Dataset Information

Hole Dynamics in Photoexcited Hematite Studied with Femtosecond Oxygen K-edge X-ray Absorption Spectroscopy.

ABSTRACT: Hematite (α-Fe₂O₃) is a photoelectrode for the water splitting process because of its relatively narrow bandgap and abundance in the earth's crust. In this study, the photoexcited state of a hematite thin film was investigated with femtosecond oxygen K-edge X-ray absorption spectroscopy (XAS) at the PAL-XFEL in order to follow the dynamics of its photoexcited states. The 200 fs decay time of the hole state in the valence band was observed via its corresponding XAS feature.

SUBMITTER: Uemura Y

PROVIDER: S-EPMC9125685 | biostudies-literature | 2022 May

REPOSITORIES: biostudies-literature

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Publications

Hole Dynamics in Photoexcited Hematite Studied with Femtosecond Oxygen K-edge X-ray Absorption Spectroscopy.

Uemura Yohei Y Ismail Ahmed S M ASM Park Sang Han SH Kwon Soonnam S Kim Minseok M Elnaggar Hebatalla H Frati Federica F Wadati Hiroki H Hirata Yasuyuki Y Zhang Yujun Y Yamagami Kohei K Yamamoto Susumu S Matsuda Iwao I Halisdemir Ufuk U Koster Gertjan G Milne Christopher C Ammann Markus M Weckhuysen Bert M BM de Groot Frank M F FMF

The journal of physical chemistry letters 20220505 19

Hematite (α-Fe<sub>2</sub>O<sub>3</sub>) is a photoelectrode for the water splitting process because of its relatively narrow bandgap and abundance in the earth's crust. In this study, the photoexcited state of a hematite thin film was investigated with femtosecond oxygen K-edge X-ray absorption spectroscopy (XAS) at the PAL-XFEL in order to follow the dynamics of its photoexcited states. The 200 fs decay time of the hole state in the valence band was observed via its corresponding XAS feature. ...[more]

PMID: 35512383

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Project description:A series of mononuclear six-coordinate tungsten compounds spanning formal oxidation states from 0 to +VI, largely in a ligand environment of inert chloride and/or phosphine, was interrogated by tungsten L-edge X-ray absorption spectroscopy. The L-edge spectra of this compound set, comprised of [W(0)(PMe3)6], [W(II)Cl2(PMePh2)4], [W(III)Cl2(dppe)2][PF6] (dppe = 1,2-bis(diphenylphosphino)ethane), [W(IV)Cl4(PMePh2)2], [W(V)(NPh)Cl3(PMe3)2], and [W(VI)Cl6], correlate with formal oxidation state and have usefulness as references for the interpretation of the L-edge spectra of tungsten compounds with redox-active ligands and ambiguous electronic structure descriptions. The utility of these spectra arises from the combined correlation of the estimated branching ratio of the L3,2-edges and the L1 rising-edge energy with metal Zeff, thereby permitting an assessment of effective metal oxidation state. An application of these reference spectra is illustrated by their use as backdrop for the L-edge X-ray absorption spectra of [W(IV)(mdt)2(CO)2] and [W(IV)(mdt)2(CN)2](2-) (mdt(2-) = 1,2-dimethylethene-1,2-dithiolate), which shows that both compounds are effectively W(IV) species even though the mdt ligands exist at different redox levels in the two compounds. Use of metal L-edge XAS to assess a compound of uncertain formulation requires: (1) Placement of that data within the context of spectra offered by unambiguous calibrant compounds, preferably with the same coordination number and similar metal ligand distances. Such spectra assist in defining upper and/or lower limits for metal Zeff in the species of interest. (2) Evaluation of that data in conjunction with information from other physical methods, especially ligand K-edge XAS. (3) Increased care in interpretation if strong ?-acceptor ligands, particularly CO, or ?-donor ligands are present. The electron-withdrawing/donating nature of these ligand types, combined with relatively short metal-ligand distances, exaggerate the difference between formal oxidation state and metal Zeff or, as in the case of [W(IV)(mdt)2(CO)2], exert the subtle effect of modulating the redox level of other ligands in the coordination sphere.

Dataset Information

Hole Dynamics in Photoexcited Hematite Studied with Femtosecond Oxygen K-edge X-ray Absorption Spectroscopy.

Publications

Hole Dynamics in Photoexcited Hematite Studied with Femtosecond Oxygen K-edge X-ray Absorption Spectroscopy.

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