Nitrogen Dioxide Sensing Using Multilayer Structure of Reduced Graphene Oxide and α-FeO.

Multilayers consisting of graphene oxide (GO) and α-FeO thin layers were deposited on the ceramic substrates by the spray LbL (layer by layer) coating technique. Graphene oxide was prepared from graphite using the modified Hummers method. Obtained GO flakes reached up to 6 nanometers in thickness and 10 micrometers in lateral size. Iron oxide FeO was obtained by the wet chemical method from FeCl and NHOH solution. Manufactured samples were deposited as 3 LbL (GO and FeO layers deposited sequentially) and 6 LbL structures with GO as a bottom layer. Electrical measurements show the decrease of multilayer resistance after the introduction of the oxidizing NO gas to the ambient air atmosphere. The concentration of NO was changed from 1 ppm to 20 ppm. The samples changed their resistance even at temperatures close to room temperature, however, the sensitivity increased with temperature. FeO is known as an n-type semiconductor, but the rGO/FeO hybrid structure behaved similarly to rGO, which is p-type. Both chemisorbed O and NO act as electron traps decreasing the concentration of electrons and increasing the effective multilayer conductivity. An explanation of the observed variations of multilayer structure resistance also the possibility of heterojunctions formation was taken into account.