Growth and Nanotribological Properties of C60 Multilayer Films on Si(111)-7×7 Surface

Abstract

C60 layer by layer films without clusters were obtained on Si(111)-7×7 reconstructed surface by controlling parameters such as the evaporation speed and the temperature of substrate during the growth process. The experiments were carried out under ultra-high vacuum (UHV) using molecular beam epitaxy (MBE). These films were observed by ultra-high vacuum scanning tunneling microscopy (UHV-STM) and the mechanism of this phenomenon was analyzed. The adhesion and frictional force curves of these C60 films with different layers were measured. Their frictional properties were found to be affected by the number of layers. The frictional force decreased obviously with the increase in layers and the frictional coefficient also showed a downward tendency. Our simulation showed that adhesion was not the main effect that led to a decrease in the frictional force. Since the increase of layers leads to a higher level of rotation for C60 molecules, we conclude that the decrease in the frictional force is caused by the rotation of the C60 molecules. C60 molecule acts as ”nano rolling bearing” here. That is, the rotation of the C60 molecules provides a channel for energy dissipation in the microstructure. These kinds of multilayer films make it possible for us to study the relationship between the rotation of C60 molecule and its other properties.