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Ogawa, Shuichi*; Taga, Ryo*; Yoshigoe, Akitaka; Takakuwa, Yuji*
Journal of Vacuum Science and Technology A, 39(4), p.043207_1 - 043207_9, 2021/07
Times Cited Count：1 Percentile：10.53(Materials Science, Coatings & Films)Nickel (Ni) is used as a catalyst for nitric oxide decomposition and ammonia production but it is easily oxidized and deactivated. Clarification of the reduction process of oxidized Ni is essential to promote more efficient use of Ni catalysts. In this study, the reduction processes were investigated by in situ time-resolved photoelectron spectroscopy. We propose a two-step reduction reaction model. The rate-limiting process for the first step is surface precipitation of O atoms and that of the second step is dissociation of H
molecules.
1 surface; In situ synchrotron radiation photoemission studyYoshigoe, Akitaka; Yamada, Yoichi*; Taga, Ryo*; Ogawa, Shuichi*; Takakuwa, Yuji*
Japanese Journal of Applied Physics, 55(10), p.100307_1 - 100307_4, 2016/09
Times Cited Count：5 Percentile：25.74(Physics, Applied)Synchrotron radiation photoelectron spectroscopy during the oxidation of the Si(100)21 surface at room temperature revealed the existence of the molecularly adsorbed oxygen, which was considered to be absent. The O 1s spectra was found to be similar to that of the oxidation of Si(111)77 surfaces. Also the molecular oxygen was appeared after the initial surface oxides, indicating that this was not a precursor for dissociation oxygen adsorption onto the clean surface. We have proposed presumable structural models for atomic configurations, where the molecular oxygen was resided on the oxidized silicon with two oxygen atoms at the backbonds.
Yoshigoe, Akitaka; Taga, Ryo*; Ogawa, Shuichi*; Takakuwa, Yuji*
no journal, ,
In this conference, the experimental evidence on the existence of molecularly adsorbed oxygen during the oxidation of Si(100)21 surface, which was considered to be absent, is reported. Synchrotron radiation photoelectron spectroscopy measurements was used to reveal its presence during the oxidation at room temperature and -150
C.
Sekihata, Yuki*; Ogawa, Shuichi*; Yoshigoe, Akitaka; Taga, Ryo*; Ishizuka, Shinji*; Takakuwa, Yuji*
no journal, ,
In this study, we investigated the oxidation reaction kinetics on p- and n-type Si surfaces using real-time ultraviolet photoelectron spectroscopy. In the room temperature oxidation, it is found that oxidation reaction coefficient on n-Si(001) is larger than that on p-Si(001). The work function of the n-Si(001) surface shows negative value but p-Si(001) is positive value. From this result, we can estimate the adsorption positions of O atoms. O atoms have a negative charge in the bond of Si-O, so it can be assumed that oxygen is placed on the n-Si(001) surfaces, but it is subsurface in case of the p-Si(001) surface. In case of n-Si(001) substrates, the doped electrons spill out into the surface because many electrons exist in the substrate. As the result, oxidation reaction is promoted in the n-Si(001) surface. From these results, we found that there is a difference of oxidation kinetics depending on the conductivity.
Ogawa, Shuichi*; Yamada, Takatoshi*; Taga, Ryo*; Yoshigoe, Akitaka; Takakuwa, Yuji*
no journal, ,
The molecular adsorption on graphene causes the modulation of conductivity of graphene, so that the application of graphene for gas sensors are expected. To evaluate the type of conductivity of graphene by photoelectron spectroscopy (PES), the angle-resolved PES is widely used. However, ARPES measurements have been performed usually in synchrotron facility or using monochromatic ultraviolet light. In this study, we try to evaluate the valence band of graphene using angle-integrated PES using non-monochromatic He I line in order to evaluate the changes of valence band of graphene during adsorption and/or desorption of molecules. As summary, we can measure the changes of shift of Fermi level depending on the temperature by using filter based on Fourier transform. This change is caused by desorption of absorbed molecules on graphene, and we can follow up the change because of using high-intensity non-monochromatic He I resonance line.
