Preparation Of Nanographite Thin Films Andtheir Infrared Thermal Radiation Properties

Infrared thermal radiation exists widely in nature.Dynamically regulating object’s infrared thermal radiation has a wide application prospect in infrared stealth,thermal management,thermal information processing,energy and environment fields.Graphene material has unique wide band and adjustable optical absorption/radiation properties,under the excitation of light,heat,electric field and other external fields,the infrared thermal emissivity can achieve controllable modulation,so it is expected to be used in the construction of flexible infrared radiation modulator.Due to the low optical absorptivity of single-layer graphene,the infrared radiation properties of graphene are generally studied based on multilayer graphene thin films,which are controlled by electrically regulating the insertion of ionic liquid.It has been shown that multilayer graphene films have the maximum emittance modulation depth at the thickness of about100 nm(about 150 layers of graphene).On this basis,the influences of ionic liquid,back electrode and applied voltage on the thermal radiation regulatory properties of graphene thin films have also been confirmed.However,the effects of the morphology and structure of graphene thin films on the thermal radiation properties are still lack of systematic and in-depth studies.In this paper,based on the preparation of about 500 nm thickness of the nanographite film,we construct the infrared thermal radiation regulation devices,and study its infrared thermal radiation performance.The specific research content and conclusions are as follows:1.Preparation and characterization of nanographite filmNanographene film was prepared on nickel substrate by chemical vapor deposition.By optimizing the growth temperature,cooling rate and hydrogen flow rate,500～700nm nanocrystalline graphene films with surface folds and high crystallinity were prepared.And their morphology and structure were characterized by Raman spectroscopy and scanning electron microscopy.2.Assembly and testing of infrared radiation modulator based on nanographite filmOn the basis of the experimental preparation,the nanographite film was transferred and assembled to construct the "graphite film /PE diaphragm + ionic liquid/copper foil" infrared thermal radiation device.The influence of ionic liquid insertion on the infrared radiation properties of nanographite film under the bias control was studied.It was found that the infrared emissivity of the nanographene films could be reduced from 0.38 to 0.06 in the voltage regulation range of 0～4V,and the infrared emissivity tuning property was reversible.The nanographite film is thin,super soft features,can be used as a new intelligent thermal surface material for dynamic thermal exterior camouflage in complex backgrounds.Because of the thin and super soft properties,nanographite film is a new kind of flexible and intelligent thermal surface material,which can be used for dynamic thermal camouflage in complex background.3.Effect of morphology on the infrared radiation properties of graphene/graphene filmThe effects of surface morphology and structure of graphene/graphene film on the performance of infrared thermal radiation modulator were verified by experiments and simulations.Although studies have shown that the modulation depth increases and then decreases with the increase of the thickness of multilayer graphene films,the modulation depth of our mid-infrared radiation modulator based on 500 nm thick graphene films can reach 0.32～0.37,which is comparable to the performance of commercial multilayer graphene films with a thickness of 100 nm.High frequency electromagnetic field simulation studies show that the thermal radiation modulation performance of nanographene,which is better than expected is due to the improvement of graphene surface wrinkles and defects.This performance compensates for the decrease of thermal radiation modulation performance caused by the increase of film thickness.Therefore,the surface thermal emissivity of the infrared thermal radiation modulator based on nano graphene film can be regulated by intercalated ionic liquid.Graphene /graphene films with a folded surface have a greater emittance modulation depth than those with a flat surfacen in this paper.We can achieve superior performance by precisely controlling the surface morphology of graphene/graphene films,which is of great significance for the practical application of graphene/graphene as smart thermal surface materials,and it has great application potential in thermal camouflage,personal thermal management,infrared communication and so on.