ngmyoung Ju

Thin-film fabrication method for organic light-emitting diodes using electrospray deposition.

A new method for fabricating micropatterns of MEH-PPV thin films with surface roughnesses below 1nm is proposed, using electrospray deposition and a dual-solvent technique. The basic concept is that nanoparticles are deposited on the target substrate just before they become completely dry, by adding a solvent that has an evaporation speed relatively lower than that of the original solution.

Control of highly migratory cells by microstructured surface based on transient change in cell behavior

Cell migration control techniques have been proposed for cells with relatively low migratory activity, based on static analyses performed with cells that attain a temporally homogenous state after being exposed to a cell guiding stimulus. To elucidate new functions of substrate topography, we investigated the transient change in the behavior of highly migratory cells coming from a flat surface to a grooved surface on a silicon substrate covered with SiO(2). A single line groove (1.5 μm in width, 20 μm in depth) and intersecting grooves (1.5 μm in width, 5 μm in spacing, 20 μm in depth) functioned as an effective cell repellent. In the case of wider grooves, a single line groove (4 μm in width; 20 μm in width) had no specified function. In contrast, intersecting grooves (4 μm in width, 5 μm in spacing) functioned as a trap for the cells. Our findings yield a new design concept of cell repelling and trapping surfaces which are applicable to cell guiding methods and single or multiple cell confinement on cell culture substrates, and thus may contribute to development of more advanced biomaterials.

Improved Power Conversion Efficiency of Organic Photovoltaic Cell Fabricated by Electrospray Deposition Method by Mixing Different Solvents

A smooth surface of the poly(3-hexylthiophene) (P3HT)-doped-(6,6)-phenyl-C61-butyric acid methyl ester (PCBM) thin film was achieved by mixing different solvents for the electrospray deposition method. As a result, the high power-conversion efficiency (PCE) of the bulk-heterojunction organic photovoltaic cell (OPV) was comparable to that obtained in the case of the spin-coating method. By optimizing the additional solvent in o-dichlorobenzene, the P3HT/PCBM active layer with the root-means-square roughness of 2.23 nm and the PCE of 2.2% was fabricated employing acetonitrile as the additional solvent.

Characteristics of motility-based filtering of adherent cells on microgrooved surfaces.

Topographical features are known to physically affect cell behavior and are expected to have great potential for non-invasive control of such behavior. To provide a design concept of a microstructured surface for elaborate non-invasive control of cell migration, we systematically analyzed the effect of microgrooves on cell migration. We fabricated silicon microstructured surfaces covered with SiO(2) with microgrooves of various sizes, and characterized the behavior of cells moving from the flat surface to the grooved surface. The intersecting microgrooves with well-defined groove width absorbed or repelled cells precisely according to the angle of approach of the cell to the boundary with the grooved surface. This filtering process was explained by the difference in the magnitude of the lamellar dragging effect resulting from the number of the grooves interacting with the lamella of the cell. This study provides a framework to tailor the microgrooved surface for non-invasive control of cell migration with label-free detection of a specific property of the target cells. This should offer significant benefits to biomedical research and applications.

High Frequency Surface Acoustic Wave Atomizer

A high-frequency Surface Acoustic Wave (SAW) atomizer which resonance frequency is 50 MHz is newly constructed and tested. Atomization characteristics are evaluated by means of electrostatic deposition (SAW-ED) and drop sensing with Laser Doppler Anemometry (LDA). In the electrostatic deposition methods, mean size of deposited dry particles is 0.7 mum, and its estimated size of atomized droplets is approximately 8.5 mum. In case of LDA measurement, average drop size is 8.3 mum. Based on these results, proposed 50 MHz SAW atomizer shows good performance in terms of drop size, compared with former lower-frequency type.

Research toward the development of compact neutron interference imaging instrument with gratings

The neutron interference imaging experiment with two absorption gratings has been done. We develop new way to fabricate absorption gratings for neutron with the pitch of 150 μ m, 180 μ m, and 200 μ m. Compact imaging detector system is developed, whose weight is 2kg. Small break in an acrylic plate, the welded place of Nb plate were observed, it reveals that the neutron interference imaging method can become new method of a nondestructive inspection for reinforced plastics and composite material such as CFRP and so on.

A Study on Atomization Characteristics of Surface Acoustic Wave Atomizer using Laser Doppler Anemometry

In this report, to evaluate atomization characteristics of surface acoustic wave atomizer and electrostatic deposition method (SAW-ED), Laser Doppler Anemometry (LDA) is used. In the case of SAW-ED method, atomized sample is collected by electrostatic force, and measured by field-emission scanning electron microscope (FE-SEM). In LDA method, scattered beam is measured and drop speed is calculated. Applied RF power is in the range from 0.97 to 1.03 W. In the results of SAW-ED, particle size and input RF power is 0.36 μm (0.97 W), 0.38 μm (1 W), and 0.4 μm (1.03 W), respectively. In the case of LDA method, drop speed is 0.16 m/s (0.97 W), 0.19 m/s (1 W) and 0.26 m/s (1.03 W). As a result, atomization characteristics of SAW atomizer were sensitively changed by the variation of input power.