Crystal-Defect-Dependent Gas-Sensing Mechanism of the Single ZnO Nanowire Sensors

Abstract

Though the chemical origin of a metal oxide gas sensor is widely accepted to be the surface reaction of detectants with ionsorbed oxygen, how the sensing material transduces the chemical reaction into an electrical signal (i.e., resistance change) is still not well-recognized. Herein, the single ZnO NW is used as a model to investigate the relationship between the microstructure and sensing performance. It is found that the acetone responses arrive at the maximum at the NW diameter (D) of ∼110 nm at the D range of 80 to 400 nm, which is temperature independent in the temperature region of 200 °C–375 °C. The electrical properties of the single NW field effect transistors illustrate that the electron mobility decreases but electron concentration increases with the D ranging from ∼60 nm to ∼150 nm, inferring the good crystal quality of thinner ZnO NWs and the abundant crystal defects in thicker NWs. Subsequently, the surface charge layer (L) is calculated to be a constant of 43.6 ± 3.7 nm at this D range, which cannot be explained by the conventional D–L model in which the gas-sensing maximum appears when D approximates 2L. Furthermore, the crystal defects in the single ZnO NW are probed by employing the microphotoluminescence technique. The mechanism is proposed to be the compromise of the two kinds of crystal defects in ZnO (i.e., more donors and fewer acceptors favor the gas-sensing performance), which is again verified by the gas sensors based on the NW contacts.

Ethanol Gas Sensing by a Zn-Terminated ZnO(0001) Bulk Single-Crystalline Substrate

“…The thickness W of the space charge layer is described as where ε r is the relative permittivity of the sensing material, ε 0 is the dielectric constant of vacuum, φ is the surface barrier potential, e is the electron charge, and n e is the charge carrier density. 34 , 35 For ZnO, it is reported to be 43 nm for a nanowire 35 and 400 nm for a single-crystalline substrate at 300 °C. 36 The large W of the single crystal is due to the low density of the defect-originated charge carrier.…”

SAM Functionalized ZnO Nanowires for Selective Acetone Detection: Optimized Surface Specific Interaction Using APTMS and GLYMO Monolayers

“…[ 30 ] In another report by Zhou et al. [ 31 ] single crystalline ZnO NWs (diameter = 110 nm) showed response around 60 for acetone at 350 °C. Furthermore, Kaur et al.…”

Ethanol Sensing Properties and First Principles Study of Au Supported on Mesoporous ZnO Derived from Metal Organic Framework ZIF-8

“…The modification of Au nanoparticles can increase the O V content in ZnO materials, which can be attributed to the “spillover effect” of precious metals [ 26 , 27 ]. The increase of O V can generate more free electrons, which will enhance the adsorption of surface gas, thus improving the gas-sensitive property of the materials [ 28 , 29 ].…”