Novel liquid-liquid interface deposition method for thin films of two-dimensional solids.

Thin films and van der Waals heterostructures (vdWHs) derived from two-dimensional solids offer enormous potential for a broad range of novel, energy efficient devices, however their use is currently hampered by slow, labour-intensive fabrication methods often employing hazardous chemicals. We demonstrate a liquid-liquid interface technique for rapid, low-cost, and low environmental impact production of ultra-thin films and vdWHs of two-dimensional solids from aqueous surfactant-stabilised suspensions. The approach is generic to two-dimensional materials which can be stabilised in aqueous suspension by a surfactant and the resulting films can be transferred to an arbitrary substrate by a range of approaches. The wide applicability of this technique is demonstrated through production of thin films on a variety of substrates, deposition of transparent, highly conductive few-layer graphene films with conductivities between 7.7 × 103-1.26 × 105 S m-1 and transmittances of 55-75%, and by the fabrication of a vdWH of MoS2, WS2, and few-layer graphene.