Effects of space low energy proton irradiation on optical properties of diamond thin films

Diamond films are transparent in a wide range of wavelengths (ultraviolet-far-infrared-terahertz bands are transmitted), and are used in optical windows, aircraft missile hoods, etc., where low-energy protons (keV magnitude) in space will create gaps, vacancies and other material radiation effects. In this paper, diamond films with different grain sizes were grown on the surface of fused silica by microwave plasma chemical vapor deposition, and the influence of proton irradiation on the surface morphology, optical transmittance and Raman spectrum of diamond films was studied. The ion distribution and vacancy distribution of diamond thin films under proton irradiation were calculated and analyzed by calculation (Monte Carlo method). When the flow ratio of methane/hydrogen was 1%, by adjusting the height of the sample stage, diamond nanocrystalline films with different growth temperatures were prepared on the surface of fused silica. After proton irradiation, the transmittance curve of the film has a slight red shift, and the transmittance decreases significantly in the wavelength range of 500-900nm, and the maximum transmittance decreases by 5-7%. After proton irradiation, the peak intensities of the Raman spectra become weaker, and the peak intensities of both the diamond phase and the non-diamond phase are weakened. Under the irradiation of protons with energy of 50keV, the main action depth of the diamond film is in the range of 2-5 microns, and the effect on the surface and deeper regions is not obvious, but gaps and vacancies are generated at a depth of several micrometers.