The Design And Preparation Of The Coatings With Selective Low Emissivities

As the development of infrared technology,the proportion of infrared stealth is higher and higher.The traditional materials always have low emissivities in the whole infrared band,and cannot take into account the factor of radiation.The accumulation of heat will lead to the risen of the temperature,the result is that for the traditional infrared stealth materials,the ability of reducing the intensity of infrared radiation is decreased.The materials with selective low emissivities stand for the direction of infrared stealth's development,the related reports about the materials is quite rare.The passage did the research of the design and preparation of the coatings based on the photonic crystals with the characteristic of selective low emissivities.Based on the theory of electromagnetic transmission,the Ge/ZnS and Ge/MgF2 coatings with selective low emissivities were designed.The preparation of the coatings was magnetron sputtering,and after the preparation,the micro structure and the infrared optical properties were analyzed.The design of the coatings was based on the structure of one-dimensional photonic crystals(1 DPC).The substrate of the coatings is SiC,the structure of 1 DPC were Ge/ZnS or Ge/MgF2.The target of the structure design of the coatings is infrared spectrally selective low emissivities,the structure of the coatings were determined based on the theory of electromagnetic transmission.The theoretical results of the calculations were that,in the 3~5?m and 8~14?m bands,the emissivities of the coatings were about 0.15;and in the 5~8?m band,the emissivities of the coatings were about 0.9.The preparation of the coating was by magnetron sputtering.The passage did the research of the preparation of the sublayers in the coatings first,making the research of different crafts' influence on the layers' growth velocity,micro-structure and composition,and got the optimum preparation parametres.The results showed that under certain processes,the Ge,ZnS and MgF2 sublayers had the high qualities with the properties of continuous surface,stable component and uniform grain.And also we realized the accurate control of the growth velocity of the sublayers.After that,the passage made the research of the preparation of the Ge/ZnS and Ge/MgF2 coatings,and made the characterization with the help of field emission TEM(Titan G2 60-300),dual-beam microscopic electron microscopy(HELIOS NanoLab 600i)and so on.For the Ge/ZnS coatings,the characterization results showed that the sublayers in the coatings layered obviously,the diffusion phenomenon did not appeared in the structure.However,the results showed that the growth velocity of the sublayers in the coatings decreased obviously because of the thinning effect of the sputtered particles with high energy.After the optimization of the preparation process,reducing the sputtering power to cut down the high energy of the sputtered particles,the thickness of the sublayers in the coatings were close to the expected values.But the properties of selective low emissivities did not reflected because of the slight deviation of the thickness of the sublayers in the Ge/ZnS coatings.For the Ge/MgF2 coatings,the characterization results showed that the growth velocity of the sublayers decreased obviously,the structure of the MgF2 sublayers were destroyed,the elements were distributed in the multilayered structure.The experiments did not get the expected structure after the optimization of the preparation process.The results indicated that even though it has the better effect of selective low emissivities theoretically,the Ge/MgF2 multilayered structure cannot be prepared by magnetron sputtering.