• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.204.2-204.2
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• 2013

Wide band gap II-VI semiconductors have attracted the interest of many research groups during the past few years due to the possibility of their applications in light-emitting diodes and laser diodes. Among the II-VI semiconductors, ZnO is an important optoelectronic device material for use in the violet and blue regions because of its wide direct band gap (Eg ~3.37 eV) and large exciton binding energy (60 meV). F-doped ZnO (FZO) and undoped ZnO thin films were grown onto quartz substrate by the sol-gel spin-coating method. The doping level in the solution, designated by F/Zn atomic ratio of was varied from 0 to 5 in 1 steps. To investigate the effects of the structure and optical properties of FZO thin films were investigated using X-ray diffraction (XRD), UV-visible spectroscopy, and photoluminescence (PL). In the XRD, the residual stress, FWHM, bond length, and average grain size were changed with increasing the doping concentration. For the PL spectra, the high INBE/IDLE ratio of the FZO thin films doping concentration at 1 at.% than the other samples.

• 열처리공학회지
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• 제31권4호
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• pp.171-179
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• 2018

Copper powder dispersed with 4 vol.% of $Cr_2O_3$ was successfully produced by a simple milling at 210 K with a mixture of $Cu_2O$, Cu and Cr elemental powders, followed by Hot Pressing (HP) at 1123 K and 50 MPa for 2h to consolidate the milled powder. The microstructure of the HPed material was characterized by standard metallographic techniques such as XRD (X-ray Diffraction), TEM and STEM-EDS. The results of STEMEDS analysis showed that the HPed materials comprised a mixture of nanocrystalline Cu matrix and $Cr_2O_3$ dispersoid with a homogeneous bimodal size distribution. The mechanical properties of the HPed materials were characterized by micro Vickers hardness test at room temperature. The thermodynamic considerations on the heat of formation, the incubation time to ignite MSR (Mechanically induced Self-sustaining Reaction), and the adiabatic temperature for the heat of displacement reaction between the oxide-metal are made for the delayed formation of $Cr_2O_3$ dispersoid in terms of MSR suppression. The results of TEM observation and hardness test indicated that the relatively large dispersoids in the HPed materials are attributed to the significant coarsening for the high temperature consolidation; this leads to the low Vickers hardness value. Based on the thermodynamic calculation for the operating processes with a limited number of parameters, the formation kinetics and coarsening of the $Cr_2O_3$ dispersoid are discussed.

• Advances in materials Research
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• 제2권2호
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• pp.77-91
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• 2013

High quality nanoparticles of neodymium barium niobium ($NdBa_2NbO_6$) perovskites have been synthesized using an auto ignition combustion technique for the first time. The nanoparticles thus obtained have been characterized by powder X-ray diffraction, thermo gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, Raman spectroscopy and transmission electron microscopy. UV-Visible absorption and photoluminescence spectra of the samples are also recorded. The structural analysis shows that the nano powder is phase pure with the average particle size of 35 nm. The band gap determined for $NdBa_2NbO_6$ is 3.9 eV which corresponds to UV-radiation for optical inter band transition with a wavelength of 370nm. The nanopowder could be sintered to 96% of the theoretical density at $1325^{\circ}C$ for 2h. The ultrafine cuboidal nature of nanopowders with fewer degree of agglomeration improved the sinterability for compactness at relatively lower temperature and time. During the sintering process the wide band gap semiconducting behavior diminishes and the material turns to a high permittivity dielectric. The microstructure of the sintered surface was examined using scanning electron microscopy. The striking value of dielectric constant ${\varepsilon}_r=43$, loss factor tan ${\delta}=1.97{\times}10^{-4}$ and the observed band gap value make it suitable for many dielectric devices.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.441-441
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• 2009

Dye-sensitized solar cells (DSSCs) have been widely investigated as a next-generation solar cell because of their simple fabrication process and low coats. The cells use a porous nanocrystalline TiO2 matrix coated with a sensitizer dye that acts as the light-harvesting element. The photo-exited dye injects electrons into the $TiO_2$ particles, and the oxide dye reacts with I- in the electrolyte in regenerative cycle that is completed by the reduction of $I_3^-$ at a platinum-coated counter electrode. Since $TiO_2$ porous film plays a key role in the enhancement of photoelectric conversion efficiency of DSSC, many scientists focus their researches on it. Especially, a high light-to-electricity conversion efficiency results from particle size and crystallographic phase, film porosity, surface structure, charge and surface area to volume ratio of porous $TiO_2$ electrodes, on which the dye can be sufficiently adsorbed. Effective treatment of the photoanode is important to improve DSSC performance. In this paper, to obtain properties of surface and dispersion as nitric acid treated $TiO_2$ photoelectrode was investigate. The photovoltaic characteristics of DSSCs based the electrode fabricated by nitric acid pre-treatment $TiO_2$ materials gave better performances on both of short circuit current density and open circuit voltage. We compare dispersion of $TiO_2$ nanoparticles before and after nitric acid treatment and measured Ti oxidized state from XPS. Low charge transfer resistance was obtained in nitric acid treated sample than that of untreated sample. The dye-sensitized solar cell based on the nitric acid treatment had open-circuit voltage of 0.71 V, a short-circuit current of 15.2 mAcm-2 and an energy conversion efficiency of 6.6 % under light intensity of $100\;mWcm^{-2}$. About 14 % increases in efficiency obtained when the $TiO_2$ electrode was treated by nitric acid.

• 한국결정성장학회지
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• 제12권5호
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• pp.240-246
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• 2002

티타늄 나프테네이트를 출발 원료로 사용하고 스핀코팅-열분해법을 이용하여 소다-라임-실리카 슬라이드 유리기판 위에 $TiO_2$ 박막을 제조하였다. 도포된 박막은 $500^{\circ}C$로 10분간 공기분위기에서 전열처리를 행하였고, 최종 열처리는 500, 550과 $600^{\circ}C$로 30분간 공기분위기에서 각각 행하였다. X-선 회절분석법을 이용하여 박막의 결정화도를 조사하였고, 전계 방출 주사형 전자 현미경과 원자간력 현미경을 이용하여 $TiO_2$ 박막의 표면미세구조와 표면 거칠기를 조사하였다. 550 과 $600^{\circ}C$로 최종 열처리한 박막의 X-선 회절분석 결과, 아나타제 상만이 존재하였다. 500과 $550^{\circ}C$로 열처리한 박막의 표면은 균질하였으나, 열처리온도가 $600^{\circ}C$로 증가함에 따라서, 박막의 표면에는 바늘모양의 상이 3차원적으로 성장하였다. 모든 박막에 있어서 가시영역에서의 투과율은 500nm에서 90% 이상의 높은 값을 나타냈다. 박막의 광촉매특성을 조사하기 위하여 stearic acid가 코팅된 박막에 365nm 파장의 UV를 2.4mW/$\textrm{cm}^2$의 강도로 조사하여 C-H모드에 대한 IR 흡수단의 변화를 관찰하였다.

• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2012년도 추계학술대회
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• pp.1000-1002
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• 2012

고감도 바이오센서를 제작하기 위해서는 높은 생체적합성 및 물리적/화학적 안정성을 가진 재질이 필요하며 다양한 재질들이 바이오산업에 응용 가능 여부를 평가 받고 있다. 근래, 카본재질의 다이아몬드 및 그라핀 박막은 많은 주목을 받고 있으며 그 가능성이 부분적으로 평가되고 있다. 다이아몬드는 넓은 전위창(3.0~3.5 V), 낮은 누설전류, 물리/화학적 안정성과 같은 전기화학적이고 생물학적 응용의 장점이 있으며, 그라핀 또한 물리/화학적 안정성과 전도성이 뛰어난 장점을 가지고 있다. 본 논문에서는 나노결정 다이아몬드, 마이크로결정 다이아몬드, 그라핀 및 세포배양판 표면에 사람의 신경세포(SH-SY5Y)를 배양하고 세포독성시험(MTT assay)을 이용하여 재질에 따른 배양 특성을 비교 평가하였다. 그 결과 기존 사용되고 있는 세포배양판과 카본재질은 세포 배양 특성이 유사하였다. 우리는 본 연구결과를 바탕으로 카본재질이 향후 바이오센서와 같은 바이오산업에 응용될 것으로 예상된다.

• Korean Chemical Engineering Research
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• 제51권4호
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• pp.411-417
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• 2013

리튬 2차전지 음전극 활물질로 사용하기 위해, 실리콘(Si) 나노입자(평균입경 100 nm, 0~50 wt%)와 흑연 분말(평균입경 $15{\mu}m$)을 사용하여 볼밀링법으로 흑연-실리콘 복합체 분말을 제조하고 그 전기화학적 특성을 조사하였다. 실리콘 함량이 증가할수록 흑연은 볼밀링에 의해 입경이 작아지고 무정형 특성을 보이는 반면, 실리콘 입자는 나노결정성의 변화 없이 무정형 흑연 내에 싸여진 형태로 유지되었다. 저속 사이클릭 볼타메트리 특성상 0.2~0.35 V와 0.55~0.6 V에서 각각 흑연과 실리콘의 전형적 산화피크가 검출되었고 가역성도 우수(첫 사이클 제외)한 반면, 고속 거동에서는 사이클 반복에 따른 비가역성이 현저하게 나타났다. 또한 충방전 초기에는 큰 비가역 용량이 나타나지만 사이클 경과에 따라 감소하였으며, 특히 실리콘을 20 wt% 정도 포함하는 복합체가 50 사이클에서 약 485 mAh $g^{-1}$의 포화된 방전용량을 나타내었다. 이것은 실리콘을 싸고 있는 흑연의 무정형 상이 실리콘-리튬의 합금/탈합금에 따른 체적 변화를 안정적으로 완충할 수 있는 모폴로지가 재료의 적정 조성(흑연:실리콘=8:2 w/w)에 의해 형성되었기 때문이다.

• Bulletin of the Korean Chemical Society
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• 제30권12호
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• pp.3011-3015
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• 2009

Structural and thermo-analytical studies were carried out to understand the phase formation kinetics of the single phase $Bi_5Ti_3FeO_{15}$ (BTFO) nanocrystals in $Bi_2O_3-Fe_2O_3-TiO_2$, during the polymerized complex (PC) synthesis method. The crystallization of Aurivillius phase $Bi_5Ti_3FeO_{15}$ layered perovskite was found to be initiated and achieved under the temperature conditions in the range of ${\sim}$800 to 1050$^{\circ}C$. The activation energy for grain growth of $Bi_5Ti_3FeO_{15}$ nanocrystals (NCs) was very low in case of NCs formed by PC (2.61 kJ/mol) than that formed by the solid state reaction (SSR) method (10.9 kJ/mol). The energy involved in the phase transformation of Aurivillius phase $Bi_5Ti_3FeO_{15}$ from $Bi_2O_3-Fe_2O_3-TiO_2$ system was ${\sim}$ 69.8 kJ/mol. The formation kinetics study of $Bi_5Ti_3FeO_{15}$ synthesized by SSR and PC methods would not only render a large impact in the nanocrystalline material development but also in achieving highly efficient visible photocatalysts.