Growth Control Of C₆₀ Molecules On Si(111)-7×7 Surface And Study Of Their Nanotribological Properties

C₆₀ layer by layer films without the formation of clusters wereobtained on Si(111)-7×7 reconstructed surface by controlling parameterssuch as the evaporation speed and the temperature of substrate during thegrowth process. The experiments were carried out under ultra-high vacuum(UHV) using molecular beam epitaxy (MBE). These films were observedby ultra-high vacuum scanning tunneling microscopy (UHV-STM) and themechanism of this phenomenon was analyzed. The adhesion and frictionalforce curves of these C₆₀ films with different layers were measured. Theirfrictional properties were found to be affected by the number of layers. Thefrictional force decreased obviously with the increase in layers and thefrictional coefficient also showed a downward tendency. Since the increaseof layers leads to a higher level of rotation for C₆₀ molecules, we concludethat the decrease in the frictional force is caused by the rotation of the C₆₀molecules. C₆₀ molecule acts as"nano rolling bearing"here. That is, the rotation of the C₆₀ molecules provides a channel for energy dissipation inthe microstructure. And, the effect of annealing temperature on the degreeof order of C₆₀ monolayers on Si(111)-7×7 was also studied. It's found that,the degree of order of C₆₀ monolayers increases with the increase ofannealing temperature under 800K. The frictional force curves of thesemonolayers with different degree of order were measured. The frictionalforce was found to decrease with the increase in the degree of order.