Nam seok. Baik

Bio: Nam seok. Baik is an academic researcher from Kyushu University. The author has contributed to research in topics: Crystallite & Tin oxide. The author has an hindex of 5, co-authored 5 publications receiving 529 citations.

Gas sensing properties of tin oxide thin films fabricated from hydrothermally treated nanoparticles: Dependence of CO and H2 response on film thickness

Abstract: Thin film SnO2 sensors with various thicknesses were spin-coated from a hydrothermally treated SnO2 sol suspension. The FE-SEM observation revealed that the films prepared from the 1.8 wt.% SnO2 containing sol suspension had good uniformity packed with nano-crystalline SnO2 even after calcination at 600°C when its thickness was up to about 300 nm, though many cracks were observed for thicker films. The gas sensing characteristics to H2 and CO were evaluated as a function of film thickness (80–300 nm) in dry air. The electrical resistance of thin films decreased monotonically with increasing film thickness. It was found that the sensor response to H2 similarly decreased with an increase in film thickness, while the CO response was found to be almost independent of the film thickness. The relationship between gas sensing properties and film thickness was discussed on the basis of diffusivity and reactivity of the gases inside the oxide films.

Hydrothermally treated sol solution of tin oxide for thin-film gas sensor

Abstract: A sol solution containing SnO2 particles (crystallites) of 6 nm in average diameter was prepared by a hydrothermal treatment. The hydrothermal treatment was found to be very effective for suppressing the thermal growth of SnO2 grains. A thin-film sensor device, fabricated by spin-coating from the sol solution, consisted of SnO2 crystallites with 6 nm in mean diameter after calcination at 600°C. The device proved for better properties in sensitivity and response transient than a conventional sintered-block sensor device using SnO2 precipitated gel.

Preparation of Stabilized Nanosized Tin Oxide Particles by Hydrothermal Treatment

Abstract: Stable colloidal suspensions of tin oxide (content 0.9–6.1 wt%) were synthesized by subjecting conventionally prepared tin oxide gels to hydrothermal treatment with an ammonia solution (pH 10.5) at 200°C for 3 h in an autoclave. Based on X-ray diffractometry analyses, the tin oxide crystallites after hydrothermal treatment were resistant to thermal growth at elevated temperatures, and this feature became more conspicuous as the tin oxide content of the colloidal suspension decreased. For the powder derived from a 1.8 wt% colloidal suspension, for example, the mean sizes of the tin oxide crystallites were 7.5 and 13 nm after calcination at 600° and 900°C, respectively, in comparison with corresponding values of 13.5 and 29 nm for the untreated gel-derived powder. Thin film spin-coated from the same suspension had good uniformity, packed with tin oxide grains (crystallites) of a mean size of 6 nm after calcination at 600°C. Optical determination of the tin oxide sol particle size, as well as gravimetric analysis of the dehydration from the powder samples, were conducted to determine effects of hydrothermal treatment.

Hydrothermal treatment of tin oxide sol solution for preparation of thin-film sensor with enhanced thermal stability and gas sensitivity

Abstract: The effects of treating tin oxide gel hydrothermally in an ammonia solution at 200°C for 3 h were studied. The size of sol particles increased with increasing concentration of the resulting sol solution, i.e., 5, 8, 10 and 32 nm for 1.8, 3.2, 6.1 and 8.6 wt.% tin oxide sol as determined by an optical analyzer, whereas the crystallite size of tin oxide determined by X-ray diffraction analysis remained to be about 5–7 nm for all the solutions. The tin oxide powder collected was found to be resistant to grain growth on calcination, depending on the concentration of the sol solution. This tendency was maintained in the thin-films spin-coated on an alumina substrate from the sol solutions. The grain size of the film derived from 1.8 wt.% tin oxide sol was smaller than 10 nm in diameter after calcination at 600°C. This particular film exhibited an outstanding by high sensitivity to 800 ppm H 2 at 350°C, compared with conventional tin oxide elements of a sintered block type.

Preparation of Stabilized Nanosized Tin Oxide Particles by Hydrothermal Treatment.

Abstract: Stable colloidal suspensions of tin oxide (content 0.9–6.1 wt%) were synthesized by subjecting conventionally prepared tin oxide gels to hydrothermal treatment with an ammonia solution (pH 10.5) at 200°C for 3 h in an autoclave. Based on X-ray diffractometry analyses, the tin oxide crystallites after hydrothermal treatment were resistant to thermal growth at elevated temperatures, and this feature became more conspicuous as the tin oxide content of the colloidal suspension decreased. For the powder derived from a 1.8 wt% colloidal suspension, for example, the mean sizes of the tin oxide crystallites were 7.5 and 13 nm after calcination at 600° and 900°C, respectively, in comparison with corresponding values of 13.5 and 29 nm for the untreated gel-derived powder. Thin film spin-coated from the same suspension had good uniformity, packed with tin oxide grains (crystallites) of a mean size of 6 nm after calcination at 600°C. Optical determination of the tin oxide sol particle size, as well as gravimetric analysis of the dehydration from the powder samples, were conducted to determine effects of hydrothermal treatment.

Metal oxides for solid-state gas sensors: What determines our choice?

Abstract: The analysis of various parameters of metal oxides and the search of criteria, which could be used during material selection for solid-state gas sensor applications, were the main objectives of this review. For these purposes the correlation between electro-physical (band gap, electroconductivity, type of conductivity, oxygen diffusion), thermodynamic, surface, electronic, structural properties, catalytic activity and gas-sensing characteristics of metal oxides designed for solid-state sensors was established. It has been discussed the role of metal oxide manufacturability, chemical activity, and parameter's stability in sensing material choice as well.

Oxide semiconductor gas sensors

Abstract: Semiconductor gas sensors utilize porous polycrystalline resistors made of semiconducting oxides. The working principle involves the receptor function played by the surface of each oxide grain and the transducer function played by each grain boundary. In addition, the utility factor of the sensing body also takes part in determining the gas response. Therefore, the concepts of sensor design are determined by considering each of these three key factors. The requirements are selection of a base oxide with high mobility of conduction electrons and satisfactory stability (transducer function), selection of a foreign receptor which enhances surface reactions or adsorption of target gas (receptor function), and fabrication of a highly porous, thin sensing body (utility factor). Recent progress in sensor design based on these factors is described.

Hydrogen sensing using titania nanotubes

Abstract: Titanium dioxide nanotubes, made by anodization, are highly sensitive to hydrogen; for example, cycling between nitrogen atmosphere and 1000 ppm hydrogen a variation in measured resistance of 10 3 is seen for 46 nm diameter nanotubes at 290 °C. The hydrogen sensors are completely reversible and have response times of approximately 150 s. Field emission scanning electron microscopy and Glancing angle X-ray diffraction (GAXRD) are used to study the surface morphology and crystal structure of the nanotubes.

Porous Metal Oxides as Gas Sensors

Abstract: Semiconducting metal oxides are frequently used as gas-sensing materials. Apart from large surface-to-volume ratios, well-defined and uniform pore structures are particularly desired for improved sensing performance. This article addresses the role of some key structural aspects in porous gas sensors, such as grain size and agglomeration, pore size or crack-free film morphology. New synthesis concepts, for example, the utilisation of rigid matrices for structure replication, allow to control these parameters independently, providing the opportunity to create self-diagnostic sensors with enhanced sensitivity and reproducible selectivity.

Theory of gas-diffusion controlled sensitivity for thin film semiconductor gas sensor

Abstract: Influences of gas transport phenomena on the sensitivity of a thin film semiconductor gas sensor were investigated theoretically. A diffusion equation was formulated by assuming that an inflammable gas (target gas) moves inside the film by Knudsen diffusion, while it reacts with the adsorbed oxygen following a first-order reaction kinetic. By solving this equation under steady-state conditions, the target gas concentration inside the film was derived as a function of depth (x) from the film surface, Knudsen diffusion coefficient (DK), rate constant (k) and film thickness (L). The gas concentration profile thus obtained allowed to estimate the gas sensitivity (S) defined as the resistance ratio (Ra/Rg), under the assumption that the sheet conductance of the film at depth x is linear to the gas concentration there with a proportionality constant (sensitivity coefficient), a. The derived equation shows that S decreases sigmoidally down to unity with an increase in L k/D K . Further by assuming that the temperature dependence of rate constant (k) and sensitivity coefficient (a) follows Arrenius type ones with respective activation energies, it was possible to derive a general expression of S involving temperature (T). The expression shows that, when the activation energies are selected properly, the S versus T correlation results in a volcano-shaped one, its height increasing with decreasing L. The dependence of S on L at constant T as well as on T at constant L can thus be simulated fairly well based on the equation.