Bu-Jong Kim

Carrier transport mechanisms of the writing and the erasing processes for Al∕ZnO nanoparticles embedded in a polyimide layer/p-Si diodes

Capacitance-voltage measurements on Al∕ZnO nanocrystals embedded in polyimide (PI) layer/p-Si diodes at 300K showed a metal-insulator-semiconductor behavior with a flatband voltage shift. Current-voltage (I-V) measurements on the diodes showed that carrier transport processes were attributed to the Poole-Frenkel effect and to thermionic emission. Possible carrier transport mechanisms of the writing and the erasing processes for the Al∕ZnO nanocrystals embedded in PI layer/p-Si diodes are described on the basis of the I-V results.

Emission stability enhancement of a tip-type carbon-nanotube-based field emitter via hafnium interlayer deposition and thermal treatment

Carbon nanotubes (CNTs) were deposited on a tip-type tungsten substrate via electrophoretic deposition, in which a hafnium thin film was used as an interlayer. The long-term (up to 24 h) emission stability of the CNT-based field emitter was remarkably enhanced when the hafnium interlayer was coated and thermally treated. This is attributed to the enhanced adhesion between the substrate and the CNTs. An x-ray photoelectron spectroscopy study and nano-scratch measurement provided a convincing evidence of the increase in the adhesive force.

Visibility and oxidation stability of hybrid-type copper mesh electrodes with combined nickel–carbon nanotube coating

Hybrid-type transparent conductive electrodes (TCEs) were fabricated by coating copper (Cu) meshes with carbon nanotube (CNT) via electrophoretic deposition, and with nickel (Ni) via electroplating. For the fabricated electrodes, the effects of the coating with CNT and Ni on their transmittance and reflectance in the visible-light range, electrical sheet resistance, and chromatic parameters (e.g., redness and yellowness) were characterized. Also, an oxidation stability test was performed by exposing the electrodes to air for 20 d at 85 °C and 85% temperature and humidity conditions, respectively. It was discovered that the CNT coating considerably reduced the reflectance of the Cu meshes, and that the Ni coating effectively protected the Cu meshes against oxidation. Furthermore, after the coating with CNT, both the redness and yellowness of the Cu mesh regardless of the Ni coating approached almost zero, indicating a natural color. The experiment results confirmed that the hybrid-type Cu meshes with combined Ni-CNT coating improved characteristics in terms of reflectance, sheet resistance, oxidation stability, and color, superior to those of the primitive Cu mesh, and also simultaneously satisfied most of the requirements for TCEs.

Improvement in color properties of copper mesh electrodes via electrophoretic coating with nano-structured carbon materials

In this study, the effects of coating with nano-structured carbon materials, such as carbon nanotube (CNT) and graphene, on the characteristics of transparent conductive electrodes based on copper (Cu) meshes, particularly on the visibility related to their color properties, were examined. The electrical sheet resistance of the Cu meshes remained almost unchanged regardless of the coating with CNT and graphene. Through the electrophoretic deposition method, the CNT and graphene layers were selectively used to coat only the regions where Cu mesh patterns had been formed, which helped minimize the transmittance loss caused by the coating with CNT and graphene. The reflectance of the Cu mesh was substantially reduced by the coating with CNT and graphene, meaning that the CNT or graphene coating layer played the role of suppressing the visible light reflected from the Cu mesh. In addition, the reflectance reduction effect was greater when the Cu mesh was coated with CNT rather than with graphene, which was at...

Flexible grid-mesh electrodes fabricated by electroless copper plating on corona-treated PET substrates and coating with graphene for transparent film heaters

In this study, we present solution-based processes for producing copper (Cu) meshes which can be utilized as transparent conductive electrodes (TCEs) for flexible film heaters. The surface modification of polyethylene terephthalate (PET) substrates was done via corona treatment at atmospheric pressure and room temperature. The Cu layer was deposited on the corona-treated PET substrate via electroless plating and then patterned via lithography to have mesh dimensions of a 200 μm line-to-line spacing and a 6 μm line width. Also, graphene was coated on the Cu mesh via electrophoretic deposition (EPD). The chemical and physical changes in the PET surfaces were characterized according to the corona treatment conditions. The measurements of contact angles and surface energies of the corona-treated PET substrates indicated that the PET surfaces changed from hydrophobic to hydrophilic after corona treatment, leading to the improvement in the adhesion between the PET substrates and the Cu meshes. The flexibility of the Cu meshes was inspected by performing bending and twisting tests and by directly measuring the adhesion strength between the Cu layers and the PET substrates through scratch tests. The effects of graphene coating on the characteristics of the Cu meshes were examined in terms of their surface morphologies, electrical sheet resistances, transmittances and reflectances in the visible-light wavelength range, and color differences. Finally, the film heaters produced by employing the graphene-coated Cu meshes yielded a temperature rise over 85 °C with a response time shorter than 20 s.