SnO2-ZnO core-shell nanofibers were synthesized via a novel two-step process. First, SnO2 nanofibers were synthesized by electrospinning. In sequence, ZnO shell layers were deposited using atomic layer deposition on the electrospinning synthesized SnO2 nanofibers. To demonstrate the practical applications of the synthesized core-shell nanofibers, we investigated their sensing properties to O2 and NO2. The high sensitivity and dynamic repeatability observed in these sensors reveal that the core-shell nanofibers are promising as sensitive and reliable chemical sensors.

We report a dual functional sensing mechanism for ultrasensitive chemoresistive sensors based on SnO2-ZnO core-shell nanowires (C-S NWs) for detection of trace amounts of reducing gases. C-S NWs were synthesized by a two-step process, in which core SnO2 nanowires were first prepared by vapor-liquid-solid growth and ZnO shell layers were subsequently deposited by atomic layer deposition. The radial modulation of the electron-depleted shell layer was accomplished by controlling its thickness. The sensing capabilities of C-S NWs were investigated in terms of CO, which is a typical reducing gas. At an optimized shell thickness, C-S NWs showed the best CO sensing ability, which was quite superior to that of pure SnO2 nanowires without a shell. The dual functional sensing mechanism is proposed as the sensing mechanism in these nanowires and is based on the combination of the radial modulation effect of the electron-depleted shell and the electric field smearing effect.

Based on the radial modulation of electron-depleted shell layers in SnO 2 -ZnO core-shell nanofibers (CSNs), a novel approach is proposed for the detection of very low concentrations of reducing gases. In this work, SnO 2 -ZnO CSNs were synthesized by a two-step process: core SnO 2 nanofibers were first prepared by electrospinning, followed by the preparation of ZnO shell layers by atomic layer deposition. The radial modulation of electron depletion in the CSN shells was accomplished by controlling the shell thickness.The sensing capabilities of CSNs were investigated with respect to CO and NO 2 that represent typical reducing and oxidizing gases, respectively. In the case of CO at a critical shell thickness, the CSN-based sensors showed greatly improved sensing capabilities compared with those fabricated on the basis of either pure SnO 2 or pure ZnO nanofibers. In sharp contrast, CSN sensors revealed inferior sensing capabilities for NO 2 . The results can be explained by a model based on the radial modulation of the electron-depleted CSN shells. The model suggests that CSNs comprising dissimilar materials having different energy-band structures represent an effective sensing platform for the detection of low concentrations of reducing gases when the shell thickness is equivalent to the Debye length.

We propose a novel approach to improve the gas-sensing properties of n-type nanofibers (NFs) that involves creation of local p-n heterojunctions with p-type reduced graphene oxide (RGO) nanosheets (NSs). This work investigates the sensing behaviors of n-SnO2 NFs loaded with p-RGO NSs as a model system. n-SnO2 NFs demonstrated greatly improved gas-sensing performances when loaded with an optimized amount of p-RGO NSs. Loading an optimized amount of RGOs resulted in a 20-fold higher sensor response than that of pristine SnO2 NFs. The sensing mechanism of monolithic SnO2 NFs is based on the joint effects of modulation of the potential barrier at nanograin boundaries and radial modulation of the electron-depletion layer. In addition to the sensing mechanisms described above, enhanced sensing was obtained for p-RGO NS-loaded SnO2 NFs due to creation of local p-n heterojunctions, which not only provided a potential barrier, but also functioned as a local electron absorption reservoir. These mechanisms markedly increased the resistance of SnO2 NFs, and were the origin of intensified resistance modulation during interaction of analyte gases with preadsorbed oxygen species or with the surfaces and grain boundaries of NFs. The approach used in this work can be used to fabricate sensitive gas sensors based on n-type NFs.

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We fabricated TiO2–ZnO core‐shell nanofibers via a novel two‐step process. In the first step, the TiO2 core nanofibers were synthesized by electrospinning. Subsequently, the ZnO shell layers were grown in a controlled manner using atomic layer deposition. The methodology proposed in this work is expected to be one of most suitable methods for preparing various kinds of oxide core‐shell nanofibers or nanowires. We investigated the O2 sensing properties of the synthesized core‐shell nanofibers. Good sensitivity and dynamic repeatability were observed for the sensor, demonstrating that the core‐shell nanofibers hold promise for the realization of sensitive and reliable chemical sensors.

On the basis of a selective growth of SnO2 nanowires by the vapor–liquid–solid growth method, networked SnO2 nanowire sensors were fabricated. Then, their sensing properties were systematically investigated in terms of NO2. The density of junctions was controlled by altering the spacing of the patterned-interdigital electrodes (PIEs), on which SnO2 nanowires selectively grew and touched the nanowires grown on neighboring PIEs, eventually producing junctions. The sensing mechanism was attributed to the change not only in the width of the space charge region along the length direction of each nanowire but also in the height of the built-in potential at the junctions during adsorption and desorption of gaseous species. Narrower spacings of PIEs led to an increasing the density of junctions projected to the plane and, consequently, superior properties for gas sensing. Importantly, a general principle to prepare networked nanowires of superior sensing capabilities was suggested from the point of view of nanowire shape and electrode configuration.