Power spectrum analysis of lateral friction of MoS2: A theoretical and experimental study

The remarkable properties of two-dimensional materials have generated great enthusiasm among researchers. Very recently, MoS2, the representative of transition metal dichalcogenides, has triggered increasing attention and hold huge potential for many applications. Although the tribological properties of MoS2 has been studied for decades, the atomic-scale motion between tip and MoS2 surface is quite rare. Furthermore, the mechanism underlying the friction variation is still unclear. To explore the unknown territory, we carry out both theoretical and experimental research on the power spectrum variation of lateral friction between probe and MoS2. Lateral Friction Microcopy (LFM) was utilized to acquire atomic images for analysis. The friction signals of MoS2 in different angles that obtained from original atomic images were then processed by fast Fourier transform (FFT). We observed distinct characteristic in power spectrum variation between special (zigzag and armchair) and general lattice orientations for the first time. To explain this phenomenon for both cases, we establish a complete motion model and further deduce the different frequencies that the motion model contain. The theoretical analysis well illustrated the different power spectrum variation of actual friction signals for special and general lattice orientations. The results of this paper pave an avenue to fully revel the friction variation mechanism of MoS2 and develop an effective method to detect the lattice orientations of MoS2.