| 1. |
- Dicke, B., et al.
(author)
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Transferring the entatic-state principle to copper photochemistry
- 2018
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In: Nature Chemistry. - : NATURE PUBLISHING GROUP. - 1755-4330 .- 1755-4349. ; 10:3, s. 355-362
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Journal article (peer-reviewed)abstract
- The entatic state denotes a distorted coordination geometry of a complex from its typical arrangement that generates an improvement to its function. The entatic-state principle has been observed to apply to copper electron-transfer proteins and it results in a lowering of the reorganization energy of the electron-transfer process. It is thus crucial for a multitude of biochemical processes, but its importance to photoactive complexes is unexplored. Here we study a copper complex-with a specifically designed constraining ligand geometry-that exhibits metal-to-ligand charge-transfer state lifetimes that are very short. The guanidine-quinoline ligand used here acts on the bis(chelated) copper(I) centre, allowing only small structural changes after photoexcitation that result in very fast structural dynamics. The data were collected using a multimethod approach that featured time-resolved ultraviolet-visible, infrared and X-ray absorption and optical emission spectroscopy. Through supporting density functional calculations, we deliver a detailed picture of the structural dynamics in the picosecond-to-nanosecond time range.
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| 2. |
- Bäckström, Joakim, et al.
(author)
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Raman scattering in \RmYBa$_2$Cu$_4$O$_8$ and PrBa$_2$Cu$_4$O$_8$ : Indications of pseudogap effects in non-superconducting \RmPrBa$_2$Cu$_4$O$_8$
- 2000
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 61, s. 7049-7054
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Journal article (peer-reviewed)abstract
- By analysis of the Raman spectra of superconducting YBa2Cu4O8 (Y-124), we observe a suppression of low-energy electronic density of states that we link to changes in the linewidth of the Ba-phonon mode. These effects occur at a temperature below 150 K, where also anomalies in resistivity and other physical properties take place. We argue that these changes in the Raman spectra of Y-124 are connected to the opening of a pseudogap. Analogous anomalies in resistivity and the Ba-phonon width in the nonsuperconducting homologue PrBa2Cu4O8 (Pr-124) below 150 K suggest that similar pseudogap effects can occur without a following transition to a superconducting state at a lower temperature.
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| 3. |
- Bäckström, Joakim, et al.
(author)
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Raman scattering in YBa2Cu4O8 and PrBa2Cu4O8 - indications of pseudogap effects in non-superconducting PrBa2Cu4O8
- 2000
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In: Physica. C, Superconductivity. - 0921-4534 .- 1873-2143. ; 341, s. 2251-2252
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Journal article (peer-reviewed)abstract
- By analysis of the temperature evolution of Raman spectra, we connect an observed supression in low-energy electronic density of states to an anomalous sharpening of the Ba-phonon mode in superconducting YBa2Cu4O8 (Y-124) at around T=150 K. We link the supression of electronic excitations to an opening of a pseudogap. Similar effects observed for the Ba-phonon mode at roughly the same temperature in non-superconducting PrBa2Cu4O8 (Pr-124) suggests that a pseduogap opens up around 150 K also in this material.
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| 4. |
- Chumakov, A., et al.
(author)
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Sprayed Nanometer-Thick Hard-Magnetic Coatings with Strong Perpendicular Anisotropy for Data Storage Applications
- 2022
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In: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 5:7, s. 8741-8754
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Journal article (peer-reviewed)abstract
- The rapid growth of digital information in the world necessitates a big leap in improving the existing technologies for magnetic recording. For the best modern perpendicular recording, the highest coercivity materials with minimal volume are required. We present a study of a facile technology for establishing mono- and multilayer surfaces from various single-domain flat magnetic nanoparticles that exhibit a strong perpendicular-oriented magnetic moment on solid and flexible substrates. Surfactant-free, hard ferromagnetic, and single-domain anisotropic strontium hexaferrite SrFe12O19nanoparticles with a perpendicular magnetic moment orientation and two different aspect ratios are self-ordered into magnetic thin nanofilms, exploiting the templating effect of cellulose nanofibrils and magnetic fields. Uniform magnetic coatings obtained by the scalable layer-by-layer spray deposition from a monolayer coverage up to thicknesses of a few tens of nanometers show a preferred in-plane orientation of the hard-magnetic nanoparticles. High coercivities of the films of up to 5 kOe and a high perpendicular anisotropy of Mr⊥/Ms> 80% are found. The application of the magnetic field during film deposition ensures additional improvement in perpendicular magnetic anisotropy and the appearance of residual magnetization in the film of up to 0.6Ms. For low-aspect-ratio nanoparticles stacked in periodic planar structures, the signs of the photonic band gap are revealed. The ability to create scalable, thin magnetic structures based on nanosized particles/building blocks opens great opportunities for their application in a wide variety of optoelectronic and magnetic storage devices.
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| 5. |
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| 6. |
- Naumova, M., et al.
(author)
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Structural dynamics upon photoexcitation-induced charge transfer in a dicopper(i)-disulfide complex
- 2018
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 20:9, s. 6274-6286
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Journal article (peer-reviewed)abstract
- The structural dynamics of charge-transfer states of nitrogen-ligated copper complexes has been extensively investigated in recent years following the development of pump-probe X-ray techniques. In this study we extend this approach towards copper complexes with sulfur coordination and investigate the influence of charge transfer states on the structure of a dicopper(i) complex with coordination by bridging disulfide ligands and additionally tetramethylguanidine units [Cu I 2 (NSSN) 2 ] 2+ . In order to directly observe and refine the photoinduced structural changes in the solvated complex we applied picosecond pump-probe X-ray absorption spectroscopy (XAS) and wide-angle X-ray scattering (WAXS). Additionally, the ultrafast evolution of the electronic excited states was monitored by femtosecond transient absorption spectroscopy in the UV-Vis probe range. DFT calculations were used to predict molecular geometries and electronic structures of the ground and metal-to-ligand charge transfer states with singlet and triplet spin multiplicities, i.e. S 0 , 1 MLCT and 3 MLCT, respectively. Combining these techniques we elucidate the electronic and structural dynamics of the solvated complex upon photoexcitation to the MLCT states. In particular, femtosecond optical transient spectroscopy reveals three distinct timescales of 650 fs, 10 ps and > 100 ps, which were assigned as internal conversion to the ground state (S n → S 0 ), intersystem crossing 1 MLCT → 3 MLCT, and subsequent relaxation of the triplet to the ground state, respectively. Experimental data collected using both X-ray techniques are in agreement with the DFT-predicted structure for the triplet state, where coordination bond lengths change and one of the S-S bridges is cleaved, causing the movement of two halves of the molecule relative to each other. Extended X-ray absorption fine structure spectroscopy resolves changes in Cu-ligand bond lengths with precision on the order of 0.01 Å, whereas WAXS is sensitive to changes in the global shape related to relative movement of parts of the molecule. The results presented herein widen the knowledge on the electronic and structural dynamics of photoexcited copper-sulfur complexes and demonstrate the potential of combining the pump-probe X-ray absorption and scattering for studies on photoinduced structural dynamics in copper-based coordination complexes.
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| 7. |
- Rauer, R., et al.
(author)
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Thickness dependent phase separation in La0.7Ca0.3MnO3 films
- 2002
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In: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 81, s. 3777-3779
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Journal article (peer-reviewed)abstract
- The complex dielectric function of La0.7Ca0.3MnO3 films with various thicknesses and on different substrates was determined by the analysis of measured ellipsometric parameters. The temperature-dependent redistribution of low-energy spectral weight shows that the metallicity is developed gradually below an onset temperature that is found to depend strongly on global and local strain properties, not on film thickness alone. Importantly, the 2 nm film shows no metallic conduction but an optical charge-carrier response below 240 K. This suggests that ultrathin films are characterized by phase separation and a percolation-type transition. (C) 2002 American Institute of Physics.
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| 8. |
- Bjornsson, P., et al.
(author)
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Lattice and charge excitations in La1-xSrxMnO3
- 2000
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 61, s. 1193-1197
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Journal article (peer-reviewed)abstract
- We employ inelastic Light scattering to study the dependence of the lattice and charge excitations in La1-xSrxMnO3 compounds on doping and temperature. The phonons reveal strong local lattice distortions in the paramagnetic state, which gradually vanish below the ferromagnetic transition. We identify charge excitations in the metallic state. They exhibit a dependence on the doping level and symmetry selection rules typical for a plasmonlike excitation. Their energy scale of 100 meV requires a low-carrier-density component of the plasma outlining the importance of electronic interactions in La1-xSrxMnO3.
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| 9. |
- Espinoza, S., et al.
(author)
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User oriented end-station on VUV pump-probe magneto-optical ellipsometry at ELI beamlines
- 2017
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In: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 421, s. 378-382
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Journal article (peer-reviewed)abstract
- A state of the art ellipsometer for user operations is being implemented at ELI Beamlines in Prague, Czech Republic. It combines three of the most promising and exotic forms of ellipsometry: VUV, pump-probe and magneto-optical ellipsometry. This new ellipsometer covers a spectral operational range from the NIR up to the VUV, with high through-put between 1 and 40 eV. The ellipsometer also allows measurements of magneto-optical spectra with a 1 kHz switchable magnetic field of up to 1.5 T across the sample combining ellipsometry and Kerr spectroscopy measurements in an unprecedented spectral range. This form of generalized ellipsometry enables users to address diagonal and off-diagonal components of the dielectric tensor within one measurement. Pump-probe measurements enable users to study the dynamic behaviour of the dielectric tensor in order to resolve the time-domain phenomena in the femto to 100 ns range.
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| 10. |
- Rusydi, A., et al.
(author)
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Metal-insulator transition in manganites: Changes in optical conductivity up to 22 eV
- 2008
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In: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 78:12, s. 125110 (art. no.)-
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Journal article (peer-reviewed)abstract
- The electronic response of doped manganites at the transition from the paramagnetic insulating to the ferromagnetic metallic state in La(1-x)Ca(x)MnO(3) for x=0.3 and 0.2 was investigated by dc conductivity, ellipsometry, and vacuum ultraviolet reflectance for energies between 0 and 22 eV. A stabilized Kramers-Kronig transformation yields the optical conductivity and reveals changes in the optical spectral weight up to 22 eV at the metal-to-insulator transition. In the observed energy range, the spectral weight is conserved within 0.3%. The redistribution of spectral weight in this surprisingly broad energy range has important ramifications for the effective low-energy physics. We discuss the importance of the charge-transfer, Coulomb on-site, Jahn-Teller, and long-range Coulomb screening effects to the electronic structure.
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