Fig. 5: BEE for asymmetric message hiding.
From: Asymmetric optical camouflage: tuneable reflective colour accompanied by the optical Janus effect
a Schematic illustration showing different fAu and fCYTOP values for viewing-direction-sensitive message hiding. b, c Top-view (upper) and cross-sectional view (lower) SEM images of Regions I b and III c. Scale bars, 200 nm. d Calculated reflective colour gradation in each region seen from both sides (insets show enlarged photographs of e). e Photographs of the solvent-immersed BEE (Region I for the background and Region III for the message) demonstrating asymmetric message hiding seen from the frontside (upper) and backside (lower) under media of n = 1.0 (air) and nsolvent = 1.3, 1.4, 1.5, 1.6, and 1.7 (solvents). Scale bars, 1 cm. f, g Calculated spectral positions of the maximum reflectance in Regions I (black line) and III (blue line) seen from the frontside f and backside g as a function of nsolvent = 1.0–1.7. h, i ΔE* between Regions I and III as a function of nsolvent obtained from calculated (red line) and measured (black line) reflectance spectra seen from the frontside h and backside i
