We report on experimental studies of NH_3 adsorption/desorption on graphene surfaces. The study employs bottom-gated graphene field effect transistors supported on Si/SiO_2 substrates. Detection of NH_3 occurs through the shift of the source—drain resistance maximum (`Dirac peak') with the gate voltage. The observed shift of the Dirac peak toward negative gate voltages in response to NH_3 exposure is consistent with a small charge transfer (f — 0.068 ± 0.004 electrons per molecule at pristine sites) from NH_3 to graphene. The desorption kinetics involves a very rapid loss of NH_3 from the top surface and a much slower removal from the bottom surface at the interface with the SiO_2 that we identify with a Fickian diffusion process.
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