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Surface probe microscopy: From new methods to new results

Yasuhiro Sugawara, Yan Jun Li (Osaka University, Japan)

Pavilón QUTE, Auditórium – 2. poschodie, FÚ SAV

Abstract:

After a brief general introduction of the activities of the Sugawara/Li SPM group, two projects, both focusing the catalytic CO oxidation reaction, will be presented more in detail:

  1. Investigation of Pd nanoparticles on Al2O3/NiAl(110) under CO gas by AFM/ KPFM,
  2. Elucidation of the local dipole moment on TiO2(110) surface by electrostatic force.

Subject 1. has strong application ramifications as metal nanoparticles supported on a metal oxide are well known as outstanding three-way catalysts for oxidation of CO. Charging of the supported clusters plays a key role in promoting their chemical activity [1]. We investigated Pd nanoparticles (NPs) under CO gas condition by AFM/ KPFM [2]. The measured local contact potential difference (LCPD) for the adsorption of CO molecules on the interface between Pd NPs and Al2O3 thin film demonstrates a back donation of electrons to CO molecules. LCPD of Pd NPs increases with their size, and so does the electrons transfer from the NiAl(110) substrate to Pd NPs. These results will be elucidated by a model.

As for 2), also Au/TiO2(110) displays extremely high catalytic reactivity in the CO oxidation reaction [3]. Several models have been proposed, however, no comprehensive experimental clarification of the injection/extraction mechanism of electrons and the reaction process exists as yet. In order to shed new light on the mechanisms, we propose a novel method to measure dipole moment distribution induced local surface potential and apply it to the TiO2(110) surface. In the experiment, the DC bias added with AC bias voltage is applied between the tip and sample. The nonlinear dielectric constants are a function of DC bias and can be cancelled. Three lock-in amplifiers are used to detect frequency shift of fm, f2m and f3m. The contact potential difference is numerically calculated from the divided result of fm and f2m signals [4, 5] and dipole moment induced surface potential is obtained from the DC bias feedback. These new experimental data will be reported.

Figure. Pd MPs on Al2O3/NiAl(110) surface under CO gas condition. (a) Topographic image and line profile, (b) VLCPD image and line profile.

[1] Yoon et al., Science 307, 21 (2005).
[2] Y. J. Li et al., Nanotech. 26, 50 (2015).
[3] M. Haruta. Catal. Today. 36, 153 (1997).
[4] L. L. Kou, Z. M. Ma, Y. J. Li, Y. Naitoh, M. Komiyama and Y. Sugawara, Nanotechnology 26, 195701 (2015).
[5] O. Takeuchi, Y. Ohrai. S. Yoshida and H. Shigekawa, Jpn. J. Appl. Phys. 46, 8B (2007).

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