The effect of thermal and microwave treatments on the properties of amorphous dLC-films formed by deposition in CH₄ plasma

Due to the discovery of the possibility of synthesizing two-dimensional (2D) materials such as graphene, interest in carbon films has increased significantly in recent decades. An important factor in the practical use of carbon films is the scalability of production. Natural carbon structures, such as diamond and graphite, have found wide application in various fields of human activity. The popularity of these materials is due to the uniqueness of the bonds of carbon atoms in the states with sp²- (graphite) and sp³-hybridization (diamond). The ability to control the ratio of the proportions of carbon atoms in the state of spn hybridization contributes to the production of materials with controlled properties. Although existing methods of PECVD make it possible to control the growth of film structures, the development of a fast, cheap, and eco-friendly technique for synthesis still remains a topical issue. Hence, in this work, the carbon films formed on silicon substrates by a two-step process were studied. The carbon atoms were deposited by the deposition in methane plasma at the first stage. At the second stage, some of the samples annealed at a temperature of 700°C for 30 minutes. The other samples were irradiated with microwave radiation at a frequency of 2.45 GHz for 5 minutes. The methods of Raman, X-ray energy-dispersive spectroscopies, and current-voltage (C-V) characteristics for a comparative analysis of the synthesized films were measured. It follows from the results of measurements of the Raman spectra that the formed films are a nanocrystalline carbon structure with crystallite size (La) from 5 to 10 nm. Moreover, in carbon films exposed to microwaves, there is a high content of hydrogenated amorphous carbon (a-C:H) and a higher C/O ratio. The effect of illumination with a halogen lamp on the C-V characteristics showed that the sheet resistance of films irradiated with microwave waves decreases by a 3–4 order, while in annealed samples the resistance changes only up to 10%. At the same time, in absolute values, the photocurrents for both types of samples are of the same order.

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