• Journal of the Korean Ceramic Society
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• v.51 no.4
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• pp.362-366
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• 2014

Dye-sensitized solar cells (DSSCs) were synthesized using a $0.25cm^2$ area of a $TiO_2$ nanoparticle layer as the electrode and platinum (Pt) as the counter electrode. The $TiO_2$ nanoparticle layers (12 to 22 ${\mu}m$) were screen-printed on fluorine-doped tin oxide glass. Glancing angle X-ray diffraction results indicated that the $TiO_2$ layer is composed of pure anatase with no traces of rutile $TiO_2$. The Pt counter electrode and the ruthenium dye anchored $TiO_2$ electrode were then assembled. The best photovoltaic performance of DSSC, which consists of a $18{\mu}m$ thick $TiO_2$ nanoparticle layer, was observed at a short circuit current density ($J_{sc}$) of $14.68mA{\cdot}cm^{-2}$, an open circuit voltage ($V_{oc}$) of 0.72V, a fill factor (FF) of 63.0%, and an energy conversion efficiency (${\eta}$) of 6.65%. It can be concluded that the electrode thickness is attributed to the energy conversion efficiency of DSSCs.

• Korean Journal of Optics and Photonics
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• v.19 no.1
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• pp.73-79
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• 2008

We propose a novel metal-waveguide structure for sustaining long-range surface-plasmon-polaritons (LRSPP). The LRSPP waveguides are composed basically of two asymmetric metal layers: a very thin, finite-width metal strip on top of a metal slab with a dielectric gap in between them. Mode cut-off of LRSPPs excited on the double-metal waveguides is characterized by consistently investigating their dispersion relations and mode profiles. We also confirm experimentally the existence of low-loss, well-confined LRSPP modes by measuring far-field outputs emerging from an edge of the asymmetric double-metal waveguides. In the experiment, we have fabricated several types of SPP waveguide devices including straight lines, S-bend, and Y-branch consisting of gold strips (20 nm-thick, $5{\mu}m$-wide). Overall propagation loss of the proposed double-metal waveguides is quite comparable to that of single metal-strip waveguides, in addition the mode sizes can be tuned by increasing the core-insulator gap between the metal layers to get a higher coupling efficiency with a single-mode fiber in telecom wavelength. The proposed LRSPP waveguides may open up realization of SPP-waveguide sensors or nonlinear SPP-devices by replacing the core-insulator with a bio-fluid or a nonlinear medium.

• Korean Journal of Optics and Photonics
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• v.6 no.4
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• pp.259-265
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• 1995

Antireflection coatings on optical lenses commertially available in domestic market are optically analyzed. Transmission spectra and reflection spectra are collected using spectrophotometers. The apparent absorption spectra around the absorption band edge are dominated by the substrate absorption. The reflection spectra and the apparent absorption spectra at visible region between 400nm and 700nm show very strong correlation to each other except a couple samples. The discrepency observed in the latters are due to an increased absorption in visible region by the substrate, which is negative effect of these samples. An antireflection coating consisted of $SiO_2/TiO_2/SiO_2/ZrO_2/Cr$ is made on c-Si substrate for spectroscopic ellispometry analysis. A film-by-film coating is accomplished and between each film deposition, ex-situ spectroscopic ellipsometry measurements are made. The analysis of the spectroscopic ellipsometry data reveals that the average film densities of $ZrO_2$ and $TiO_2$ reach only 80% of their respective packing densities and thick films are inhomogeneous along film growth direction. Discussions are made toward in-situ, real-time monitoring of the film growth so that a real-time feedback is possible to achieve a post-correction to minor deviations occured in the previous step. step.

• Korean Journal of Materials Research
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• v.14 no.4
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• pp.235-238
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• 2004

The LT-MBE (low temperature molecular beam epitaxy) allows to dope GaAs with Mn over its solubility limit. A 75 urn thick GaMnAs layers are grown on a low temperature grown LT-GaAs buffer layer at a substrate temperature of $260^{\circ}C$ by varying Mn contents ranged from 0.03 to 0.05. The typical growth rate for GaMnAs layer is fixed at 0.97 $\mu\textrm{m}$/h and the V/III ratio is varied from 25 to 34. The electrical and magnetic properties are investigated by Hall effect and superconducting quantum interference device(SQUID) measurements, respectively. Double crystal X-ray diffraction(DCXRD) is also performed to investigate the crystallinity of GaMnAs layers. The $T_{c}$ of the $Ga_{l-x}$ /$Mn_{x}$ As films grown by LT-MBE are enhanced from 38 K to 65 K as x increases from 0.03 into 0.05 whereas the $T_{c}$ becomes lower to 45 K when the V/III ratio increases up to 34 at the same composition of x=0.05. This means that the ferromagnetic exchange coupling between Mn-ion and a hole is affected by the growth condition of the enhanced V/III ratio in which the excess-As and As-antisite defects may be easily incorporated into GaMnAs layer.

• Journal of the Korean Ceramic Society
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• v.53 no.6
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• pp.641-646
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• 2016

The effects of water addition on $Y_2O_3$ coatings or thick films prepared by plasma suspension spray (SPS) have been investigated. Water addition in suspension media was found to be effective to control the color of a $Y_2O_3$ coating prepared by SPS. The color changed with water addition at the shortest stand-off distance of 50 mm even if samples had the same crystalline phase. Change was not correlated with fragmentation behavior of liquid suspension inside the plasma jet. Water content over 50 vol% was found to produce unmelted particles, indicating that water suppressed heat transfer to the particles. However, plasma jet temperature was not affected. Instead, the coating fabricated with water addition has higher oxygen and lower carbon content compared to these characteristics of the coating without water addition. This was attributed to the retarded complete evaporation of liquid media from the suspension droplet, resulting in inhibition of excessive heating and evaporation of the molten $Y_2O_3$ droplet. In this regard, crystalline phase development with respect to stand-off distance and water addition was discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.347-347
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• 2008

본 연구에서는 별도의 소결과정 없이 상온에서 치밀한 복합체 후막의 제조가 가능한 Aerosol Deposition Method (ADM)를 이용하여 SOP를 실현시키기 위한 기판 재료로서 알루미나 기반의 알루미나-폴리이미드 복합체를 제조하고 그 특성에 대한 평가를 진행하였다. SEM 관찰결과 기공이 거의 없고 치밀한 구조의 복합체가 상온에서 성공적으로 형성되었음이 확인되었다. XRD 와 FT-IR 분석 결과 알루미나와 폴리이미드 모두가 복합체에 존재함을 확인할 수 있었다. 또한 XRD 분석결과 출발 원료에 폴리이미드 함량이 증가할수록 ADM으로 제조된 복합체 내부의 알루미나의 결정자 크기가 증가하는 결과를 보였다. 복합체의 알루미나 충진율을 확인하기 위한 간접적인 방법으로 복합체 후막을 연마하여 복합체 내부를 노출시킨 후 폴리이미드의 용매인 Methyl Ethyl Ketone으로 폴리이미드를 식각시켜 남아있는 알루미나 영역을 관찰한 SEM 분석결과 알루미나가 60% 이상 복합체의 대부분을 이루고 있다는 사실을 관찰할 수 있었다. 복합체의 미세구조를 확인하기 위하여 TEM 분석결과 기존에 보고된 ADM으로 제조된 알루미나 후막의 결정자 크기인 10~20 nm 보다 큰 100 nm 범위의 결정자 크기를 관찰 할 수 있었다. 유전특성평가 결과 유전율과 tan$\delta$는 1 MHz에서 각각 9.0, 0.0072로서 알루미나만을 원료로 성막시킨 후막의 유전 특성을 크게 떨어뜨리지 않으며 알루미나 후막과 유사한 결과를 보였다. 추후 복합체의 균일성 향상 및 고주파 영역의 유전 특성 향상을 통하여 세라믹의 취성 및 가공성이 개선된 3 차원 적층 기판재료로의 응용이 기대될 것으로 전망된다.

• Journal of the Korean Magnetics Society
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• v.23 no.1
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• pp.12-17
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• 2013

Nanocrystalline nickel (Ni) tick films were synthesized by direct current electrodeposition at current density from 1 to $30mA/cm^2$ and pH = 4. The basic composition of the bath, which was prepared by dissolving Ni metal particles in HCl, was 0.2M Ni ions. The effects of the current density on the average grain size of Ni deposits were investigated by XRD and SEM techniques. The results showed that the surface roughness was decreased as the saccharin addition was increased up to 2 g/l. The experimental results showed that the increase in the current density had a considerable effect on the average grain size of the Ni deposits. The perpendicular magnetization was raised as the thickness of coating layer was increased.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.8
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• pp.560-564
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• 2003

Thick oxide layer was fabricated by anodic reaction and complex oxidation performed by combining low temperature thermal oxidation (50$0^{\circ}C$, 1 hr at $H_2O$/O$_2$) and a RTO (rapid thermal oxidation) process (105$0^{\circ}C$, 1 min). Electrical characteristics of OPSL (oxidized porous silicon layer) were almost the same as those of thermal silicon dioxide prepared at high temperature. The leakage current through the OPSL of 20${\mu}{\textrm}{m}$ thickness was about 100 - 500 ㎀ in the range 0 V to 50 V. The average value of breakdown field was about 3.9 MV/cm. From the XPS analysis, surface and internal oxide films of OPSL prepared by complex process were confirmed completely oxidized and also the role of RTO process was important for the densification of PSL (porous silicon layer) oxidized at low temperature.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.5
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• pp.9-15
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• 2000

The 3 ${\mu}{\textrm}{m}$-thick PVDF (polyvinylidene fluoride) thin film have been prepared using physical vapor deposition with electric field, and its FT-IR spectrum, dielectric property and electric conduction phenomenon have been investigated. Since the characteristic peaks are detected at 509.45 ［$cm^{-1}$ /］ and 1273.6 ［$cm^{-1}$ /］in the FT-IR spectrum, we are confirmed that the $\beta$ -phase is dominant in the PVDF thin film. In the results of dielectric properties, the PVDF thin film shows anomalous dispersion, i.e. gradual decrease of dielectric constant with increase of frequency, and also that the dielectric absorption point changes from 200 Hz to 7000 Hz with increasing temperature of thin film, which is consistent with the Debye's theory. The activation energy ( $\Delta$H) obtained from temperature dependence of dielectric loss is 21.64 ㎉/mole. We confirm that the electric conduction mechanism of PVDF thin film is dominated by ionic conduction by investigating the dependence of the leakage current of the thin film on the temperature and the electric field.

• Corrosion Science and Technology
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• v.11 no.2
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• pp.65-69
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• 2012

One dimensional(1D) $Na_2Ti_6O_{13}$ nanorods with 70 nm in diameter was synthesized by a molten salt method. Using the synthesized nanorods, about 750 nm thick $Na_2Ti_6O_{13}$ film was coated on Fluorine-doped tin oxide(FTO) glasss substrate by the Layer-by-layer self-assembly(LBL-SA) method in which a repetitive self-assembling of ions containing an opposite electric charge in an aqueous solution was utilized. Using the Kubelka-Munk function, the band gap energy of the 1D-$Na_2Ti_6O_{13}$ nanorods was nalyzed to be 3.5 eV. On the other hand, the band gap energy of the $Na_2Ti_6O_{13}$ film coated on FTO was found to be a reduced value of 2.9 eV, resulting from the nano-scale and high porosity of the film processed by LBL-SA method, which was favorable for the photo absorption capability. A significant improvement of photocurrent and onset voltage was observed with the $Na_2Ti_6O_{13}$ film incorporated into the conventional $Fe_2O_3$ photoelectrode: the photocurrent increased from 0.25 to 0.82 mA/$cm^2$, the onset voltage decreased from 0.95 to 0.78 V.