Recent advances in fabrication of monolayer colloidal crystals and their inverse replicas

Monolayer colloidal crystals (MCCs) are two-dimensional (2D) colloidal crystals consisting of a monolayer of monodisperse colloidal particles arrayed with a 2D periodic order. In recent years, MCCs have attracted intensive interest because they can act as 2D photonic crystals and be used as versatile templates for fabrication of various 2D nanostructure arrays. In this review, we provide an overview of the recent progress in the controllable fabrication of MCCs and their inverse replicas. First, some newly-developed methods for the self-assembly of MCCs based on different strategies including interfacial assembly and convective assembly are introduced. Second, some representative novel methods regarding the fabrication of various functional 2D inverse replicas of MCCs, such as 2D arrays of nanobowls, nanocaps, and hollow spheres, as well as 2D monolayer inverse opals (MIOs), are described. In addition, the potential applications of MCCs and their inverse replicas are discussed.