Abstract Yasukazu Murakami is a distinguished professor at Kyushu University (department of applied quantum physics and nuclear engineering). Since 2022, he serves as the director of the Ultramicroscopy Research Center, Kyushu University. His research interests include (1) electron holography studies on magnetic nanostructures, (2) precision improvement of electron holography to measure weak electromagnetic field, (3) in situ electron microscopy about phase transformations and pattern formations in crystals, etc. He received several awards, the Gold Medal from the Japanese Society of Microscopy (2010), Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology (2024), and others.Figure 1. (a),(b) Lattice images of Pt nanoparticles and (c),(d) phase images (outside of nanoparticles) revealed by the amplitude/phase reconstruction using electron holography. The amount of charging (Qave) was presented in the unit of elementary charge (qe). Adopted from [2].42Understanding of the charging state in a metallic nanoparticle supported on oxide surface is vitally important in science and engineering of heterogeneous catalysts. Indeed, the charging affects adsorption and/or dissociation of molecules on the catalyst surface via a change in the electronic occupancy of the antibonding state.As a pioneering study on the charging state in a heterogeneous catalyst, X-ray photoemission spectroscopy revealed the charge amount per nanoparticle [1] although the result was the average from many nanoparticles. The author and his collaborators attempted “particle-by-particle analysis” of the charging state in Pt nanoparticles supported on a TiO2 crystal by using off-axis electron holography [2]. The phase-shift analysis revealed a slight change in the electrostatic potential due to the weak charging of Pt nanoparticle: i.e., only 1–6 electrons per nanoparticle. Importantly, Pt nanoparticles could be charged either positively or negatively depending on the orientation relationship with the TiO2 crysta1 [Fig. 1]. The results could be explained by first-principles calculations, in terms of the charge transfer between Pt and TiO2. The impact of oxygen-gas pressures on the charging state (examinations from another catalyst Au/CeO2) will be also discussed.[1] Y. Lykhach et al., Nat. Mater., 15, 284-289 (2016).[2] R. Aso et al., Science, 378, 202-206 (2022).Professor, The Ultramicroscopy Research Center, Kyushu University, JapanElectron Holography Studies on the Charging State of Catalyst NanoparticlesYasukazu MurakamiInvited Talk: S4-1
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