• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2010.06a
• /
• pp.60-60
• /
• 2010

1-D nanostructured materials have much more attention because of their outstanding properties and wide applicability in device fabrication. Bismuth oxide($Bi_2O_3$) is an important p-type semiconductor with main crystallographic polymorphs denoted by $\alpha-$, $\beta-$, $\gamma-$, and $\delta-Bi_2O_3$[1]. Due to its unique optical and electrical properties, $Bi_2O_3$ has been extensively investigated for various applications in gas sensors, photovoltaic cells, fuel cells, supercapacitors[2-4]. In this study, $Bi_2O_3$ NWs were grown by two step annealing process: in the first step, after annealing at $270^{\circ}C$ for 10h in a vaccum($3{\times}10^{-6}$ torr), we can obtain the bismuth nanowires. In the second step, after annealing at $300^{\circ}C$ for 2h in $O_2$ ambient, we successfully fabicated $Bi_2O_3$nanowires.

• Journal of Sensor Science and Technology
• /
• v.20 no.6
• /
• pp.406-411
• /
• 2011

$Co_3O_4$ thick film gas sensor using the powder prepared by hydrothermal reaction method(HRM) was fabricated. For comparison study, we also prepared the sensor using commercial $Co_3O_4$ powder under the same fabrication conditions. Sensitivity, time response, and selectivity of them to variable gases such as iso-$C_4H_{10}$, CO, $NH_3$, and $CH_4$ were investigated. The sensor from the powder prepared by HRM showed higher sensitivity to every gas than those from commercial powder. For iso-$C_4H_{10}$ gas, the sensitivities of both sensor to 100 ppm are 160 % and 40 %, respectively. Time response and selectivity of the sensor using the powder prepared by HRM were better than those of the sensor using commercial powder.

• Journal of Surface Science and Engineering
• /
• v.51 no.6
• /
• pp.360-364
• /
• 2018

A facile method to fabricate freestanding CuO nanoleaves and CuO nanowires-based films was demonstrated. $Cu(OH)_2$ nanoleaves and nanowires were prepared by a hydrolysis reaction in aqueous solution including pyridine and NaOH with the tailored concentrations at room temperature. The films of freestanding CuO nanoleaves and CuO nanowires can be successfully obtained via the simple vacuum infiltration following a thermal dehydration reaction. The morphologies and crystallinity of the $Cu(OH)_2$ nanoleaves/nanowires and CuO nanoleaves/nanowires were characterized by XRD, SEM, TEM and FT-IR. The films fabricated with freestanding CuO nanoleaves and nanowires in this study may be applicable for building high-efficiency organic binder-free devices, such as gas sensors, batteries, photoelectrodes for water splitting and so on.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.222-222
• /
• 2012

Metal oxide gas sensors based on semiconductor type have attracted a great deal of attention due to their low cost, flexible production and simple usability. However, most works have been focused on n-type oxides, while the characteristics of p-type oxide gas sensors have been barely studied. An investigation on p-type oxides is very important in that the use of them makes possible the novel sensors such as p-n diode and tandem devices. Monoclinic cupric oxide (CuO) is p-type semiconductor with narrow band gap (~1.2 eV). This is composed of abundant, nontoxic elements on earth, and thus low-cost, environment-friendly devices can be realized. However, gas sensing properties of neat CuO were rarely explored and the mechanism still remains unclear. In this work, the neat CuO layers with highly ordered mesoporous structures were prepared by a template-free, one-pot solution-based method using novel ink solutions, formulated with copper formate tetrahydrate, hexylamine and ethyl cellulose. The shear viscosity of the formulated solutions was 5.79 Pa s at a shear rate of 1 s-1. The solutions were coated on SiO2/Si substrates by spin-coating (ink) and calcined for 1 h at the temperature of $200{\sim}600^{\circ}C$ in air. The surface and cross-sectional morphologies of the formed CuO layers were observed by a focused ion beam scanning electron microscopy (FIB-SEM) and porosity was determined by image analysis using simple computer-programming. XRD analysis showed phase evolutions of the layers, depending on the calcination temperature, and thermal decompositions of the neat precursor and the formulated ink were investigated by TGA and DSC. As a result, the formation of the porous structures was attributed to the vaporization of ethyl cellulose contained in the solutions. Mesoporous CuO, formed with the ink solution, consisted of grains and pores with nano-meter size. All of them were strongly dependent on calcination temperature. Sensing properties toward H2 and C2H5OH gases were examined as a function of operating temperature. High and fast responses toward H2 and C2H5OH gases were discussed in terms of crystallinity, nonstoichiometry and morphological factors such as porosity, grain size and surface-to-volume ratio. To our knowledge, the responses toward H2 and C2H5OH gases of these CuO gas sensors are comparable to previously reported values.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.37 no.11
• /
• pp.9-17
• /
• 2000

A sensor array with 10 discrete sensors integrated on a substrate was developed for discriminating the kinds and quantities of explosive gases. The sensor array consisted of 10 oxide semiconductor gas sensors with $SnO_2$ as base material and had broad sensitivity to specific gas. The sensor array was designed with uniform thermal distribution and had also high sensitivity and reproductivity to low gas concentration through nano-sized sensing materials with different additives. By using the sensitivity signal of the sensor array at $400^{\circ}C$, we could reliably discriminate the kinds and quantities of explosive gases like butane, propane and methane under the lower explosion limit through the principal component analysis (PCA) method.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2011.02a
• /
• pp.72-72
• /
• 2011

Recently, Zinc oxide (ZnO) nano-structures have been received attractive attention because of their outstanding optical and electrical properties. It might be a promising material considered for applications to photonic and electronic devices such as ultraviolet light emitting diode, thin film transistor, and gas sensors. ZnO nano-structures can be typically synthesized by the VLS growth mode and self-assembly. In the VLS growth mode using various growth techniques, the noble metal catalysts such as Au and Sn were used. However, the growth of ZnO nano-structures on nano-crystalline Au seeds using radio frequency (RF) magnetron sputtering might be explained by the profile coating, i.e. the ZnO nano-structures were a morphological replica of Au seeds. Ga doped ZnO (ZnO:Ga) nano-structures using this concept were synthesized and characterized by XRD, AFM, SEM, and TEM. We found that surface morphology is drastically changed from initial islands to later sun-flower typed nano-structures. We will present the structural evolution of ZnO:Ga nano-structures with increasing the film thickness.

• Journal of Sensor Science and Technology
• /
• v.23 no.6
• /
• pp.383-387
• /
• 2014

Electrically conductive polypyrrole-polyvinylpyrrolidone (PPy-PVP) nanofiber mats with a core-shell structure have been successfully fabricated by a two-step process: the formation of FeCl3-containing PVP nanofiber mat by electrospinning, and the vapor-phase polymerization (VPP) of pyrrole monomer on the mat in a sealed chamber at room temperature. Surface morphology and chemical composition of the PPy-PVP mat were characterized by SEM, EDX and FTIR analyses. The as-prepared nonwoven mat was composed of PPy-PVP nanofibers with an average diameter of 300 nm. The sheet conductivity of the nanofiber mat was measured to be approximately 0.01 S/cm by a four-point probe. We have also investigated gas-sensing properties of PPy-PVP nanofiber mat upon exposure to methanol vapor. The PPy-PVP nanofiber sensors were observed to have excellent methanol-sensing performance. The nanofiber-based core-shell nanostructure could give an opportunity to fabricate a highly sensitive and fast response sensor due to its high surfaceto-volume ratio.

• Journal of Sensor Science and Technology
• /
• v.17 no.5
• /
• pp.361-368
• /
• 2008

Nanosized $SnO_2$ particles were synthesized by homogeneous precipitation method using tin chloride ($SnCl_4{\cdot}5H_{2}O$) and urea ($CO(NH_2)_2$). The powders were heated at $500^{\circ}C$ and $600^{\circ}C$ for 2h. The crystal structure, microstructure, thermal behavior, specific surface area were analyzed using XRD, FE-SEM, TGA and BET, respectively. The initial resistance and the $H_2$ sensing properties were measured as a function of ${Sb_2}{O_3}$ and Pd doping concentrations. The resistance was decreased with the addition of ${Sb_2}{O_3}$ and the sensitivity for $H_2$ gas was increased with the addition of Pd. Thus, the optimum $H_2$ gas sensing property was obtained in the 0.25.mol% ${Sb_2}{O_3}$ and 1.w% added $SnO_2$ powders.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.27 no.4
• /
• pp.257-261
• /
• 2014

Carbon nanotubes (CNT) has the excellent physical characteristics in the sensor, medicine, manufacturing and energy fields, and it has been studied in those fields for the several years. We fabricated the NOx gas sensors of MOS-FET type using the MWCNT. The fabricated sensor was used to detect the NOx gas for the variation of $V_{gs}$ (gate-source voltage) with the ambient temperature. The gas sensor absorbed the NOx gas molecules showed the decrease of resistance, and the sensitivity of sensor was reduced by the NOx gas molecules accumulated on the MWCNT surface. Furthermore, when the voltage ($V_{gs}$) was applied to the gas sensor, the term of the decrease in resistance was increased. On the other hand, the sensor sensitivity for the injection of NOx gas was the highest value at the ambient temperature of $40^{\circ}C$. We also obtained the adsorption energy ($40^{\circ}C$) using the Arrhenius plots by the reduction of resistance due to the $V_{gs}$ voltage variations. As a result, we obtained that the adsorption energy also was increased with the increasement of the applied $V_{gs}$ voltages.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.21 no.4
• /
• pp.164-168
• /
• 2011

Etch selectivities of mask materials to ZnO and $SnO_2$ films were studied in $BCl_3$/Ar and $CF_4$/Ar inductively coupled plasmas for fabrication of nanostructure-based gas sensing layer with high aspect ratios. In $25BCl_3$/10Ar ICP discharges, selectivities of 5.1~6.1 were obtained for ZnO over Ni while no practical selectivity was obtained for ZnO over Al. High selectivities of 7 ~ 17 for ZnO over Ni were produced in $25CF_4$/10Ar mixtures. $SnO_2$ showed much higher etch rates than Ni and a maximum selectivity of 67 was observed for $SnO_2$ over Ni.