Study On Preparation Of Carbon Nanotube Thin Films For Electromagnetic Interference Shielding Of Sapphire Infrared Windows

With the development of modern science, military optoelectronic equipments would serve in complex electromagnetic environment. The electromagnetic interference shielding of sapphire infrared window attracts more and more attentions. However, there are few reports on preparing carbon nanotube electromagnetic shielding thin films for sapphire infrared window. In this paper, carbon nanotube thin films on sapphire substrates were prepared by both spray coating method and chemical vapor deposition method to improve the electromagnetic shielding ability of sapphire infrared window for the irregular shape of sapphire optical window. The influences of preparation parameters on surface morphology and optoelectronic properties of carbon nanotube thin film were studied. Finally, Si O2 transition layers were inserted between sapphire substrate and carbon nanotube film. Also, the thickness of Si O2 layers were adjusted to improve the optoelectronic performance of carbon nanotube thin films.The experiments of preparing single walled carbon nanotube dispersion by ultrasonic dispersion method showed that sodium dodecyl benzene sulfonate(SDBS) has better dispersion ability compared with Triton X-100. By UV-Vis absorption spectrum analysis of single walled carbon nanotube dispersion with different content of SDBS, the optimum mass fraction of SDBS to disperse carbon nanotube is 1.5%. Whether the mass fraction of SDBS is too low or too high, the carbon nanotube cannot be dispersed effectively.The experiments of preparing carbon nanotube thin films on sapphire substrate using spray coating method showed that the mass fraction of SDBS can influence the surface morphology and optoelectronic properties of carbon nanotube thin films. When the mass fraction of SDBS is 1.5%, the as-obtained carbon nanotube thin films have good surface morphology and optoelectronic properties. Single-walled carbon nanotube thin films with different thickness were prepared using the optimum mass fraction of SDBS, then the surface topography and optoelectronic properties were studied. By comparing quality factors of carbon nanotube films with different thickness, the optimum thickness of single-walled carbon nanotube thin film prepared by spray coating method is 232 nm.The experiments of preparing carbon nanotube thin films on sapphire substrate by chemical vapor deposition method showed quite a lot of reaction parameters can influence the surface morphology and optoelectronic performance of carbon nanotube thin films such as the deposition time of Ni, the reaction time, the flux of Ar, H2 and CH4. By comparing the surface morphology and Raman spectrum of carbon nanotube thin films prepared with different parameters, the optimum parameters of preparing carbon nanotube film are determined to be catalyst deposition time of 30 s, reaction temperature of 1000 ℃. In addition, the flux of Ar, CH4 and H2 are 100 sccm, 60 sccm and 40 sccm, respectively. Then, carbon nanotube thin films with different thickness were prepared under the optimum condition. The optimum thickness of carbon nanotube thin film prepared by chemical vapor deposition method is 270 nm by analyzing optoelectronic properties of as-deposited carbon nanotube thin films with different thickness. Also, as to Si O2 transition layers inserted between sapphire substrates and carbon nanotube thin films,when the thickness of Si O2 transition layer is 164 nm, as-deposited carbon nanotube thin filmhas ideal optoelectronic properties with its square resistance of 68.2 Ω/sq and transmittance of 86.6%, which shows great potential for sapphire infrared window application.