Abstract MoS2 is expected to replace silicon-based field-effect transistors and continue Moore’s law. However, thin-film MoS2 transistors on flexible substrates are prone to nanocracking under bending conditions. Although classical fracture mechanics provides a broad understandings of its crack tip field, how the higher-order T-stress term influences the nanofracture remains to be investigated. Using molecular dynamic simulations and modified boundary layer models, we show that T-stress regulates the nonlinear stress, plastic zones, and distortion around the crack tip, thereby changes fracture toughness and cracking direction. Under mode I loading, fracture toughness increases monotonically with rising T-stress. With the introduction of mode II loading (K II), the interplay between T-stress and K II can decrease fracture toughness as T-stress exceeds a critical value. Furthermore, negative T-stress tends to impedes crack deflection, whereas positive T-stress tends to promote it. However, owing to the local anisotropy in MoS2 lattices, crack deflection always occurs in the discrete zigzag lattice orientations. Our study might provide new insights into the fracture of MoS2 transistors under complex loads.
Read full abstract