| 1. |
- Aziz, Emad F, et al.
(författare)
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Probing the electronic structure of the hemoglobin active center in physiological solutions.
- 2009
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:6, s. 068103-
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Tidskriftsartikel (refereegranskat)abstract
- Soft-x-ray absorption spectroscopy at the L_{2,3} edge of the iron center in bovine hemoglobin and hemin under physiological conditions is reported for the first time. Spectra of the same compounds in solid form are presented for comparison. Striking differences in the electronic structure of the metalloporphyrin are observed between the liquid and solid compounds. We unambiguously show that hemoglobin and hemin are in a high-spin ferric state in solution, and that the 2p spin-orbit coupling decreases for hemin compared to the hemoglobin, while this is not the case in solids. The spectra were simulated using ligand field multiplet theory, in good agreement with the experiment, allowing quantification of the amount of charge transfer between the porphyrin and Fe3+ ion in hemoglobin and in hemin.
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| 2. |
- Cannelli, Oliviero, et al.
(författare)
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Atomic-Level Description of Thermal Fluctuations in Inorganic Lead Halide Perovskites
- 2022
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 13:15, s. 3382-3391
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive microscopic description of thermally induced distortions in lead halide perovskites is crucial for their realistic applications, yet still unclear. Here, we quantify the effects of thermal activation in CsPbBr3 nanocrystals across length scales with atomic-level precision, and we provide a framework for the description of phase transitions therein, beyond the simplistic picture of unit-cell symmetry increase upon heating. The temperature increase significantly enhances the short-range structural distortions of the lead halide framework as a consequence of the phonon anharmonicity, which causes the excess free energy surface to change as a function of temperature. As a result, phase transitions can be rationalized via the soft-mode model, which also describes displacive thermal phase transitions in oxide perovskites. Our findings allow to reconcile temperature-dependent modifications of physical properties, such as changes in the optical band gap, that are incompatible with the perovskite time- and space-average structures.
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| 3. |
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| 4. |
- Chergui, Majed, et al.
(författare)
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Progress and prospects in nonlinear extreme-ultraviolet and X-ray optics and spectroscopy
- 2023
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Ingår i: Nature reviews physics. - 2522-5820. ; :5, s. 578-596
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Forskningsöversikt (refereegranskat)abstract
- Free-electron lasers and high-harmonic-generation table-top systems are new sources of extreme-ultraviolet to hard X-ray photons, providing ultrashort pulses that are intense, coherent and tunable. They are enabling a broad range of nonlinear optical and spectroscopic methods at short wavelengths, similar to those developed in the terahertz to ultraviolet regimes over the past 60 years. The extreme-ultraviolet to X-ray wavelengths access core transitions that can provide element and orbital selectivity, structural resolution down to the sub-nanometre scale and, for some methods, high momentum transfers across typical Brillouin zones; the possibilities for polarization control and sub-femtosecond time resolution are opening up new frontiers in research. In this Roadmap, we review the emergence of this field over the past 10 years or so, covering methods such as sum or difference frequency generation and second-harmonic generation, two-photon absorption, stimulated emission or Raman spectroscopy and transient grating spectroscopy. We then discuss the unique opportunities provided by these techniques for probing elementary dynamics in a wide variety of systems. X-ray free-electron lasers and high-harmonic-generation sources of extreme-ultraviolet (EUV) to hard X-ray photons deliver intense ultrashort pulses and enable the extension of nonlinear methods to much shorter wavelengths.EUV to X-ray wavelengths access core transitions that can provide element and orbital selectivity. These wavelengths also achieve sub-nanometre structural resolution and high momentum transfer, with femtosecond and attosecond time resolution.Nonlinear EUV/X-ray methods that have emerged include sum or difference frequency generation, parametric down-conversion, second-harmonic generation, two-photon absorption, stimulated emission or Raman spectroscopy and transient grating spectroscopy.Nonlinear EUV/X-ray science is developing hand-in-hand with instrumentation, to improve pulse features and enhance accessibility with the use of table-top systems or compact accelerators.These techniques offer unique opportunities for probing dynamical events in a wide variety of systems, including surface and interface processes, chirality, nanoscale transport and multidimensional core-level spectroscopy. New sources of extreme-ultraviolet to hard X-ray photons have enabled a wide range of short-wavelength nonlinear optical and spectroscopic methods over the past decade, and, for the future, offer unique opportunities to probe elementary dynamics in various systems.
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| 5. |
- Milne, Christopher J., et al.
(författare)
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Disentangling the evolution of electrons and holes in photoexcited ZnO nanoparticles
- 2023
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Ingår i: Structural Dynamics. - : American Institute of Physics (AIP). - 2329-7778. ; 10:6
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of charge carriers in photoexcited room temperature ZnO nanoparticles in solution is investigated using ultrafast ultraviolet photoluminescence spectroscopy, ultrafast Zn K-edge absorption spectroscopy, and ab initio molecular dynamics (MD) simulations. The photoluminescence is excited at 4.66 eV, well above the band edge, and shows that electron cooling in the conduction band and exciton formation occur in <500 fs, in excellent agreement with theoretical predictions. The x-ray absorption measurements, obtained upon excitation close to the band edge at 3.49 eV, are sensitive to the migration and trapping of holes. They reveal that the 2 ps transient largely reproduces the previously reported transient obtained at 100 ps time delay in synchrotron studies. In addition, the x-ray absorption signal is found to rise in similar to 1.4 ps, which we attribute to the diffusion of holes through the lattice prior to their trapping at singly charged oxygen vacancies. Indeed, the MD simulations show that impulsive trapping of holes induces an ultrafast expansion of the cage of Zn atoms in <200 fs, followed by an oscillatory response at a frequency of similar to 100 cm-1, which corresponds to a phonon mode of the system involving the Zn sub-lattice.
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| 6. |
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| 7. |
- Sá, Jacinto, et al.
(författare)
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Transient mid-IR study of electron dynamics in TiO2 conduction band.
- 2013
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Ingår i: The Analyst. - : Royal Society of Chemistry (RSC). - 0003-2654 .- 1364-5528. ; 138:7, s. 1966-70
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of TiO2 conduction band electrons were followed with a novel broadband synchrotron-based transient mid-IR spectroscopy setup. The lifetime of conduction band electrons was found to be dependent on the injection method used. Direct band gap excitation results in a lifetime of 2.5 ns, whereas indirect excitation at 532 nm via Ru-N719 dye followed by injection from the dye into TiO2 results in a lifetime of 5.9 ns.
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