22 research outputs found
Electronic structure and symmetry of valence states of epitaxial NiTiSn and NiZrHfSn thin films by hard x-ray photoelectron spectroscopy
The electronic band structure of thin films and superlattices made of Heusler
compounds with NiTiSn and NiZrHfSn composition was studied by
means of polarization dependent hard x-ray photoelectron spectroscopy. The
linear dichroism allowed to distinguish the symmetry of the valence states of
the different types of layered structures. The films exhibit a larger amount of
{\it "in-gap"} states compared to bulk samples. It is shown that the films and
superlattices grown with NiTiSn as starting layer exhibit an electronic
structure close to bulk materials
Magnetic dichroism in angular-resolved hard X-ray photoelectron spectroscopy from buried layers
This work reports the measurement of magnetic dichroism in angular-resolved
photoemission from in-plane magnetized buried thin films. The high bulk
sensitivity of hard X-ray photoelectron spectroscopy (HAXPES) in combination
with circularly polarized radiation enables the investigation of the magnetic
properties of buried layers. HAXPES experiments with an excitation energy of 8
keV were performed on exchange-biased magnetic layers covered by thin oxide
films. Two types of structures were investigated with the IrMn exchange-biasing
layer either above or below the ferromagnetic layer: one with a CoFe layer on
top and another with a CoFeAl layer buried beneath the IrMn layer. A
pronounced magnetic dichroism is found in the Co and Fe states of both
materials. The localization of the magnetic moments at the Fe site conditioning
the peculiar characteristics of the CoFeAl Heusler compound, predicted to
be a half-metallic ferromagnet, is revealed from the magnetic dichroism
detected in the Fe states
Cu Modified TiO<sub>2</sub> Catalyst for Electrochemical Reduction of Carbon Dioxide to Methane
Electrochemical reduction of CO2 (ECO2R) is gaining attention as a promising approach to store excess or intermittent electricity generated from renewable energies in the form of valuable chemicals such as CO, HCOOH, CH4, and so on. Selective ECO2R to CH4 is a challenging target because the rate-determining step of CH4 formation, namely CO* protonation, competes with hydrogen evolution reaction and the C–C coupling toward the production of longer-chain chemicals. Herein, a Cu-TiO2 composite catalyst consisting of CuOx clusters or Cu nanoparticles (CuNPs), which are isolated on the TiO2 grain surface, was synthesized using a one-pot solvothermal method and subsequent thermal treatment. The Cu-TiO2 catalyst exhibited high selectivity for CH4, and the ratio of FE for CH4 to total FE for all products in ECO2R reached 70%
Heterointerface Created on Au-Cluster-Loaded Unilamellar Hydroxide Electrocatalysts as a Highly Active Site for the Oxygen Evolution Reaction
The oxygen evolution reaction (OER) is a critical element for all sorts of reactions that use water as a hydrogen source, such as hydrogen evolution and electrochemical CO2 reduction, and novel design principles that provide highly active sites on OER electrocatalysts push the limits of their practical applications. Herein, Au-cluster loading on unilamellar exfoliated layered double hydroxide (ULDH) electrocatalysts for the OER is demonstrated to fabricate a heterointerface between Au clusters and ULDHs as an active site, which is accompanied by the oxidation state modulation of the active site and interfacial direct O-O coupling ("interfacial DOOC"). The Au-cluster-loaded ULDHs exhibit excellent activities for the OER with an overpotential of 189 mV at 10 mA cm(-2). X-ray absorption fine structure measurements reveal that charge transfer from the Au clusters to ULDHs modifies the oxidation states of trivalent metal ions, which can be active sites on the ULDHs. The present study, supported by highly sensitive spectroscopy combining reflection absorption infrared spectroscopy and modulation-excitation spectroscopy and density functional theory calculations, indicates that active sites at the interface between the Au clusters and ULDHs promote a novel OER mechanism through interfacial DOOC, thereby achieving outstanding catalytic performance
Impact of Ir-Valence Control and Surface Nanostructure on Oxygen Evolution Reaction over a Highly Efficient Ir-TiO2 Nanorod Catalyst
Impact of Ir-Valence Control and Surface Nanostructure on Oxygen Evolution Reaction over a Highly Efficient Ir-TiO2 Nanorod Catalys