  The isolation of a growing number of two-dimensional (2D) materials has
inspired worldwide efforts to integrate distinct 2D materials into van der
Waals (vdW) heterostructures. Given that any passivated, dangling bond-free
surface will interact with another via vdW forces, the vdW heterostructure
concept can be extended to include the integration of 2D materials with non-2D
materials that adhere primarily through noncovalent interactions. In this
review, we present a succinct and critical survey of emerging mixed-dimensional
(2D + nD, where n is 0, 1 or 3) heterostructure devices. By comparing and
contrasting with all-2D vdW heterostructures as well as with competing
conventional technologies, the challenges and opportunities for
mixed-dimensional vdW heterostructures are highlighted.

Materials Science;Mesoscale and Nanoscale Physics