Han Jae Shin

Characteristics of Silicon Oxynitride Barrier Films Grown on Poly(ethylene naphthalate) by Ion-Beam-Assisted Deposition

For the application of transparent barriers to water vapor permeation for plastic substrates, we have prepared silicon oxynitride thin films on a poly(ethylene naphthalate) substrate at room temperature by the ion-beam-assisted electron beam evaporation method and investigated their characteristics with respect to N2 flow rate in the ion source. The experimental results reveal that when N2 flow rate increases, the nitrogen concentration and Si–N bonding in SiOxNy films increase owing to the assisted N2 ion incorporations during the film deposition process. Also, with increasing N2 flow rate, the surface roughness and optical transmittance of the barrier film decrease, whereas refractive index and film density increase. It is confirmed that the water vapor transmission rate of our barrier films decreases with the incorporation of N2 ions into the films, being strongly dependent on surface roughness and film density.

Surface Properties of Poly(ethylene terephthalate) Films Modified by Inductively Coupled Plasma with Ar/N2 Mixture Gases

We have investigated the effects of an inductively coupled plasma (ICP) treatment using Ar and N2 gas mixtures on the surfaces properties of poly(ethylene terephthalate) (PET) films. The Ar/N2 ICP-modified PET surfaces have been characterized by X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle measurements. The experimental results reveal that ICP treatment with Ar/N2 mixture gas induces physical and chemical changes of PET surface, showing the increases of surface roughness and hydrophilic functional groups in the surface Also, the contact angle of distilled water on the surface becomes smaller with increasing RF power applied to ICP antenna, resulting in higher adhesion energy.

Fabrication of Transparent Semiconducting Indium Zinc Tin Oxide Thin Films and Its Wet Chemical Etching Characteristics in Hydrochloric Acid

We have fabricated the transparent semiconducting indium zinc tin oxide (IZTO) thin films on polymeric substrates at room temperature by RF-magnetron sputtering method, and investigated their wet chemical etching behavior in HCl solution. The study has revealed that the control of O2 flow rate during deposition attribute to the variation of resistivity for IZTO films, resulting in the conductor–semiconductor conductivity transition. The increasing etchant molarity and temperature of etching solution lead to the increase in etching rate of IZTO films according to the chemical dissolution reaction. As a result, the IZTO active channel is defined successfully, suggesting sufficient possibility for the application to flexible transparent thin film transistors.

Surface Modification of Poly(ethylene terephthalate) Polymeric Films by Inductively Coupled Oxygen Plasma

In this study, the surfaces of poly(ethylene terephthalate) (PET) films have been modified by high density inductively coupled plasma (ICP) using the oxygen gas. The ICP-modified PET surfaces have been characterized by atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle measurement as a function of RF power applied to ICP antenna. The experimental results reveal that the exposure of PET films to ICP leads to the roughening surface and the increase of oxygen containing-functional groups such as O–C=O and C–O at the surface. Also, the contact angle of distilled water on the surface decreases with increasing RF power, resulting in the increase in the adhesion energy.

Transparent Zn-Doped In2O3 Electrode Prepared by Radio Frequency Facing Target Sputtering for Flexible Dye-Sensitized Solar Cells

For the application to transparent electrode in flexible dye-sensitized solar cells (DSSCs), Zn-doped In2O3 (In2O3:Zn) thin films have been fabricated on polyethylene naphthalate (PEN) substrate by the radio frequency facing target sputtering method, and their characteristics have been investigated as a function of deposition pressure. X-ray diffraction study reveal that the structure of In2O3:Zn thin films is amorphous nature. The film morphology is slightly sensitive to the deposition pressure. At the sputtering pressure of 0.40 Pa, In2O3:Zn thin film on PEN exhibits a sheet resistance of about 12.4 Ω/□ and average transmittance of about 85% at 550 nm wavelength, resulting in the highest value for figure of merit. The flexible DSSC device with the In2O3:Zn electrode shows the efficient solar-to-electrical power conversion efficiency (η), which is the maximum η value of 4.6% under simulated air mass 1.5 irradiation (100 mW/cm2).

Chemical Surface Pre-treatment of Carbon Nanotube for Improving the Thermal Conductivity of Carbon Nanotube-Epoxy Composite

For improving the thermal conductivity of carbon nanotube-epoxy composite, we have performed the chemical surface pre-treatment of multi-walled carbon nanotube (MWCNT) and investigated its effects. In the experiments, the mixtures of nitric and sulfuric acid have been used as the surface modifier for MWCNT. The chemical surface pre-treatments by acid mixtures lead to the production of oxygen-containing functional groups on the surfaces of MWCNT. Also, the surface area and pore volume of acid-treated MWCNT (AT-MWCNT) become larger than those of pristine MWCNT. By actions of the chemical pre-treatment, AT-MWCNT is well dispersed and forms the heat flow network in epoxy matrix, resulting in higher thermal conductivity of carbon nanotube-epoxy composite.

Characteristics of Facing Target-Sputtered Amorphous InGaZnO Thin Films as the Active Channel Layer in Transparent Thin Film Transistor on Polymeric Substrate

For an application to the channel layer in flexible transparent thin-film transistor (TFT), we have prepared the amorphous indium gallium zinc oxide (a-InGaZnO) thin films on unheated polyethylene naphthalate (PEN) substrate by facing target sputtering. Two types of a-InGaZnO TFT design, one top gate configuration and the other bottom gate, have been fabricated for comparison with each other. The experimental results reveal that the top gate a-InGaZnO TFT is shown to be superior TFT performances, compared with bottom-gate structure. As a result, the top gate a-InGaZnO TFTs operate in depletion mode with a threshold voltage of −0.5 V, a mobility of 6.0 cm2/Vs, an on-off ratio of >106, and a sub-threshold slope of 0.95 V/decade. In addition, the optical transmittance of about 74% at 550nm wavelength is represented for the top gate a-InGaZnO TFT on PEN.

Effect of surface wettability controlled by ultraviolet-ozone treatment on spin-coated ZnO seed layer and ZnO nanowires grown by hydrothermal method

We presented improved density and aspect ratio of ZnO nanowires which were hydrothermally grown on spin coated ZnO seed layer. After UVO treatment on silicon surface, spin coated ZnO seed layer showed a high coverage density due to increased surface wettability without forming island like growth in conventional method. ZnO active nucleation sites showed a positive increasing relation with increase in coverage density. Whereas, increased spin coating time had risen surface roughness with rise in coverage area, UVO treated surface wettability change had showed lower surface roughness. Moreover, seed layer thickness remained unaffected for surface wettability changing effect. This let ZnO nanowires grow on the increased ZnO active nucleation sites without hindrance of other nanowires. Hence, higher density and aspect ratio ZnO nanowires were achieved by controlling surface wettability via UVO treatment.