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Energy Spectral Properties of 2D Bloch Electrons under Spatially Modulated Magnetic Fields
Oh, Gi-Yeong,Chung, Jaegwan 안성산업대학교 1997 論文集 Vol.29 No.2
일차원 및 이차원 공간 변조 자기장이 이차원 정방격자의 전자적 성질에 미치는 연향을 연구하였다. 공간 변조 자기장의 예로 싸인 및 코싸인 형태의 변조 자기장을 연구함으로써 에너지 밴드 폭의 확대와 에너지 갭의 생성이 균일한 자기장 효과와는 확연히 대비되는 변조의 특성임을 밝혔다. 또한 이 특성의 근원이 각 밴드간의 교차와 접촉에 있음도 명확히 밝혔다. 에너지 밴드 폭의 확대에너지 갭의 생성 현상은 균일한 자기장 하에서의 에너지 스펙트럼, 즉 Hosftadter butterfly pattern에서 나타나는 자기유사성을 깨뜨리는 원인이 됨도 밝혔다.
Unipolar Resistive Switching of EuxOy Polycrystalline Films
박배호,김상훈,최진식,이장원,JaeGwan Chung,서선애 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2
Polycrystallized EuxOy thin films show unipolar resistive switching. The ratios of the resistance values of the high-resistance state to those of the low-resistance state are as large as 108. The deposited EuxOy thin films show mixed phases, Eu2O3 and Eu3O4. The relative concentration of the phases could be controlled by using the oxygen gas flow rate during growth. A high oxygen concentration leads to broadening the distribution of the switching voltages, inducing transitions between the high-resistance state and the low-resistance state. We observe that the distribution of the switching voltage from the high-resistance state to the low-resistance state (VSET ) is smaller than or comparable to that of the switching voltage inducing the opposite transition (VRESET ) in well-controlled EuxOy thin films.
Ahn, Dong A,Lee, Seungjun,Chung, Jaegwan,Park, Yongsup,Suh, Min Chul American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.27
<P>We investigated interfacial mixing of solution-processed organic light-emitting devices (OLEDs) using impedance spectroscopy (IS) and ultraviolet photoelectron spectroscopy (UPS) and its impact on device performance. We focused on interfacial mixing between a solution processed cross-linkable hole transport layer (XM) and an emitting layer (EML), formed either by solution processing or vacuum evaporation. The results of IS and UPS clearly indicated that extensive interfacial mixing was unavoidable, even after the XM was cross-linked to make it insoluble and rinsed to remove residual soluble species, if the subsequent EML was solution processed. In addition, we also demonstrated that interfacial mixing indeed increased hole current density in corresponding hole only device (HOD). In fact, the hole injection efficiency could be an order of magnitude better when the EML was solution processed rather than vacuum evaporated. We investigated such behavior to find the desirable process condition of solution-processed OLEDs.</P>
HyunJoon Shin,Mikang Kim,Namdong Kim,Hyeong-Do Kim,Changhoon Jung,JaeGwan Chung,KiHong Kim,Woo Sung Jeon 한국진공학회(ASCT) 2020 Applied Science and Convergence Technology Vol.29 No.4
Pristine and 4.35 V charged-state particles of the Li1.0Ni0.88Co0.08Mn0.04O₂ lithium–ion battery (LIB) cathode material were cross-sectioned by the focused-ion-beam method to allow the acquisition of spatially resolved Ni L₃-edge, Co L₃-edge, Mn L₃-edge, and O K-edge X-ray absorption spectra by scanning transmission X-ray microscopy with a spatial resolution of ~30 ㎚. The Co L₃-edge and the Mn L₃-edge spectra, respectively, displayed almost the same features throughout the particles for both the pristine-state and charged-state samples. The average oxidation states of the Co and Mn ions were estimated to be ~3+ and ~4+, respectively. The Ni L₃-edge and O K-edge spectra included different features, depending on the charge state and intra-particle location. The estimated average oxidation state of the Ni ions ranged from ~2.7+ to ~3.0+ for the pristine-state sample (space-averaged value: ~2.9+) and from ~2.7+ to ~3.5+ for the charged-state sample (space-averaged value: ~3.3+). A correlation was observed between the changes in the features of the O K-edge and Ni L₃-edge. These results would provide important implications for the development of high-performance LIBs.
Yun, Dong-Jin,Lim, Sungjin,Won, Jung Yeon,Kim, Kihong,Lee, HyungIk,Hwang, Junsik,Chung, JaeGwan,Kim, Yong Su,Kwon, Young-Nam,Lee, Eunha,Baik, Jaeyoon,Yang, Woo-Young Elsevier 2018 Journal of Power Sources Vol.399 No.-
<P><B>Abstract</B></P> <P>Lithium phosphorus oxynitride and lithium phosphate layers are prepared by controlling nitrogen composition using an optimized chemical vapor deposition process. Besides the predictable lithium phosphate layer decomposition process, progressive changes are observed in the lithium phosphorus oxynitride layer in air over time. These changes influence both the performance and stability of Lithium phosphorus oxynitride, utilized as solid-electrolytes or interface barriers in batteries. Therefore, to clarify the transition mechanism of them in air, a unique experiment is designed based on x-ray photoelectron spectroscopy. The results indicate that changes in the chemical structures of lithium phosphorus oxynitride and lithium phosphate occurred alongside morphological variations. Lithium phosphorus oxynitride layers undergo steady attacks by reactive gases in air, such as O<SUB>2</SUB>, CO<SUB>2</SUB>, and H<SUB>2</SUB>O, resulting in an increased number of imperfect or dangling bonds and internal chemical reactions that in turn cause morphological changes. In addition, a graphene layer is employed to reduce the reactions of Lithium phosphorus oxynitride layers with reactive gases. The results show that the graphene-coated domains have relatively lower degradation rate than other regions. Overall, our results reveal the stability problems of lithium phosphorus oxynitride and lithium phosphate by demonstrating significant changes in the chemical/morphological structures exposed to air.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The nitrogen composition effects on LiPON stability are clarified. </LI> <LI> The degradation mechanism of LiPON solid-electrolyte in air is illustrated. </LI> <LI> X-ray spectroscopy and atomic force microscopy explain well the degradation process. </LI> <LI> Graphene layer can slow down the aging process of LiPON solid-electrolyte. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>