Large Area Nanocrystalline Graphite Films on SiC for Gas Sensing Applications

Large area nanocrystalline graphite films are formed by solid state decomposition of the surface of a semi-insulating 6 H SiC substrate at 2000degC. The temperature dependences of the sheet resistance and carrier concentration are measured. The change in resistance of these large area films in response to polar molecules acetone, water and varying concentrations (9-100 ppm) NO₂ gas is investigated. NO₂ concentrations as low as 9 ppm are detected at a power budget <9muW. The time derivative of the resistance change is found to be a strong function of NO₂ concentration, and can be used as a metric to quantify the gas concentration. NO₂ concentrations as low as 600 ppb were detected using scanning Kelvin probe microscopy (SKPM) to monitor the surface potential in response to the NO₂ gas. The sensitivity of this large area film shows, for the first time, the potential for mass-produced carbon-based films on SiC for sensing applications.