| Photonic crystal,developed as a structural material whose dielectric constant changes periodically,has been widely used in the optical field due to their photonic band gap,photonic localization and the ability to manipulate and control photons in specific directions and bands.At present,there has been numerous researches on the application of photonic crystal in the infrared and visible band,while little theoretical and experimental study has been paid attention to on the ultraviolet band,especially the soft X-ray band.This phenomenon can be attributed to the fact that there are few alternative materials due to limitations of material properties（larger light absorption）and process conditions.SiO2 is the main component of common mesoporous nano-film materials.The imaginary part of the dielectric constant exhibits a near-zero characteristic in the visible,ultraviolet and soft X-ray bands,resulting in very small light absorption.Moreover,the mesoporous pore structure of SiO2 is periodically arranged,and the periodic lattice constant corresponds to the soft X-ray band.Therefore,SiO2 is likely to be applied as a two-dimensional photonic crystal mirror to the soft X-ray band.With the aim to explore the possibility of SiO2 application,SiO2 thin film material with one-dimensional hexagonal mesopores was investigated in this paper.Different mesoporous SiO2 film structure models were built.Based on these models,the optical bandgap structure was theoretically calculated by the transfer matrix method in the range of0°-90°incident angle.Moreover,the effects of pore filling materials,filling ratio,monocyte constant and deflection angle on the optical properties were investigated to find the optimal band gap film structure.In addition,on the basis of calculation,the optimal band gap film structure was prepared by electrochemically assisted self-assembly method.At the same time,The effects of different process parameters on film integrity,uniformity,thickness and channel orientation,and pore size were observed.By analyzing theoretical calculation and experimental results,the following conclusions can be drawn:（1）Comparing the results of the band gap calculations of the unfilled channels and the channels filling W and Ir,it can be seen that if the channels are filled with metal,the band gaps in different incident ranges would be widened in the TE and TM modes,while the bandgap reflectance decreased in some angles and bands.Considering the complexity of the filling metal and the difficulty of preparation,it was preferable to select the band gap structure with the unfilled channels.The best band gap characteristics were as follows:The angle of incidence of the band gap was 19°-90°,the width of the overlap band gap was 0.72-7.1nm in both modes over a wide angle range（33°-90°）,and the bandgap reflectance was 100%.（2）The band gap characteristics of different filling ratios,monocyte parameters and deflection angles were analyzed.The results displayed that the filling ratio had less influence on the band gap,whereas had a greater effect on the monocyte constant.Specifically,the overlap bandgap width in the large angle range in both modes became wider as the monocyte constant becomes smaller.And when the monocyte parameter was 2 nm,the width of the overlapping band gap reached 0.3-7.1 nm,which covered the entire soft X-ray band.In addition,when examining the influence of deflection angle on optical properties,it was found that the optical properties were better when the channel was perpendicular to the substrate than when the channel was parallel to the substrate.（3）Based on the above theoretical calculation results,a vertically oriented mesoporous SiO2 film was prepared and the effects of silicon source concentration and deposition voltage on film uniformity,integrity and channel orientation were investigated.According to the characterization results,the uniformity and orientation of the film were relatively ineffectual when the voltage and concentration were low,especially when the concentration was low,the integrity was poor.Conversely,when the voltage and concentration were high,the directivity of the film decreases and the surface of the film was covered with particles.It was worth noting that the uniformity,integrity and channel orientation of the film were better than others when the concentration range was 50-60 mM and the voltage was-1.2 V and-1.3 V.（4）The effect of time on film quality was investigated under optimum TEOS concentration and voltage conditions.The characterization results illustrated that the deposition time mainly affected the thickness of the film,but had little effect on the uniformity and orientation of the film.In addition,a vertically oriented mesoporous SiO2film with the monocyte constant of 4 nm and excellent quality at different thickness can be obtained by precisely adjusting the deposition time.In order to further optimize the optical properties,the carbon chain length of surfactants was adjusted to obtain mesoporous SiO2 film with small monocyte constant.The characterization results demonstrated that the channels became worm-like structure with poor order and orientation when the chain length of the template agent was shortened to C12 and C10. |
