In order to elucidate the role of plasticity on interface crack initiation from a free edge and crack propagation in a nano-component, delamination experiments were conducted by a proposed nano-cantilever bend method using a specimen consisting of ductile Cu and brittle Si and by a modified four-point bend method. The stress fields along the Cu/Si interface at the critical loads of crack initiation and crack propagation were analyzed by the finite element method. The results reveal that intensified elastic stresses in the vicinity of the interface edge and the crack tip are very different, although the Cu/Si interface is identical in both experiments. The plasticity of Cu was then estimated on the basis of the nano-cantilever deflection measured by in situ transmission electron microscopy. The plasticity affects the stress fields; the normal stress near the interface edge is intensified while that near the crack tip is much reduced. Both the elasto-plastic stresses are close to each other in the region of about 10 nm. This suggests that the local interface fracture, namely, the crack initiation at the interface edge and the crack propagation along the interface, is governed by elasto-plastic normal stress on the order of 10 nm.
We investigate electromechanical properties of two-dimensional hexagonal and pentagonal materials as a function of electron and hole dopings. We found that the actuator performance of graphene and penta-graphene is much improved by the hydrogenation.
Borophene, a two-dimensional material, has grown fast in the nanomaterials field because of its unique electronic and mechanical properties. In this work, we demonstrate that the unique properties of borophene make this material with a high-performance electromechanical actuator by using first-principles calculations. We find a high Young’s modulus about 376.55 N m−1 of a striped borophene, which is larger than that of graphene (∼336 N m−1) in the unit of N m−1. In addition, upon hole injection, maximum actuator strain is up to 1.67% that is over 7 times larger than that of graphene at the same value of hole doping (0.04 e/atom). Therefore, the striped borophene shows a high work-area-density per cycle of 22 MJ m−3·nm, it is approximately 28 and 11 times larger than that of graphene (0.78 MJ m−3·nm) and metallic 1T-MoS2 (2.05 MJ m−3·nm), respectively. Furthermore, the striped borophene still maintains the metal property under charge doping. Thus, an actuator device based on borophene can work under a low applied voltage. Finally, the charge doping effects on the mechanical strength of borophene are investigated. Interestingly, the mechanical strength is increased by 15.8% in the case of electron doping.
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