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Nature Communications 13(1), 892 (2022). doi:10.1038/s41467-022-28486-3, We correlate spatially resolved fluorescence (-lifetime) measurements with X-ray nanodiffractionto reveal surface defects in supercrystals of self-assembled cesium lead halideperovskite nanocrystals and study their effect on the fluorescence properties. Upon comparisonwith density functional modeling, we show that a loss in structural coherence, anincreasing atomic misalignment between adjacent nanocrystals, and growing compressivestrain near the surface of the supercrystal are responsible for the observed fluorescenceblueshift and decreased fluorescence lifetimes. Such surface defect-related optical propertiesextend the frequently assumed analogy between atoms and nanocrystals as so-called quasiatoms.Our results emphasize the importance of minimizing strain during the self-assemblyof perovskite nanocrystals into supercrystals for lighting application such as superfluorescentemitters., Published by Nature Publishing Group UK, [London]

Science advances 7(40), eabh0757 (2021). doi:10.1126/sciadv.abh0757, The imaging of active nanoparticles represents a milestone in decoding heterogeneous catalysts’ dynamics. We report the facet-resolved, surface strain state of a single PtRh alloy nanoparticle on SrTiO$_3$ determined by coherent x-ray diffraction imaging under catalytic reaction conditions. Density functional theory calculations allow us to correlate the facet surface strain state to its reaction environment–dependent chemical composition. We find that the initially Pt-terminated nanoparticle surface gets Rh-enriched under CO oxidation reaction conditions. The local composition is facet orientation dependent, and the Rh enrichment is nonreversible under subsequent CO reduction. Tracking facet-resolved strain and composition under operando conditions is crucial for a rational design of more efficient heterogeneous catalysts with tailored activity, selectivity, and lifetime., Published by Assoc., Washington, DC [u.a.]

Structural dynamics 8(4), 044305 (2021). doi:10.1063/4.0000127, Second-order intensity interferometry was employed to study the spatial and temporal properties of the European X-ray Free-Electron Laser(EuXFEL). Measurements were performed at the soft x-ray Self-Amplified Spontaneous Emission (SASE3) undulator beamline at a photonenergy of 1.2 keV in the Self-Amplified Spontaneous Emission (SASE) mode. Two high-power regimes of the SASE3 undulator settings, i.e.,linear and quadratic undulator tapering at saturation, were studied in detail and compared with the linear gain regime. The statistical analysisshowed an exceptionally high degree of spatial coherence up to 90% for the linear undulator tapering. Analysis of the measured data in spectraland spatial domains provided an average pulse duration of about 10 fs in our measurements. The obtained results will be valuable for theexperiments requiring and exploiting short pulse duration and utilizing high coherence properties of the EuXFEL., Published by AIP Publishing LLC, Melville, NY