• Transactions on Electrical and Electronic Materials
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• v.9 no.2
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• pp.67-72
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• 2008

Al-doped p-type ZnO thin films were fabricated by RF magnetron sputtering on n-Si (100) and homo-buffer layers in pure oxygen ambient. ZnO ceramic mixed with 2 wt% $Al_2O_3$ was selected as a sputtering target. XRD spectra show that the Al-doped ZnO thin films have ZnO crystal structure. Hall Effect experiments with Van der Pauw configuration show that p-type carrier concentrations are arranged from $1.66{\times}10^{16}$ to $4.04{\times}10^{18}\;cm^{-2}$, mobilities from 0.194 to $198\;cm^2V{-1}s^{-1}$ and resistivities from 0.0963 to $18.4\;{\Omega}cm$. FESEM cross section images of different parts of a p-type ZnO:Al thin film annealed at $800^{\circ}C$ show a compact structure. Measurement for same sample shows that density is $5.40\;cm^{-3}$ which is smaller than theoretically calculated value of $5.67\;cm^{-3}$. Photoluminescence (PL) spectra at 10 K show a shoulder peak of p-type ZnO film at about 3.117 eV which is ascribed to electron transition from donor level to acceptor level (DAP).

• Bulletin of the Korean Chemical Society
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• v.18 no.11
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• pp.1158-1161
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• 1997

The potentiometric methods have been used to determined the protonation constants (logKiH) for the synthesized 1,7,13-trioxa-4,10,16-triazacyclooctadecane-N,N',N''-tri(methylacetic acid) [N3O3-tri(methylacetic acid)] and the stability constants (logKML) of the complexes of divalent and trivalent metal ions with the ligand N3O3-tri(methylacetic acid). The protonation constants of N3O3-tri(methylacetic acid) were 9.70 for logK1H, 9.18 for logK2H, 7.27 for logK3H, 3.38 for logK4H, and 2.94 for logK5H. The stability constants for the complexes of divalent metal ions with N3O3-tri(methylacetic acid) were 10.39 for Co2+, 10.68 for Ni2+, 13.45 for Cu2+, and 13.00 for Zn2+. The order of the stability constants for the complexes of the divalent metal ions with N3O3-tri(methylacetic acid) was Co2+ < Ni2+ < Zn2+ < Cu2+. The stability constants for the complexes of trivalent metal ions with N3O3-tri(methylacetic acid) were 16.20 for Ce3+, 16.40 for Eu3+, 16.27 for Gd3+, and 15.80 for Yb3+. The results obtained in this study were compared to those obtained for similar ligands, 1,7-dioxa-4,10,13-triazacyclopentadecane-N,N',N"-tri(methylacetic acid) and 1,7,13-trioxa-4,10,16-triazacyclooctadecane-N,N',N"-triacetic acid, which have been previously reported.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.178-178
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• 2007

II-VI의 넓은 밴드갭 (3.37 eV)을 가지는 ZnO는 solar cells, transparent conductive electrodes, ultraviolet light emitters, and chemical sensors 등에 응용되고 있다. 특히 고효율 ZnO계 발광 소자 구현을 위하여 MgO (7.7eV), CdO (2.0eV) 등의 고용을 통한 밴드갭을 엔지니어링 하며, 단파장 영역의 광원을 확보하기 위하여 MgO 첨가를 통한 밴드갭 에너지를 증가시키는 방향으로의 연구가 활발하다. 그러나 ZnO의 wurtzite 구조와 MgO의 rocksalt 구조의 상이한 결정구조로 인하여 Mg의 고용한계는 4 at. %, 4.1 eV 알려져 있다. 본 실험에서는 p-type Si (100), c-sapphire (0002)과 GaN 기판 위에 MgO (99.999 %)와 ZnO (99.999 %) 두가지 타겟을 사용하여 RF co-스퍼터링법으로 ZnMgO 박막을 증착 하였다. 이때 ZnO 타겟의 power 밀도는 고정 시키고 MgO 타겟의 power 밀도를 변화 시키며 Mg의 함량을 조절하여 그에 따른 광학적 구조적 특성의 변화를 연구 하였다. 성장된 ZnMgO 박막은 MgO 타겟의 power 밀도가 증가할 때 Mg의 함량이 10 at. %까지 증가 하며, 그에 따른 표면의 거칠기 및 입계 크기가 감소하며, 박막의 성장속도 또한 감소함을 SEM과 AFM을 통하여 알 수 있었다. XRD를 동하여 ZnMgO 박막의 (0002) peak의 위치는 $34.50^{\circ}{\sim}34.7^{\circ}$로 오른쪽으로 이동하며, c-축으로 성장하였음을 알 수 있다. PL과 UV룰 동하여, Mg의 함량이 증가 할수록 박막의 밴드갭 에너지는 3.2 eV에서 4.1 eV 로 증가하였다.

• Applied Chemistry for Engineering
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• v.9 no.7
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• pp.956-960
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• 1998

Cu-Zn and Cu-Zn-Ti catalysts for the steam reforming of methanol were prepared. This reaction was carried out at atmospheric pressure, $250^{\circ}C$, steam/methanol molar ratio 1.5, and contact time 0.1 g-cat.hr/mL-feed. In case of the catalyst with 3 mol% of $TiO_2$, the activity was superior to that of catalysts without $TiO_2$. The reaction products were mainly hydrogen and carbon dioxide. It was found that catalytic activity was not related to specific surface area but affected by metallic copper area which was measured by $N_2O$ decomposition and increased with the addition of $TiO_2$ content. XPS and XRD showed that the oxidation state of zinc was not changed during reaction, but oxidation states of copper existed in Cu(0) or Cu(I).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.68-69
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• 2007

We have prepared p-type ZnO:Al films in pure oxygen ambient on n-type Si (100) and homo buffer layers by RF magnetron sputtering system. Hall effect measurement shows that the film annealed at $600^{\circ}C$ possesses p-type conductivity and the film annealed $800^{\circ}C$ does not. PL spectra show different properties of p- and n-type ZnO film. The corresponding peaks of PL spectra of p- and n-type show at about same positions. The intensities of high photon energy of n-type film on buffer shows decreasing tendency.

• Journal of Sensor Science and Technology
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• v.31 no.5
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• pp.337-342
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• 2022

Hydrogen (H₂) gas is widely preferred for use as a renewable energy source owing to its characteristics such as environmental friendliness and a high energy density. However, H₂ can easily reverse or explode due to minor external factors. Therefore, H₂ gas monitoring is crucial, especially when the H₂ concentration is close to the lower explosive limit. In this study, metal oxide materials and their p-n heterojunctions were synthesized by a hydrothermal-assisted dip-coating method. The synthesized thin films were used as sensing materials for H₂ gas. When the H₂ concentration was varied, all metal oxide materials exhibited different gas sensitivities. The performance of the metal oxide gas sensor was analyzed to identify parameters that could improve the performance, such as the choice of the metal oxide material, effect of the p-n heterojunctions, and operating temperature conditions of the gas sensor. The experimental results demonstrated that a CuO/ZnO gas sensor with a p-n heterojunction exhibited a high sensitivity and fast response time (134.9% and 8 s, respectively) to 5% H₂ gas at an operating temperature of 300℃.

• Applied Chemistry for Engineering
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• v.21 no.3
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• pp.328-332
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• 2010

In this study, porous ZnO sphere and Cu-ZnO composite were synthesized by coprecipitation method in diethylene glycol solvent. The physicochemical properties of as-prepared composite materials were characterized by SEM, XRD, $N_2$-sorption and $H_2$-TPR. A series of porous Cu-ZnO with different Cu contents (0, 6.6, 21.3, 36.4, 54.6, 77.8 wt%) was investigated for CO oxidation activity in a fixed bed reactor system. With increasing Cu content in Cu-ZnO the surface area and micropore volume of Cu-ZnO are decreased and Cu (36.4 wt%)-ZnO shows higher activity for CO oxidation compared to the others.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.524-525
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• 2005

The principal problems in development of dielectric paste materials for PDP(plasma display panel)are PbO free paste and low melting temperature. We prepared PbO free paste from glasses in the system $ZnO-B_2O_3-Bi_2O_3-SiO_2$, DTA, and XRD were used to characterize $ZnO-B_2O_3-Bi_2O_3-SiO$ glasses. In this present study, PbO free paste had thermal expansion of $74\times10^{-7}/^{\circ}C$, DTA transformation point of $470^{\circ}C$, and firing condition of $540^{\circ}C$, 20min.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.2
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• pp.27-37
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• 1997

Photoluminescent and cathodoluminescent charcteristics of inorganic luminescent materials were investigated ot develop possible phosphors for thin film electroluminescent (TFEL) device applications. Mg, Zn, and Photoluminescent and cathodoluminescent charcteristics of inorganic luminescent materials were investigated ot develop possible phosphors for thin film electroluminescent (TFEL) device applications. Mg, Zn, and $Si_3N_4$ powders were used to synthesize $(Mg_xZn_{1-x})SiN_2$ host materials. $Tb_4O_7$ and $Eu_2O_3$ powdrs were added as luminescent centers. Very sharp emission spectra of $Tb^{3+}$ ions were observed from $Mg._5Zn._5SiN_2:Tb$ sampels sintered at $1400^{\circ}C$ for an hour and the maximum intensity of emission spectra occured at wavelength of 550nm (green light). Synthetic conditions of $(Mg_xZn_{1-x})SiN_2:Eu$ phosphors were optimized for the hghest luminescence. The Eu concentrations were varied from 0.2% to 1.6%. Before firing, the powders were mixed using ballmills, methanol, acetone, or D.I. water. The Mg/Zn ratio also were varied from x=0.3 to x=0.7. The maximum PL intensity was obtained from a sample with 1.2% Eu concentration and the powder was mixed with methanol and dried before firing. The maximum intensity of the emission spectra occurred t the wavelength of 470nm(blue light). TFEL devices fabricated by using sputter deposition of $(Mg._3Zn._7)SiN_2:Eu$ phosphor layer showed yellowish white emission at the phosphor field of 2MV/cm.

• Korean Journal of Materials Research
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• v.20 no.11
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• pp.623-627
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• 2010

Semiconducting metal oxides have been frequently used as gas sensing materials. While zinc oxide is a popular material for such applications, structures such as nanowires, nanorods and nanotubes, due to their large surface area, are natural candidates for use as gas sensors of higher sensitivity. The compound ZnO has been studied, due to its chemical and thermal stability, for use as an n-type semiconducting gas sensor. ZnO has a large exciton binding energy and a large bandgap energy at room temperature. Also, ZnO is sensitive to toxic and combustible gases. The NO gas properties of zinc oxide-single wall carbon nanotube (ZnO-SWCNT) composites were investigated. Fabrication includes the deposition of porous SWCNTs on thermally oxidized $SiO_2$ substrates followed by sputter deposition of Zn and thermal oxidation at $400^{\circ}C$ in oxygen. The Zn films were controlled to 50 nm thicknesses. The effects of microstructure and gas sensing properties were studied for process optimization through comparison of ZnO-SWCNT composites with ZnO film. The basic sensor response behavior to 10 ppm NO gas were checked at different operation temperatures in the range of $150-300^{\circ}C$. The highest sensor responses were observed at $300^{\circ}C$ in ZnO film and $250^{\circ}C$ in ZnO-SWCNT composites. The ZnO-SWCNT composite sensor showed a sensor response (~1300%) five times higher than that of pure ZnO thin film sensors at an operation temperature of $250^{\circ}C$.