• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.12
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• pp.19-26
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• 2005

We have studied the relationship between static mode behavior and dynamic characteristics of multiple transverse-mode VCSELs by measuring the modal L-I and I-V characteristics. Dependence of the resonance frequencies of RIN (relative intensity noise) spectra on the injection current can be understood by modal L-I characteristics and mode-coupling effects. Each transverse mode behaves as an independent diode laser with the different threshold current in large active-area VCSELs, and the multiple-step turn-on is observed when step-current input is applied. This multiple-step turn-on is a result of different turn-on delay times of the transverse modes. Since the multiple-step turn-on increases the rise-time significantly, the wide active-area VCSELs are not suitable for high-speed optical transmitters unless the input current is adjusted for single transverse-mode operation.

• Journal of IKEEE
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• v.3 no.1 s.4
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• pp.133-140
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• 1999

When the current optical communication system is used for the DWDM, it raise the serious interference because an interval between the adjacent channels is narrow. The FBG filter for the DWDM is able to reduce the interferences between the adjacent channels. In this paper, therefore, we find the reflection spectrums for the three types of induced index changes, that is, uniform, Gaussian apodized, and raised-cosine apodized. From the obtained results in this paper, we can see that uniform FBG does not fit, and that the smaller the maximum induced index change ${\sigma}$ is and the larger the value of parameter C in the raised-cosine apodized FBG and G in the Gaussian apodized FBG are, the fitter they are on the narrow filter for DWDM. But, we can also see that the raised-cosine apodized FBG has more excellent property than the Gaussian apodized FBG because it has the narrower maximum reflection spectrum band and the lower sidelobes than the other.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.139.1-139.1
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• 2016

Multiferroic materials are of great interest because of its potential applications in the design of devices combining magnetic, electronic and optical functionalities. Among various multiferroic materials, $BiFeO_3$(BFO) is known to be one of the intensively focused mainly due to the possibility of multiferroism at device working temperature (> $200^{\circ}C$). However, leakage current and weak polarization resulting from oxygen deficiency and crystalline defect should be resolved. Furthermore the magnetic ordering of pure BFO mainly prefers to have antiferromagnetic coupling. Up to now many attempts have been performed to improve the ferromagnetic and the ferroelectric properties of BFO by doping. In this work, we investigated the effects of Ni substitution on the multiferroism of bulk BFO. Four BFO samples (a pure BFO and three Ni-doped BFO's; $BiFe_{0.99}Ni_{0.01}O_3$, $BiFe_{0.98}Ni_{0.02}O_3$ and $BiFe_{0.97}Ni_{0.03}O_3$) were synthesized by the standard solid-state reaction and rapid sintering technique. The XRD results reveal that Ni atoms are substituted into Fe-sites and give rise to phase transition of cubic to rhombohedal. By using vibrating sample magnetometer and standard ferroelectric tester, the multiferroic properties at room temperature were characterized. We found that the magnetic moment of Ni-doped BFO turned out to be maximized for 3% of Ni dopant.

• Bulletin of the Korean Chemical Society
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• v.30 no.9
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• pp.1933-1938
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• 2009

New $\pi$-conjugated polymer with vinylene linkage, poly((10-hexyl-3,7-phenothiazine)-alt-(4-(4-butyl-phenyl)- 3,5-diphenyl-4H-[1,2,4]triazole)-3,5-vinylene) (PTV-TAZ) was synthesized by the Heck coupling reaction. The photoluminescence (PL) maximum wavelength and the band gap energy of PTV-TAZ film were 555 nm and 2.41 eV, respectively. The HOMO energy level of PTV-TAZ was -4.99 eV, which was slightly lower than that of PTV (-4.89 eV). Electron deficient aromatic 1,2,4-triazole (TAZ) in the polymer backbone does not affect the HOMO energy level significantly. The maximum efficiency and brightness of double layer structured electroluminescent (EL) device (ITO/PEDOT (30 nm)/PTV-TAZ (60 nm)/Al) were 0.247 cd/A and 553 cd/$m^2$, respectively, which were significantly higher than those of the device based PTV (1.65 ${\times}\;10^{-4}$ cd/A and 4.3 cd/$m^2$). This is due to that TAZ unit improves electron transporting ability in the emissive layer. The turn-on voltage (defined as the voltage required to give a luminescence of 1 cd/$m^2$) of brightness of the device based on PTV-TAZ was 12.0 V, which was similar to that the based on PTV (11.5 V). This is due to that the ionization potential of PTV-TAZ is very similar to that of PTV.

• Smart Structures and Systems
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• v.8 no.1
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• pp.17-37
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• 2011

The microcantilever (MCL) sensor is one of the most promising platforms for next-generation label-free biosensing applications. It outperforms conventional label-free detection methods in terms of portability and parallelization. In this paper, an overview of recent advances in our understanding of the coupling between biomolecular interactions and MCL responses is given. A dual compact optical MCL sensing platform was built to enable biosensing experiments both in gas-phase environments and in solutions. The thermal bimorph effect was found to be an effective nanomanipulator for the MCL platform calibration. The study of the alkanethiol self-assembly monolayer (SAM) chain length effect revealed that 1-octanethiol ($C_8H_{17}SH$) induced a larger deflection than that from 1-dodecanethiol ($C_{12}H_{25}SH$) in solutions. Using the clinically relevant biomarker C-reactive protein (CRP), we revealed that the analytical sensitivity of the MCL reached a diagnostic level of $1{\sim}500{\mu}g/ml$ within a 7% coefficient of variation. Using grazing incident x-ray diffractometer (GIXRD) analysis, we found that the gold surface was dominated by the (111) crystalline plane. Moreover, using X-ray photoelectron spectroscopy (XPS) analysis, we confirmed that the Au-S covalent bonds occurred in SAM adsorption whereas CRP molecular bindings occurred in protein analysis. First principles density functional theory (DFT) simulations were also used to examine biomolecular adsorption mechanisms. Multiscale modeling was then developed to connect the interactions at the molecular level with the MCL mechanical response. The alkanethiol SAM chain length effect in air was successfully predicted using the multiscale scheme.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.913-918
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• 2014

Five mol % tungsten-doped tin oxide ($W_{0.05}Sn_{0.95}O_2$, TTO5) was prepared by co-precipitation of $SnCl_4{\cdot}5H_2O$ and $WCl_4$, followed by calcination at $1000^{\circ}C$. The as-prepared TTO5 was in the pure cassiterite phase with a particle size of ~50 nm and optical bandgap of 2.51 eV. Herein it was applied for the formation of TTO5/$TiO_2$ heterojunctions by covering the TTO5 surface with $TiO_2$ by sol-gel method. Under visible-light irradiation (${\lambda}{\geq}420$ nm), TTO5/$TiO_2$ showed a significantly high photocatalytic activity in removing gaseous 2-propanol (IP) and evolving $CO_2$. It is deduced that its high visible-light activity is caused by inter-semiconductor holetransfer between the valence band (VB) of TTO5 and $TiO_2$, since the TTO5 nanoparticle (NP) exhibits the absorption edge at ~450 nm and its VB level is located more positive side than that of $TiO_2$. The evidence for the hole-transport mechanism between TTO5 and $TiO_2$ was also investigated by monitoring the holescavenging reaction with 1,4-terephthalic acid (TA).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.230-233
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• 2004

The stochiometric mix of evaporating materials for the $CuInS_2$ single crystal thin films was prepared from horizontal furnance. Using extrapolation method of X-ray diffraction patterns for the $CuInS_2$ polycrystal, it was found tetragonal structure whose lattice constant $a_0$ and $c_0$ were $5.524\;{\AA}$ and $11.142\;{\AA}$, respectively. To obtain the single crystal thin films, $CuInS_2$ mixed crystal was deposited on throughly etched semi-insulator GaAs(100) substrate by the hot wall epitaxy (HWE) system. The source and substrate temperature were 640 t and 430 t, respectively and the thickness of the single crystal thin films was $2{\mu}m$. Hall effect on this sample was measured by the method of van dot Pauw and studied on carrier density and temperature dependence of mobility. The carrier density and mobility deduced from Hall data are $9.64{\times}10^{22}/m^3,\;2.95{\times}10^{-2}\;m^2/V{\cdot}s$ at 293 K, respectively The optical energy gaps were found to be 1.53 eV at room temperature. From the photocurrent spectrum by illumination of perpendicular light on the c - axis of the thin film, we have found that the values of spin orbit coupling splitting ${\Delta}So$ and the crystal field splitting ${\Delta}Cr$ were 0.0211 eV and 0.0045 eV at 10 K, respectively. From PL peaks measured at 10K, 807.7nm (1.5350ev) mean Ex peak of the free exciton emission, also 810.3nm (1.5301eV) expresses $I_2$ peak of donor-bound exciton emission and 815.6nm (1.5201eV) emerges $I_1$ peak of acceptor-bound exciton emission. In addition, the peak observed at 862.0nm (1.4383eV) was analyzed to be PL peak due to donor-acceptor pair(DAP).

• Journal of the Korean Magnetics Society
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• v.25 no.2
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• pp.39-42
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• 2015

After preparing carbon-doped FePt films by dc magnetron sputtering, we observed ultrafast demagnetization and its recovery by means of a time-resolved magneto-optical Kerr effect technique. We confirm that the degree of $L1_0$ ordering is decreased and coercivity is changed, as the carbon concentration increases. All samples are demagnetized within ~5 ps after the femtosecond laser pulse heated the sample. Interestingly, ultrafast relaxation time, which indicates fast magnetization recovery, increases as the carbon concentration increases due to the low spin-orbit coupling of carbon.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.1
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• pp.147-154
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• 2009

This paper presents a grating~integrated SPR (Surface Plasmon Resonance) sensor chip for simple and inexpensive biomolecule detection. The grating-integrated SPR sensor chip has two sensing channels having a nano grating for SPR coupling. An external mirror is used for multi channel SPR sensing. The present sensor chip replaces bulky and expensive optical components, such as fiber-optic switches or special shaped prisms, resulting in a simple and inexpensive wavelength modulated multi-channel SPR sensing system. We fabricate a SPR sensor chip integrated with 835 nm-pitch gratings by a micromolding technique to reduce the fabrication cost. In the experimental characterization, the refractive index sensitivity of each sensing channel is measured as $321.8{\pm}8.1nm$/RI and $514.3{\pm}8.lnm$/RI, respectively. 0.5uM of the target biomolecule (streptavidin) was detected by a $1.13{\pm}0.16nm$ shift of the SPR dip in the 10%-biotinylated sample channel, while the SPR dip in the reference channel for environmental perturbation monitoring remained at the same position. From the experimental results, multi-channel biomolecule detection capability of the present grating-integrated SPR sensor chip has been verified. On the basis of the preliminary experiments, we successfully measured the binding reaction rate for the $2\;nM{\sim}200\;nM$ monoclonal-antibiotin, thus verifying biomolecule concentration detectability of the present SPR sensor chip. The binding reaction rates measured from the present SPR sensor chip agredd well with those from a commercialized SPR sensor.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.6
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• pp.846-851
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• 2010

A liquid-air interface sensing system using the flat end surfaces of a fused-silica fiber coupler has been demonstrated. The principle is based on the additional optical loss caused by changing the refractive index of the external material at the boundary of the end face made of a fiber. The immersion characteristics of this system with respect to the different splitting ratios of the couplers were investigated to determine the sensitivity when it responses to water and air. These experimental data are very useful for selecting the coupling ratio of a coupler in order to develop a multiple sensing probe system. In the proposed sensor structure, it can be emphasize that the sensing probe can be appropriately arrayed on the basis of splitting ratio of the coupler. As a result, it is expected that the proposed liquid-air interface sensors can also be applied to monitor flooding that occurs in multiple areas at the same time.