Ammonia sensors based on in situ fabricated nanocrystalline graphene field-effect devices

By transfer-free in situ catalytic chemical vapor deposition (CCVD) hundreds of nanocrystalline graphene field-effect transistors (ncGFETs) have been fabricated on a single 2″ silicon substrate. Raman spectroscopic analysis of the grown nanocrystalline graphene shows a clear signature of the G and a weak 2D peak in accoordance with the Raman spectra of nanocrystalline graphene from Schmidt et al. [1]. Using a grounded backgate ncGFET, the detection of ammonia (NH3) is demonstrated for room temperature (300 K) and 425 K, achieving detection down to a volume concentration of 100 parts-per-billion-volume (ppbv). By this method, a sensitivity of S4ppm, 425 k = 80.6% can be found for a volume concentration of 4 parts-per-million-volume (ppmv) of NH3 at a temperature of 425 K. In addition, by evaluation of the input characteristics of our ncGFET under different volume concentrations of ammonia we observe a global increase in the conductivity, which influences the sensitivity of our devices as well as of the negative shift of the charge neutrality point.