In Sung Hwang

Facile Control of C2H5OH Sensing Characteristics by Decorating Discrete Ag Nanoclusters on SnO2 Nanowire Networks

The effect of Ag decoration on the gas sensing characteristics of SnO(2) nanowire (NW) networks was investigated. The Ag layers with thicknesses of 5-50 nm were uniformly coated on the surface of SnO(2) NWs via e-beam evaporation, which were converted into isolated or continuous configurations of Ag islands by heat treatment at 450 °C for 2 h. The SnO(2) NWs decorated by isolated Ag nano-islands displayed a 3.7-fold enhancement in gas response to 100 ppm C(2)H(5)OH at 450 °C compared to pristine SnO(2) NWs. In contrast, as the Ag decoration layers became continuous, the response to C(2)H(5)OH decreased significantly. The enhancement and deterioration of the C(2)H(5)OH sensing characteristics by the introduction of the Ag decoration layer were strongly governed by the morphological configurations of the Ag catalysts on SnO(2) NWs and their sensitization mechanism.

Ultrasensitive and selective C2H5OH sensors using Rh-loaded In2O3 hollow spheres

Rh-loaded In2O3 hollow spheres with diameters of ∼2 μm were prepared by a one-pot hydrothermal reaction of aqueous solution containing indium nitrate, rhodium chloride, and glucose and subsequent heat treatment at 500 °C for 2 h. The response to 100 ppm C2H5OH (Ra/Rg, Ra: resistance in air, Rg: resistance in gas) of 1.67 at% Rh-loaded In2O3 hollow spheres was 4748, which was ∼180 times higher than that of pure In2O3 hollow spheres. Rh loading decreased the temperature for maximum gas response from 475 °C to 371 °C, which also enhanced the selectivity to C2H5OH 15.1–24.7 times and recovery speed. The ultrahigh sensitivity and selectivity to C2H5OH, the lower sensing temperature, and the reduced recovery time were attributed to electronic interactions between Rh and In2O3 and the promotion of catalytic dissociation of C2H5OH into reactive gases.

Microstructural control and selective C2H5OH sensing properties of Zn2SnO4 nanofibers prepared by electrospinning.

Microstructural evolution of spinel Zn(2)SnO(4) nanofibers was manipulated via an in situ phase separation process of inorganic precursors and a matrix polymer during electrospinning and calcination. Chemiresistive gas sensors using porous Zn(2)SnO(4) fibers exhibited superior C(2)H(5)OH sensing response.

Phase evolution of perovskite LaNiO3 nanofibers for supercapacitor application and p-type gas sensing properties of LaOCl–NiO composite nanofibers

This study reports the fabrication and characterization of LaOCl–NiO composite and LaNiO3 nanofiber mats and their potential applications for p-type gas sensors and electrochemical capacitors. One-dimensional LaOCl–NiO composite and LaNiO3 fibers were prepared via the electrospinning of LaNiO3 precursor/poly(vinyl acetate) composite fibers followed by subsequent thermal annealing. The size and distribution of the primary particles within the LaOCl–NiO composite and LaNiO3 fibers were largely governed by the calcination conditions (from 450 to 950 °C). The perovskite LaNiO3 phase started to form at calcination temperatures that exceeded 750 °C. Upon the formation of the perovskite LaNiO3 phase, the electrical resistivity decreased remarkably from 1.1 × 106 to 0.692 Ω cm. LaOCl–NiO composite fiber mats calcined at 550 °C and 650 °C showed p-type semiconducting gas sensing properties and exhibited significantly enhanced C2H5OH sensitivity against CO, H2, NH3 and NO2 gases. The conducting LaNiO3 fiber mats calcined at 750 °C were used as the basis of a hybrid electrochemical capacitor in which the fiber mats served as the conducting core for electrostatic spray-deposited manganese oxide overlayers. The manganese oxide/LaNiO3 stacked electrodes exhibited a high specific capacitance of ∼160 F g−1 at 10 mV s−1.

Design of Selective Gas Sensors Using Additive-Loaded In2O3 Hollow Spheres Prepared by Combinatorial Hydrothermal Reactions

A combinatorial hydrothermal reaction has been used to prepare pure and additive (Sb, Cu, Nb, Pd, and Ni)-loaded In2O3 hollow spheres for gas sensor applications. The operation of Pd- and Cu-loaded In2O3 sensors at 371 °C leads to selective H2S detection. Selective detection of CO and NH3 was achieved by the Ni-In2O3 sensor at sensing temperatures of 371 and 440 °C, respectively. The gas responses of six different sensors to NH3, H2S, H2, CO and CH4 produced unique gas sensing patterns that can be used for the artificial recognition of these gases.

Brush-shaped ZnO heteronanorods synthesized using thermal-assisted pulsed laser deposition.

Brush-shaped ZnO heteronanostructures were synthesized using a newly designed thermal-assisted pulsed laser deposition (T-PLD) system that combines the advantages of pulsed laser deposition (PLD) and a hot furnace system. Branched ZnO nanostructures were successfully grown onto CVD-grown backbone nanowires by T-PLD. Although ZnO growth at 300 °C resulted in core-shell structures, brush-shaped hierarchical nanostructures were formed at 500-600 °C. Materials properties were studied via photoluminescence (PL), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations. The enhanced photocurrent of a SnO(2)-ZnO heterostructures device by irradiation with 365 nm wavelength ultraviolet (UV) light was also investigated by the current-voltage characteristics.

Detection of CO and NH 3 mixed gas using single-walled carbon nanotubes

We fabricated a carbon nanotube based gas sensor for the detection of CO and NH3 mixed gas. Conventional photolithography technology was applied for the localization of sensing materials and the sensor fabrication. Single walled carbon nanotubes were dispersed in Sodium Dodecyl Sulfate(SDS) solution. The whole surface was covered by a photoresist except window areas between two electrodes. Carbon nanotubes were carefully dropped over the window areas and dried at 220°C over a hot plate. Then, the photoresist was removed using acetone. CO and NH3 mixed gas was delivered into a chamber at room temperature with nitrogen as a carrier gas. For comparison, each gas was applied to our sensor separately. Electrical resistance was measured for sensing performance.

Degradation pattern of SnO 2 nanowire field effect transistors

The degradation pattern of SnO(2) nanowire field effect transistors (FETs) was investigated by using an individual SnO(2) nanowire that was passivated in sections by either a PMMA (polymethylmethacrylate) or an Al(2)O(3) layer. The PMMA passivated section showed the best mobility performance with a significant positive shift in the threshold voltage. The distinctive two-dimensional R(s)-μ diagram based on a serial resistor connected FET model suggested that this would be a useful tool for evaluating the efficiency for post-treatments that would improve the device performance of a single nanowire transistor.

ZnO-SnO 2 core-shell nanowire networks and their gas sensing characteristics

The ZnO nanowires (NWs) are grown by carbothermal reaction and SnO<inf>2</inf> shell layers are subsequently coated by vapor phase growth. The crystalline SnO<inf>2</inf> shell layer with the thickness of 5–20 nm was uniformly coated on the ZnO NWs with the diameter of 50–100 nm. The gas response of ZnO-SnO<inf>2</inf> core-shell NWs sensor to 10 ppm NO<inf>2</inf> at 200°C was increased up to ∼33 times compared to those of ZnO NWs. The enhancement of gas responses to NO<inf>2</inf> was discussed in relation to the thin SnO<inf>2</inf> shell layer and core-shell configuration of NWs.