Temperature dependence of nanoscale friction on topological insulator Bi₂Se₃surfaces

The topological insulator Bi₂Se₃is an insulator in the bulk and has unusual metallic surface states that consist of spin-polarized Dirac fermions. Although the electronic properties of topological insulators have been extensively studied, the friction characteristic that is a key factor for further applications is barely known. In this study, conductive friction force microscopy (c-FFM) in ultrahigh vacuum (UHV) conditions was used to probe the nanoscale friction on freshly cleaved Bi₂Se₃planes (0001) as a function of surface temperature from 105.0 K to 300.0 K. The experimental results demonstrate a non-monotonic enhancement of dry friction, with distinct friction peaks emerging atT1=245.0±5K andT2=125.0±5K. While the widths of the friction peaks are nearly independent of the normal force, the relative peak height increases and the peak temperature decreases with normal load. We reveal that this anomalous friction behavior originates from the formation and rupture of multiple thermally activated sub-contacts, which is further confirmed by velocity dependence measurements. These results for multiple thermally activated sub-contact formation and rupture provide a deep insight into the frictional behaviors of Bi₂Se₃.