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Jouhahn Lee,Yongsup Park 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.1
We have studied the interface electronic structures of Ca/tris-(8-hydorxyquinoline)aluminum (Alq3), Ca/NaF/Alq3, and Ca/MgF2/Alq3 by using X-ray and UV photoelectron spectroscopy (XPS and UPS). The UPS revealed that the Ca deposition on MgF2/Alq3 created weak gap states similar to Ca/Alq3 case, while the deposition of Ca on NaF/Alq3 showed relatively strong gap states. The N 1s core level peak measured with XPS exhibited a large satellite peak when Ca was deposited on NaF/Alq3, which was not seen in Ca/MgF2/Alq3. These changes indicate that both Na and Ca contribute to the charge transfer to the Alq3 molecules in Ca/NaF/Alq3, similar to Ca on LiF/Alq3. In contrast, only Ca or Mg plays a role in charge transfer in Ca/MgF2/Alq3, much like in Ca/Alq3. These observations suggest that charge transfer and chemical reactions at these interfaces could be important factors in energy-level alignments that determine the electron-injection barrier height.
이주한,Lee, Jouhahn 한국진공학회 2014 진공 이야기 Vol.1 No.1
The new materials such as graphene and other nano scale structured materials are attracting great attention due to its expandability for the future electronic devices. In this presentation, a variety of analysis techniques will be introduced for the latest new material applications such as graphene and organic materials with number of metals. The basic properties of next generation device should be carefully analyzed without being exposed to ambient surrounding since the physical and chemical properties of new material or interface states are easily and drastically changed by ambient condition. With the combination of the fabrication process and precise analysis instruments, it is expected to set the facilities supporting the nanotechnology industry and other research groups. This system will give strong support nanotechnology and other complex science with qualified data and information on basic knowledge on the new-forthcoming materials for the future.
An electrochemical approach to graphene oxide coated sulfur for long cycle life
Moon, Joonhee,Park, Jungjin,Jeon, Cheolho,Lee, Jouhahn,Jo, Insu,Yu, Seung-Ho,Cho, Sung-Pyo,Sung, Yung-Eun,Hong, Byung Hee The Royal Society of Chemistry 2015 Nanoscale Vol.7 No.31
<P>Owing to the possibilities of achieving high theoretical energy density and gravimetric capacity, sulfur has been considered as a promising cathode material for rechargeable lithium batteries. However, sulfur shows rapid capacity fading due to the irreversible loss of soluble polysulfides and the decrease in active sites needed for conducting agents. Furthermore, the low electrical conductivity of sulfur hampers the full utilization of active materials. Here we report that graphene oxide coated sulfur composites (GO-S/CB) exhibit improved electrochemical stability as well as enhanced rate performance, evidenced by various electrochemical analyses. The cyclic voltammetry and the galvanostatic cycling analysis revealed that the GO plays key roles in homogenizing the nanocomposite structures of the electrodes, in improving the electrochemical contact, and in minimizing the loss of soluble polysulfide intermediates. An electrochemical impedance spectroscopy analysis also confirms the enhanced structural stability of the GO-S/CB composites after battery operation. As a result, the GO-S/CB exhibited excellent cycle stability and specific capacity as high as ???723.7 mA h g(-1) even after 100 cycles at 0.5 C.</P>
Position-selective metal oxide nano-structures using graphene catalyst for gas sensors
Lee, Aram,Park, Jinheon,Choi, Kyoung Soon,Lee, Jouhahn,Yoo, Ilhan,Cho, In Sun,Ahn, Byungmin,Seo, Hyungtak,Choi, Jae-Young,Yu, Hak Ki Elsevier 2017 Carbon Vol.125 No.-
<P>The thermal transport growth of various metal oxide (MOx) nanostructures using graphene as a catalytic layer was studied. Graphene was synthesized by Cu-catalyzed chemical vapor deposition and transferred onto a SiO2-covered Si substrate using bubble transfer methods. Due to the catalytic activity of the atomic-thick carbon layer, control of the position of the MOx nanostructures as well as the growth parameters, such as nucleation density and growth rate, could be achieved. The position-selective and density-controlled MOx nanostructures were evaluated for hydrogen gas sensor applications, where different responses were obtained with hydrogen molecules. (C) 2017 Elsevier Ltd. All rights reserved.</P>