Sun Jung Kim

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.

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.

Chemical synthesis of CoO-ZnO: Co hetero-nanostructures and their ferromagnetism at room temperature

One-dimensional CoO–ZnO:Co hetero-nanostructures were prepared by vapor phase growth. Ferromagnetism was observed at room temperature, which is ascribed to Co diffusion into ZnO nanorods grown over CoO nanowires. Strong enhancement in green emission intensity was also observed.

Gas Sensing Characteristics of Sb-doped SnO 2 Nanofibers

Undoped and Sb-doped nanofibers were prepared by electrospinning and their responses to , CO, , , and were measured. In the undoped nanofibers, the gas response (, : resistance in air, : resistance in gas) to 100 ppm was very high(33.9), while that to the other gases ranged from 1.6 to 2.2. By doping with 2.65 wt% Sb, the response to 100 ppm was decreased to 4.5, whereas the response to was increased to 3.0. This demonstrates the possibility of detecting a high concentration with minimum interference from and the potential to control the gas selectivity by Sb doping.

Preparation of Ni-GDC Powders by the Solution Reduction Method Using Hydrazine and Its Electrical Properties

Ni-GDC (gadolinia-doped ceria) composite powders, the anode material for the application of solid oxide fuel cells, were prepared by a solution reduction method using hydrazine. The distribution of Ni particles in the composite powders was homogeneous. The Ni-GDC powders were sintered at 1400˚C for 2 h and then reduced at 800˚C for 24 h in 3% H2. The percolation limit of Ni of the sintered composite was 20 vol%, which was significantly lower than these values in the literature (30-35 vol%). The marked decrease of percolation limit is attributed to the small size of the Ni particles and the high degree of dispersion. The hydrazine method suggests a facile chemical route to prepare well-dispersed Ni-GDC composite powders.

VOCs(Volatile Organic Compounds) sensor using SnO 2 nanowires

VOCs (Volatile Organic Compound) sensors were fabricated using nanowires-based thin films and its gas sensing behaviors were studied. The nanowires synthesized from a thermal evaporation process were dispersed in a solution and the sensor film was prepared by dropping the slurry on the substrate with the electrodes and an embedded heater. The gas response (Ra/Rg, Ra: resistance in air, Rg: resistance in gas) to ppm Benzene, Ethyl Benzene, o-xylene were in the range of , which were significantly higher than those to 50 ppm of CO, and ().

Preparation of nanocrystalline CuO powders by hydrazine method and their gas sensing characteristics

CuO is an important transition metal oxide with many practical applications such as catalysts, p-type semiconductor, solar cells, magnetic storage media and cathode materials. In this contribution, nanocrystalline CuO powders were prepared by solution reduction method using copper chloride (), hydrazine () and NaOH and subsequent heat treatment. The gas sensor using nanocrystalline CuO powders showed high sensitivities to acetone and ethanol.

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.

Design of Selective Gas Sensors Using Combinatorial Solution Deposition of Oxide Semiconductor Films

The study examined sensing behavior of multicompositional gas sensing materials prepared through combinatorial deposition of SnO2, ZnO, and WO3 sols. Selective detection of C2H5OH and CH3COCH3 in the presence of CO, C3H8, H2 and NO2 was accomplished by combinatorial manipulation of the gas sensor composition. A further tuning of the gas-sensing materials and gas-sensing temperature allowed discrimination between C2H5OH and CH3COCH3, which is a challenging issue due to their similar chemical nature. The discrimination of similar gases and selective gas detection are discussed with respect to the gas sensing mechanism. Combinatorial approach is very convenient and useful for determining an optimal composition for selective-gas detection.