• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.445-445
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• 2011

본 연구에서는 편극 패턴된 강유전체 단결정 $LiNbO_3$ 기판에 광화학적 반응에 의해 금속(Au, Ag, Cu)나노입자를 표면에 선택적으로 성장하였다. 강유전체는 자발편극성의 특성을 지니고 있기 때문에 선택적으로 전압을 가하여 편극성의 역전에 의해 표면의 편극성을 선택적으로 패터닝이 가능하다. 본 연구에서는 주기적으로 양의 편극 영역과 음의 편극 영역이 패턴된 $LiNbO_3$ 기판을 사용하였다. 표면의 편극성은 압전소자반응현미경법(PFM)을 이용하여 확인하였으며, 극성은 R-V curve로 확인하였다. 금속입자는 금속입자를 포함하는 용액에 기판을 넣고 자외선을 조사하여 성장시켰다. 성장된 금속입자의 표면 분포 및 분석은 AFM을 이용하여 측정하였다. Ag 입자를 성장시킨 결과, (-z)편극 영역보다 (+z)편극영역에서 보다 많은 금속 나노입자들이 환원반응을 일으켜 나노입자를 형성하였으며, 경계영역 (inversion domain boundary)에 가장 많은 나노구조체가 형성되었다. Au 입자의 경우, (+z)편극영역이 (-z)편극영역의 표면보다 더 많은 입자가 형성되었지만 Ag입자처럼 편극영역의 경계에서 많이 증착되는 경향성은 보이지 않았다. Cu 입자의 경우 광화학반응을 거의 일으키지 않았으며, 편극영역에 따른 증착 경향성도 보이지 않았다. 이와 같은 결과를 증착된 금속 나노입자의 편극에 따른 표면분포를 강유전체 표면 극성에 따른 표면 밴드구조와, 각 입자가 지닌 환원전위와 전자친화도에 관련된 모델로 설명할 것이다.

• Journal of the Korean Chemical Society
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• v.35 no.5
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• pp.469-479
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• 1991

According to the recent paper by B. Fricke (J. Chem. Phys. 84, 862 (1986)), it is reported that the atomic polarizability (${\alpha}$) correlates very strongly with the first ionization potential (IP) within the groups of elements. In our study, we obtained very significant correlations between $ln\alpha$ and IP as well as lnIP by employing the least squares method. In examining the correlations of various atomic electronegativities with their first ionization potentials and the atomic polarizability within the groups of elements, good correlation coefficients are obtained except for groups 3a and 4a. Within the periods of elements, good correlation coefficients are obtained with no exception. This allows a very good prediction of various atomic polarizabilities undetermined.

• Journal of the Korean Vacuum Society
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• v.20 no.4
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• pp.300-306
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• 2011

We report the surface distribution of metal (Ag, Au) nanoparticles grown on polarity-patterned ferroelectric substrates by photochemical reaction. Single crystal periodically polarity-patterned $LiNbO_3$(PPLN) was used as a ferroelectric substrate. The nanoparticles were grown by ultra-violet (UV) light exposure of the PPLN in the aqueous solutions including metas. The surface distribution of the grown nanoparticles were measured by atomic force microscopy and identification of the orientation of the polarity of the ferroelectric surface was performed by piezoelectric force microscopy. The Ag- and Au-nanoparticles grown on +z polarity regions are larger and denser than that on -z polarity regions. In particlur, the largest and denser Ag-nanoparticles were grwon on the polarity boundary regions of the PPLN while Au-nanoparticles were not specifically grown on the boundary regions. Thus, we found that the size and position of metal nanoparticles grown on ferroelectric surfaces can be controlled by UV-exposure time and polarity pattern structures. Also, we discuss the difference of the surface distribution of the metal nano-particles depending on the polarity of the ferroelectric surfaces in terms of surface band structures, reduced work fucntion, and inhomogeneous electric field distribution.

• Journal of the Korean Chemical Society
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• v.29 no.4
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• pp.341-347
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• 1985

Formation of metal complex is the first step in the many biological actions of metal ions present in the biological systems. In this work the not electron affinity necessary for the formation of such metal complexes has been determined for a series of metal ions. It has been found that excess polarizing strength can be adopted as a measure of electron affinity and trend is the excess polarizing strength is related to Irving-Williams series. Those metal ions having greater than 0.22 in value of excess polarizing strength have been found to show carcinogenicity and other metal ions, which are supposed to be carcinogenic, have shows to have greater than 0. 22 in value of excess polarizing strength, demonstrating that excess polarizing strength could be used to determine if any metal ion possesses carcinogenic activity.

• Journal of the Korean Magnetics Society
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• v.17 no.5
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• pp.194-197
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• 2007

Understanding the spin polarization (P) has been an ongoing research challenge. The $Co_{1-x}Mn_x$ (x=0.27, 1) and $Co_{1-x}Fe_x$ (x=0, 0.5, 1) films were prepared using UHV-MBE system. For these films, the magnetic properties and spin polarization were investigated using SQUID and Meservey-Tedrow technique, respectively. Although measured P is uncorrelated to the bulk magnetic moment (M) in Co-Fe and Ni-Fe alloy films, it correlates with M in some alloys such as Co-Mn and Ni-Cu. The results can be understood by the tunneling currents made up of the hybridized sp-d electrons near the Fermi-energy level. Our work shows the feasibility to tailor new materials with large P values.

• Journal of the Korean Chemical Society
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• v.32 no.2
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• pp.85-93
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• 1988

Solvolyses of t-butylhalides (X = Cl, Br, I) in quasi isodielectric solvent system, MeOH-nitromethane, MeOH-nitrobenzene and MeOH-ethyleneglycol have been studied kinetically. Methanolyses for t-butylhalides in MeOH-NM and MeOH-NB show rate maxima at 40~100 % (v/v) MeOH. The rate maxima observed have been interpreted as a result of cooperative enhancement of polarity-polarizability and hydrogen bonddonor ability of solvents. The influences of polarity-polarizability and hydrogen bonddonor ability on reactivities of substrates have been discussed in terms of Y value changes. The solvolysis rates for t-butylhalides in E.G. are more than 20 fold faster than those in MeOH and this was attributed to the solvent structure of E.G.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.8
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• pp.598-605
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• 2011

The main object of this study is to investigate the Dust Collection Characteristics of multi-layer multi-stage porous plate system with polarization charging mechanism, experimentally. The experiment is carried to analyze the characteristics of pressure drop and collection efficiency for the present system with the experimental parameters such as applied voltage, inlet velocity, inlet concentration and stage number, etc. In results, the pressure drop becomes 18 to $134mmH_2O$, with increment of stage number (1 to 5) at inlet velocity $v_{in}$ = 3.11 m/s ($v_t$ = 18 m/s) and inlet concentration 3 g/m3 for inflow current. In case of both applied voltage 0 kV and non-inflow current, the collection efficiency of 5 stage is 92.5% at $v_{in}$ = 2.58 m/s ($v_t$ = 15 m/s), while it is estimated that the collection efficiency becomes about 6% higher than that of 0 kV and non-inflow as 98.5% at $v_{in}$ = 2.58 m/s for both alternating polarization charge (applied voltage 2.5 kV) and inflow current system.

• Journal of the Korean Magnetics Society
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• v.19 no.4
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• pp.133-137
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• 2009

$MnGeP_2$ thin films grown on GaAs exhibit room-temperature ferromagnetism with $T_C{\sim}$320 K, based on both magnetization and resistance measurements. The coercive fields at 5, 250, and 300 K are 3870, 1380 and 155 Oe, respectively. The anomalous Hall effect was observed, indicating spin polarization of the carriers. Hysteresis has been observed in both magnetoresistance and Hall measurements. The current-voltage characteristics of a $MnGeP_2$ film grown on an n-type GaAs substrate display semiconducting behavior.

• The Korean Journal of Rheology
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• v.10 no.4
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• pp.195-201
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• 1998

We have studied the rheological and electrical properties of two types of electrorheological (ER) fluids based on semi-conductive polymers (poly(p-phenylene) and polyaniline). These semi-conductive polymer-based suspensions showed a dramatic increase in viscosity on the application of the static electric field due to the large value of conductivity ratio between particle and medium. The dynamic yield stresses of these ER suspensions exhibited a quadratic dependence on electric field strength at low electric fields and a linear one for high fields. They showed a maximum and then decreased with increasing bulk conductivity of particles. These yield stress behaviors under the static electric field were found to be closely related to the dielectric properties, which is in accord with Maxwell-Wagner interfacial polarization induced by the conductivity effects. In order to achieve better understanding of interfacial polarization effect on ER response and to improve the stability of ER suspension, different kinds of surfactants were employed for controlling the ER activity as well as for enhancing the colloidal stability of suspensions.

• Proceedings of the KSMRM Conference
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• 1999.11a
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• pp.19-25
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• 1999

허파에 대한 수소 자기공명영상은 현재까지 거의 불가능한 것으로 알려져 있다. 허파의 조직과 비어있는 공간 사이의 심한 자화율(susceptibility) 차이로 인해서 영상왜곡 현상이 유발되어 그릇된 영상정보를 만들기 때문이다. 본 강좌에서는 이러한 문제를 해결할 수 있는 레이저 광펌핑 방법으로 초편극화된 비활성기체를 이용한 자기공명연구를 소개한다. 일반적인 자기공명 신호와 쳐편극화된 비활성기체를 이용한 자기공명 연구를 소개한다. 일반적인 자기공명 신호와 초편극화 기체를 이용한 신호의 차이와 물리적인 원리를 고찰할 것이다 . 비활성기체가 초편극화 되었을 때, 일반적인 자기공명의 경우에 (자기장: 1 Tesla, 온도는 $30^{\circ}C$의 열평형상태) 비해서 약 $10^{5}$ 정도의 magnetizaion 향상을 기대할 수 있으며, 기체상태라는 점이 감안된다 해도 의미 있는 자기공명신호를 획득할 수 있다. 비활성기체를 초편exchange 방법을 통하여 간접적으로 가스를 편극화 시키는 두 가지 방법이 있다. 이들의 기본적인 원리와 두 방법의 장단점 등을 알아 볼 것이다. 더불어, 초편극화 정도가 외부자기장의 세기 차이에 의한 영향을 받지 않는 다는 특성을 이용하는 경우, 비용을 최소화 하면서 고해상도의 영상을 얻을 수 있으며, 이동성이 용이한 낮은 자기고명진단기가 가능한데 이에 대한 소개를 할 것이다. 그리고, 초편극화가스를 이용한 자기공명영상 연구의 현재 동향 및 미래에 대해서 논의한다.