Research On Optical Properties And Reason Of Surface Color Change For Nanostructures Of Butterfly Wing Scales

On the micrometre-scaled Morpho scales, the tree-like ridge-lamellae structures arrange in parallel and equally spaced rows. This nanometre-scaled ridge-lamellae structure is composed of alternating micrometre-thick films with air and transparent cuticle. Metallic blue structural color appears because of white light that has been reflected through the ridge-lamellae structures that exhibits reflectance at selective wavelengths. In this thesis, experiments, simulations and optic theories have been combined to investigate the optical properties and reason of surface color change for Morpho butterfly wing scales.Three simplified models were designed from the natural ridge-lamellae structure for simulation analysis. The rigorous coupled wave analysis technique (RCWA) was employed to analyze response property of each structural parameter of the three models. Main parameters which made marked effect to optical properties were generalized from simulation analysis. The conclusions were critically important for designing ridge-lamellae model with structural color. The specific material and size of ridge-lamellae model can deduced from the simulation conclusions and multilayer-thin-film interference theory.In this thesis the response characteristic of the Morpho butterfly to different background media was investigated. The structural color would change obviously with different liquid media. The ridge-lamellae structures on Morpho scales demonstrated highly selective liquid response. It was found that the reason of the selective response is the liquid media formed nanometre-thick films between Morpho's lamellae and changed the constructive interference wavelength. Our research discovered that there was linear relation between the structural color (wavelegnth) of ridge-lamellae structure and index of liquid background media. This linear relation was verified through experiment, simulation and optic theory.The structures demonstrated selective vapor response. The discrepancy of reflectance spectras of the wing scale immerged in different organic vapor was discriminable. A method to calculate the relative difference of the reflectance spectra was introduced to amplify this discrepancy and help us to distinguish different media effectively. Exposures to vapours were modelled as two kinds of models:heterogeneous media model and nanometre-thick liquid films model. The simulation results of nanometre-thick liquid films model can fit with the experimental result very well. That indicated the selective vapor response resulted in formation of nanometre-thick solvent films onto Morpho ridge-lamellae structures.Research on optical properties of the butterfly scales'nanostructures and its applications in liquid and vapor environmental detection help us have a deep understanding of the mechanism of the structural color and its sensitivity. It provided a reference for designing and nanofabricating color-controlled structure. The conlusion of this thesis can be used to steer the design, nanofabrication of the bionic nanometre structures and sensors for environmental detection.