Exploration Research On Synthesis And Optical Properties Of Germanium With Butterfly Wings Photonic Structure

Photonic crystal?PC?is composed of periodically repeating regions of high and low refractive index,which can be used for controlling light propagation by defining a photonic stop band.It was demonstrated that there are two factors that affect the optical properties of PCs:structure and refractive index.Different structures display completely different optical properties.And usually the materials with high refractive index are usually desired for producing PCs with larger photonic stop band gap.Some up-bottom methods such as nano-etching and some bottom-up methods like template assisted synthesis are widely used to fabricate PCs.But these methods are limited by structural diversity.However,nature provides us a variety of 1D,2D and 3D PCs.We can use these natural PCs as template to obtain PCs that cannot synthesized by artificial methods.Even though the kaleidoscopic microstructures in natural PCs,thanks to the similarity in constituents?such as polysaccharide chitin?,once a fabrication route has been established,a diversity of functional materials with various PC structures could be obtained via the same process.Among conventional semiconductors,Ge almost has the highest refractive index?5.748 at 590.38 nm?,which make it become a hot spot in the field of PCs.However,to the best of our knowledge,replicating natural PCs with Ge are still largely unexplored,mainly because moisture-sensitive germanium alkoxides or germanium chlorides were usually needed as germanium source,making synthesis conditions very harsh.Herein,Ge PC was synthesized by replicating butterfly wing with GeO₂ via a facile liquid phase deposition followed by a reducing process and the main results are shown as follows:1.The Ge PC with butterfly-wing structure was prepared by a bio-template liquid phase deposition process including four steps:activation of the butterfly wings,liquid deposition,sintering and reduction.The structure of the scales,parallel ridges interconnected by ribs,was successfully replicated in the as-prepared Ge PC.2.The optical properties of the as-synthesized samples were studied in detail.The reflectance peak of original wing is located at about 397 nm,but red shift to 600⁶50 nm after replicating the butterfly wing with GeO₂.Such red shift can also be seen in the reflection spectra of the reduced sample,up to an averaged peak of 780 nm.The red shift is demonstrated to be caused by the 50%shrinkage of structural sizes and change of refractive index from original butterfly wings to sintered sample,but change of refractive index from sintered sample to reduced sample.Besides,the Ge PC with the structure of butterfly wing shows an interesting angle-dependent optical properties that the reflection peak red shifted with the increase of the incident angle.3.Much research has been done for positive-phase replication,but less for inverse-phase replication.In this study,a similar route was studied to replicate the inverse structure of butterfly wings.This route successfully replicated both the window structure,parallel ridges interconnected by ribs,and the micro-structure of the ridge,which really provides us another kind of thoughts to replicate the natural PCs and enriches structures of high refractive index medium PCs.4.Even though the kaleidoscopic microstructures in natural PCs,thanks to the similarity in constituents?such as polysaccharide chitin?,this fabrication route may be used to replicate other natural PCs.In this study,the method was studied and analyzed in detail,which will provide a theoretical basis for transplanting this method to other natural PCs.