Uniaxial Tensile Behavior of β-InSe Nanosheets: Thickness-Dependent Strength and Progressive Failure

Layered indium selenide (InSe) is a promising semiconductor for optoelectronic, thermoelectric, and flexible-device applications, for which mechanical reliability is essential to device integration and operation. In this study, the mechanical behavior of β-InSe nanosheets was investigated using device-assisted in situ scanning electron microscopy (SEM) uniaxial tensile testing. Within the investigated thickness range, the first-instability stress generally increased with decreasing thickness, reaching a maximum measured value of 0.972 GPa, while the first-instability strain reached up to 7.383%. Notably, first instability did not lead to immediate complete fracture: some specimens continued to sustain load after initial instability, with the highest final failure strain reaching approximately 19.099%. Experimental results further showed that different portions of the nanosheet thickness fractured sequentially at different spatial locations, leading to progressive failure rather than instantaneous rupture of the entire load-bearing cross-section. These findings provide experimental insight into the thickness-dependent tensile response and progressive failure behavior of layered InSe nanosheets at the micro-/nanoscale.