  Combining atomically-thin van der Waals materials into heterostructures
provides a powerful path towards the creation of designer electronic devices.
The interaction strength between neighboring layers, most easily controlled
through their interlayer separation, can have significant influence on the
electronic properties of these composite materials. Here, we demonstrate
unprecedented control over interlayer interactions by locally modifying the
interlayer separation between graphene and boron nitride, which we achieve by
applying pressure with a scanning tunneling microscopy tip. For the special
case of aligned or nearly-aligned graphene on boron nitride, the graphene
lattice can stretch and compress locally to compensate for the slight lattice
mismatch between the two materials. We find that modifying the interlayer
separation directly tunes the lattice strain and induces commensurate stacking
underneath the tip. Our results motivate future studies tailoring the
electronic properties of van der Waals heterostructures by controlling the
interlayer separation of the entire device using hydrostatic pressure.
