Anisotropic Fatigue Characterization of Black Phosphorus Nanosheet for Applications in Flexible Nanoelectronic Devices

Investigating the fatigue characteristics of two-dimensional (2D) materials is of great significance for the reliability of flexible nanoelectronic devices, but its mechanism remains unclear. This paper systematically studies the fatigue processes of black phosphorus (BP) nanosheet with prenotches under sinusoidal excitation in different directions. The results show that the fatigue life exhibits significant anisotropy, with the fatigue life in the armchair direction being much higher than that in the zigzag direction. This is mainly attributed to the anisotropy of Young’s modulus and stiffness, which affects the in-plane stress distribution, thereby modulating the energy dissipation in fatigue process. We also discover that the natural frequency of the BP sheet is also anisotropic, and the fatigue life in different loading directions is related to the excitation frequency and natural frequency. When the excitation frequency approaches the natural frequency, fatigue resonance occurs, leading to a sharp reduction in fatigue life. Furthermore, elevated temperatures accelerate bond breaking via thermal activation, which reduces fatigue life but does not change natural frequency. These findings provide theoretical guidance for designing nano devices based on 2D materials by considering the anisotropy of fatigue life.