Ex) Article Title, Author, Keywords
Abstract : Co60Fe20B20 (CoFeB) films was prepared on a 3° mis-cut (0001) Al2O3 substrate by using DC Sputtering, and their magnetic properties were studied. An atomic force microscopy image showed that the CoFeB film had a step-terrace surface, and the magneto-optical Kerr effect measurement suggested that magnetic hysteresis had a clear difference for in-plane direction. CoFeB films had a magnetic easy axis along the longitudinal direction of the step-terrace, and the saturation magnetic field values were about 4.3 Oe for the easy-axis direction and about 48 Oe for the hard-axis direction, which is perpendicular to the step-terrace. CoFeB films had an uniaixal magnetic anisotropy with a period of 180° within the plane. The shape magnetic anisotropy energy in the step-terrace CoFeB film was roughly 2.5 times larger than a depsition magnetic anisotropy energy in a flat surface film. The surface morphology of the step-terrace was maintained up to a thickness of 50 nm, which was about 20 times the step-height, but the effect of the shape magnetic anisotropy decreased with increasing thickness. The direction dependent magnetic hysteresis behavior could be qualitativly explained by using a modified Stoner-Wohlfarth model.
Abstract : A carbon whisker-shaped thin film, similar to a carbon tube, was fabricated, instead of conventional diamond crystal particles, by applying a bias voltage to the silicon substrate. The fabricated thin film was analyzed for shape and composition by using scanning electron microscopy and Raman spectroscopy. As the bias current was increased, the shape of the carbon whiskers tended to become thinner and longer, causing an increase in the field emission current. Additionally, an increase in the CH4 concentration and substrate temperature increased the whisker diameter. Moreover, an addition of NH3 increased the growth rate and caused the formation of sharp edges on the whiskers, resulting in a decreased operating voltage in field emission.
Abstract : We fabricated a series of Sr2.96SiO5:0.04Eu(2+/3+) phosphors by using powders of a raw-material, SiO2, with various grainsizes, and we studied the effect of grain particle size on optical properties, such as excitation and emission spectra of Eu(2+/3+) ions doped in Sr3SiO5 and the crystallinity of Sr2.96SiO5:0.04Eu(2+/3+). Some of the samples studied using x-ray diffiaction had the same crystal structure as that of the standard sample Sr3SiO5(JCPDS-260984), but the crystallinity and the optical properties of Sr2.96SiO5:0.04Eu(2+/3+) depended greatly on the size of the particles in the SiO2 powder. The studied Sr2.96SiO5:0.04Eu2+ phosphors showed the maximum emission intensity at 582 nm with a full width at half maximum of about 70 nm and had good excitation efficiencies in the 240-500 nm region. Thus, we can conclude that the combination of ultraviolet or blue LED chips with a Sr2.96SiO5:0.04Eu2+ phosphor can be used as a source of warm white light with many potential applications. Through this study, we experimentally confirmed that the fabrication of Sr2.96SiO5:0.04Eu2+ phosphors was very sensitive to the powder size of SiO2 raw material.
Abstract : CFRP (carbon fiber reinforced plastic) composites have superior chemical resistance, vibrationdamping properties, electrical insulation, dimensional safety, etc. than conventional metal materials. Also, applications of these composites are gradually being attempted in various fields, such as the automobile, shipbuilding, medical equipment, and aerospace and aviation industries, and the scope of applications is expanding. CFRP composites have properties such as imbalance and anisotropy because they are manufactured with a desired stacking order and fiber arrangement angle by using a one-way prepreg sheet. In the additive process, defects such as pores, uneven thickness, resin distribution, and micro-cracks can occur due to sliding or stacking defects and can cause the destruction of the fibers and parent materials, interfacial separation, and fracture, Thus, the characteristics for the shape of CFRP Composite lamination must be evaluate, so In this study, an evaluating of the characteristics was performed by analyzing the ultrasonic A-scan (Amplitude-scan) signal and C-scan (Contrast-scan) image for CFRP composite lamination
Abstract : Carbon dots (CDs) originating from sucrose were synthesized by using a solvothermal method. The morphological, structural and luminescent properties of those CDs were analyzed to investigate the effect of the synthesis temperature on the CDs. TEM images of the CDs showed that increasing the synthesis temperature caused an increase in the particle size and aggregation of the CDs. The FT-IR and XPS spectra of the prepared CDs indicated that an increase in the synthesis temperature eliminated the surface functionalized ligands and the defects in CDs fabricated using the solvothermal reduction. Under 400-nm excitation, the PL spectra of the CDs exhibited a blue emission band with a maximum at 477 nm. When the synthesis temperature was 220 °C, the maximum emission intensity of the CDs was the highest. When the synthesis temperature was 250 °C, the dominant emission wavelength and emission intensity decreased due to the removed of defect states in the bandgap. The results in this study, clearly show that the synthesis temperature can be used to control the morphological, structural, luminescent properties of CDs.
Nguyen Ngoc DUY*, Latsamy XAYAVONG, Nguyen Kim UYEN, Vinh Nguyen Thanh PHAM, Tran Viet NHAM HAO
New Phys.: Sae Mulli 2019; 69(10): 1091-1100
Byeong-Hyeon JEONG, Ji-Sang PARK*
New Phys.: Sae Mulli 2020; 70(8): 630-636
Chang Dong SHIN, Kyung Kwang JOO*, Dong Ho MOON, Myoung Youl PAC, Junghwan GOH
New Phys.: Sae Mulli 2019; 69(8): 813-817