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Papers by Yoobin Koh
Journal of the Korean Physical Society, 2019
The performance test of a laboratory based ambient pressure X-ray photoelectron spectroscopy (AP-... more The performance test of a laboratory based ambient pressure X-ray photoelectron spectroscopy (AP-XPS) system at the Gwangju Institute of Science and Technology (GIST) was carried out. The system, consisted of a Scienta R4000 HiPP-3 electron analyzer and a monochromatized Al Kα X-ray source, is designed to operate a gas pressure of up to 25 Torr. An Al polyimide X-ray window is used to isolate the X-ray source from the back-filled-type ambient pressure measurement chamber. Two modes of XPS operations were tested, a one-dimensional chemical imaging mode and a transmission mode. In the transmission mode, the lens voltage of analyzer was optimized for maximum detection of photo-excited electrons under elevated pressure condition, i.e., a typical standard lens operation mode. On the other hand, in the imaging mode, spatial information on the outgoing electrons is conserved to generate a one-dimensional chemical image of surface being measured. The test of the imaging mode on a Au/Si reference sample showed a spatial resolution of ∼10 μm under an Ar gas pressure of 500 mTorr. With the superb design of the differential pump and the electron transfer optics, a good signal-to-noise ratio was obtained for the XPS core-level spectra at Ar gas pressure up to 1 Torr.
Carbon, 2019
Tuning the fine structure of carbon support is crucial for modifying the metal-support interface ... more Tuning the fine structure of carbon support is crucial for modifying the metal-support interface (MSI) in order to harvest a high-performance catalysis. Herein, a coreeshell sp 3 @sp 2 nanocarbon (nanodiamond@graphene, ND@G) and a pure sp 2 carbon derivative (onion-like carbon, OLC) were applied to support Pd nanoparticles. We found that Pd/ND@G displayed a superior catalytic activity for CO oxidation reaction with a TOF of 2.9 times higher than that of Pd/OLC at 46 C. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and ambient pressure Xray photoelectron spectroscopy (AP-XPS) revealed that, different with the Pd/OLC system, a unique interface microstructure was formed in Pd/ND@G, which not only provides a high exposure of active sites, but also enhances the Pd surface reactivity toward oxygen species, thus leading to a superior catalytic activity of Pd/ND@G. Moreover, the temperature-programmed surface reaction (TPSR) results showed that CO oxidation on Pd/ND@G undergoes an unusual termolecular EleyeRideal (TER) mechanism, which has a lower energy barrier as compared to the traditional Langmuir-Hinshelwood (LH) and ER mechanism.
Journal of physics. Condensed matter : an Institute of Physics journal, Jan 25, 2017
The study of CO oxidation on Pt(110) surface is revisited using ambient pressure x-ray photoemiss... more The study of CO oxidation on Pt(110) surface is revisited using ambient pressure x-ray photoemission spectroscopy. When the surface temperature reaches the activation temperature for CO oxidation under elevated pressure condition, both the -phase of PtO2 oxide and chemisorbed oxygen are formed simultaneously on the surface. Due to exothermic nature of CO oxidation, the temperature of Pt surface increases as CO oxidation takes places. As the CO/O2 ratio increases, the production of CO2 increases continuously and the surface temperature also increases. Interestingly, during the mass transfer limiting regions, the amount of surface oxide changes little while the chemisorbed oxygen is being reduced. 
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Journal of the Korean Physical Society, 2019
The performance test of a laboratory based ambient pressure X-ray photoelectron spectroscopy (AP-... more The performance test of a laboratory based ambient pressure X-ray photoelectron spectroscopy (AP-XPS) system at the Gwangju Institute of Science and Technology (GIST) was carried out. The system, consisted of a Scienta R4000 HiPP-3 electron analyzer and a monochromatized Al Kα X-ray source, is designed to operate a gas pressure of up to 25 Torr. An Al polyimide X-ray window is used to isolate the X-ray source from the back-filled-type ambient pressure measurement chamber. Two modes of XPS operations were tested, a one-dimensional chemical imaging mode and a transmission mode. In the transmission mode, the lens voltage of analyzer was optimized for maximum detection of photo-excited electrons under elevated pressure condition, i.e., a typical standard lens operation mode. On the other hand, in the imaging mode, spatial information on the outgoing electrons is conserved to generate a one-dimensional chemical image of surface being measured. The test of the imaging mode on a Au/Si reference sample showed a spatial resolution of ∼10 μm under an Ar gas pressure of 500 mTorr. With the superb design of the differential pump and the electron transfer optics, a good signal-to-noise ratio was obtained for the XPS core-level spectra at Ar gas pressure up to 1 Torr.
Carbon, 2019
Tuning the fine structure of carbon support is crucial for modifying the metal-support interface ... more Tuning the fine structure of carbon support is crucial for modifying the metal-support interface (MSI) in order to harvest a high-performance catalysis. Herein, a coreeshell sp 3 @sp 2 nanocarbon (nanodiamond@graphene, ND@G) and a pure sp 2 carbon derivative (onion-like carbon, OLC) were applied to support Pd nanoparticles. We found that Pd/ND@G displayed a superior catalytic activity for CO oxidation reaction with a TOF of 2.9 times higher than that of Pd/OLC at 46 C. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and ambient pressure Xray photoelectron spectroscopy (AP-XPS) revealed that, different with the Pd/OLC system, a unique interface microstructure was formed in Pd/ND@G, which not only provides a high exposure of active sites, but also enhances the Pd surface reactivity toward oxygen species, thus leading to a superior catalytic activity of Pd/ND@G. Moreover, the temperature-programmed surface reaction (TPSR) results showed that CO oxidation on Pd/ND@G undergoes an unusual termolecular EleyeRideal (TER) mechanism, which has a lower energy barrier as compared to the traditional Langmuir-Hinshelwood (LH) and ER mechanism.
Journal of physics. Condensed matter : an Institute of Physics journal, Jan 25, 2017
The study of CO oxidation on Pt(110) surface is revisited using ambient pressure x-ray photoemiss... more The study of CO oxidation on Pt(110) surface is revisited using ambient pressure x-ray photoemission spectroscopy. When the surface temperature reaches the activation temperature for CO oxidation under elevated pressure condition, both the -phase of PtO2 oxide and chemisorbed oxygen are formed simultaneously on the surface. Due to exothermic nature of CO oxidation, the temperature of Pt surface increases as CO oxidation takes places. As the CO/O2 ratio increases, the production of CO2 increases continuously and the surface temperature also increases. Interestingly, during the mass transfer limiting regions, the amount of surface oxide changes little while the chemisorbed oxygen is being reduced. 
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