• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1700-1702
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• 2004

Diamond films including nanocrystallites are grown by microwave plasma chemical vapor deposition using $O_2$ additives and negative substrate bias at growth step. Effects of growth parameters on film properties are characterized by Raman spectra, SEM, and AFM images. It is found that the surface roughness and the microstructure of grown films can be controlled by changing $O_2$ gas ratio. The I-V characteristics are also investigated in terms of growth conditions of diamond films. The surface roughness and the $sp^2$ phase of the grown diamond films turn out to be crucial factors for reducing leakage currents at diamond/metal interfaces.

• Bulletin of the Korean Chemical Society
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• v.35 no.5
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• pp.1491-1494
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• 2014

High-crystallinity poly(3-hexylthiophene) (P3HT) thin films were prepared by aging the precursor solutions, prepared using a good solvent, chloroform, at low temperatures prior to spin-casting. Lower solution temperatures significantly improved the molecular ordering in the spin-cast P3HT films and, therefore, the electrical properties of field-effect transistors prepared using these films. Solution cooling enhanced the electrical properties by shifting the P3HT configuration equilibrium away from random coils and toward more ordered aggregates. At room temperature, the P3HT molecules were completely solvated in chloroform and adopted a random coil conformation. Upon cooling, however, the chloroform poorly solvated the P3HT molecules, favoring the formation of ordered P3HT aggregates, which then yielded more highly crystalline molecular ordering in the P3HT thin films produced from the solution.

• Applied Microscopy
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• v.45 no.1
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• pp.23-31
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• 2015

Dark field (DF) transmission electron microscopy image has become a popular characterization method for two-dimensional material, graphene, since it can visualize grain structure and multilayer islands, and further provide structural information such as crystal orientation relations, defects, etc. unlike other imaging tools. Here we present microstructure of graphene, particularly, using DF imaging. High-angle grain boundary formation wass observed in heat-treated chemical vapor deposition-grown graphene on the Si substrate using patch-quilted DF imaging processing, which is supposed to occur by strain around multilayer islands. Upon the crystal orientation between layers the multilayer islands were categorized into the oriented one and the twisted one, and their local structure were compared. In addition information from each diffraction spot in selected area diffraction pattern was summarized.

• Journal of the Korean Ceramic Society
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• v.55 no.3
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• pp.285-289
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• 2018

We synthesized silicon carbide (${\beta}-SiC$) nanowires with nano-scale diameter (30 - 400 nm) and micro-scale length ($50-200{\mu}m$) on a porous body using low-grade silica and carbon black powder by carbothermal reduction at $1300-1600^{\circ}C$. The SiC nanowires were formed by vapor-liquid-solid deposition with self-evaporated Fe catalysts in low-grade silica. We investigated the characteristics of the SiC nanowires, which were grown on a porous body with Ar flowing in a vacuum furnace. Their structural, optical, and electrical properties were analyzed with X-ray diffraction (XRD), transmission electron microscopy (TEM), and selective area electron diffraction (SAED). We obtained high-quality SiC single crystalline nanowire without stacking faults that may have uses in industrial applications.

• Journal of Magnetics
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• v.21 no.3
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• pp.303-307
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• 2016

$Y_{3-x}R_xFe_5O_{12}$ (R = La, Nd, and Gd) powder were fabricated using a sol-gel pyrolysis method. Their magnetic properties and crystalline structures were investigated using x-ray diffraction (XRD), a vibrating sample magnetometer (VSM), and $M{\ddot{o}}ssbauer$ Spectrometer. The $M{\ddot{o}}ssbauer$ spectra for the powders were taken at various temperatures ranging from 12 K to Curie temperature (Tc). The isomer shifts indicated that the valence states of Fe ions for the 16(a) and 24(d) sites have a ferric character. The saturation magnetization (Ms) increases from 32 to 34 (emu/g) for the YIG, and Nd-YIG, respectively. However, Ms decreases to 27 (emu/g) at Gd-YIG.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.192.1-192.1
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• 2015

We demonstrated the nonvolatile memory functionality of nano-crystalline silicon (nc-Si) and InGaZnOxide (IGZO) thin film transistors (TFTs) using mobile protons that are generated by very short time hydrogen neutral beam (H-NB) treatment in gate insulator (SiO2). The whole memory fabrication process kept under $50^{\circ}C$ (except SiO2 deposition process; $300^{\circ}C$). These devices exhibited reproducible hysteresis, reversible switching, and nonvolatile memory behaviors in comparison with those of the conventional FET devices. We also executed hydrogen treatment in order to figure out the difference of mobile proton generation between PECVD and H-NB CVD that we modified. Our study will further provide a vision of creating memory functionality and incorporating proton-based storage elements onto a probability of next generation flexible memorable electronics such as low power consumption flexible display panel.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.179.1-179.1
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• 2015

Thickness-dependent electrical, structural, and optical properties of zinc oxide (ZnO) thin films on polyethylene terephthalate (PET) substrates were investigated in the very thin thickness range of 20 to 120 nm. A very unusual transition phenomenon, in which electrical resistance increases with an increase in film thickness, was observed. From structural and compositional analyses, this transition behavior was explained to arise from metallic Zn agglomerates dispersed in non-crystalline Zn-O matrix. It was unveiled that film thickness more than 80 nm is required for the development of hexagonal crystal structure of ZnO. ZnO films on PET substrates exhibited high optical transmittance and good mechanical flexibility in the thickness range. The results of this study would provide a valuable guideline for the design of ZnO thin films on organic substrates for practical applications.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.186-186
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• 2015

We have introduced multifunctional ITO single thin films formed by normal sputtering system equipped with a plasma limiter which effectively blocks the bombardment of energetic negative oxygen ions. MFSS ITO also possesses high gas diffusion barrier properties simultaneously low resistivity even it deposited at room temperature without post annealing on plastic substrate. Nano-crystalline enhancement by Ar energy has energy window from 20 to 30 eV under blocking NOI condition. Effect of blocking NOI and optimal Ar energy window enhancement facilitate that resistivity is minimized to $3.61{\times}10^{-4}{\Omega}cm$ and the WVTR of 100 nm thick MFSS ITO is $3.9{\times}10^{-3}g/(m^2day)$ which is measured under environmental conditions of 90% relative humidity and 50oC that corresponds to a value of ${\sim}10^{-5}g/(m^2day)$ at room temperature. The multifunctional MFSS ITO with low resistivity, and low gas permeability will be highly valuable for plastic electronics applications.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.48 no.1
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• pp.5-18
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• 2016

Electron microscopy is an important investigation and analytical method for the morphological characterization of various cellulosic materials, such as micro-crystalline cellulose (MCC), microfibrillated cellulose (MFC), nanofibrillated cellulose (NFC), and cellulose nanocrystals (CNC). However, more accurate morphological analysis requires high-quality micrographs acquired from the proper use of an electron microscope and associated sample preparation methods. Understanding the interaction of electron and matter as well as the importance of sample preparation methods, including drying and staining methods, enables the production of high quality images with adequate information on the nanocellulosic materials. This paper provides a brief overview of the micro and nano structural analysis of cellulose, as investigated using transmission and scanning electron microscopy.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.851-854
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• 2001

Europium-activated Ga$_2$O$_3$powders were prepared by modified "Pechini method" from mixed aqueous solutions of gallium nitrate, europium nitrate, ethylene glycol and citric acid. The formation process and structure of the phosphor powders were investigated by means of TG/DTA, XRD and SEM. It has been found that the phosphor powders were amorphous up to 50$0^{\circ}C$ and changed into crystalline $\beta$-Ga$_2$O$_3$phase above $600^{\circ}C$. The resulting nano-sized powders were obtained. Red luminescence in emission spectra were observed at room temperature.