Field Ionization from ZnO Nanorod Arrays for Detecting Formic Acid in Air

In this paper, we present a novel field ionization sensor designed for detecting formic acid in air that utilized ZnO nanorod arrays as anode, tungsten needle as cathode. Through applying a positive bias voltage to ZnO nanorod arrays, high local electric field is generated to ionize the detected gas (formic acid molecules) between the tips of ZnO nanorod arrays and tungsten needle. The experimental results reveal that the followings: (i) The prebreakdown current between anode and cathode is varied logarithmically with the concentration of formic acid, keeping relative humidity invariable; (ii) Among three parameters, the relative humidity, the concentration of formic acid and the prebreakdown current (I_prebreakdown), there exits a three-dimensional curve relationship. Accordingly, through measuring I_prebreakdown under some relative humidity, the concentration of formic acid in air could be obtained.