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Dirac electrons in a dodecagonal graphene quasicrystal
Ahn, Sung Joon,Moon, Pilkyung,Kim, Tae-Hoon,Kim, Hyun-Woo,Shin, Ha-Chul,Kim, Eun Hye,Cha, Hyun Woo,Kahng, Se-Jong,Kim, Philip,Koshino, Mikito,Son, Young-Woo,Yang, Cheol-Woong,Ahn, Joung Real American Association for the Advancement of Scienc 2018 Science Vol.361 No.6404
<P>Quantum states of quasiparticles in solids are dictated by symmetry. We have experimentally demonstrated quantum states of Dirac electrons in a two-dimensional quasicrystal without translational symmetry. A dodecagonal quasicrystalline order was realized by epitaxial growth of twisted bilayer graphene rotated exactly 30 degrees. We grew the graphene quasicrystal up to a millimeter scale on a silicon carbide surface while maintaining the single rotation angle over an entire sample and successfully isolated the quasicrystal from a substrate, demonstrating its structural and chemical stability under ambient conditions. Multiple Dirac cones replicated with the 12-fold rotational symmetry were observed in angle-resolved photoemission spectra, which revealed anomalous strong interlayer coupling with quasi-periodicity. Our study provides a way to explore physical properties of relativistic fermions with controllable quasicrystalline orders.</P>
Electronic Structure of Graphene Grown on a Hydrogen-terminated Ge (110) Wafer
Sung Joon Ahn,Hyun Woo Kim,Ishwor Bahadur Khadka,Krishna Bahadur Rai,Joung Real Ahn,Jae-Hyun Lee,Seog Gyun Kang,Dongmok Whang 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.5
Using angle-resolved photoemission spectroscopy, we studied the electronic structure of graphene grown on a Ge (110) wafer, where a single-crystal single-layer graphene was recently grown using chemical vapor deposition. The growth mechanism of the single-layer single-crystal graphene was related to the hydrogen termination of the Ge (110) surface. To further understand the growth mechanism, we measured the electronic structure of the graphene-covered Ge (110) wafer in a vacuum as a function of the increasing temperature, which led to a deintercalation of the hydrogen atoms. Furthermore, we measured the electronic structure after the reintercalation of the hydrogen atoms between the Ge substrate and graphene. These findings show that hydrogen is intercalated between the Ge substrate and graphene after the growth of graphene using chemical vapor deposition.
박맹렬 ( Maeng Real Park ),이재호 ( Jae Ho Lee ),안지윤 ( Ji Yoon Ahn ),오범진 ( Bum Jin Oh ),김원 ( Won Kim ),임경수 ( Kyoung Soo Lim ) 대한외상학회 2006 大韓外傷學會誌 Vol.19 No.2
Tension viscerothorax (gastrothorax) is rare life-threatening disease which is caused by air trapped in viscera. A distended viscera in the hemi-thorax shifts the mediastinal structures and causes extra-cardiac obstructive shock. A defective diaphragm is caused by abdominal trauma or a congenital anomaly. Traumatic diaphragmatic injury can be missed until herniation develops several years after blunt trauma. In our case, a 10-year old boy developed hemodynamic compromise in the emergency department. Three years earlier, he had suffered blunt abdominal trauma during a pedestrian traffic accident, but there was no evidence of diaphragmatic injury at that time. He was successfully resuscitated by gastric decompression and an emergent thoracic operation. The operation finding revealed a traumatic diaphragmatic injury. Tension viscerothorax is a rare, but catastrophic, condition, so we suggest that addition of tension viscerothorax to the Advanced Trauma and Life Support (ATLS) guidelines may be helpful. (J Korean Soc Traumatol 2006;19:201-205)
Kim,Yuen-Chung,Ahn,Jeong-Jun,Kim,Jae-Min,Won,Chung-Yuen,Kim,Young-Real 성균관대학교 1998 학술회의지원논문목록집 Vol.1998 No.-
Because of simple control algorithm and easy implementation, the coilventional PI controller has been widely used in industrial application. But. it is very difficult to find the optimal PI control gain. Therefore, in improperly tuned PI controller or parameter variation, to obtain optimal performance, the novel PI controller, which consist of conventional PI controller and 4-rule based fuzzy logic, are presented in this paper. The novel PI controller which exhibits a stabilizing effects on the closed-loop system, has good robustness regarding the improperly tuned PI conrtoller or parameter variation. The simulations are performed to verify the capability of proposed control method on induction motor.
Origin of the Modied Electronic Properties of Au Formed on Pentacene
정석민,허혜은,임규욱,Joung-Real Ahn,송우석,홍준용,박종윤,강태희 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2
A Au lm formed on a pentacene layer, as a model system of a metal contact on a pentacenebased field-effect transistor, has been investigated. Unexpected pentacene derivatives and coarse morphology depending on the Au thickness are suggested as origins of the abnormal electronic structure of the Au film and the poor reproducibility of organic-based devices. The morphology of the Au film shows a strong dependency on the Au coverage. At 600 A of Au, a lift of the pentacene layer is shown as a result of deformation of the cracked Au film induced by a relaxation of the intergranular stresses accumulated during the growth process.
B. G. Shin,D. H. Oh,Joung Real Ahn 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.5
The relation of orbital hybridization between graphene and an adsorbate to the atomic and electronic structures of monolayer graphene was studied using first-principles calculations, where hydrogenated graphene was used as a prototype. The atomic and electronic structures of hydrogenated graphene were calculated as functions of the distance between graphene and hydrogen. The hybridization gap between the s orbital of hydrogen and the π orbital of graphene was tuned by changing the distance. The effect of the hybridization gap on the energy gap at the Dirac energy and the atomic structure deformation of graphene was schematically investigated, particularly when hydrogen breaks the in-plane symmetry.
Yuen-Chung Kim,Jeong-Joon Ahn,Jae-Mun Kim,Chung-Yuen Won,Young-Real Kim 전력전자학회 1998 ICPE(ISPE)논문집 Vol.- No.-
Because of simple control algorithm and easy implementation, the conventional PI controller has been widely used in industrial application. But, it is very difficult to find the optimal PI control gain. Therefore, in improperly tuned PI controller or parameter variation, to obtain optimal performance, the novel PI controller, which consist of conventional PI controller and 4-rule based fuzzy logic, are presented in this paper The novel PI controller which exhibits a stabilizing effects on the closed-loop system, has good robustness regarding the improperly tuned PI controller or parameter variation. The simulations are performed to verify the capability of proposed control method on induction motor.<br/>