Friction hysteresis, a common event in ultrathin two-dimensional materials, is significantly influenced by their deformation. This study explores the friction hysteresis of suspended graphene with varying thicknesses using atomic force microscopy (AFM) conducted under controlled humidity conditions. Compared with that in the supported case, the friction in the suspended graphene cases demonstrates significant hysteresis. The degree of friction hysteresis on suspended graphene increased with decreasing thickness and increasing relative humidity and cut-off load. Both deformation hysteresis and adhesion hysteresis contribute to the friction hysteresis of suspended graphene, with deformation hysteresis playing a dominant role. The finite element simulation revealed that the sliding process enhanced deformation and increased the contact area for the major friction hysteresis. The deformation hysteresis of suspended graphene expands the contact area and increases energy dissipation during unloading, resulting in significant friction hysteresis. These findings advance our understanding of friction hysteresis on graphene in terms of deformation hysteresis.

The nanofriction properties of hexagonal boron nitride (h-BN) are vital for its application as a substrate for graphene devices and solid lubricants in micro- and nano-electromechanical devices. In this work, the nanofriction characteristics of h-BN on Si/SiO₂ substrates with a bias voltage are explored using a conductive atomic force microscopy (AFM) tip sliding on the h-BN surface under different substrate bias voltages. The results show that the nanofriction on h-BN increases with an increase in the applied bias difference (V_t-s) between the conductive tip and the substrate. The nanofriction under negative V_t-s is larger than that under positive V_t-s. The variation in nanofriction is relevant to the electrostatic interaction caused by the charging effect. The electrostatic force between opposite charges localized on the conductive tip and at the SiO₂/Si interface increases with an increase in V_t-s. Owing to the characteristics of p-type silicon, a positive V_t-s will first cause depletion of majority carriers, which results in a difference of nanofriction under positive and negative V_t-s. Our findings provide an approach for manipulating the nanofriction of 2D insulating material surfaces through an applied electric field, and are helpful for designing a substrate for graphene devices.