Nanocomposites of ZnO Nanostructures and Reduced Graphene Oxide Nanosheets for NO₂ Gas Sensing

A depletion region formed at the junction of two materials depends on the charge carrier concentration and the barrier height. The depletion width can be controlled by the overlayer thickness. Modification of the depletion width after gas exposure is mainly contributing to the sensor response. The maximum effect of gas molecules can be realized when the depletion width becomes comparable to the Debye length. Consequently, the selection of an appropriate overlayer thickness is very crucial. In the present work, chemiresistive gas sensing characteristics of ZnO nanowire (NW) films modified with different thicknesses of reduced graphene oxide (rGO) have been studied. The hybrid films showed selective outstanding NO 2 response as compared to pure ZnO NW films. At an optimum rGO thickness of ∼15.3 nm, the response toward NO 2 (with a minimum detection limit of 400 ppb) was found to be the highest that is nearly three times higher than that of pure ZnO nanowire films. A synergetic balance of the depletion width at the ZnO/rGO interface with the Debye length is attributed to the improved selective NO 2 response of hybrid films.