Slower Load-Dependent Increase and Logarithmic Rate Dependence of Friction in Suspended WS2

Suspended two-dimensional (2D) materials in high-performance devices exhibit unique properties that are critically important for nanoscale mechanical and electromechanical applications, while their frictional laws remain poorly understood. Here, we investigate the nanoscale frictional behavior of suspended WS2 flakes under varying applied loads and scanning rates using atomic force microscopy (AFM), and successfully employ the Bowden–Tabor theory and the thermally activated Prandtl–Tomlinson (PTT) model to analyze the load- and scanning-rate-dependent friction characteristics of suspended 2D systems. The results show that suspended WS2 exhibits higher friction than supported WS2, whereas its friction increases more slowly with applied load, which can be well described by the Bowden–Tabor theory. Moreover, the friction exhibits a logarithmic dependence on scanning rate for both suspended and supported WS2. Quantitative analysis within the framework of the PTT model demonstrates that this model can be successfully extended to describe the rate-dependent friction of suspended WS2, providing a unified framework for both supported interfaces and suspended 2D systems. This work provides valuable guidance for understanding frictional dissipation mechanisms relevant to the design and optimization of WS2-based devices.