Two-Dimensional Binary and Ternary Nanocrystal Superlattices: The Case of Monolayers and Bilayers

The modular assembly of multicomponent nanocrystal (NC) superlattices enables new metamaterials with programmable properties. While self-assembly of three-dimensional (3D) binary NC superlattices (BNSLs) has advanced significantly in the past decade, limited progress has been made to grow 2D BNSLs such as monolayers and bilayers over extended areas. Here, we report the growth of large-area (similar to 1 cm(2)), transferable BNSL monolayers using the liquid-air interfacial assembly approach. The BNSL monolayers are formed by an entropy-driven assembly process with structures tunable by varying the NC size ratio. We further demonstrate the liquid-air interfacial assembly of BNSL bilayers which exhibit unique superlattice structures that have not been observed in the 3D BNSLs. As a further extension, bilayered ternary NC superlattices (TNSLs) are obtained by the cocrystallization of three types of NCs at the liquid-air interface.