Nadine Leisgang received the Nano Image Award 2021 for the optical micrograph image of a gated van der Waals heterostructure. The device consists of two monolayers of transition metal dichalcogenides encapsulated between insulating hexagonal boron nitride flakes. Direct gold contacts allow tuning the carrier concentration in the optically active layers in the middle of the structure. Few-layer graphene sheets on the top and bottom of the stack serve as local gates to apply an electric field across the device.
This image reflects the complexity and – at the same time – the beauty of the fabrication of van der Waals heterostructures.