Optimum shell thickness and underlying sensing mechanism in p–n CuO–ZnO core–shell nanowires

The Morphologies of the Semiconductor Oxides and Their Gas-Sensing Properties

“…Kim et al investigated the role of the shell thickness of CuO/ZnO core-shell nanowires in the sensing mechanism, as shown in Figure 5 . In the case where the shell thickness was nearly identical to λ D of the shell material, a complete electron depletion was generated [ 35 ]. When exposed to CO gas, the adsorbed oxygen species would react with CO gas and release the trapped electrons back into the conduction band to recover its original configuration, leading to an enhanced gas response, as shown in Figure 5 a.…”

“…( a ) thinner than ZnO’s Debye length; ( b ) thicker than ZnO’s Debye length. Reprinted from [ 35 ] with permission. Copyright (2015) Elsevier.…”

Enhanced UV and ethanol vapour sensing of a single 3-D ZnO tetrapod alloyed with Fe2O3 nanoparticles

“…It is well known that the main disadvantage of micro-and nanostructures of pure semiconducting oxides, such as SnO2 and ZnO, is their low selectivity and poor stability to environments with a high relative humidity (RH) [1][2][3]. Thus, a variety of meth-ods has been elaborated for an improvement of gas sensors based on semiconducting oxides, including the synthesis of different morphologies [4], doping [5], surface functionalization with noble metals [6], polymers [7] and other semiconducting oxides for the formation of nanoscale hetero-junctions or core-shell structures [8]. Many of these methods combine important disadvantages such as additional technological steps, poor longtime stability and repeatability, with advantages such as improved selectivity, sensi-tivity and stability to high RH.…”

Highly sensitive NO2 sensors based on core‐shell array of silicon nanowires/polypyrrole and new insight into gas sensing mechanism of organic/inorganic hetero‐contact

“…In previous works regarding semiconductor metal oxide C-S heteronanowires sensors, there generally exists a critical thickness of oxide shell, at which the C-S sensors can achieve superior sensing abilities. Jae-Hun et al ever reported that the CuO-ZnO C-S nanowires sensor showed the highest response to CO and C 6 H 6 at a shell thickness close to Debye length (λ D ) of ZnO [32]; while according to the investigation from Park et al, the critical thickness for the shell in In 2 O 3 -ZnO C-S nanowires sensor was very close to 2λ D of ZnO [33]. The sensing mechanism of these metal oxide C-S structures has been demonstrated with several models such as the potential barrier-controlled carrier transport and the radial modulation effect in the electrondepleted shell [34][35][36][37][38].…”