Graphitic Nanoporous Carbon Thin Films: Fabrication Method, Structural, Electrical and Gas Sensor Properties

Carbon nanoporous thin films are very attractive for application in fields of supercapacitors, fuel cells, gas sensors and others. However due to it very high resistance an employment of this material for resistance gas sensor is problematic. At the same time graphene based materials are very sensitive to different gas ambient and have a resistivity suitable for testing. In this work the new method of formation of high porous graphite-like thin films by RF magnetron plasma enhanced chemical vapor deposition (MPECVD) from argon-methane/argon-acetylene gas mixture followed by annealing at 650ºC, is suggested. A comparative study of transformation of nanoporous carbon film produced in different carbon-hydrogen atmosphere into graphitic one, their structural and electrical properties are presented. The films of nanoporous carbon were fabricated on silicon or SiO 2 /Si wafers. To clarify chemical structure of the film FTIR spectroscopy and XPS were used. Micro-Raman spectroscopy and AFM were applied to determine of structure and surface morphology correspondingly. X-ray refraction (XRR) method allows us to determine a density and a thickness of the films. Four point probe method and transmittance line (TSL) technique were used for the analysis of electrical properties. Additionally, electrical conductivity at different temperature and frequency was examined by measurement of resistance between two nearest Ni contacts. The same contacts were used to estimate of the gas sensitivity. It was shown that initial deposited films have mainly sp 3 C-H bonds without appearance of silicon bonds. AFM demonstrates nanostructured surface morphology with size of the surface fluctuation about 3 nm; a density of the films is about 1.3 g/cm 3 for both carbon films, that corresponds to nanoporous carbon; resistivity is about 10 8 Ohm×cm. After thermal annealing at 650°C for 30 min in N 2 atmosphere the sp 3 C-H bonds are disappeared, and C=C sp 2 bonds are formed. Besides the resistivity the films synthesized in argon-methane gas mixture decreases to 10 4 Ohm×cm whereas the films synthesized in argon-acetylene gas mixture decreases their resistivity up to 10 2 Ohm×cm. The density of the C films synthesized in in argon-methane gas mixture reaches about 1.5 g/cm 3 that corresponds to 34% of porosity, and material shows layered structure. The density of the C films synthesized in in argon-acetylene gas mixture falls to 1.01 g/cm 3 that corresponds to 55% of porosity. Graphitized fil