Synthesis of carbon films by electrochemical etching of SiC with hydrofluoric acid in nonaqueous solvents

Carbon films on SiC have many applications, ranging from tribology to electrical energy storage. Formation of epitaxial or heteroepitaxial layers of carbon on SiC by "soft solution process," such as electro- or photochemical ones, is attractive for various fields of application, decreasing the energy consumption and making the process compatible with electronic device fabrication. We have demonstrated formation of a carbon layer on SiC ceramics by electrochemical etching in a nonaqueous electrolyte. The selective etching of Si from SiC in a single step reaction with hydrofluoric acid (HF) in different organic solvents has been carried out and the role of polarity, surface tension, density, and viscosity of the organic solvents in the formation of the carbon layer has been investigated. The solution of 1:4.6 ratio HF and ethanol at low current densities (10 and 20 mA/cm²) allows the best control over selective etching of Si forming amorphous and ordered carbon on the SiC surface. The presence of an intense G band of graphitic carbon in Raman spectra and high resolution transmission electron microscopy analysis indicate formation of ordered carbon on the surface of SiC. X-ray diffraction shows that the etching rate of α-SiC is much higher when compared to β-SiC.