Preparation Of DLC Films And Their Optical Properties In The THz Band

Carbon, as the most widely distributed element in nature, constitutes all life on the earth. Due to the variety of stable hybridization, it has a great number of allotropes, diamond-like carbon (DLC) is a typical non-crystal material. The DLC films have much excellent properties like Diamond, which can be tuned by the ratio of the number of sp3and sp2hybridization atoms. The ratio of sp3/sp2varies with the fabrication method and process parameters. So far, a lot of reports concentrate on the mechanical, electrical, and optical properties of DLC films. For the optical properties, researches are focused on the visible and infrared regions, but in other frequency region, especially, in the terahertz region, its optical properties are not clear.Terahertz wave lies in the special position in the electromagnetic spectrum, which is the transition region of electronics and optics. The terahertz spectrum of material contends a lot of physical and chemica! information, so it has a great significance to the material research. THz time-domain spectroscopy is a new type of coherent measurement, it use the electro-optical and electro-optical resistance measurement to directly record the amplitude of THz time-domain wave form. The phase distribution spectrum can be obtained by doing a Fourier transformation. Then the complex dielectric index, absorption and dispersion relation can be obtained. Carbon materials have been extensively investigated, but research of DLC films in this region is still vacant.The DLC films fabricated by ion beam deposition are characterized using Raman spectra. Result shows the value of I(D)/I(G) in Raman spectrum decreases with the increasing major ion beam energy and working pressure, but increases with the auxiliary ion beam energy. On the other hand, we deposit DLC films by magnetron sputtering, the value of I(D)/I(G) decreases with the pressure increasing, resistance of the sample increases with the pressure increasing. Pressure has a great influence on the DLC film fabrication, sputtering energy is also dependent on the pressure. By studying DLC films with different thickness, the value of I(D)/I(G) and resistance decrease rapidly with the thickness increasing, if the thickness of the film exceed500nm, they stop rising. Transmission spectrum of DLC film is measured in the terahertz range, and optical properties of DLC films is obtained. Refraction index, permittivity and extinction coefficient of DLC films fabricated under the power300W decreases with the frequency increasing. The film fabricated under the pressure1Pa has small value of imaginary part of refraction index, permittivity and extinction coefficient, but the real part of refraction index increases with the pressure and frequency increasing. Films fabricated under the pressure0.3Pa, optical parameters of which increases firstly then decrease with the power varying from30W to300W, and the optical parameters of DLC films decrease with films getting thinner.We investigate the structure of DLC films depending on the process parameters using Raman spectroscopy. And the terahertz transmission spectrum of DLC films are firstly obtained, thus so do the optical parameters. It will lay the foundation to the application of DLC film based terahertz optical devices.