Research On Properties And Fabrication Of Micro-nano Structure To Regulate Thermal Radiation

Thermal radiation is a basic way of energy transfer,which has very extensive and important applications in the field of thermoelectric conversion,infrared target stealth,infrared thermal imaging,detection and so on.In recent decades,with the rapid development of material preparation and micro-nano processing technologies,a variety of electromagnetic micro-nano structures have been formed,including metamaterials,nanowire arrays,photonic crystals,multilayer films and other forms,which have better flexible than traditional natural materials in high emissivity,spectrum selectivity and temperature characteristic of thermal radiation.Through the interaction between electromagnetic wave and material,such as surface plasmon polaritons(SPPs),resonance effect and photonic band gap effect,the control of thermal radiation in the spectrum,direction and intensity is realized,which open up a new direction for the control and utilization of thermal radiation.Heterostructures combine the advantages of various components and play an outstanding role in expanding the application range,performance improvement and multi-functional application of optical devices.Therefore,photonic heterostructures composed of micro-nano structures with thermal radiation regulation characteristics show obvious advantages in improving the performance and multi-functional application of thermal radiation devices.Focusing on the thermal radiation control mechanism and multi-functional application of micro-nano structure system,this dissertation creatively proposes the idea of combining the thermal radiation control micro-nano structure with thermoelectric conversion and visible light camouflage based on heterostructures.Bismuth telluride(Bi₂Te₃)single-phase nanowires array structure is proposed,which not only realizes thermoelectric conversion,but also realizes infrared camouflage.In order to combine the metal nanowires array with one-dimensional thermoelectric nanowires array structure,the gold(Au)-Bi₂Te₃ heterostructure nanowires array structure is proposed.Compared with Bi₂Te₃ single-phase nanowires array structure,the heterostructure not only improves the thermal radiation control efficiency of nanowire array structure,but also improves the device performance.In addition to nanowire as the thermal radiation control structure,film structure and photonic crystal are common thermal radiation control structure.Therefore,the titanium dioxide(TiO₂)nanoparticle film-polystyrene(PS)microsphere photonic crystal photonic heterostructure is proposed.The novel function of visible and infrared dual-band anti-counterfeiting is realized.Based on the regulation of PS microsphere photonic crystal on thermal radiation in visible band,the TiO₂ microsphere photonic crystal is proposed to explored its infrared thermal radiation regulation characteristics.The main research contents and innovations are as follows:(1)A preparation method of Bi₂Te₃ nanowires array based on AAO template is proposed.By studying the principle of electrochemical deposition of nanowires array,the influencing factors of deposition potential and substance concentration on the deposition of nanowires are analyzed.It is found that low deposition rate(?10 nm·s^-1)is favorable for the growth of nanowires in AAO template holes,and uniform and highly ordered Bi₂Te₃ nanowires array is obtained.The nanowires array structure produces temperature difference on both ends of the device through the thermoelectric effect,which not only achieve the conversion from thermal energy to electrical energy,but also reduce the thermal equilibrium temperature of the device surface to meet the demand of the related target infrared camouflage.(2)Based on the dipole resonance effect of metal nanowires array,the Au-Bi₂Te₃heterojunction nanowires array structural thermal radiation device is designed and fabricated,which improves the thermal radiation control efficiency of nanowire array.By adjusting the deposition potential of Au nanowires and optimizing the electrochemical deposition process,the interface compatibility problem of the two types of nanowires is solved.Compared with the Bi₂Te₃ single-phase structure,the heterostructure increases the mid and long wave phonon scattering by introducing the scattering at the interface to reduce the lattice thermal conductivity?_ph and improve the thermoelectric efficiency.At the heat source temperature of 170?,the cooling temperature increases by 12.6?,the conversion efficiency of heat energy to electric energy increases by 1.25 times and the radiation temperature difference increases by 8?in infrared camouflage effect.Heterostructure obviously improves the performance of optical devices.(3)Self-assembled metamaterial(MM)-photonic crystal(Ph C)photonic heterostructure is realized for the first time by optical modes segmentation in design and two-step self-assembly in fabrication,and demonstrate the functional integration in a dual-band manner.Sedimentation of TiO₂ nanoparticles in horizontal mode and polystyrene(PS)microspheres in vertical mode self-assembles a van der Waals interface,connecting TiO₂ MM and PS Ph C to form heterostructure.Difference of characteristic length scales between two components support photonic bandgap engineering in the visible band,and creates a concrete interface at mid-infrared to prevent interference.Consequently,a novel anti-counterfeiting label is introduced to demonstrate the dual-band function of our heterostructure.In the visible band,the PS Ph C with/without structure color in different background media can hide/show the encoded TiO₂ MM.In the infrared band,due to the high transmittance of PS Ph C and the high emission of TiO₂MM,the coding pattern is detected by the infrared thermal imaging.Through the visible and infrared imaging results,the dual-band anti-counterfeiting function of the heterostructure is successfully demonstrated.The good compatibility of optical modes in heterostructures paves the way for multifunctional photonic heterostructures.(4)Based on photonic bandgap theory,the amorphous TiO₂ microspheres Ph C structure shows advantages in thermal radiation regulation.By numerical analysis,thermal radiation control of TiO₂ microspheres Ph C is explored.Through adjusting the diameter of microspheres(0.8?m,1.5?m,2?m),the spontaneous radiation in different frequency bands(2.63-2.83?m,4.11-4.39?m,5.9-6.3?m)are inhibited.Amorphous TiO₂ microspheres Ph Cs with three kinds diameters are prepared via horizontal deposition self-assembly method.By measuring the transmission spectrum of samples,it is found that the low transmittance of amorphous TiO₂ microsphere Ph Cs are generated at 2.936?m,4.248?m and 6.104?m,respectively.The robustness of Ph Cs is revealed.In a certain disorder state,amorphous Ph C retains the band gap characteristic of Ph C.In term of experimental preparation,amorphous Ph Cs are simpler than Ph Cs and can be prepared in a large area,showing certain advantages in thermal radiation control technology.To sum up,in view of the micro-nano structure thermal radiation control mechanism and multiple functional application problems,this dissertation has carried out a series of researches based on the nanowire arrays,photonic crystals,nanoparticles film micro-nano structures and photonic heterostructure and realized the design and fabrication of novel functions,such as thermoelectric conversion,infrared camouflage and visible and infrared dual band anti-counterfeiting.This dissertation further promotes the application and development of micro-nano structures with different configurations in thermal radiation regulation,performance optimization and multi-function expansion.