Jin-Yeol Kim

Diffusion barrier and electrical characteristics of a self-aligned MgO layer obtained from a Cu(Mg) alloy film

Diffusion barrier characteristics and electrical properties of self-aligned MgO layers obtained from a Cu(Mg) alloy film have been investigated. Self-aligned surface and interfacial MgO layers were formed upon annealing a Cu(Mg) film in an oxygen ambient and prevented interdiffusion of Cu in SiO2 up to 700 °C. The thermal stability of a pure Cu/TiN/Si multilayer system has been significantly enhanced up to 800 °C by the MgO layers by forming a MgO/Cu/MgO/TiN/Si multilayer system. A combined structure of Si3N4(500 A)/MgO(100 A) increased the breakdown voltage up to 20 V from 15 V and reduced the leakage current density down to 3×10−9 A/cm2 from 1×10−8 A/cm2 compared to a pure copper system. Consequently, the deposition of Cu(Mg) alloy followed by annealing in an oxygen ambient gives rise to the formation of a self-aligned MgO layer with excellent diffusion barrier and electrical characteristics and the film can be applied as a gate electrode in thin-film transistor/liquid-crystal displays, resulting in a r...

Polymer-dispersed liquid crystal devices using highly conducting polymers as electrodes

Flexible all-organic polymer-dispersed liquid crystal (PDLC) devices were fabricated by using highly transparent and conductive poly(3,4-ethylenedioxy thiophene): p-toluene sulfonate (PEDOT:PTS) films, as electrode layers. These conductive PEDOT:PTS films have a high transparency up to 80%, and possess a very low sheet resistance of 100Ωsq−1 at 100nm thickness. We report on the fabrication and characterization of a PDLC device using a highly conductive PEDOT:PTS for the electrodes and demonstrate its superior performance relative to that of a similar device using the indium tin oxide layer as the electrodes.

High-pressure polyol synthesis of ultrathin silver nanowires: Electrical and optical properties

Silver nanowires whose diameters could be controlled in the range of 15–30 nm and lengths up to ∼20 μm were prepared by the high-pressure polyol method. The first step involved the formation of Ag nanoparticles by reducing silver nitrate in the presence of NaCl and KBr with ethylene glycol. At the growing step, the adjustable reaction pressure controls the diameter of the silver nanowires, which were in the range 15–22 nm when the pressure was 200 psi. These Ag nanowires showed an electrical conductivity of 0.4 × 105 S/cm, and the intensity of scattered light and the optical transmittance were largely improved.

Synthesis and optoelectronic characteristics of 20 nm diameter silver nanowires for highly transparent electrode films

We demonstrate the polyol synthesis of ultrathin Ag nanowires with diameters of 20 nm and an aspect ratio as high as ∼1000 under high-pressure conditions. The increase in pressure increases density and enhances solubility, making the reactive solution rapidly reach super-saturation and increase the nucleation rate to effect a near-instantaneous formation of Ag nuclei. Clearly, the particle size was small at high pressure and an increase in pressure promoted the formation of small-size Ag seed-particles and small diameter wires. As a result, the Ag nanostructures in this study were initially formed as Ag seed particles with a diameter of 20 nm and subsequently grew into well-defined Ag nanowires with a uniform and narrow diameter distribution in the range of 16–22 nm, with a long dimension of up to 20 μm. Fabrication of random networks of the 20 nm diameter Ag nanowires synthesized lead to the fabrication of flexible transparent electrodes with excellent optoelectronic performance, with a sheet resistance of 30 Ω sq−1 and 94% transmittance with a very low haze value of ≤1.0%, making them suitable for electronic display applications.

Deposition and in-situ Plasma Doping of Plasma-Polymerized Thiophene Films Using PECVD

Highly transparent, thin polythiophene (PT) films were successfully synthesized by the plasma polymerization of thiophene. These films were doped with O2 plasma byin-situ doping technique. The plasma polymerized PT films were deposited at about 50 to 340 nm/min, depending on the temperature and plasma power. A resultant transparency as high as 85% was achieved. The plasma polymerized PT films exhibited the characteristics of an insulator or semiconductor (1010–12 Ω/□, 10−7 S/cm). The conductivity was immediately increased up to 10 O/? and 10−2 S/cm, when doped with O2 plasma. The plasma-doped PT films exhibited an increased surface roughness resulting in a decreased contact angle. However, the thickness of the PT layer was partially decomposed and/or etched with increasing voltage above 40 W.

Fabrication of nanopatterns using block copolymer and controlling surface morphology

This paper reports an approach for patterning substrates on the nanoscale using a block copolymer, polystyrene-b-polymethylmethacrylate (PS-b-PMMA), which forms cylindrical microdomains. The morphology of the polymer surface was strongly dependent on the thickness of the polymer layer. Spin coating the polymer solution onto the substrate followed by baking resulted in the self-assembly of the components of the polymer. Exposure to ultraviolet radiation degraded the PMMA chain, which could be removed by rinsing in acetic acid to give patterned holes. However, the small size of the hole limits the applications of the template. This problem was solved by sonicating the sample in different solutions in a series of steps to produce a fingerprint pattern or patterns containing PS cylindrical domains having large interstitial spaces with an average of >30 nm. The morphology of the polymer film surface was examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM).

High-performance flexible transparent electrode films based on silver nanowire-PEDOT:PSS hybrid-gels

We have developed highly transparent and electrically conductive hybrid-gel films based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and thin silver nanowires (Ag NWs) with diameters of 20 nm. Ionic gels based on PEDOT:PSS are ionic conductors consisting of anionic PSS and cationic PEDOT. Ag NWs were combined with the conductive PEDOT:PSS chains to assemble electrically conductive gels. The hybrid-gel films were created with a structure that incorporates Ag NWs into the conductive PEDOT chain matrix. We found that the conductivity significantly increased with Ag NW content. The optimized Ag NW-PEDOT:PSS hybrid-gel films exhibited excellent performance with a high transmittance of 92% and a small haze of 1.1% at a low sheet resistance of 20 Ω sq−1, and good mechanical flexibility. Because of the high-performance, it is believed that the Ag NW-PEDOT:PSS hybrid-gel electrodes are highly suitable for practical use in flexible electronics.

Solvent spray method for simple fabrication of surface nanostructures of molecular thin films

In this work, zinc phthalocyanine (ZnPc) nanorods with various aspect ratios were effectively fabricated by spraying acetone/water mixed solvents onto the surface of ZnPc thin films. The lengths of the nanorods formed varied with the composition of the solvents used. The electronic absorption band of the film was broadened by the treatment, but it was almost completely recovered by post-annealing the film at 200 °C. This spray method is very simple compared to conventional surface nanostructuring technologies such as nanoimprinting and applicable to most organic films since the amount and composition of the solvents used are easily controllable.

Highly clear conductive polymer electrode films hybridized with gold nanoparticles

Improved conductive poly(3,4-ethylenedioxy thiophene) (PEDOT) electrode films were made through hybridization with charged gold nanoparticles. The conductivity of these hybrid films increased more than seven times than the value for the PEDOT alone. The optimized films show a sheet resistance value down to 85 ohm·sq−1 at 85% transparency when PEDOT was hybridized with gold particles of 12 nm diameter, and the organic light-emitting diode devices deposited on these electrodes show a performance equivalent to that of devices based on a conventional indium tin oxide electrode.

High electrical resistivity Nd-Fe-B die-upset magnet doped with eutectic DyF3–LiF salt mixture

Nd-Fe-B-type die-upset magnet with high electrical resistivity was prepared by doping of eutectic DyF3–LiF salt mixture. Mixture of melt-spun Nd-Fe-B flakes (MQU-F: Nd13.6Fe73.6Co6.6Ga0.6B5.6) and eutectic binary (DyF3–LiF) salt (25 mol% DyF3 – 75 mol% LiF) was hot-pressed and then die-upset. By adding the eutectic salt mixture (> 4 wt%), electrical resistivity of the die-upset magnet was enhanced to over 400 μΩ.cm compared to 190 μΩ.cm of the un-doped magnet. Remarkable enhancement of the electrical resistivity was attributed to homogeneous and continuous coverage of the interface between flakes by the easily melted eutectic salt dielectric mixture. It was revealed that active substitution of the Nd atoms in neighboring flakes by the Dy atoms from the added (DyF3–LiF) salt mixture had occurred during such a quick thermal processing of hot-pressing and die-upsetting. This Dy substitution led to coercivity enhancement in the die-upset magnet doped with the eutectic (DyF3–LiF) salt mixture. Coercivity and r...