Temperature-Dependent Adhesion in van der Waals Heterostructures

The interlayer coupling between 2D materials is immensely important for both the fundamental understanding of these systems, and for the development of transfer techniques for the fabrication of van der Waals (vdW) heterostructures. A number of uncertainties remain with respect to their adhesion characteristics due to the elusive nature of measured adhesion interactions. Moreover, it is theoretically predicted that the intrinsic ripples in 2D materials give rise to a temperature dependence in adhesion, although the vdW interactions themselves are principally independent of temperature. Here, direct measurements of the adhesion between reduced graphene oxide - coated by solution deposition on atomic force microscopy tips - and graphene, h-BN, and MoS2 supported on SiO2 substrates and as freestanding membranes are presented. The in situ nanomechanical characterization reveals a prominent reduction in the adhesion energies with increasing temperature which is ascribed to the thermally induced ripples in the 2D materials.