Scanning tunneling microscopy of C₆₀ on graphite

Scanning tunneling microscopy investigation shows that C₆₀ molecules adsorbed on graphite tend to form clusters of different sizes, which often further aggregate to form massive stacks. Occasionally, the molecules can form quasi-close-packed monolayer structures in small areas. From these areas, with low bias voltages and high tunnel currents we have obtained STM images of C₆₀ molecules, which have the highest resolution and contain the richest structural features, in comparison with those C₆₀ images obtained in previous works. The success of obtaining those low-bias images indicates that those molecules had electronic states around E_F. This fact together with the fact that the C₆₀ molecules imaged in the high resolution images were not rotating imply that the graphite substrate may have strong interaction with C₆₀ molecules. We believe that those atomic-scale features are closely related to the intramolecular structure of C₆₀, even though to interpret them in terms of the molecular structure needs further investigation.