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

Epitaxial graphene grown on SiC substrate is one of the most promising methods for achieving large area uniform graphene films. Our experimental results demonstrate graphene layers grown on both Si and C-faces of semi-insulating 6H-SiC can offer very high detection sensitivity, selectivity, and 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 concentration of commonly interfering gases, namely, CO₂ (20%), HζO (saturated vapor), NH₃ (550 ppm), and pure O₂ increased the conductivity by a maximum of only ~2%. Graphene on C-face of SiC resulted in somewhat lower sensitivity for the test gases, with the conductivity changing in opposite direction compared to Si-face for any particular gas. The conductance change due to molecular adsorption was compared to changes in surface work function (SWF) as well as the charge transfer between the adsorbed molecules and the graphene surface. Measurements conducted at higher temperature showed significantly larger change in conductivity and faster response time.