  The assembly of individual two-dimensional materials into van der Waals
heterostructures enables the construction of layered three-dimensional
materials with desirable electronic and optical properties. A core problem in
the fabrication of these structures is the formation of clean interfaces
between the individual two-dimensional materials which would affect device
performance. We present here a technique for the rapid batch fabrication of van
der Waals heterostructures, demonstrated by the controlled production of 22
mono-, bi- and trilayer graphene stacks encapsulated in hexagonal boron nitride
with close to 100% yield. For the monolayer devices we found semiclassical mean
free paths up to 0.9 micrometer, with the narrowest samples showing clear
indications of the transport being affected by boundary scattering. The
presented method readily lends itself to fabrication of van der Waals
heterostructures in both ambient and controlled atmospheres, while the ability
to assemble pre-patterned layers paves the way for complex three-dimensional
architectures.
