• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.439-439
• /
• 2012

ZnO 나노로드는 큰 밴드갭 에너지(~3.37 eV)와 60 meV의 높은 엑시톤 결합 에너지(exciton binding energy)를 갖고 있으며, 우수한 전기적, 광학적 특성을 지닌 1차원 나노구조의 금속산화물로서 태양전지 및 광전소자 널리 응용되고 있다. 이러한 ZnO 나노로드를 성장하는 방법 중에 전기화학증착법(electrochemical deposition method)은 전도성 물질위에 증착된 시드층(seed layer)을 성장용액에 담그어 전압을 인가하여 만들기 때문에 기존의 수열합성법(hydrothermal method), 졸-겔 법(sol-gel method)보다 비교적 간단한 공정과정으로 저온에서 빠르게 물질을 성장시킬 수 있는 장점이 있다. 한편, 디스플레이 산업에서 ITO (indium tin oxide)는 투명 전도성 산화물(transparent conductive oxide)로써 가시광 파장영역에서 높은 투과율과 전도성을 가지며, 액정디스플레이, LED (Light emitting diode), 태양전지 등의 다양한 소자에 투명전극 재료로 쓰이고 있다. 또한 최근 ITO를 유연한 PET (polyethylene terephthalate) 기판 위에 증착은 얇고, 가볍고, 휘어지기 쉬워 휴대하기 편하기 때문에 차세대 광전자소자 응용에 가능성이 크다. 본 연구에서는 ZnO 나노로드를 ITO/PET 기판위에 전기화학증착법으로 성장하여, 구조적 및 광학적 특성을 분석하였다. 시드층을 형성하기 위해 RF 마그네트론 스퍼터를 이용하여 ~20 nm 두께의 ZnO 박막을 증착시킨 후, zinc nitrate와 hexamethylenetetramine이 포함된 수용액에 시료를 담그어 전압을 인가하였다. 용액의 농도와 인가전압을 조절하여 여러 가지 성장조건에 대한 ZnO 나노로드의 구조적, 광학적 특성을 비교하였다. 성장된 시료의 형태와 결정성을 조사하기 위해, field-emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD)을 사용하였으며, UV-vis-NIS spectrophotometer, photoluminescence (PL) 측정장비를 사용하여 광학적 특성을 분석하였다.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.400-400
• /
• 2012

산화물 반도체는 넓은 에너지갭을 가지고 높은 이동성과 높은 투명성을 가지기 때문에 초고 속 박막 트랜지스터(Thin film transistor; TFT)에 많이 응용되고 있다. 그러나 ZnO 및 $In_2O_3$ 산화물 반도체를 박막트랜지스터에 사용할 경우 소자가 불안정하여 전기적 성질이 저하되고 문턱전압의 이동이 일어난다. TFT에 사용되는 산화물 반도체로는 GaInZnO, ZrInZnO, HfInZnO 및 GaSnZnO의 전기적 특성에 관한 연구가 많이 되었다. 그러나 titanium-indium-zinc-oxide (TIZO) TFT에 대한 연구는 비교적 적게 수행 되었다. 본 연구에서는 TFTs의 안정성을 향상하기 위하여 TFT의 채널로 사용되는 TiInZnO를 형성하는데 간단한 제조 공정과 낮은 비용의 용액 증착방법을 사용하였다. 졸-겔 전해액은 Titanium (IV) isopropoxide $[Ti(OCH(CH_3)_2)_4]$, 0.1 M Zinc acetate dihydrate $[Zn(CH_3COO)_2{\cdot}2H_2O]$ 그리고 indium nitrate hydrate $[In(NO_3)_3{\cdot}xH_2O]$을 2-methoxyethanol의 용액에 합성하였다. $70^{\circ}C$에서 한 시간 동안 혼합 하였다. Ti의 몰 비율은 10%, 20% 및 40% 로 각각 달리하여 제작하였다. $SiO_2$층 위에 2,500 rpm 속도로 25초 동안 스핀 코팅하여 TFT를 제작하였다. TIZO 박막에 대한 X-선 광전자 스펙트럼 관측 결과는 Ti 몰 비율이 증가함에 따라 Ti 2p1/2피크의 세기가 증가함을 보여주었다. TiZO 박막에 Ti 원자를 첨가하면 $O^{2-}$ 이온이 감소하기 때문에 전하의 농도가 변화하였다. 전하 농도의 변화는 TiZO 채널을 사용하여 제작한 TFT의 문턱전압을 양 방향으로 이동 하였으며 off-전류를 감소하였다. TiZO 채널을 사용하여 제작한 TFT의 드레인 전류-게이트 전압 특성은 on/off비율이 $0.21{\times}107$ 만큼 크며 이것은 TFT 소자로서 우수한 성능을 보여주고 있다.

• Korean Journal of Materials Research
• /
• v.24 no.1
• /
• pp.48-52
• /
• 2014

The Mg-enriched magnesium aluminum silicate (MAS) glass is known for its higher mechanical strength and chemical resistance. Among such glasses, cordierite ($Mg_2Al_4Si_5O_{18}$) is well known to have a low thermal expansion and low melting point. Polycrystalline engineering ceramics such as alumina can be strengthened by a surface modification with low thermal expansion materials. The present study involves the synthesis of cordierite by a sol-gel process and investigates the effect of glass penetration on the surface of alumina. The cordierite powders were prepared from $Al(OC_3H_7)_3$, $Mg(OC_2H_5)_2$ and tetraethyl orthosilicate by hydrolysis and condensation reaction. The cordierite powders were characterized by X-ray diffraction (XRD, Rigaku), scanning electron microscope (SEM, JEOL: JSM-5610), energy dispersive spectroscopy (EDS, JEOL: JSM-5610), and universal testing machine (UTM, INSTRON). The X-ray diffraction patterns showed that the synthesized particles were ${\mu}$-cordierite calcined at $1100^{\circ}C$ for 1 h. The shape of synthesized cordierite was changed from ${\mu}$-cordierite to ${\alpha}$-cordierite with increasing calcination temperature. Synthesized cordierite was used for surface modification of alumina. Cordierite powders penetrated deeply into the alumina sample along grain boundaries with increasing temperature. The results of surface modification tests showed that the strength of the prepared alumina sample increased after surface modification. The strength of a surface modified with synthesized cordierite increased the most, to about 134.6MPa.

• Membrane Journal
• /
• v.11 no.3
• /
• pp.116-123
• /
• 2001

Polyimide-silica hybrid membranes were prepared and the effect of silica content on the structural properties and the gas transport properties was studied. The hybrid membranes were obtained by the sol-gel process starting from 1,2,4,5-benzenetetracarboxylic dianhydride(PMDA), 4,4`-diamino- diphenyl oxide(ODA) and tetraethoxysilane(TEOS) in N,N` dimethylacetatmide (DMAc) solvent. The structural characterizations of the membrane were performed by FT-IR, EDX, TGA and SEM. The gas permeation experiments with ${N_2}, {O_2}, {H_2}, {CO_2}and ${CH_4}$ were carried out at the temperature of $25^{\circ}C$ and in the range of pressure from 3atm to 7atm. the hybrid membranes showed higher thermal stability than PI membranes. The silica patricles were uniformly embedded in the polyimide matrix and the size of silica particles increased with increasing silica content. The permeability coefficients of ${N_2}, {O_2}, {H_2}, {CO_2}and ${CH_4}$ increased with increasing silica content but the diffusion coefficients might appear to be a result of a solubility enhancement. In spite of the permeability enhancement, an increase in the selectivities of ${H_2}/{N_2}, ${H_2}/{O_2} and ${H_2}/{CO_2} was observed.

• Korean Journal of Materials Research
• /
• v.9 no.12
• /
• pp.1181-1187
• /
• 1999

PZT(53/47) precursor 1M sols were prepared using a diol based Sol-Gel process, and thin films were deposited by spin coating onto Pt/Ti/$SiO_2$/Si substrates. With a single coating, final film thickness of aproximately 0.9${\mu}m $ was achieved from diol-based PZT sol. Since PZT crystallized in a ferroelectric perovskite phase from an intermediate nonferroelectric pyrochlore phase, the effects of the presence of perovskite PZT seeds on the phase transformation of PZT were investigated. Seeded PZT films were prepared from the seeded PZT 1M sols in which seeds with less than 0.2${\mu}m $ in size and 1wt% were dispersed in n-propanol before mixing with the PZT stock solution. The seeding effects were confirmed by the fact that the formation temperature of perovskite phase decreased by 50$^{\circ}C$ with less than 1wt% seeds.

• Korean Journal of Materials Research
• /
• v.26 no.2
• /
• pp.73-78
• /
• 2016

$TiO_2$ nanoparticles were synthesized by a sol-gel process using titanium tetra isopropoxide as a precursor at room temperature. Ag-doped $TiO_2$ nanoparticles were prepared by photoreduction of $AgNO_3$ on $TiO_2$ under UV light irradiation and calcinated at $400^{\circ}C$. Ag-doped $TiO_2$ nanoparticles were characterized for their structural and morphological properties by X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). The photocatalytic properties of the $TiO_2$ and Ag-doped $TiO_2$ nanoparticles were evaluated according to the degree of photocatalytic degradation of gaseous benzene under UV and visible light irradiation. To estimate the rate of photolysis under UV (${\lambda}=365nm$) and visible (${\lambda}{\geq}410nm$) light, the residual concentration of benzene was monitored by gas chromatography (GC). Both undoped/doped nanoparticles showed about 80 % of photolysis of benzene under UV light. However, under visible light irradiation Ag-doped $TiO_2$ nanoparticles exhibited a photocatalytic reaction toward the photodegradation of benzene more efficient than that of bare $TiO_2$. The enhanced photocatalytic reaction of Ag-doped $TiO_2$ nanoparticles is attributed to the decrease in the activation energy and to the existence of Ag in the $TiO_2$ host lattice, which increases the absorption capacity in the visible region by acting as an electron trapper and promotes charge separation of the photoinduced electrons ($e^-$) and holes ($h^+$). The use of Ag-doped $TiO_2$ nanoparticles preserved the option of an environmentally benign photocatalytic reaction using visible light; These particles can be applicable to environmental cleaning applications.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.24 no.3
• /
• pp.99-105
• /
• 2014

$LiCoO_2$ thin film have received attention as cathodes of thin-film microbatteries. In this study, $LiCoO_2$ thin films were synthesized on Au substrates by sol-gel spin coating method and electrochemical properties were investigated under annealing temperature and time. The phycochemical properties of $LiCoO_2$ thin film were investigated by X-ray diffraction, scaning electron microscopy and atomic force microscopy. The electrochemical properties were characterized using galvanostatic charging/discharging cycling tests. From X-ray diffraction, as-grown films annealed at $550^{\circ}C$ and $750^{\circ}C$ are presumed to be spinel structure and a single phase of the layered-rock-salt, respectively. The RMS roughness and grain size of the films which annealed at $750^{\circ}C$ has similar values for annealing time 10 and 30 min, while for annealing time 120 min surface roughness, grain size increase and pore appearance were observed. The first discharge capacity of $LiCoO_2$ thin films annealed at $750^{\circ}C$ for 10, 30 and 120 min is about 54.5, 56.8 and $51.87{\mu}Ah/cm^2{\mu}m$, respectively. Corresponding capacity retention at 50th cycle is 97.25, 76.69, 77.19%.

• Membrane Journal
• /
• v.6 no.2
• /
• pp.101-108
• /
• 1996

The oxidation/degradation efficiency of formic acid through the photoelectrochemical reaction has been investigated as a basic research in order to develope the process for degrading toxic organic compounds dissolved in water. A $TiO_{2}$ photoelectro-membrane reactor for purification of water, in which filtration as well as photoelectrocatalytic oxidation of organic compounds could be carried out simultaneously, was developed. Porous $SnO_{2}$ tubes prepared by slip casting and commercial porous stainless steel tubes, being electrically conductive, were used as not only supports but also working electrodes. The UV light with the wavelength of 365 nm was applied as a light source for photocatalytic reactions. The photoelectrocatatytic composite membranes were prepared by coating the support surface with the $TiO_{2}$ sol of pH 1.45. The oxidation efficiency of formic acid increased with the reaction time and the applied voltage, but was almost independent of the solution flux. The results showed that more than 90% of formic acid could he dograded at 27V using the $TiO_{2}$/stainless steel composite membrane, while about 77% in case of the $TiO_{2}/SnO_{2}$ Composite membrane. It was also concluded that the oxidation efficiencies of formic acid could be significantly improved by about 6~7 times by the photoelectrochemical reaction in comparison with those by the photocatalytic reaction only.

• Korean Chemical Engineering Research
• /
• v.50 no.2
• /
• pp.292-299
• /
• 2012

We made 8 wt% silica dispersion system with fumed silica and photo curable acrylic monomer by beads mill process. These dispersions could be applied in organic/inorganic hybrid coating systems. These dispersions could be applied in organic/inorganic hybrid coating systems. The 4 species of photo curable acrylic monomer which was presence of hydroxyl group, different solubility parameter, and different molecular size were used in the silica dispersions. Stability of polar solvent, isopropyl alcohol, in silica dispersions was investigated. We investigated the stability of silica dispersions by using steady-state and dynamic rheology. As the monomer has hydroxyl group increased in mono and binary monomer silica dispersions, they showed non flocculated stable sol (loss modulus (G")> storage modulus (G')). When polar solvent IPA was added into slightly flocculated silica dispersions, they changed to non flocculated stable sol.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.29 no.2
• /
• pp.71-76
• /
• 2019

Recently, the demand of labels for product management is increasing, as the automation system becomes more common. the development of functional labels which can be used in various environments has been rapidly proceeded. In the case of a printed circuit board, barcode labels with thermal and chemical stability are generally used due to a high temperature process around $300^{\circ}C$ and chemical cleaning in the manufacturing process. However, the yellowing phenomenon of labels that can lower the resolution of printed barcode image still needs to be prevented. In this study, we prepared a composite coating layer using a silica inorganic binder and a titanium dioxide white pigment, and developed a functional labels with thermal and chemical stability. The silica inorganic binder prepared by sol-gel process was confirmed to show excellent adhesion and abrasion resistance with the polyimide film. The white coating layer could be formed on the polyimide film with mixing the silica inorganic binder and titanium dioxide white pigment. The prepared coating layer showed excellent whiteness and glossiness above $400^{\circ}C$. The excellent chemical stability of the coating layer was also confirmed by the chemical treatment with acidic (pH 1.6) and basic (pH 13.6) cleaners.