Photonic Janus Films with Highly Tunable Janus Balance.

Asymmetric Janus materials are of wide-spread interest due to their unique anisotropic and directional features. In our work, through a simple combination of nanosphere lithography at the solution interface and dopamine chemistry, a new approach for the facile synthesis of large, asymmetric, free-standing, 2D photonic Janus films with a highly tunable Janus balance and multiple functionalities is developed. Herein we rationally exploit the unique properties (reducibility, self-adhesive nature, and post-modification ability) of the polydopamine (PDA) layer and the good deformation and dissolution ability of polystyrene (PS). The precisely controllable chemical compositions on the PDA layer and the multi-variable morphologies from the PS part offer us a great chance to tune the Janus balance of the film in different dimensions. As a demonstration of the resultant Janus films for potential applications, femtoliter cup arrays are achieved after the removal of PS, which are used for confined crystallization. Good surface-enhanced Raman scattering (SERS) enhancement of the Ag-metallic Janus film is shown, which confirms this excellent platform for creating new functional materials. Our study not only bridges dopamine chemistry with 2D photonic crystals but also opens up new avenues for artificially designed Janus nanoarchitectures with multi­ple functions. [ABSTRACT FROM AUTHOR]