Publication date: Jun 30, 2021
Interlayer binding strength is an important property of two-dimensional (2D) materials in various occasions including exfoliation and heterostructure construction. Though there are already many calculations and experimental measurements for interlayer binding energy, few calculation references regarding the interlayer binding force can be found which is often the quantity been directly measured in experiments. Moreover, binding force rather than binding energy should be considered more closely related to whether a layered structure can be exfoliated or not under certain circumstances. To our best knowledge, there exists no such a database for 2D materials interlayer binding forces. In this work, with a descent algorithm designed to work with first-principles code, maximum interlayer binding force with the accuracy down to 1 meV/Å per atom is directly calculated for 230 common 2D materials using both the vdW-DF2 and optB88-vdW functionals. The results show significant inconsistency between the trend of maximum binding energies and binding forces, which means large binding energy does not necessarily lead to large binding force. Based on these results, a relationship between the two quantities is found valid for more than 200 different systems among the total of 230. To confirm the validity of these calculated forces, interlayer force measurements are performed for graphene (G), h-BN and In2Se3 by coating them on tipless probes and measuring the cohesive force using atomic force microscopy. The measurements show F_G > F_h-BN > F_In2Se3 , which is consistent with the calculated results, and the estimated per-unit-area force is of the same magnitude to the predicted values. Our work can help determine appropriate exfoliation methods for different 2D materials, and provide a reliable reference for interlayer adhesion studies.
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