Bismuth vanadate (BiVO4) is a key prototypical photocatalyst for water splitting, due to efficient collection of sunlight with an absorption onset at 2.5 eV, close to the maximum flux of the solar spectrum, and high solar to hydrogen conversion efficiency of up to 9.2%. Despite these promising characteristics, the fundamental nature and dynamics of photoexcitations in BiVO4 remain unclear. We now use advances in x-ray pump-probe techniques at sub-picosecond timescales to study the interactions of photo-excitations with the crystal lattice and connected changes of the atomic valency state in BiVO4 thin films. We measure pump-probe X-Ray Diffraction (XRD), X-ray Diffuse Scattering (XDS) and X-ray Absorption Near-Edge (XANES) at EuXFEL and APS to resolve structural and electronic dynamics. We find an unexpected ultrafast photoinduced structure change from monoclinic to tetragonal phases. From dynamics of related electronic valency changes and lattice strain fields, we draw up a detailed mechanistic model of our observations.
From the birth of plasmonics, the generation of hot carriers in nanostructured metals has been recognized as a fundamental challenge towards effectively harnessing light energy stored in sub-diffraction plasmon modes. However, the observation of hot-carrier transport at metal/dielectric Schottky junctions has reframed this challenge as a distinctive opportunity to facilitate precise control over photochemical and photophysical processes in a manner that is both spectrally selective and spatially precise. To further diversify the array of prospective applicationsin this research area, we showcase the generation of terahertz (THz) electromagnetic waves using the ultrafast formation and interfacial transport of plasmonic hot carriers in hybrid metal/dielectric nano-systems. The introduced hot-carrier-based coherent THz sources mitigate stringent materials requirements pertinent to state-of-the-art technologies for producing THz waves.
Oscillating microelectromechanical systems (MEMS) devices can manipulate synchrotron x-ray beams at ultrafast rates. By selectively diffracting x-rays, these devices can “pick” or even “slice” x-ray pulses from a beam; diffractive time windows less than 1 ns have been demonstrated. Here we demonstrate the use of MEMS devices to produce modulated x-ray beams with a high x-ray throughput that modify the timing structure of a synchrotron beam, which can be applied to perform time-resolved x-ray diffraction experiments.
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