• Korean Journal of Materials Research
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• v.9 no.5
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• pp.473-477
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• 1999

Xerographic properties of double-layer photoconductor doped with 4-butyl-4'-methoxyazobenzene (BMAB) as charge-carrier transport material were investigated. BMAB can undergo reversible trans-cis isomerization by light with appropriate wavelength. In the results of measured surface voltage properties for photoconductor doped with BMAB, TNF: BMAB(4-wt%) sample with trans form showed the lowest dark decay, the lowest residual voltage, and the highest sensitivity among cis form. The trans isomer of BMAB has ordering orientation because the molecule possesses a rodlike shape, while the cis isomer has random orientation due to its bent shape. Therefore the molecular arrangement of trans form enhanced charge-carrier transport mobility.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.777-779
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• 2002

We report the performance of pentacene-based organic thin film transistors (OTFT) with PMMA (polymethyl methacrylate) as the gate insulator which was spin-coated on the ITO (indium tin oxide) glass substrate which was used as the gate contact. The pentacene thin film was deposited on the PMMA film and then Au source/drain contacts were deposited through shadow mask. The pentacene film shows better molecular ordering on PMMA compared with $SiO_2$ of Si wafer. The devices exhibited the field effect mobility of ${\sim}0.004cm^2$/Vs and on/off current ratio of ${\sim}10^3$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.3-4
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• 2007

Orientational ordering of polar molecules and excess charges at the interface are main origins of surface polarization. For organic electronics, probing and control of these two surface polarization phenomena are key issues. In this presentation, I report a novel electrical measurement that can directly probe orientational dipolar motion in surface monolayers by Maxwell-displacement-current, and also report a novel optical technique that allows carrier motions in organic materials by measuring the optical second harmonic signals activated by the electric field. Then I discuss how the control of dipolar motions and carrier motions are linked to organic electronics applications such as organic field effect transistors.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.05a
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• pp.164-168
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• 2005

We report high performance poly (3-hexylthiophene) organic field-effect transistors fabricated on a plastic substrate. The polymer active channel layer was directly printed by the rubber stamp printing method with a pre-patterned elastomer stamp. As a result. organic transistors having average field-effect mobility of 0.079 $cm^2/Vs$ and on/off ratio of $10^4{\sim}10^5$ were realized on a plastic substrate. Also, through the investigation of the molecular ordering of rubber-stamp-printed poly (3-hexylthiophene) films using synchrotron grazing-incidence X-ray diffraction measurements, the films were found to have edge-on structure which is favorable in realizing high performance organic transistors.

• Journal of the Korean Ceramic Society
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• v.40 no.4
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• pp.354-359
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• 2003

The microwave dielectric characteristics of (1-x)(Al$\_$$\frac{1}{2}$/Ta$\_$$\frac{1}{2}$/)O$_2$-x(Mg$\_$1/3/Ta$\_$2/3/)O$_2$ (0$\leq$x$\leq$1.0) ceramics were investigated by crystalstructure, variations of ionic polarizability, and microstructures. As x increased, (1-x)(Al$\_$$\frac{1}{2}$/Ta$\_$$\frac{1}{2}$/)O$_2$-x(Mg$\_$1/3/Ta$\_$2/3/)O$_2$ transformed to tetragonal structure. Because the ionic radius of (Mg$\_$1/3/Ta$\_$2/3/)$\^$4+/was slightly bigger than one of (Al$\_$$\frac{1}{2}$/Ta$\_$$\frac{1}{2}$/)$\^$4+/, the cell parameters increased with increase of (Mg$\_$1/3/Ta$\_$2/3/)O$_2$concentration and coincided with prediction of the molecular additivity rule. As x increased, the compositions revealed ordered phase and were of single phase above 60 mol%. The increase of the ordered phase and grain size enhanced the Q and when ordering was completed at x over 0.6, the grain size was major factor for the increase in the a. Though the grain size increased, however, the porosity deteriorated the q. Therefore, the a depended on the order/disorder, the porosity, and the grain size in regular order.

• Applied Chemistry for Engineering
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• v.18 no.5
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• pp.506-510
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• 2007

Vacuum deposited 4,4',4''-tris(N-(1-naphthyl)-N-phenylamino)-triphenylamine (1-TNATA), a widely-used semiconductor material, is placed as a thin interlayer between indium tin oxide (ITO) electrode and a hole transporting layer (HTL) in OLEDs and a well-stacked 1-TNATA layer leads to stable and high efficiency devices by reducing the carrier injection barrier at the interface between the ITO anode and hole transport layers. According to Raman spectra, thermal annealing after deposition as well as electromagnetic field treatment during deposition lead to closer stacking of 1-TNATA molecules and resulted in molecular ordering. By thermal annealing at about $110^{\circ}C$, an increase in current flow through the film by over 25% was observed. Molecularly-ordered 1-TNATA films played an important role in achieving higher luminance efficiency as well as higher power efficiency of the multi-layered organic EL devices in the present work. Electromagnetic field treatment during deposition was less effective compared to thermal annealing

• Journal of Life Science
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• v.27 no.1
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• pp.15-22
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• 2017

Streptococcus mutans (S. mutans), which plays a major role in the etiology of human dental caries, is able to tolerate exposure to acid shock in addition to its acidogenicity. We investigated the effects of pH stress on membrane fluidity, activities and expression levels of F-ATPase, and proton permeability in S. mutans. Using 1,6-diphenyl-1,3,5-hexatriene, we observed membrane ordering at pH 4.8 and pH 8.8. The ordering effects were larger at pH 4.8 in cytoplasmic membranes isolated from S. mutans (CMSM). Increasing pH resulted in a decrease in the activities and expression levels of F-ATPase. The proton permeability was decreased at both acidic and alkaline pHs, and the lowest permeability was observed at pH 4.8. The lower permeability at pH 8.8 than pH 6.8 is likely to be caused by the decreased proton influx due to the decreased CMSM fluidity. In addition, it seems to be evident that extremely low permeability at pH 4.8 was caused by the decreased proton influx due to the decreased CMSM fluidity as well as the increased proton efflux due to the increased activity and expression level of F-ATPase. It is likely that CMSM fluidity and F-ATPase activity are two major key factors that determine proton permeability in S. mutans. We suggest that CMSM fluidity plays an important role in the determination of proton permeability, which sheds light on the possibility of using nonspecific membrane fluidizers, e.g., ethanol, for anti-caries purposes.

• Korean Journal of Optics and Photonics
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• v.13 no.4
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• pp.356-362
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• 2002

The molecular orientational dynamics of the nonlinear optical(NLO) side-chain polymer N-(4-nitrophenyl)-(L)-prolinol-poly (pphenylene terephthalates) have been studied using nonlinear optical responses as measured by second harmonic generation (SHG). A new pulsed corona poling is used to orient the NLO chromophores and the polymer segments into the noncentrosymmetric structure required to obtain the SHG signal. By corona poling of negative high voltage pulses with variable repetition rates (between 0.5 and 10 ㎑) at temperature between 25$^{\circ}C$ and 80$^{\circ}C$, well below and about the glass transition temperature 70$^{\circ}C$, the side-chain chromophores and the polymer chain contour rearrange themselves and create the domain structure observed by atomic force microscopy(AFM). The pulsed corona voltage enhances the orientational ordering of the NLO chromophores and also significantly influences the growth of SHG signal and the improved relaxation behavior after the poling field is removed, reducing the visible damage to the polymer film dramatically. This new pulsed corona poling experiment gave direct in situ evidence that the NLO chromophore and the polymer backbone undergo anisotropic rearrangement during the poling process.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.3
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• pp.105-110
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• 2002

J-aggregates in the mutual mixing LB films of [6Me-DS]$_{1-x}$ [DO]$_{x}$,[DS]$_{1-x}$ [DO]$_{x}$ and [DSe]$_{1-x}$ [DO]$_{x}$ have been studied by optical absorption, fluorescence and surface pressure-area isotherms. In [6Me-DS]$_{1-x}$ [DO]$_{x}$ films, sharp J-band absorption and fluorescence of [6Me-DS] are linearly shifted to the longer wavelength for the replacement of [6Me-DS] by [DO]. According to the x, a smooth shift of the limited area has been cleared. In the [DS]-[DO] system, the J-band is enhanced at 1:1 composition and strong fluorescence is also observed. Also, the presence of phase separation was suggested in the [DSe]-[DO] system, because the absorption spectra were decomposed into [DSe] and [DO] spectra. On the other hand, in the pressure-area isothermal study, reduction in the molecular occupying area of monolayers has been clarified. This could be ascribed to the enhancement of molecular ordering in J-aggregates. These facts are also believed to reflect the most closely packed arrangement of chromophores in the merocyanine dye monolayers. Thus, it was confirmed that the interaction between mixed dye molecules and the CdC1$_2$+KHCO$_3$subphases affected the J-aggregates of the LB films. Also. it is thought that the J-aggregates are formed non-dimensionally in LB films, such as solution synthesized [DX:DO] assemblies on mixing.s on mixing.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.148-151
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• 2003

The spin density of ${\beta}-MnO_2$ structure was theoretically investigated by $DV-X_{\alpha}$ (the discrete variation $X{\alpha}$) method, which is a sort of the first principle molecular orbital method using Hatre-Fock-Slater approximation. The used cluster model was $[Mn_{14}O_{56}]^{-52}$. The ${\beta}-MnO_2$ is a paramagnetic oxide semiconductor material having the energy band gap of 0.18 eV and an 3 loan-pair electrons in the 3d orbital of an cation. This material exhibits spin-only magnetism and has the magnetic ordering temperature of 94 K. Below this temperature its magnetism appears as antiferromagnetism. The calculations of electronic state showed that if the initial spin condition of input parameters changed, the magnetic state changed from paramagnetic to antiferromagnetic. When d orbital of all Mn atoms in cluster had same initial spin state as only up spin, paramagnetic spin density distribution appeared by the calculation. On the other way, d orbital had alternately changed spin state along special direction the resulted spin distribution showed antiferromagnetism.