Generation of nanogaps on porous ZnO sheets via Li-ion implantation: NO₂ gas sensing with ultrafast recovery time

Nanoscale defect structures on material surfaces introduce diverse chemical physics and have received substantial attention. However, nano structure distortions due to low stability and poor reproducibility have indicated the limitation for further electro-device applications using defect control. In this study, the higher activated electron transfer from the nanogaps (NGs) enhances the sensitivity and accelerated depletion region purifying the porous- ZnO (P-ZnO) sheets for NO₂ gas-sensor applications. ∼2.2 nm width of NGs on the (101̅0) orientated P-ZnO sheets and 12% higher surface oxygen vacancies (V_O) are formed by using Li-ion implantation via the lithiation process. This intrinsic electron-doped ZnO by NGs shows a reduced work function (φ) and an elevated Fermi level (E_F) compared to pristine ZnO. Therefore, the reaction between NO₂ gas and ZnO significantly accelerates owing to the activated electron transfer that carries ultrafast recovery time (∼16 s), and a low limit of detection (∼4 ppb) at 150 ℃ are obtained for the NG-P-ZnO sheet-based gas sensor. The generation of NGs on the surface via Li-ion implantation with reliable stability provides a new strategy to improve the electrochemical reactivity of semiconducting metal oxides beyond that obtained using conventional material engineering approaches, such as size, shape, and dimension control.