Carbon Coating of Gan Nanostructures for Enhanced Sensitivity and Selectivity of Chemical Vapours

The chemical vapour sensing behaviour of pristine gallium nitride (GaN) and variously carbon coated GaN (CGaN) nanostructures towards polar protic (methanol, lactic acid, ammonia, water), polar aprotic (acetone) and apolar (toluene) analytes is investigated. The thickness of the carbon layer on GaN was controlled by using argon or nitrogen as carrier gases for toluene. TEM micrographs revealed dependence of the carbon layer on the carrier gas; with nitrogen (-2.6 +/- 0.6 nm) leading to a thinner layer than argon (-3.4 +/- 0.7 nm). Interestingly, chemical sensing performance studies showed that the carbon coating improved the sensitivity of GaN to polar protic analytes, especially to toxic ammonia. Most importantly, enhanced sensitivity was observed for water molecules on the C-GaN based devices in comparison to water sensitivity on bare GaN devices. In contrast, the carbon coating was observed to have little or no influence on the sensitivity towards polar aprotic and apolar analytes. In summary, the study demonstrates the importance of coating GaN nanoparticles with a thin carbonaceous layer for enhanced room temperature sensitive and selective detection of chemical vapour analytes.