Fig. 4: Site-selectively etched BEE for symmetric message hiding.
From: Asymmetric optical camouflage: tuneable reflective colour accompanied by the optical Janus effect
a Schematic illustration showing different fCYTOP values for symmetric message hiding. b, c Photographs of the site-selectively etched BEE (Region I for the message and Region II for the background) demonstrating symmetric message hiding in reflection (upper row) and transmission (lower row) modes seen from the frontside b and backside c under air, methanol, and toluene. Scale bars, 1 cm. d, e Calculated spectral positions of the maximum reflectance in Regions I (black line) and II (red line) seen from the frontside d and backside e as a function of nsolvent
