  In the 1960s, Lifshitz et al. predicted that quantum fluctuations can change
the van der Waals (vdW) interactions from attraction to repulsion. However, the
vdW repulsion, or its long-range counterpart - the Casimir repulsion, has only
been demonstrated in liquid. Here we show that the atomic thickness and
birefringent nature of two-dimensional materials make them a versatile medium
to tailor the Lifshitz-vdW interactions. Based on our theoretical prediction,
we present direct force measurement of vdW repulsion on 2D material surfaces
without liquid immersion and demonstrate their substantial influence on
epitaxial properties. For example, heteroepitaxy of gold on a sheet of
freestanding graphene leads to the growth of ultrathin platelets, owing to the
vdW repulsion-induced ultrafast diffusion of gold clusters. The creation of
repulsive force in nanoscale proximity offers technological opportunities such
as single-molecule actuation and atomic assembly.
