  Atomically thin 2D materials span the common components of electronic
circuits as metals, semi-conductors, and insulators, and can manifest
correlated phases such as superconductivity, charge density waves, and
magnetism. An ongoing challenge in the field is to incorporate these 2D
materials into multi-layer hetero-structures with robust electrical contacts
while preventing disorder and degradation. In particular, preserving and
studying air-sensitive 2D materials has presented a significant challenge since
they readily oxidize under atmospheric conditions. We report a new technique
for contacting 2D materials, in which metal via contacts are integrated into
flakes of insulating hexagonal boron nitride, and then placed onto the desired
conducting 2D layer, avoiding direct lithographic patterning onto the 2D
conductor. The metal contacts are planar with the bottom surface of the boron
nitride and form robust contacts to multiple 2D materials. These structures
protect air-sensitive 2D materials for months with no degradation in
performance. This via contact technique will provide the capability to produce
atomic printed circuit boards that can form the basis of more complex
multi-layer heterostructures.
