발간논문

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To enhance the efficiency of dye sensitized solar cells, we proposed crystalline anatase-TiO2 by using a low temperature process (150℃~250℃). We successfully fabricated 30 nm-TiO2 at a fixed atomic layer deposition condition of 1.0 sec of TDMAT pulse, 20 sec of TDMAT purge, 0.5 sec of H2O pulse, and 20 sec of H2O purge. In order to examine the microstructure, phase, and band-gap of the TiO2 respectively, we employed a Nano-Spec, transmission electron microscope, high resolution XRD, Auger electron spectroscopy, scanning probe microscope, and UV-VIS-NIR. We were able to fabricate a crystalline anatase-phase of 30 nm-TiO2 successfully at temperatures above 180℃. Our results showed that our proposed low temperature ALD process (below 200℃) might be applicable to glass and flexible polymer substrates.

keyword : thin films, deposition, crystallization, TEM, ALD

We investigated the In-based ohmic contacts on Nitrogen-face (N-face) n-type GaN, as well as Gaface n-type GaN, for InGaN-based vertical Light Emitting Diodes (LEDs). For this purpose, we fabricated Circular Transfer Length Method (CTLM) patterns on the N-face n-GaN that were prepared by using a laserlift off method, as well as on the Ga-face n-GaN that were prepared by using a dry etching method. Then, In/transparent conducting oxide (TCO) and In/TiW schemes were deposited on the CTLM in order for low resistance ohmic contacts to form. The In/TCO scheme on the Ga-face n-GaN showed high specific contact resistance, while the minimum specific contact resistance was only 3×10(-2) Ω-cm2 after annealing at 300℃, which can be attributed to the high sheet resistance of the TCO layer. In contrast, the In/TiW scheme on the Ga-face n-GaN produced low specific contact resistance of 2.1×10(5) Ω-cm2 after annealing at 500℃ for 1 min. In addition, the In/TiW scheme on the N-face n-GaN also resulted in a low specific contact resistance of 2.2×10(-4) Ω-cm2 after annealing at 300℃. These results suggest that both the Ga-face n-GaN and N-face n-GaN.

keyword : semiconductors, sputtering, electrical properties electrical

Carbon Nanotubes (CNTs) have recently emerged as a material with outstanding properties. It has shown promising potential for applications in many engineering fields as electronic devices, thermal conductors, and light-weight composites. Researchers have investigated their use as reinforcements in themetal matrix composites of CNTs. In the present work, we decorated CNTs with Ni particles by electroless plating. The CNTs were wet-ball milled for various milling times with a nickel sulfate solution. The precipitated Ni particles were observed mainly by FESEM. In this study, the dispersion of the CNTs and Ni particles was improved with the addition of the surfactant. Also, as the CNTs were shortened and widened by an increased ball milling time, the size of the precipitated Ni particles increased. It was estimated that the CNTs were deformed and caused some defects on their surface during the ball milling process. Those defects were assumed to be heterogeneous nucleation sites for the Ni particles.

keyword : carbon, deposition, nucleation, image analysis wet-ball milling

In this study, the interfacial bond strength of a squeeze infiltrated Al18B4O33/AS52 Mg composite was investigated by using a finite element method. Three types of Mg composites with volume fractions of 15, 25 and 35% were fabricated. Three-dimensional models of the composite were developed by using a unit cell model in order to determine the effective elastic modulus of the metal matrix composite and the interfacial bond strength between the whisker and magnesium matrix. After modeling, numerical results were compared with the experimental tensile test results of Al18B4O33/AS52 Mg composites. The results showed that the effective modulus of the composite strongly depended on the interfacial strength between the matrix and reinforcement. Based on the numerical and experimental findings, it was found that the strong interfacial bond was achieved by the interfacial reaction product of 30 nm thick MgO, which led to an improvement in the mechanical properties of the Al18B4O33/AS52 Mg composites.

keyword : composites, infiltration, interfaces, computer simulation, finite element method