Hamaker Constants of van der Waals Materials under Clean-Interface Conditions.

Adhesion stabilizes van der Waals materials and heterostructures, yet reported interaction strengths show a wide dispersion that hinders a consistent link between microscopic dispersive forces and macroscopic observables. Here, we determine clean-interface adhesion by measuring tip-sample interactions in ultrahigh vacuum using calibrated AFM probes of different radii, in situ thermal cleaning, and realistic contact distances. This approach isolates the dispersive interaction of clean interfaces and allows us to extract mixed Hamaker constants for SiO2 interacting with few-layer graphene (12 × 10-20 J), MoS2 (13 × 10-20 J), and SiO2 (6.1 × 10-20 J). Agreement between static adhesion spectroscopy and noncontact frequency-modulation AFM (FM-AFM) provides an internal consistency check of the interaction scale. Controlled humidity cycles further show that even very dry ambient conditions already enhance adhesion, while higher humidity produces a strong reversible increase associated with capillary forces, explaining one major contribution to the large spread of commonly reported values. These results establish clean-interface experimental benchmark values for dispersive interactions in representative layered materials, enabling quantitative comparison with dielectric-response and Lifshitz-based models that relate Hamaker constants to binding energy and macroscopic properties of van der Waals crystals.