Nanostructured carbon films obtained by CH4 plasma deposition and annealing at high temperature: structural features and their effects on electrical and optoelectronic properties

Abstract

This article is dedicated to the study of the structural, electrical, and optoelectronic properties of nanostructured carbon films obtained by methane plasma deposition, followed by annealing at high temperatures (650–800 °C). The conditions for obtaining the films affected the final physicochemical parameters. We studied the film morphology using atomic force microscopy, scanning electron microscopy, Raman spectroscopy, X-ray energy-dispersive analysis, and analysis of the current voltage (C-V) characteristics. The film thickness ranged from 20 to 150 nm, with a C/O ratio of 4:1. Structural studies have shown that the resulting nanostructured carbon films consist mainly of nanographite flakes, the lateral dimensions of which lie in the lateral size (La) range of 5 to 12 nm, and contain different fractional concentrations of sp3/sp2 crystalline phases of carbon. We have established that with an increase in the annealing temperature, the defectiveness of the carbon film structure increases; however, at the same time, the degree of graphitization increases, as indicated by the Raman spectroscopy data and the calculated values of layer resistances from the C-V characteristics. The values of photocurrents were calculated, from which it was found that the samples exhibited photosensitivity in the temperature range of room temperature to –173 °C, based on the temperature dependences of the C-V. The obtained results can be useful in creating day and night light sensors as well as temperature sensors suitable for use at low temperatures.