Fundamental Insights into Graphene Strain Sensing

Interfacial Stress Transfer and Fracture in van der Waals Heterostructures

Artificially stacking 2D materials (2DMs) into vdW heterostructures creates materials with properties not present in nature that offer great potential for various applications such as flexible electronics. Properties of such stacked structures are controlled largely by the interfacial interactions and the structural integrity of the 2DMs. In spite of their crucial roles, interfacial stress transfer and the failure mechanisms of the vdW heterostructures, particularly during deformation, have not been well addressed so far. In this work, the interfacial stress transfer and failure mechanisms of a MoS2/graphene vdW heterostructure are studied, through the strain distributions both laterally in individual 2DMs and vertically across different 2DMs revealed in-situ. The fracture of the MoS2 and the associated states of stress and strain are monitored experimentally. This enables various interfacial properties, such as the interfacial shear strength and interfacial fracture energy, to be estimated. Based only on the measured strength and interfacial properties of a single vdW heterostructure, a failure criterion is proposed to predict the failure mechanisms of similar vdW heterostructures with any lateral dimensions. This work provides an insight to the deformation micromechanics of vdW heterostructures that are of great value for their miniaturization and applications, especially in flexible electronics.

Deformation of and Interfacial Stress Transfer in Ti3C2 MXene-Polymer Composites

Transitional metal carbides and nitrides (MXenes) have promise for incorporation into multifunctional composites due to their high electrical conductivity and excellent mechanical and tribological properties. It is unclear, however, to what extent MXenes are also able to improve the mechanical properties of the composites and, if so, what would be the optimal flake size and morphology. Herein, Ti₃C₂T_x MXene is demonstrated to be indeed a good candidate for mechanical reinforcement in polymer matrices. In the present work, the strain-induced Raman band shifts of mono-/few-/multilayer MXenes flakes have been used to study the mechanical properties of MXene and the interlayer/interfacial stress transfer on a polymer substrate. The mechanical performance of MXene was found to be less dependent upon flake thickness compared to that of graphene. This enables Ti₃C₂T_x MXene to offer an efficient mechanical reinforcement to a polymer matrix with a flake length of >10 μm and a thickness of 10s of nanometers. Therefore, the degree of exfoliation of MXenes is not as demanding as other two-dimensional (2D) materials for the purpose of mechanical enhancement in polymers. In addition, the active surface chemistry of MXene facilitates possible functionalization to enable a stronger interface with polymers for applications, such as strain engineering and mechanical enhancement, and in materials including membranes, coatings, and textiles.