arXiv subjects

Tomoya Kawaguchi

Publications and source records attributed to Tomoya Kawaguchi.

6 recordsLinked to original sources

arXiv2020

Stern Layers on Surfaces of RuO2(100), RuO2(110), and Pt(111): Surface X-ray Scattering Studies

Surface X-ray scattering studies of electrochemical Stern layer are reported. The Stern layers formed at the interfaces of RuO2 (110) and (100) in 0.1 M CsF electrolyte are compared to the previously reported Stern layer on Pt(111) [Liu et al., J. Phys. Chem. Lett., 9 (2018) 1265]. While the Cs+ density profiles at the potentials close to hydrogen evolution reaction are similar, the hydration layers intervening the surface and the Cs+ layer on RuO2 surfaces are significantly denser than the hydration layer on Pt(111) surface possibly due to the oxygen termination of RuO2 surfaces. We also discuss in-plane ordering in the Stern layer on Pt(111) surface.

cond-mat.mtrl-sci↗

arXiv2019

Studying Internal Compositions of Binary Alloy Pd-Rh Nanoparticles Using Bragg Coherent Diffraction Imaging

Bragg coherent diffraction imaging (BCDI), the well-established technique for imaging internal strain of nanoparticles, was used to image the internal compositional distribution of binary alloys in thermal equilibrium. The images experimentally obtained for Pd-Rh alloy nanoparticles are presented and discussed. The direct correspondence between the lattice strain and the compositional deviation is discussed in the derivation of the BCDI displacement field aided by illustrations.

cond-mat.mes-hall↗

arXiv2019

Gas-induced segregation in Pt-Rh alloy nanoparticles observed by in-situ Bragg coherent diffraction imaging

Bimetallic catalysts can undergo segregation or redistribution of the metals driven by oxidizing and reducing environments. Bragg coherent diffraction imaging (BCDI) was used to relate displacement fields to compositional distributions in crystalline Pt-Rh alloy nanoparticles. 3D images of internal composition showed that the radial distribution of compositions reverses partially between the surface shell and the core when gas flow changes between O2 and H2. Our observation suggests that the elemental segregation of nanoparticle catalysts should be highly active during heterogeneous catalysis and can be a controlling factor in synthesis of electrocatalysts. In addition, our study exemplifies applications of BCDI for in situ 3D imaging of internal equilibrium compositions in other bimetallic alloy nanoparticles.

cond-mat.mtrl-sci↗

arXiv2018

Dynamics of the photoinduced insulator-to-metal transition in a nickelate film

The control of materials properties with light is a promising approach towards the realization of faster and smaller electronic devices. With phases that can be controlled via strain, pressure, chemical composition or dimensionality, nickelates are good candidates for the development of a new generation of high performance and low consumption devices. Here we analyze the photoinduced dynamics in a single crystalline NdNiO$_3$ film upon excitation across the electronic gap. Using time-resolved reflectivity and resonant x-ray diffraction, we show that the pump pulse induces an insulator-to-metal transition, accompanied by the melting of the charge order. Finally we compare our results to similar studies in manganites and show that the same model can be used to describe the dynamics in nickelates, hinting towards a unified description of these photoinduced phase transitions.

cond-mat.str-el↗

arXiv2018

Direct determination of one-dimensional interphase structures using normalized crystal truncation rod analysis

A one-dimensional non-iterative direct method was employed for normalized crystal truncation rod. The non-iterative approach, utilizing Kramers-Kronig relation, avoids the ambiguities due to the improper initial model or the incomplete convergence in the conventional iterative methods. The validity and limitation of the present method are demonstrated through both numerical simulations and experiments with Pt (111) in 0.1 M CsF aqueous solution. The present method is compared to conventional iterative phase-retrieval methods.

cond-mat.other↗

arXiv2017

In situ and non situ surface x-ray scattering studies of in plane Cs+ ordering in Helmholtz planes of Pt(111) surface

In-plane ordering of Cs+ layers in Helmhotlz planes was studied on Pt(111) surface in 0.1 M CsF electrolyte solutions with synchtrotron surface x-ray scattering techniques. The ordering was measured in a new transmission cell, designed for in situ and non situ measurements and high-temperature sample annealing all in the cell without sample transfer steps. At -850 mV vs. Ag/AgCl, (2x2) in-plane scattering peaks were weak under in situ condition and grew rapidly under non situ condition as the surface emersed from the electrolyte. The models for the (2x2) structures are presented and differences between in situ and non situ conditions are discussed.

cond-mat.mtrl-sci↗