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Volume 194, 2016
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Towards efficient time-resolved X-ray absorption studies of electron dynamics at photocatalytic interfaces

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We present a picosecond time-resolved X-ray absorption spectroscopy (tr-XAS) setup designed for synchrotron-based studies of interfacial photochemical dynamics. The apparatus combines a high power, variable repetition rate picosecond laser system with a time-resolved X-ray fluorescence yield detection technique. Time-tagging of the detected fluorescence signals enables the parallel acquisition of X-ray absorption spectra at a variety of pump–probe delays employing the well-defined time structure of the X-ray pulse trains. The viability of the setup is demonstrated by resolving dynamic changes in the fine structure near the O1s X-ray absorption edge of cuprous oxide (Cu2O) after photo-excitation with a 355 nm laser pulse. Two distinct responses are detected. A pronounced, quasi-static, reversible change of the Cu2O O1s X-ray absorption spectrum by up to ∼30% compared to its static line shape corresponds to a redshift of the absorption edge by ∼1 eV. This value is small compared to the 2.2 eV band gap of Cu2O but in agreement with previously published results. The lifetime of this effect exceeds the laser pulse-to-pulse period of 8 μs, resulting in a quasi-static spectral change that persists as long as the sample is exposed to the laser light, and completely vanishes once the laser is blocked. Additionally, a short-lived response corresponding to a laser-induced shift of the main absorption line by ∼2 eV to lower energies appears within <200 ps and decays with a characteristic timescale of 43 ± 5 ns. Both the picosecond rise and nanosecond decay of this X-ray response are simultaneously captured by making use of a time-tagging approach – highlighting the prospects of the experimental setup for efficient probing of the electronic and structural dynamics in photocatalytic systems on multiple timescales.

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Publication details

The article was received on 10 May 2016, accepted on 18 May 2016 and first published on 18 May 2016

Article type: Paper
DOI: 10.1039/C6FD00125D
Citation: Faraday Discuss., 2016,194, 659-682
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    Towards efficient time-resolved X-ray absorption studies of electron dynamics at photocatalytic interfaces

    S. Neppl, J. Mahl, A. S. Tremsin, B. Rude, R. Qiao, W. Yang, J. Guo and O. Gessner, Faraday Discuss., 2016, 194, 659
    DOI: 10.1039/C6FD00125D

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