New devices and new physical effects with atomically thin stacks
Materials with layered structures can be peeled apart so that 2D crystals with thicknesses of one or a few atoms can be isolated and studied. We use techniques that take advantage of the weak out-of-plane bonds in these materials to pick up and stack them into vertical heterostructures. Hundreds of layered materials are known, but modifications of only the three most commonly studied of them— graphene, black phosphorus, and transition metal dichalcogenides such as MoS2—continuously span the range of band gaps between 0 and 2 eV. These metals and semiconductors, combined with the large band gap insulator hexagonal boron nitride, provide the ingredients to make a wide variety of electronic and optoelectronic devices. These flexible and nearly transparent materials also have interesting physical properties including extremely strong electron-electron interactions and a valley pseudospin degree of freedom.