• Journal of Sensor Science and Technology
• /
• v.9 no.1
• /
• pp.36-43
• /
• 2000

In oder to enhance the selectivity of TMA(trimethylamine) gas, the ZnO-based films which were doped with $Al_2O_3$, $TiO_2, $In_2O_3$ and $V_2O_5$ catalysts with various weight percents were deposited in oxygen by RF magnetron sputtering method. To improve electrical stability of sensors, the ZnO-based films were annealed in oxygen at $700^{\circ}C$ for 1 hour. The TMA selectivity of sensors was defined by the magnitude($S_{TMA}/S_{DMA}$ and $S_{TMA}/S_{NH3}$) of TMA sensitivity relative to DMA and sensitivity ammonia($NH_3$) sensitivity, respectively. The $ZnO+Al_2O_3(4\;wt.%)+TiO_2(1\;wt.%)+In_2O_3(1\;wt.%)$ sensor showed high $S_{TMA}/S_{DMA}$ of 5.9 and $S_{TMA}/S_{NH3}$ of 26 to 160 ppm at the working temperature of $300^{\circ}C$ respectively.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.259-259
• /
• 2010

Periodically polarity inverted (PPI) ZnO structures on (0001) Al2O3 substrates are demonstrated by plasmas assisted molecular beam epitaxy. The patterning and re-growth methods are used to realize the PPI ZnO by employing the polarity controlling method. For the in-situ polarity controlling of ZnO films, Cr-compound buffer layers are used.[1, 2] The region with the CrN intermediate layer and the region with the Cr2O3 and Al2O3 substrate were used to grow the Zn- and O-polar ZnO films, respectively. The growth behaviors with anisotropic properties of PPI ZnO heterostructures are investigated. The periodical polarity inversion is evaluated by contrast images of piezo-response microscopy. Structural and optical interface properties of PPI ZnO are investigated by the transmission electron microcopy (TEM) and micro photoluminescence ($\mu$-PL). The inversion domain boundaries (IDBs) between the Zn and the O-polar ZnO regions were clearly observed by TEM. Moreover, the investigation of spatially resolved local photoluminescence characteristics of PPI ZnO revealed stronger excitonic emission at the interfacial region with the IDBs compared to the Zn-polar or the O-polar ZnO region. The possible mechanisms will be discussed with the consideration of the atomic configuration, carrier life time, and geometrical effects. The successful realization of PPI structures with nanometer scale period indicates the possibility for the application to the photonic band-gap structures or waveguide fabrication. The details of application and results will be discussed.

• Korean Journal of Crystallography
• /
• v.7 no.2
• /
• pp.175-182
• /
• 1996

ZnO thin films were deposited on Corning 7059 glass substrates to study fundamental properties of films. According to the experimental results, (002) preferred ZnO thin films were grown by purging Ar/O2 mixed gas, but not without oxygen gas. The structure and the orientation of ZnO thin films were much affected by the substrate temperature and rf power. High quality ZnO films were obtained by increasing their values. Optimum deposition parameters were : 300W rf power, 300℃ substrate temperature, Ar/O2=70/30. To characterize SAW propagation properties, IDT was fabricated by etching Al films deposited on diamond/Si wafer with RIE. Measured λ(wavelength) was 24μm and experimental results were well matched with simulation. Center frequency was 250MHz, and the calculated phase velocity of ZnO/ diamond structure was about 6000m/s.

• Korean Journal of Materials Research
• /
• v.23 no.4
• /
• pp.211-214
• /
• 2013

The effects of a Ni coating on the sensing properties of nano ZnO:Ni based gas sensors were studied for $CH_4$ and $CH_3CH_2CH_3$ gases. Nano ZnO sensing materials were prepared by the hydrothermal reaction method. The Ni coatings on the nano ZnO surface were deposited by the hydrolysis of zinc chloride with $NH_4OH$. The weight % of Ni coating on the ZnO surface ranged from 0 to 10 %. The nano ZnO:Ni gas sensors were fabricated by a screen printing method on alumina substrates. The structural and morphological properties of the nano ZnO : Ni sensing materials were investigated by XRD, EDS, and SEM. The XRD patterns showed that nano ZnO : Ni powders with a wurtzite structure were grown with (1 0 0), (0 0 2), and (1 0 1) dominant peaks. The particle size of nano ZnO powders was about 250 nm. The sensitivity of nano ZnO:Ni based sensors for 5 ppm $CH_4$ gas and $CH_3CH_2CH_3$ gas was measured at room temperature by comparing the resistance in air with that in target gases. The highest sensitivity of the ZnO:Ni sensor to $CH_4$ gas and $CH_3CH_2CH_3$ gas was observed at Ni 4 wt%. The response and recovery times of 4 wt% Ni coated ZnO:Ni gas sensors were 14 s and 15 s, respectively.

• Journal of the Korean institute of surface engineering
• /
• v.45 no.5
• /
• pp.193-197
• /
• 2012

The influence of annealing process in an $O_2$ atmosphere on the photoluminescence (PL) spectra properties of ZnS nanowires has been investigated. ZnS nanowires with the diameters approximately 100 nm and the lengths a few tens micrometers were synthesized by evaporating ZnS powders on Si substrates while using an Au thin film as a catalyst. ZnS nanowires had an NBE emission band at 430 nm in the violet region. The emission intensity was improved drastically by a process in which ZnS nanowires were heat-treated at $500^{\circ}C$ in an $O_2$ atmosphere for 45 minutes.

• Journal of Electrochemical Science and Technology
• /
• v.12 no.2
• /
• pp.173-187
• /
• 2021

In the present research, a simple electrochemical sensor based on a carbon paste electrode (CPE) modified with ZnO-Zn₂SnO₄-SnO₂ and graphene (ZnO-Zn₂SnO₄-SnO₂/Gr/CPE) was developed for the direct, simultaneous and individual electrochemical measurement of Acetaminophen (AC), Caffeine (Caf) and Ascorbic acid (AA). The synthesized nano-materials were investigated using scanning electron microscopy, X-ray Diffraction, Fourier-transform infrared spectroscopy, and electrochemical impedance spectroscopy techniques. Cyclic voltammetry and differential pulse voltammetry were applied for electrochemical investigation ZnO-Zn₂SnO₄-SnO₂/Gr/CPE, and the impact of scan rate and the concentration of H⁺ on the electrode's responses were investigated. The voltammograms showed a linear relationship between the response of the electrode for individual oxidation of AA, AC and, Caf in the range of 0.021-120, 0.018-85.3, and 0.02-97.51 μM with the detection limit of 8.94, 6.66 and 7.09 nM (S/N = 3), respectively. Also, the amperometric technique was applied for the measuring of the target molecules in the range of 0.013-16, 0.008-12 and, 0.01-14 μM for AA, AC and, Caf with the detection limit of 6.28, 3.64 and 3.85 nM, respectively. Besides, the ZnO-Zn₂SnO₄-SnO₂/Gr/CPE shows an excellent selectivity, stability, repeatability, and reproducibility for the determination of AA, AC and, Caf. Finally, the proposed sensor was successfully used to show the amount of AA, AC and, Caf in urine, blood serum samples with recoveries ranging between 95.8% and 104.06%.

• The Korean Journal of Ceramics
• /
• v.4 no.3
• /
• pp.207-212
• /
• 1998

By comparison of the experimental results in two systems of ZnO varistors, it's appear that Sb2O3 is the indispensable element for twining in ZnO varistors and the Zn7Sb2O12 spinel acts as the nucleus to form twins. Al2O3 is not the origin of twining in ZnO varistor, but it was found that Al2O3 could strengthen the twining and form a deformation twining by ZnAl2O4 dragging and pinning effect. The inhibition ratios of grain and nonuniformity of two systems ZnO varistors increase with the increase of Al2O3 content. The twins affect the inhibition of grain growth, the mechanism could be explained follow as: twins increase the mobility viscosity of ZrO grain and grain boundary, and drag ZrO grain and liquid grain boundary during the sintering, then the grain growth is inhibited and the microstructure becomes more uniform.

• Journal of the Korean Magnetics Society
• /
• v.18 no.2
• /
• pp.75-78
• /
• 2008

$AB_2X_4$(A, B=Transition Metal, X=O, S, Se) are cubic spinel normal ferrimagnets, in which M ions occupy the tetrahedral sites and Cr ions occupy the octahedral sites. Recently, they have been investigated for behaviour of B site ions and A-B interaction. Polycrystalline $[Co_{0.9}Zn_{0.1}]_A[Cr_{1.98}{^{57}Fe_{0.02}}]_BO_4$ compound was prepared by wet-chemical process. The ferrimagnetic transition was observed around 90K. $M\"{o}ssbauer$ absorption spectra at 4.2K show that the well-developed two sextets are superposed with small difference in hyperfine fields($H_{hf}$). The hyperfine fields of $CoCr_{1.98}{^{57}Fe_{0.02}}O_4$ and $Co_{0.9}Zn_{0.1}Cr_{1.98}{^{57}Fe_{0.02}}O_4$ were determined to be 488, 478 kOe and 486, 468 kOe, respectively. We notice that the one of the magnetic hyperfine field values changes with Zn ion substitution. These results suggest the incommensurate states and spin-reorientation temperature($T_S=18K$) changes with Zn ions substitution below spin-reorientation temperature($T_S=28K$) of $CoCr_{1.98}{^{57}Fe_{0.02}}O_4$

• Journal of the Korean Magnetics Society
• /
• v.5 no.1
• /
• pp.15-20
• /
• 1995

We have prepared 20 kinds of Mn-Zn ferrites as content of CaO(0.1 mol%), NiO(0.0~0.60 mol%) and CoO(0.0~0.8 mol%) adding by the coprecipitation method and studied the magnetic properties as content of CaO, NiO and CoO adding. Initial permeability decrease as the content of NiO and CoO adding increases, while Curie tem~ perature increase as the content of NiO and CoO adding increases. $(H_{c})$, $(B_{s})$ and $(W_{h})$ increase as content of NiO adding increases.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1999.11a
• /
• pp.378-382
• /
• 1999

저 전압용 형광체는 최근에 활발히 연구가 진행되고 있으며 가장 대표적인 형광체가 ZnO Zn 녹색 형광체이다. ZnO : Zn 형광체는 자체발광형 형광체로써 ZnO을 환원분위기 하에서 열처리를 함으로써 얻을 수 있다. 본 연구에서는 자발착화 연소반응법(Glycine Nitrate Process)을 이용하여 ZnO : Zn 분말을 합성하고 형광특성 및 분말특성을 알아보았다. 출발물질로는 Zn Nitrate와 Glycine을 이용하였고 자발연소 반웅이 발생하는데 적절한 글리신의 양을 확인하기 위해서 글리신과 양이온의 비를 변화시키며 ZnO를 합성하였다. 그리고 Zn Excess가 생겨난 앙과 그에 따른 형광특성을 관찰하기 위해 $N_2$ 분위기 에서 각기 50$0^{\circ}C$, 75$0^{\circ}C$, 95$0^{\circ}C$의 온도에서 열처리를 행하였다. 제조된 ZnO 분말의 입자형태와 결정상 태는 SEM과 XRD를 이용하여 분석하였고 TG-DTA를 측정하여 열처리온도에 따른 질량감소(Zn excess)를 관찰하였다. 또 Particle size analyzer로 분말의 크기를 알아보았고 형광체로써의 발광특성을 살펴보기 위해 PL을 이용하여 발광피크를 관찰하였다.