was investigated by dynamic contact angle measurements, Fourier transform infrared reflection-absorption spectroscopy (FTIR-RAS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). A two-step procedure was followed consisting of the chemisorption of the amine-terminated organosulfur compound on oriented gold, followed by its reaction at the solid liquid interface with C60 fullerenes. Covalent binding of fullerenes to these attachment layers was accessed by the above experimental techniques. IR-RAS showed several major features in the C60 skeleton ring vibration region along with all the characteristic features of the amino thiol. With increase in carbon to sulfur ratio, appearance of C 1s shake-up satellite peak due to characteristic π-π* transition of the C60 backbone confirmed the NH2 binding at the 6,6 double bond of the C60 cage. Atomic force microscopy showed smooth, homogeneous areas of the monomolecular films, covered by regular small microcrystalline grains on the fullerene-terminated monolayer surface. Possible explanations for these experimental findings are discussed.