Nanocomposite and nanomaterials 

Graphitic carbon film formation from nanoporous carbon: Structural, electrical and sensor properties
O. Slobodian1, A. Rusavsky2, Yu.V. Gomeniuk2, A. Vasin1,2, D. Kisyl2, O. Gudymenko2, B. Tsykaniuk2, A. Nikolenko2, T. Gorbaniuk2, V. Morozhenko2, P. Lytvyn2, A. Nazarov1,2
1 National Technical University "Igor Sikorsky KPI", 37 Peremogy Pr., 03056 Kyiv, Ukraine. 
E-mail: nazarov@lab15.kiev.ua
2 V. Lashkaryov Institute of Semiconductor Physics NAS of Ukraine, 41 Nauky pr., 03680 Kyiv, Ukraine. 

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 the work a results on transformation of nanoporous carbon film into graphitic one are presented. The films of nanoporous carbon were fabricated by RF magnetron deposition method with sputtering of c-SiC target in CH4/Ar working gas mixing on silicon or SiO2/Si wafers. Subsequent thermal annealing from 350 to 650°C in N2 atmosphere was used for graphitization of the film. 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. XRR method allows us to determine a density and a thickness of the films. The electrical properties of the films were studied by four-points method and I-V measurements and of the a-C/Si heterostructures - by I-V and C-V measurements at different temperature and frequency.
It was shown that initial deposited films have mainly sp3 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/cm3, that corresponds to nanoporous carbon; resistivity is about 108 Ohm cm. After thermal annealing at 650°C for 30 min the resistivity decreases up to 104 Ohm cm; sp3 C-H bonds are disappeared, and C=C sp2 bonds are formed. The density of the C films reaches about 1.5 g/cm3, and material shows layered structure. Graphitized films appears sensory sensitivity to moisture and acetone. The nature of the transformation is discussed.