Ex) Article Title, Author, Keywords
Abstract : In this research, we successfully fabricated a (trifluoromethanesulfonyl)-amide (TFSA)-doped graphene (TFSA-GR)/porous Si (PSi) solar cell by inserting a chemical vapor deposition-hexagonal boron nitride (h-BN) insulating layer. The photovoltaic parameters of the solar cell depent greatly on the presence or the absence of the h-BN insulating layer and TFSA-GR doping. Specifically, the h-BN insulating layer prevents carrier recombination at the TFSA-GR/PSi interface, thereby improving the charge collection/separation function and, consequently, improving the efficiency. As a result, the TFSA-GR/h-BN/PSi solar cells show a maximum PCE of 12.07%. These results demonstrate that h-BN is excellent as an insulating layer in GR/Si solar cells and is promising for use in graphene/Si-based optoelectronic device application.
Abstract : In general, science has the characteristics of pursuing universal truths or laws, and science education emphasizes teaching the nature of science. In this study, the characteristics of the process of pursuing universality, which is one facet of the nature of science, were investigated in three representative papers of Albert Einstein: general relativity, special relativity and photoelectric effect. The three research papers were found to show the following common characteristics of the process of pursuing universality: First, the pursuit of universality begins with an inconvenience caused by defects or a contradiction in the existing knowledge of physics. Second, the content of universality includes the frame-independent laws of physics, the frame-independent physical quantities (invariants), and the object-independent laws of physics. Third, the method of pursuing universality includes pointing out specific defects in existing knowledge of physics, accepting principles and concepts that should be universally respected, and making new arguments as universal ones that everyone will naturally accept.
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.
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