Chiral mesostructured SnO2 films with tunable optical activities

Abstract

New strategies for tunable optical activities (OAs) are of fundamental importance in the advancement of science and technology. Here, we report hierarchically chiral mesostructured SnO2 films (CMSFs) deposited on FTO substrates via a symmetry breaking agent-inducing method. Three levels of chiral structures exist in the film, including tertiary plates helically arranged in fan-like form, secondary subplates helically stacked along [001] direction and primary nanosheets twisted along [100] direction. The thickness of plates was significantly increased with decreasing reactants concentration due to slower and preferential growth of plates along [001] direction. The increasing number of nanosheets results in enhancement and red shift of circular dichroism (CD) signals based on electron-transition absorption and reflection–based OA, which is in accordance with the circular Bragg resonance theory. Such novel chiral films with tunable OAs and morphologies may bring new ideas for design and synthesis of chiral inorganic materials with specific chirality and OA in the nanomaterial field.