Highly sensitive and selective detection of NO2 using epitaxial graphene on 6H-SiC

Epitaxial graphene grown on SiC substrates is one of the most promising methods for achieving large-area uniform graphene films. Our experimental results demonstrate that graphene layers grown on both the Si and the C-faces of semi-insulating 6H-SiC can offer very high NO2 detection sensitivity and selectivity, as well as fast response time. Exposure to only 500 ppb NO2 reduced the conductivity by 2.25%, while 18 ppm caused a reduction of 10%. In contrast, high concentrations of commonly interfering gases, namely, CO2 (20%), H2O (saturated vapor), NH3 (550 ppm), and pure O2 increased the conductivity by a maximum of 2%. Graphene on the C-face of SiC resulted in somewhat lower sensitivity for the test gases, with the conductivity changing in an opposite direction compared to the Si-face for any particular gas. The conductance changes due to molecular adsorption were correlated with changes in the surface work function (SWF). Measurements conducted at higher temperature showed significantly higher changes in conductivity and shorter response times.