  Vertical stacking of monolayers via van der Waals assembly is an emerging
field that opens promising routes toward engineering physical properties of
two-dimensional (2D) materials. Industrial exploitation of these engineering
heterostructures as robust functional materials still requires bounding their
measured properties so to enhance theoretical tractability and assist in
experimental designs. Specifically, the short-range attractive van der Waals
forces are responsible for the adhesion of chemically inert components and are
recognized to play a dominant role in the functionality of these structures.
Here we reliably quantify the the strength of van der Waals forces in terms of
an effective Hamaker parameter for CVD-grown graphene and show how it scales by
a factor of two or three from single to multiple layers on standard supporting
surfaces such as copper or silicon oxide. Furthermore, direct measurements on
freestanding graphene provide the means to discern the interplay between the
van der Waals potential of graphene and its supporting substrate. Our results
demonstrated that the underlying substrates could enhance or reduce the van der
Waals force of graphene surfaces, and its consequences are explained in terms
of a Lifshitz theory-based analytical model.
