  Zinc oxide which is a n-type semiconducting metal oxide (SMO) has been a
promising material for detecting ethanol vapor. However, pure ZnO based ethanol
sensors often suffer from high working temperature, cross sensitivity towards
methanol and poor stability against humidity. Doping ZnO with various metal
ions has been widely explored as a proficient approach to improve its ethanol
sensing properties, while anionic dopants have been rarely considered. Here in
we demonstrate the effect of nitrogen doping on the ethanol sensing
characteristics of ZnO thin films. Nitrogen doped ZnO (N-ZnO) thin films have
been synthesized following sol-gel technique with urea as nitrogen precursor.
Ethanol sensing characteristics of the N-ZnO thin film has been com-pared with
pure ZnO sensor over a wide range of temperature and relative humidity
conditions. The N-ZnO sensor exhibits significantly large ethanol sensing
response at a lower operating temperature (~99 % at 225 {\deg}C vs ~81 % at 250
{\deg}C for ZnO), faster response time (12 s vs 33 s for ZnO), long term
stability, improved resilience against humidity and selectivity towards ethanol
over methanol and acetone. The experimental observations have been supplemented
by estimating the adsorption energies of ethanol on ZnO and N-ZnO surface using
density functional theory (DFT) calculations. We discuss that the microscopic
origin of improved ethanol sensing of N-ZnO is related to the facile adsorption
of ethanol molecules on the oxide surface which is promoted by modification of
electronic properties of ZnO by the nitrogen dopant atoms.
