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Ohmic Contact Properties of Photo-Chemically Etched Nonpolar A-Plane [Formula] GaN Films
Baik, Kwang Hyeon,Lee, Sohyun,Jang, Soohwan The Electrochemical Society 2017 ECS journal of solid state science and technology Vol.6 No.11
<P>Nonpolar <I>a-</I>plane [Formula] GaN (<I>a-</I>GaN) was photo-chemically etched under ultraviolet illumination using alkali KOH solution, and the Ohmic contact properties on the etched <I>a-</I>GaN epitaxial layer were investigated. After photo-chemical etching, the striated surface morphology along the <I>c-</I>axis [0001] direction was obtained having triangular prisms consisting of <I>m</I>-plane [Formula] facets. The properties of Ti/Al/Ni/Au Ohmic contact on surface-textured <I>a</I>-GaN films were studied with transmission line method patterns aligned along the specific crystal orientations. The minimum specific contact resistance of 9.97 × 10<SUP>−5</SUP> Ω·cm<SUP>2</SUP> was achieved along the <I>c-</I>axis on the etched GaN surface at the annealing temperature of 750°C. The etched <I>a-</I>GaN showed higher electrical conductivity along the <I>c-</I>axis than along <I>m-</I>axis. This anisotropic behavior is in contrast to that of the unetched <I>a-</I>GaN where carrier scattering by basal plane stacking faults in the direction perpendicular to the <I>c-</I>axis is a major factor in determining opposite anisotropic conductivity. The higher conductivity along the c-axis of the etched <I>a</I>-GaN film could be explained by more dominant effect of surface roughness scattering.</P>
Baik, Kwang Hyeon,Kim, Jimin,Jang, Soohwan Elsevier 2017 Sensors and actuators. B Chemical Vol.238 No.-
<P><B>Abstract</B></P> <P>In this work, a highly sensitive <I>a-</I>plane ( 11 2 ¯ 0 ) GaN (<I>a-</I>GaN) based hydrogen sensor with a large active surface area on the Schottky contact region was fabricated and characterized. By using a simple photochemical etching technique, a striated surface morphology with triangular prisms consisting of <I>m</I>-plane facets on the <I>a-</I>GaN surface was obtained. The maximum relative current change of the etched <I>a-</I>GaN diode was as high as 3.8×10<SUP>7</SUP>%, and the reduction of the effective Schottky barrier height was 0.49eV upon 4% hydrogen exposure. The photo-chemically etched <I>a-</I>GaN sensor showed a remarkably improved hydrogen response and good repeatability for cyclic exposure to hydrogen. The photo-chemically textured GaN surface with enlarged surface area increased the number of adsorption sites available for hydrogen molecules to catalytically-decompose into surface atoms, lowering the effective Schottky barrier height, thereby increasing the measured current. Furthermore, the hydrogen sensing properties of the etched <I>a</I>-GaN diodes at different values of humidity and temperature were investigated.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Photo-chemically etched <I>a-plane</I> GaN Schottky diode hydrogen sensor was developed. </LI> <LI> The etched large surface offers more active adsorption sites for hydrogen molecules. </LI> <LI> The high sensitivity of the device for hydrogen was observed up to 500°C. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Moisture Insensitive PMMA Coated Pt-AlGaN/GaN Diode Hydrogen Sensor and Its Thermal Stability
Baik, Kwang Hyeon,Jung, Sunwoo,Ren, Fan,Pearton, S. J.,Jang, Soohwan The Electrochemical Society 2018 ECS journal of solid state science and technology Vol.7 No.7
<P>Poly(methyl methacrylate) (PMMA) encapsulated Pt-AlGaN/GaN Schottky diodes show highly sensitive (100 ppm, 0.01% by volume) room temperature detection of hydrogen and are insensitive to the presence of water in the sensing ambient. These diodes show no physical degradation or loss of sensitivity when repeatedly cycled (50 x, 1 min hold at each temperature) between 25-100 degrees C. There is complete selectivity for hydrogen sensing over other gases, including CO, CO2, NO2, O-2 and CH4. The PMMA encapsulation provides an effective and robust barrier to moisture, greatly increasing the range of environments in which the sensors can be used. (C) The Author(s) 2018. Published by ECS.</P>
Kwang Hyeon Baik,Yong Gon Seo,Soon-Ku Hong,Seogwoo Lee,Jaebum Kim,Ji-Su Son,Sung-Min Hwang IEEE 2010 IEEE photonics technology letters Vol.22 No.9
<P>We report on the effects of basal stacking faults (BSFs) on the electrical anisotropy and the device characteristics of nonpolar a-plane GaN (1120) light-emitting diodes (LEDs) on r-plane (1102 ) sapphire substrates. The sheet resistance in the direction parallel to the c-axis [0001] is 18%-70% higher than the one in the direction parallel to the m-axis [1100 ]. The anisotropic conductivity of faulted a-plane GaN films can be explained by carrier scatterings from BSFs. It is also shown that the output power of nonpolar a-plane GaN LEDs are significantly influenced by the presence of BSFs, which laterally hampers the carrier transport in the n-GaN layer, especially in the direction parallel to the c-axis in faulted nonpolar nitride films.</P>
Helicobacter pylori의 Kato III 세포내 발견
백승철,이정희,고경혁,조명제,조중현,김유경,윤희상,이우곤,이광호,강수민 대한소화기학회 1998 대한소화기학회지 Vol.31 No.6
Background/Aims; Some investigaters reported that the invasion of H. pylori into the gastric epithelial cells or lamina propria had been detected by light microscopie examination using various staining methods (i,e. the Warthin-Starry stain, immunohistologic stain) or by electron microscopic examination. However, the results are hardly convinced because they may be nonspecifically stained, or the intracytoplasmic organelles of the gastric epithelial cells may be mistaken for bacteria. Thus, we combined an immunohistologic method with an electron microscopy to deterrnine whether H. pylori is invasive into the gastric epithelial cells. Metbods: To enhance bacterial invasion, we adapted an in vitro system using Kato III cells, a gastric carcinoma eell line. The cells were infected with H. pylori. The infection was confirmed by staining with polyelonal antibody against H. pylori. and an electron microscopy. Resnlts: H. pylori was found within the cytoplasm of several Kato III cells. The intracellular bacteria could be differentiated from intracellular organelles or other bacteria-looking materials by gold particles attached to the bacteria, Conclusions: We could not elucidate the invasiveness of H. pylori, but we found the presence of H. pylori in the cytoplasm of the Kato III cells. These results indicate that the invasiveness of H. pylori will remain as one of the factors participating in the pathogenesis oF H. pylori-induced chronic gastritis and peptic ulcer. Further studies will be needed to demonstrate the invasiveness of H. pylori.
Acupuncture Meridian and Intravascular Bonghan Duct
Baik, Ku Youn,Lee, Ja Woong,Lee, Byung Cheon,Johng, Hyeon Min,Nam, Tae Jeong,Sung, Baeckkyoung,Cho, Sung Il,Soh, Kwang Sup Trans Tech Publications, Ltd. 2005 Key Engineering Materials Vol.277 No.-
<P>Current anatomical theory does not recognize the existence of an extended floating threadlike structure inside the blood vessels. Nonetheless, this study developed a new method for observing such an intravascular threadlike structure. The key technique involves injecting acridineorange into the femoral vein to circulate along the blood vessels and stain the nuclei of the intravascular threads inside the blood vessels. In-situ observations were then made under a fluorescence stereomicroscope after saline-perfusion. Confocal microscope images revealed a distinctive characteristic pattern of nucleus distribution that was clearly distinguishable from fibrin, capillaries, small venules, arterioles, or lymph vessels. Accordingly, it is suggested that the identified intravascular threads are part of the Bonghan's circulatory network that is distributed throughout the body, including inside the blood vessels.</P>
박현선,백광제,김준식,전영진,한승백,신동운,김아진 대한외상학회 1999 大韓外傷學會誌 Vol.12 No.2
Blank cartridge guns are generally regarded as being harmless and are not considered to be firearms in most countries. We experienced a case of brain injury causedby an accidental blank cartridge shot at close range. The patient suffered from open compound comminuted skull fracture at th frontal area, including the orbital roof. The initial blood pressure was uncheckable, and the patient showed Cheyne-Stokes respiration. The mental status was a coma state. Bleeding was noticed continuously at the open frontal area wound, and bleeding rhinorrhea and otorrhea were noticed. After fluid resuscitation, the vital signs were stabilized, and brain computerized tomogram (CT) scan was performed. It revealed open compound comminuted skull fracture at the frontal area with intracranial hemorrhage (ICH), subdural hemorrhage (SDH), and subarachnoid hemorrhage (SAH). After resuscitation, an open craniectomy and removal of the ICH were performed. However, the patient died 6days after the operation due to severe lethal brain swelling.
GaN Based Carbon Dioxide Sensor
Jung, Sunwoo,Baik, Kwang Hyeon,Jang, Soohwan Electrochemical Society 2017 ECS Transactions Vol.77 No.6
<P>AlGaN/GaN high electron mobility transistor based carbon dioxide sensor with ZnO nanorods as a sensing material was fabricated. The response of the device to carbon dioxide gas was characterized at elevated measurement temperature. The transistor showed an increase in drain current upon 500 ppm CO<SUB>2</SUB> due to the enhanced electron channel at the interface of AlGaN and GaN from 150°C. Reliable repeatability to cyclic exposures of various concentrations of carbon dioxide gas was observed. Also, effect of humidity on sensing behavior was investigated.</P>