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Jeong, Beomgyun,Jeon, Hongrae,Toyoshima, Ryo,Crumlin, Ethan J.,Kondoh, Hiroshi,Mun, Bongjin Simon,Lee, Jaeyoung American Chemical Society 2018 The Journal of Physical Chemistry Part C Vol.122 No.4
<P>While model studies of surface science under ultrahigh vacuum (UHV) have made significant contributions to understanding electrochemistry, many issues related to electrochemical phenomena still remain unanswered due to the extreme environmental differences between UHV and liquid conditions. Electrochemical formic acid (HCOOH) oxidation is one such example. While the dehydration step in the indirect oxidation pathway (HCOOH → H<SUB>2</SUB>O + CO<SUB>ad</SUB> → 2H<SUP>+</SUP> + 2e<SUP>–</SUP> + CO<SUB>2</SUB>) is observed in the electrochemical oxidation of formic acid on Pt(111) surface, the surface science studies conducted in UHV condition reported the complete HCOOH dissociation to H<SUB>2</SUB> and CO<SUB>2</SUB> on Pt(111) surface with no adsorbed CO at room temperature. A dehydration mechanism may also exist in gas-phase HCOOH dissociation in some conditions different from UHV, but it has not been demonstrated with a surface science method due to pressure limitations. Using ambient pressure X-ray photoelectron spectroscopy (AP-XPS), we observed the dehydration mechanism of gas-phase HCOOH in unprecedented high pressure environment for the first time. This study is a demonstration of reconciling the disagreement between electrocatalysis and surface science by bridging the environment gap.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2018/jpccck.2018.122.issue-4/acs.jpcc.7b07735/production/images/medium/jp-2017-077355_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp7b07735'>ACS Electronic Supporting Info</A></P>
Kim, Geonhwa,Yoon, Joonseok,Yang, Hyukjun,Lim, Hojoon,Lee, Hyungcheol,Jeong, Changkil,Yun, Hyungjoong,Jeong, Beomgyun,Crumlin, Ethan,Lee, Jouhahn,Lee, Jaeyoung,Ju, Honglyoul,Mun, Bongjin Simon American Institute of Physics 2016 Journal of Applied Physics Vol.120 No.20
<P>The evolution of oxidation/reduction states of vanadium oxide thin film was monitored in situ as a function of oxygen pressure and temperature via ambient pressure X-ray photoemission spectroscopy. Spectra analysis showed that VO2 can be grown at a relatively low temperature, T similar to 523 K, and that V2O5 oxide develops rapidly at elevated oxygen pressure. Raman spectroscopy was applied to confirm the formation of VO2 oxide inside of the film. In addition, the temperature-dependent resistivity measurement on the grown thin film, e.g., 20 nm exhibited a desirable metal-insulator transition of VO2 with a resistivity change of similar to 1.5 x 10(3) times at 349.3 K, displaying typical characteristics of thick VO2 film, e.g., 100 nm thick. Our results not only provide important spectroscopic information for the fabrication of vanadium oxides, but also show that high quality VO2 films can be formed at relatively low temperature, which is highly critical for engineering oxide film for heat-sensitive electronic devices. Published by AIP Publishing.</P>
<i>In situ</i> analysis of post-annealing effect on Sn-doped indium oxide films
Lim, Hojoon,Yang, Hyeok-Jun,Kim, Ji Woong,Bae, Jong-Seung,Kim, Jin-Woo,Jeong, Beomgyun,Crumlin, Ethan,Park, Sungkyun,Mun, Bongjin Simon American Institute of Physics 2016 Journal of Applied Physics Vol.120 No.20
<P>Oxygen post-annealing effects on tin (Sn) doped indium oxide (ITO) film are investigated with various analytical tools as a function of temperature, including in situ XRD, ambient pressure XPS (AP-XPS), and Hall measurement. As the annealing temperature increases up to 200 degrees C under the oxygen pressure of 100 mTorr, the in situ XRD shows the evidence of crystallization of the film while the AP-XPS reveals the formation of oxygen vacancy and Sn4+ states on surface. In addition, the mobility of ITO thin film is increased as the post-annealing temperature increases, supporting the results of both in situ XRD and AP-XPS. The results of angle-resolved XPS reveal that the degree of Sn segregation changes little after post-annealing procedure. Published by AIP Publishing.</P>
Yu, Youngseok,Koh, Yoobin Esther,Lim, Hojoon,Jeong, Beomgyun,Isegawa, Kazuhisa,Kim, Daehyun,Ueda, Kohei,Kondoh, Hiroshi,Mase, Kazuhiko,Crumlin, Ethan J,Ross Jr, Philip N,Gallet, Jean-Jacques,Bournel, Institute of Physics 2017 Journal of Physics, Condensed Matter Vol.29 No.46
<P>The study of CO oxidation on Pt(1 1 0) surface is revisited using ambient pressure x-ray photoemission spectroscopy. When the surface temperature reaches the activation temperature for CO oxidation under elevated pressure conditions, both the <I>α</I>-phase of PtO<SUB>2</SUB> oxide and chemisorbed oxygen are formed simultaneously on the surface. Due to the exothermic nature of CO oxidation, the temperature of the Pt surface increases as CO oxidation takes place. As the CO/O<SUB>2</SUB> ratio increases, the production of CO<SUB>2</SUB> increases continuously and the surface temperature also increases. Interestingly, within the diffusion limited regions, the amount of surface oxide changes little while the chemisorbed oxygen is reduced.</P>