Generation And Application Of 3D Bioinspired Optical Functional Materials

As one of the frontiers and hotspots in the field of material research,optical functional material has been widely used in many areas,including display,sensing,photocatalysis,photoelectric conversion,photothermal conversion,biology,medicine and information.In order to meet the current and potential requirements of applications,researchers have put forward higher and more diversified requirements for the performance of optical functional materials.It is necessary to further develop new high-performance optical functional materials.After some millions of years of nature selection,many organisms in nature have evolved excellent optical structures and show many distinctive advantages in many functions,which provides unique sources of inspiration for the development of new optical functional materials.By directly using biological templates or employing the optical mechanisms found in some organisms to produce special functions,a large number of bioinspired optical functional materials have been successfully prepared,and have also exhibited fantastic performance in a variety of applications,which greatly promotes the researches and applications of new optical functional materials.The current researches on three-dimensional（3D）bioinspired optical functional materials,however,are inadequate.The optical mechanisms of many 3D biological structures and bioinspired optical functional materials are not well understood.There is still a lot of space for exploriton in the fabrication of bioinspired optical functional materials.Besides,the areas of application of the bioinspired optical functional materials need further expansion.In this thesis,we have further explored the 3D bioinspired optical functional materials.We have tried to reveal the optical mechanisms of the 3D bioinspired optical functional materials prepared by using the typical Morpho butterfly wings as templates,investigated the application of 3D palladium（Pd）-butterfly heterogeneous structure in hydrogen（H₂）gas sensing,extended the application of Morpho butterfly wings to the field of acoustic sensing,and made use of the oxygen plasma etching to provide a new path to modify biological templates.Moreover,inspired by the squid Galiteuthis that uses’leaky’fiber-like cells for optical camouflage,we have designed and constructed the adaptive color-change system using guided reflection of background for the camouflage of 3D target through utilizing the existing material preparation technology.Following are the main focus of this thesis:1.By using physical vapor deposition（PVD）,3D gold（Au）nanostrips were fabricated on the Morpho sulkowskyi butterfly wing.Different from the random deposition of metallic nanoparticles（NPs）or conformal coating of metallic layers on butterfly wings reported previously,3D Au nanostrips studied in this work were discrete and quasi-periodically arranged,which allowed us to investigate the plasmonic coupling effects in the 3D structure.Through refractive index matching,the optical contribution from the original butterfly wings was minimized,and thus the light interaction with the 3D Au nanostrips could be separately analyzed.By tuning the deposition thickness of Au from 30to 90 nm,the vertical gap between the Au nanostrips was gradually reduced.As a result,the long-range electromagnetic coupling effects were gradually enhanced.The near-field coupling effects were induced when the deposition thickness of Au increased to 70 nm,which generated new resonant modes.Both the optical simulation and surface-enhanced Raman scattering（SERS）experiments confirmed the near-field coupling effects between the 3D Au nanostrips and the resulted enhancement of the SERS signals.This work provides new insights into the understanding of 3D plasmonic structures,and may also offer an alternative strategy for the design and fabrication of 3D plasmonic structures.2.A 3D heterogeneous structure was fabricated by selective modification of the photonic architectures of Morpho butterfly wing scales with Pd nanostrips through PVD.Spectral measurements and optical simulation of the heterogeneous structure showed that the coupling of the plasmonic mode of the Pd nanostrips with the optical resonant mode of the Morpho biophotonic architectures generated a sharp reflectance peak at the wavelength of⁴60 nm in the spectra of Pd-modified butterfly wing,as well as enhancement of light-matter interaction in Pd nanostrips.Exposure to H₂ resulted in a rapid increase in the reflectance of the Pd-modified butterfly wing,and the pronounced response of the reflectance was at the wavelength where the plasmonic mode strongly interplayed with the optical resonant mode.Owing to the synergetic effect of Pd nanostrips and biophotonic structures,the 3D heterogeneous structure achieved rapid and sensitive response to H₂ with a H₂ detection limit of less than 10 ppm.Besides,the Pd-modified butterfly wing also exhibited good linear response and sensing repeatability.This 3D heterogeneous structure not only provides a promising approach for high-performance optical H₂ sensor,but also offers an example for developing future nanoengineered structures for various sensing applications.3.The optical response of Morpho butterfly wing with 3D photonic structure to acoustic wave has been investigated.Considering the fact that metal-based films used in optical acoustic sensors are difficult to produce large deformation response and organic films with low elastic modulus usually has low reflectivity,Morpho butterfly wing which is a low-elastic-modulus optical resonator has unique advantages in mechanics and optics for high-sensitive acoustic sensing.Mechanical analysis demonstrated that Morpho butterfly wing could generate large deformation during the pressure-induced vibration.The experimental results showed that the Morpho butterfly wing diaphragm with a diameter of 5 mm produced a response with the same frequency of the incident sound wave for the frequency range of 200 Hz-8 kHz.The butterfly wing diaphragm also exhibited a flat frequency response over the measured acoustic frequency range and the response showed a high signal to noise ratio.Under the experimental conditions,the minimum detectable pressure at 1 kHz was determined to be 241.15μPa/Hz^0.5.This work could provide some stimulation for the design of high-performance optical acoustic sensors.4.The controlled subtractive modification of the 3D photonic structures of Morpho butterfly wing was achieved by using oxygen plasma etching.With the increase of the plasma etching time,the thickness,width and layer number of lamella layers gradually decreased,and the peak of reflectance spectra at normal incidence was blue-shift accompanied by the decrease of the peak reflectance.Based on the Finite-Difference Time-Domain（FDTD）simulation of the structural changes,all the three structural parameters contribute to the blue-shift of the reflectance spectra.The decrease of the reflectance,however,is majorly due to the reduction in the optical contribution from the top lamella layers.We demonstrated that the view-angle independent performance of all the etched samples was comparable to that of the original butterfly wing sample.The controlled subtractive process provides another angle in studying the optical mechanism of Morpho photonic structures and helps the further understanding of structural optimization through natural evolution.The study also offers a new path to modify such biological nanoarchitecture.5.Inspired by the squid Galiteuthis that uses’leaky’fiber-like cells to match the background for optical camouflage,a waveguide-based adaptive color-change approach was proposed for the camouflage of a 3D target.Different from the most current color-change approaches that involve active color sensing,signal processing and active color generation,this bioinspired adaptive color-change approach directly takes the reflected light from the background,guides and displays it around the surface of the target.Therefore,the sensing and actuation components,as well as the complex signal processing components,are not required in such bioinspired color-change approach.This bioinspired adaptive color-change approach is dependent on a waveguide-based system that includes the light receiving,transporting,and display modules.Through the improvement of the efficiency in light collection,guiding,and display,we demonstrated that such bioinspired color-change system achieves both the faithful color and spectra matching with background and rapid dynamic response in the entire visible region.Through the design of pixelated modules,this new approach also shows good color adaption with patterned color background and provides a feasible route to camouflage in a complex natural background.This work provides new methods and theoretical findings for the design,fabrication and application of 3D plasmonic structures.It also offers new concept for the fabrication of 3D bioinspired optical functional materials as well as their applications in display,sensing,and camouflage.The researches in this thesis will help move forward the development of bioinspired optical functional materials,which have both important theoretical and practical implications.