| 1. |
- Berkowicz, Sharon, et al.
(författare)
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Nanofocused x-ray photon correlation spectroscopy
- 2022
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Ingår i: Physical Review Research. - 2643-1564. ; 4:3
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Tidskriftsartikel (refereegranskat)abstract
- Here, we demonstrate an experimental proof of concept for nanofocused x-ray photon correlation spectroscopy, a technique sensitive to nanoscale fluctuations present in a broad range of systems. The experiment, performed at the NanoMAX beamline at MAX IV, uses a novel event-based x-ray detector to capture nanoparticle structural dynamics with microsecond resolution. By varying the nanobeam size from σ=88 nm to σ=2.5μm, we quantify the effect of the nanofocus on the small-angle scattering lineshape and on the diffusion coefficients obtained from nano-XPCS. We observe that the use of nanobeams leads to a multifold increase in speckle contrast, which greatly improves the experimental signal-to-noise ratio, quantified from the two-time intensity correlation functions. We conclude that it is possible to account for influence of the high beam divergence on the lineshape and measured dynamics by including a convolution with the nanobeam profile in the model.
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| 2. |
- Bournel, F., et al.
(författare)
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2-Butyne on Si(001) at room temperature: An XPS and NEXAFS study
- 2011
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 184:3-6, s. 323-326
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Tidskriftsartikel (refereegranskat)abstract
- We present here a study of the adsorption of 2-butyne (CH3-C equivalent to C-CH3) on the Si(0 01)-2 x 1 silicon surface at room temperature using synchrotron radiation photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (NEXAFS). In particular, the Si2p and C1s core levels were followed by real-time photoemission (measuring while dosing). The intensity of the Si2p surface state component gradually diminishes with an increasing exposure to the gas. The C1s photoemission line is decomposed into two main components with their vibrational series, attributed to the two inner carbons (bonded to silicon) and the two methyl carbons (protruding into the vacuum), respectively. C1s real-time XPS indicates that the chemical bonding of the molecule does not change from low coverage to saturation coverage. NEXAFS spectroscopy performed at the C K-edge using linearly polarized radiation reveals the presence of a pi*(C=C) molecular orbital parallel to the surface, resulting from the opening of the triple C equivalent to C bond and the formation of two sigma(Si-C) bonds. The attachment of the molecule via C-H bond scission (conserving the CC bond) is excluded. The clear-cut observation of a C=C bond, combined to our preceding angle-resolved UV photoemission spectroscopy (ARUPS) work [Bournel et al., Surf. Sci. 601 (2007) 3750] favors the on-dimer adsorption model at saturation (similar to 3 L). (C) 2010 Elsevier B.V. All rights reserved.
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| 3. |
- Cerenius, Yngve, et al.
(författare)
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Status of the MAX IV Laboratory
- 2016
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Ingår i: Synchrotron Radiation News. - : Informa UK Limited. - 0894-0886 .- 1931-7344. ; 29:1, s. 34-38
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Tidskriftsartikel (refereegranskat)abstract
- On the day of the 2016 summer solstice, June 21, MAX IV, the new synchrotron radiation facility in Lund, Sweden, will be inaugurated. MAX IV is setting a new standard in terms of emittance, thereby providing beamlines with the best possible brilliance and coherence. At the same time, MAX IV continues a more than three-decades-long successful history of Swedish synchrotron-radiation-based research. The activities at the present MAX-lab, which officially started when the MAX I storage ring opened for users in 1986, have been concluded with a “last beamdump” ceremony for the MAX II and MAX III storage rings on December 13, 2015, Saint Lucy's Day. In Sweden, the winter solstice is celebrated with a festival of light.
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| 4. |
- Chao, Yimin, et al.
(författare)
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Soft X-ray induced oxidation on acrylic acid grafted luminescent silicon quantum dots in ultrahigh vacuum
- 2011
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Ingår i: Physica Status Solidi. A: Applications and Materials Science. - : Wiley. - 1862-6300. ; 208:10, s. 2424-2429
-
Tidskriftsartikel (refereegranskat)abstract
- Water soluble acrylic acid grafted luminescent silicon quantum dots (Si-QDs) were prepared by a simplified method. The resulting Si-QDs dissolved in water and showed stable strong luminescence with peaks at 436 and 604 nm. X-ray photoelectron spectroscopy (XPS) was employed to examine the surface electronic states after the synthesis. The co-existence of the Si2p and C1s core levels infers that the acrylic acid has been successfully grafted on the surface of silicon quantum dots. To fit the Si2p spectrum, four components were needed at 99.45, 100.28, 102.21 and 103.24 eV. The first component at 99.45 eV (I) was assigned to Si-Si within the silicon core of the Si-QDs. The second component at 100.28 eV (II) was from Si-C. The third at 102.21 eV (III) was a sub-oxide state and the fourth at 103.24 eV (IV) was from SiO2 at Si-QDs surface. With an increase in exposure to soft X-ray photons, the intensity ratio of the two peaks within the Si2p region A and B increased from 0.5 to 1.4 while the peak A intensity decreased, and eventually a steady state was reached. This observation is explained in terms of photon-induced oxidation taking place within the surface dangling bonds. As the PL profile for Si-QDs is influenced by the degree of oxidation within the nanocrystal structure, the inducement of oxidation by soft X-rays will play a role in the range of potential applications where such materials could be used - especially within biomedical labelling. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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| 5. |
- Couto, Rafael C., et al.
(författare)
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Anomalously strong two-electron one-photon X-ray decay transitions in CO caused by avoided crossing
- 2016
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- The unique opportunity to study and control electron-nuclear quantum dynamics in coupled potentials offered by the resonant inelastic X-ray scattering (RIXS) technique is utilized to unravel an anomalously strong two-electron one-photon transition from core-excited to Rydberg final states in the CO molecule. High-resolution RIXS measurements of CO in the energy region of 12-14 eV are presented and analyzed by means of quantum simulations using the wave packet propagation formalism and ab initio calculations of potential energy curves and transition dipole moments. The very good overall agreement between the experimental results and the theoretical predictions allows an in-depth interpretation of the salient spectral features in terms of Coulomb mixing of "dark" with "bright" final states leading to an effective two-electron one-photon transition. The present work illustrates that the improved spectral resolution of RIXS spectra achievable today may call for more advanced theories than what has been used in the past.
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| 6. |
- Couto, Rafael C., et al.
(författare)
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Coupled electron-nuclear dynamics in resonant 1 sigma -> 2 pi x-ray Raman scattering of CO molecules
- 2016
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Ingår i: Physical Review A. - : American Physical Society. - 2469-9926. ; 93:3
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed experimental-theoretical analysis of O K-edge resonant 1 sigma-2 pi inelastic x-ray scattering (RIXS) from carbon monoxide with unprecedented energy resolution. We employ high-level ab initio calculations to compute the potential energy curves of the states involved in the RIXS process and simulate the measured RIXS spectra using the wave-packet-propagation formalism, including Coulomb coupling in the final-state manifold. The theoretical analysis allows us to explain all the key features of the experimental spectra, including some that were not seen before. First, we clearly show the interference effect between different RIXS channels corresponding to the transition via orthogonal (1)Pi(x) and (1)Pi(y) core-excited states of CO. Second, the RIXS region of 13 eV energy loss presents a triple structure, revealed only by the high-resolution measurement. In previous studies, this region was attributed solely to a valence state. Here we show a strong Coulomb mixing of the Rydberg and valence final states, which opens the forbidden RIXS channels to the "dark" final Rydberg states and drastically changes the RIXS profile. Third, using a combination of high-resolution experiment and high-level theory, we improve the vertical bar 4 sigma(-1)2 pi(1)> final-state potential-energy curve by fitting its bottom part with the experiment. Also, the coupling constants between Rydberg and valence states were refined via comparison with the experiment. Our results illustrate the large potential of the RIXS technique for advanced studies of highly excited states of neutral molecules.
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| 7. |
- Couto, Rafael C., et al.
(författare)
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Coupled electron-nuclear dynamics in resonant 1σ→2π x-ray Raman scattering of CO molecules
- 2016
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 93:3
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed experimental-theoretical analysis of O K-edge resonant 1σ-2π inelastic x-ray scattering (RIXS) from carbon monoxide with unprecedented energy resolution. We employ high-level ab initio calculations to compute the potential energy curves of the states involved in the RIXS process and simulate the measured RIXS spectra using the wave-packet-propagation formalism, including Coulomb coupling in the final-state manifold. The theoretical analysis allows us to explain all the key features of the experimental spectra, including some that were not seen before. First, we clearly show the interference effect between different RIXS channels corresponding to the transition via orthogonal Πx1 and Πy1 core-excited states of CO. Second, the RIXS region of 13 eV energy loss presents a triple structure, revealed only by the high-resolution measurement. In previous studies, this region was attributed solely to a valence state. Here we show a strong Coulomb mixing of the Rydberg and valence final states, which opens the forbidden RIXS channels to the "dark" final Rydberg states and drastically changes the RIXS profile. Third, using a combination of high-resolution experiment and high-level theory, we improve the |4σ-12π1) final-state potential-energy curve by fitting its bottom part with the experiment. Also, the coupling constants between Rydberg and valence states were refined via comparison with the experiment. Our results illustrate the large potential of the RIXS technique for advanced studies of highly excited states of neutral molecules.
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| 8. |
- Davila, M. E., et al.
(författare)
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Comparative structural and electronic studies of hydrogen interaction with isolated versus ordered silicon nanoribbons grown on Ag(110)
- 2012
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 23:38
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the geometry and electronic structure of two different types of self-aligned silicon nanoribbons (SiNRs), forming either isolated SiNRs or a self-assembled 5 x 2/5 x 4 grating on an Ag(110) substrate, by scanning tunnelling microscopy and high resolution x-ray photoelectron spectroscopy. At room temperature we further adsorb on these SiNRs either atomic or molecular hydrogen. The hydrogen absorption process and hydrogenation mechanism are similar for isolated or 5 x 2/5 x 4 ordered SiNRs and are not site selective; the main difference arises from the fact that the isolated SiNRs are more easily attacked and destroyed faster. In fact, atomic hydrogen strongly interacts with any Si atoms, modifying their structural and electronic properties, while molecular hydrogen has first to dissociate. Hydrogen finally etches the Si nanoribbons and their complete removal from the Ag(110) surface could eventually be expected.
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| 9. |
- De Padova, Paola, et al.
(författare)
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Mn-silicide nanostructures aligned on massively parallel silicon nano-ribbons
- 2013
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 25:1
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Tidskriftsartikel (refereegranskat)abstract
- The growth of Mn nanostructures on a 1D grating of silicon nano-ribbons is investigated at atomic scale by means of scanning tunneling microscopy, low energy electron diffraction and core level photoelectron spectroscopy. The grating of silicon nano-ribbons represents an atomic scale template that can be used in a surface-driven route to control the combination of Si with Mn in the development of novel materials for spintronics devices. The Mn atoms show a preferential adsorption site on silicon atoms, forming one-dimensional nanostructures. They are parallel oriented with respect to the surface Si array, which probably predetermines the diffusion pathways of the Mn atoms during the process of nanostructure formation.
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| 10. |
- Deppe, M., et al.
(författare)
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Ultrafast charge transfer and atomic orbital polarization
- 2007
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:17
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Tidskriftsartikel (refereegranskat)abstract
- The role of orbital polarization for ultrafast charge transfer between an atomic adsorbate and a substrate is explored. Core hole clock spectroscopy with linearly polarized x-ray radiation allows to selectively excite adsorbate resonance states with defined spatial orientation relative to the substrate surface. For c(4x2)S/Ru(0001) the charge transfer times between the sulfur 2s(-1)3p(*+1) antibonding resonance and the ruthenium substrate have been studied, with the 2s electron excited into the 3p(perpendicular to)(*) state along the surface normal and the 3p(parallel to)(*) state in the surface plane. The charge transfer times are determined as 0.18 +/- 0.07 and 0.84 +/- 0.23 fs, respectively. This variation is the direct consequence of the different adsorbate-substrate orbital overlap.
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| 11. |
- Ertan, Emelie, et al.
(författare)
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Theoretical simulations of oxygen K-edge resonant inelastic x-ray scattering of kaolinite
- 2017
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 95:14
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Tidskriftsartikel (refereegranskat)abstract
- Near-edge x-ray absorption fine structure (NEXAFS) and resonant inelastic x-ray scattering (RIXS) measurements at the oxygen K edge were combined with theoretical spectrum simulations, based on periodic density functional theory and nuclear quantum dynamics, to investigate the electronic structure and chemical bonding in kaolinite Al2Si2O5(OH)(4). We simulated NEXAFS spectra of all crystallographically inequivalent oxygen atoms in the crystal and RIXS spectra of the hydroxyl groups. Detailed insight into the ground-state potential energy surface of the electronic states involved in the RIXS process were accessed by analyzing the vibrational excitations, induced by the core excitation, in quasielastic scattering back to the electronic ground state. In particular, we find that the NEXAFS pre-edge is dominated by features related to OH groups within the silica and alumina sheets, and that the vibrational progression in RIXS can be used to selectively probe vibrational modes of this subclass of OH groups. The signal is dominated by the OH stretching mode, but also other lower vibrational degrees of freedom, mainly hindered rotational modes, contribute to the RIXS signal.
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| 12. |
- Fairclough, Simon M., et al.
(författare)
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Growth and Characterization of Strained and Alloyed Type-II ZnTe/ZnSe Core-Shell Nanocrystals
- 2012
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:51, s. 26898-26907
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the growth and the physical and optical properties of type-II heterostructured ZnTe/ZnSe colloidal nanocrystals, focusing on the role of the 7% lattice mismatch between the two materials in determining growth homogeneity and band structure. We find that the lattice mismatch between the two materials places limitations on the range of structures that can be grown, and for those in which coherent growth is achieved we present clear evidence that the low bulk modulus ZnTe cores are compressed by the higher modulus ZnSe shells, accentuating the red-shift of the excitonic state with increasing shell thickness. By employing a variety of characterization tools we build a clear picture of the core-shell architecture. We show how strain is manifested in structures with sharp core-shell interfaces and how intentional alloying of the interface can influence the growth and exciton energies. We show that a (2,6)-band effective mass model is able to distinguish between the as-grown "sharp" and "alloyed" interfaces, indicating that the alloyed structures incorporate reduced strain.
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| 13. |
- Foehlisch, A., et al.
(författare)
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Charge transfer dynamics in molecular solids and adsorbates driven by local and non-local excitations
- 2012
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 606:11-12, s. 881-885
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Tidskriftsartikel (refereegranskat)abstract
- Charge transfer pathways and charge transfer times in molecular films and in adsorbate layers depend both on the details of the electronic structure as well as on the degree of the initial localization of the propagating excited electronic state. For C6F6 molecular adsorbate films on the Cu(111) surface we determined the interplay between excited state localization and charge transfer pathways. In particular we selectively prepared a free-particle-like LUMO band excitation and compared it to a molecularly localized core-excited C1s -> pi* C6F6 LUMO state using time-resolved two-photon photoemission (tr-2PPE) and core-sole-clock (CHC) spectroscopy, respectively. For the molecularly localized core-excited C1s -> pi* C6F6 LUMO state, we separate the intramolecular dynamics from the charge transfer dynamics to the metal substrate by taking the intramolecular dynamics of the free C6F6 molecule into account Our analysis yields a generally applicable description of charge transfer within molecular adsorbates and to the substrate. (C) 2011 Published by Elsevier B.V.
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| 14. |
- Gahl, Cornelius, et al.
(författare)
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A femtosecond X-ray/optical cross-correlator
- 2008
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Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 2:3, s. 165-169
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Tidskriftsartikel (refereegranskat)abstract
- For a fundamental understanding of ultrafast dynamics in chemistry, biology and materials science it has been a long-standing dream to record a molecular movie in which both the atomic trajectories and the chemical states of every atom in matter are followed in real time(1). Free- electron lasers provide this perspective as they deliver brilliant femtosecond X-ray pulses spanning a wide photon energy range, which is necessary to gather element- specific and chemical- stateselective information with femtosecond time resolution. The key challenge lies in synchronizing the free- electron lasers with separate optical lasers. We exploit the peak brilliance of the free- electron laser in Hamburg(2,3) ( FLASH) and establish X- raypulseinduced transient changes of the optical reflectivity in GaAs as a powerful tool for X- ray/ optical cross- correlation. This constitutes a breakthrough in the path towards recording a molecular movie and - equally importantly - opens up the field of femtosecond X- ray- induced dynamics, only accessible with high- brilliance X- ray free- electron lasers.
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| 15. |
- Grizolli, Walan, et al.
(författare)
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Multilayer based soft-x-ray polarimeter at MAX IV Laboratory.
- 2016
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 87:2
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Tidskriftsartikel (refereegranskat)abstract
- A high precision five rotation-axes polarimeter using transmission multilayers as polarizers and reflection multilayers as analyzers has been designed and manufactured. To cover the extreme ultraviolet regime, Mo/Si, Cr/C, Sc/Cr, and W/B4C multilayers for transmission and reflection have also been designed and produced. The polarimeter mechanics is supported on a hexapod to simplify the alignment relative to photon beam. The instrument is designed so that it can be easily transferred between different beamlines.
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| 16. |
- Grizolli, Walan, et al.
(författare)
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Use of astigmatic re-focusing at HP-XPS end-station
- 2013
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Ingår i: 11th International Conference on Synchrotron Radiation Instrumentation (SRI 2012). - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 425
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Konferensbidrag (refereegranskat)abstract
- In this paper we present the refocusing optics for the new high pressure photoelectron spectroscopy (HP-XPS) branch line at MAX-lab, based on a plane grating monochromator with vertically collimated beam. For the HP-XPS instrument, the required spot size is dictated by the small geometric acceptance of the HP-XPS electron energy analyzer. Whereas a pair of bendable mirrors in a KB configuration has some advantages as refocusing elements, we have studied whether similar performance can be achieved with a single non-bendable mirror. In this solution, however, the need for strong horizontal magnification results in a strong vertical magnification and into a very asymmetric image, the height being just a fraction of the width. We have studied through an analytical geometrical model and ray tracing simulations the use of astigmatism to increase the vertical beam size up to the geometric acceptance of the detector. As a result the vertical beam size at sample plane is mostly determined by the photon angular distribution and is not dependent on the exit slit aperture size. In addition the vertical beam size can be controlled by the grating c(ff) parameter, making possible to adjust the photon density and minimize sample damage by the radiation.
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| 17. |
- Gråsjö, Johan, et al.
(författare)
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Electronic structure of water molecules confined in a micelle lattice
- 2009
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 113:24, s. 8201-8205
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen K absorption and emission spectra of water molecules confined in dodecyltrimethyl ammonium chloride micelle structures are presented. The local electronic structure of the water molecules is found to be dramatically different from the electronic structure of water molecules in the gas-phase as well as in liquid water. Hybridization with states of the ions in the surrounding ions is directly observed, and evidence for stabilization of the water molecules relative to molecules in bulk water is found.
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| 18. |
- Gråsjö, Johan, et al.
(författare)
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Local Electronic Structure of Functional Groups in Glycine As Anion, Zwitterion, and Cation in Aqueous Solution
- 2009
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 113:49, s. 16002-16006
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen and oxygen K emission spectra of glycine in the form of anions, zwitterions, and cations in aqueous solution are presented. It is shown that protonation has a dramatic influence on the local electronic structure and that the functional groups give a distinct spectral fingerprint.
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| 19. |
- Hellmann, S., et al.
(författare)
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Time-resolved x-ray photoelectron spectroscopy at FLASH
- 2012
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- The technique of time-resolved pump-probe x-ray photoelectron spectroscopy using the free-electron laser in Hamburg (FLASH) is described in detail. Particular foci lie on the macrobunch resolving detection scheme, the role of vacuum space-charge effects and the synchronization of pump and probe lasers. In an exemplary case study, the complete Ta 4f core-level dynamics in the layered charge-density-wave (CDW) compound 1T-TaS2 in response to impulsive optical excitation is measured on the sub-picosecond to nanosecond timescale. The observed multi-component dynamics is related to the intrinsic melting and reformation of the CDW as well as to extrinsic pump-laser-induced vacuum space-charge effects.
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| 20. |
- Hellmann, S., et al.
(författare)
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Ultrafast Melting of a Charge-Density Wave in the Mott Insulator 1T-TaS2
- 2010
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Ingår i: Physical Review Letters. - 1079-7114. ; 105:18
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Tidskriftsartikel (refereegranskat)abstract
- Femtosecond time-resolved core-level photoemission spectroscopy with a free-electron laser is used to measure the atomic-site specific charge-order dynamics of the charge-density wave in the Mott insulator 1T-TaS2. After strong photoexcitation, a prompt loss of charge order and subsequent fast equilibration dynamics of the electron-lattice system are observed. On the time scale of electron-phonon thermalization, about 1 ps, the system is driven across a phase transition from a long-range charge ordered state to a quasiequilibrium state with domainlike short-range charge and lattice order. The experiment opens the way to study the nonequilibrium dynamics of condensed matter systems with full elemental, chemical, and atomic-site selectivity.
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| 21. |
- Hennies, Franz, et al.
(författare)
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Resonant Inelastic Scattering Spectra of Free Molecules with Vibrational Resolution
- 2010
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:19, s. 193002-
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Tidskriftsartikel (refereegranskat)abstract
- Inelastic x-ray scattering spectra excited at the 1s(-1) pi* resonance of gas phase O-2 have been recorded with an overall energy resolution that allows for well-resolved vibrational progressions. The nuclear wave packet dynamics in the intermediate state is reflected in vibrational excitations of the electronic ground state, and by fine-tuning the excitation energy the dissociation dynamics in the predissociative B' (3) Pi(g) final state is controlled.
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| 22. |
- Kunnus, Kristjan, et al.
(författare)
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A setup for resonant inelastic soft x-ray scattering on liquids at free electron laser light sources
- 2012
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 83:12
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Tidskriftsartikel (refereegranskat)abstract
- We present a flexible and compact experimental setup that combines an in vacuum liquid jet with an x-ray emission spectrometer to enable static and femtosecond time-resolved resonant inelastic soft x-ray scattering (RIXS) measurements from liquids at free electron laser (FEL) light sources. We demonstrate the feasibility of this type of experiments with the measurements performed at the Linac Coherent Light Source FEL facility. At the FEL we observed changes in the RIXS spectra at high peak fluences which currently sets a limit to maximum attainable count rate at FELs. The setup presented here opens up new possibilities to study the structure and dynamics in liquids. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4772685]
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| 23. |
- Kunnus, Kristjan, et al.
(författare)
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Anti-Stokes resonant x-ray Raman scattering for atom specific and excited state selective dynamics
- 2016
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 18
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafast electronic and structural dynamics of matter govern rate and selectivity of chemical reactions, as well as phase transitions and efficient switching in functional materials. Since x-rays determine electronic and structural properties with elemental, chemical, orbital and magnetic selectivity, short pulse x-ray sources have become central enablers of ultrafast science. Despite of these strengths, ultrafast x-rays have been poor at picking up excited state moieties from the unexcited ones. With time-resolved anti-Stokes resonant x-ray Raman scattering (AS-RXRS) performed at the LCLS, and ab initio theory we establish background free excited state selectivity in addition to the elemental, chemical, orbital and magnetic selectivity of x-rays. This unparalleled selectivity extracts low concentration excited state species along the pathway of photo induced ligand exchange of Fe(CO)(5) in ethanol. Conceptually a full theoretical treatment of all accessible insights to excited state dynamics with AS-RXRS with transform-limited x-ray pulses is given-which will be covered experimentally by upcoming transform-limited x-ray sources.
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| 24. |
- Kunnus, K., et al.
(författare)
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Identification of the dominant photochemical pathways and mechanistic insights to the ultrafast ligand exchange of Fe(CO)(5) to Fe(CO)(4)EtOH
- 2016
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Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 3:4
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Tidskriftsartikel (refereegranskat)abstract
- We utilized femtosecond time-resolved resonant inelastic X-ray scattering and ab initio theory to study the transient electronic structure and the photoinduced molecular dynamics of a model metal carbonyl photocatalyst Fe(CO)(5) in ethanol solution. We propose mechanistic explanation for the parallel ultrafast intra-molecular spin crossover and ligation of the Fe(CO)(4) which are observed following a charge transfer photoexcitation of Fe(CO)(5) as reported in our previous study [ Wernet et al., Nature 520, 78 (2015)]. We find that branching of the reaction pathway likely happens in the (1)A(1) state of Fe(CO)(4). A sub-picosecond time constant of the spin crossover from B-1(2) to B-3(2) is rationalized by the proposed B-1(2) -> (1)A(1) -> B-3(2) mechanism. Ultrafast ligation of the B-1(2) Fe(CO)(4) state is significantly faster than the spin-forbidden and diffusion limited ligation process occurring from the B-3(2) Fe(CO)(4) ground state that has been observed in the previous studies. We propose that the ultrafast ligation occurs via B-1(2) -> (1)A(1) -> (1)A'Fe(CO)(4)EtOH pathway and the time scale of the (1)A(1) Fe(CO)(4) state ligation is governed by the solute-solvent collision frequency. Our study emphasizes the importance of understanding the interaction of molecular excited states with the surrounding environment to explain the relaxation pathways of photoexcited metal carbonyls in solution.
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| 25. |
- Mathieu, C., et al.
(författare)
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Nitrogen 1s NEXAFS and XPS spectroscopy of NH3-saturated Si(001)-2x1: Theoretical predictions and experimental observations at 300 K
- 2009
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 79:20
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Tidskriftsartikel (refereegranskat)abstract
- In the light of hybrid functional density-functional theory calculations of the core-excited and core-ionized states, this paper discusses original N 1s x-ray photoemission spectroscopy (XPS) and near-edge x-ray absorption fine-structure (NEXAFS) experimental data on the single-domain (vicinal) Si(001)-2x1 surface saturated by NH3 at 300 K. The theoretical approach enables to discuss the vibrational shape of the N 1s XPS spectrum and quantifies the binding-energy splitting due to intrarow and inter-row hydrogen bondings between amine pairs. The observed N 1s NEXAFS peaks are interpreted through the analysis of the contour maps of the antibonding Kohn-Sham orbitals of the NH2 adsorbate and through the Delta Kohn-Sham calculation of the transition energies, laying a theoretical basis for a discussion of the adsorbate spatial orientation. Finally, suggestions are given for future directions of research to get a further knowledge of a system that has potential applications as a template for molecular layer deposition and supramolecular assembly.
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| 26. |
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| 27. |
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| 28. |
- Nilson, K., et al.
(författare)
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Potassium-intercalated H2Pc films : Alkali-induced electronic and geometrical modifications
- 2012
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 137:4, s. 044708-
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray spectroscopy studies of potassium intercalated metal-free phthalocyanine multilayers adsorbed on Al(110) have been undertaken. Photoelectron spectroscopy measurements show the presence of several charge states of the molecules upon K intercalation, due to a charge transfer from the alkali. In addition, the comparison of valence band photoemission spectra with the density functional theory calculations of the density of states of the H2Pc- anion indicates a filling of the formerly lowest unoccupied molecular orbital by charge transfer from the alkali. This is further confirmed by x-ray absorption spectroscopy (XAS) studies, which show a decreased density of unoccupied states. XAS measurements in different experimental geometries reveal that the molecules in the pristine film are standing upright on the surface or are only slightly tilted away from the surface normal but upon K intercalation, the molecular orientation is changed in that the tilt angle of the molecules increases.
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| 29. |
- Palmgren, Pål, et al.
(författare)
-
Changing adsorption mode of FePc on TiO2(110) by surface modification with bipyridine
- 2008
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 129:7, s. 074707-
-
Tidskriftsartikel (refereegranskat)abstract
- Surface modification of reactive oxide substrates to obtain a less strongly interacting template for dye adsorption may be a way to enhance performance in dye-sensitized solar cells. In this work, we have investigated the electronic and structural properties of 4,4(')-bipyridine (bipy) as modifier adsorbed on the TiO2(110) surface. The modified surface is then coated with iron phthalocyanine (FePc) and the properties of this heterostructure are investigated with synchrotron based photoelectron spectroscopy, x-ray absorption spectroscopy, and scanning tunneling microscopy. We find that a saturated monolayer consisting of standing bipy molecules with one nitrogen atom pointing outward is formed on the oxide surface. FePc adsorb in molecular chains along the [001] direction on top of bipy and ordered in a tilted arrangement with adjacent molecules partially overlapping. Already from the first layer, the electronic properties of FePc resemble those of multilayer films. FePc alone is oxidized on the TiO2(110) surface, but preadsorbed bipy prevents this reaction. The energy level lineup at the interface is clarified.
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| 30. |
- Palmgren, Pål, et al.
(författare)
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Strong interactions in dye-sensitized interfaces
- 2008
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:15, s. 5972-5977
-
Tidskriftsartikel (refereegranskat)abstract
- Phthalocyanines (Pcs) are capable of converting sunlight into electric energy when adsorbed on TiO2 in a dye-sensitized solar cell. Of special interest in this type of cell is the energy level alignment as well as how molecules adsorb on the surface as it determines the output of the cell. We investigated the FePc-TiO2(110) interface using scanning tunneling microscopy, synchrotron-based photoelectron spectroscopy, and X-ray absorption spectroscopy. We found a strong coupling of the first-layer FePc to the substrate resulting in an alteration of the electronic structure and charge transfer from the molecules. The FePc in the second layer is not severely affected by the bonding to the surface and has bulk-like electronic properties. The growth of FePc thin films proceeds in a layer plus island mode, and the molecular plane is parallel to the surface. The energy level alignment at the interface is determined, and the lowest unoccupied molecular orbital is found above the conduction band minimum of the oxide substrate.
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| 31. |
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| 32. |
- Pietzsch, A, et al.
(författare)
-
Snapshots of the Fluctuating Hydrogen Bond Network in Liquid Water on the Sub-Femtosecond Timescale with Vibrational Resonant Inelastic x-ray Scattering.
- 2015
-
Ingår i: Physical Review Letters. - 1079-7114. ; 114:8
-
Tidskriftsartikel (refereegranskat)abstract
- Liquid water molecules interact strongly with each other, forming a fluctuating hydrogen bond network and thereby giving rise to the anomalous phase diagram of liquid water. Consequently, symmetric and asymmetric water molecules have been found in the picosecond time average with IR and optical Raman spectroscopy. With subnatural linewidth resonant inelastic x-ray scattering (RIXS) at vibrational resolution, we take sub-femtosecond snapshots of the electronic and structural properties of water molecules in the hydrogen bond network. We derive a strong dominance of nonsymmetric molecules in liquid water in contrast to the gas phase on the sub-femtosecond timescale of RIXS and determine the fraction of highly asymmetrically distorted molecules.
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| 33. |
- Pietzsch, Annette, et al.
(författare)
-
Spatial Quantum Beats in Vibrational Resonant Inelastic Soft X-Ray Scattering at Dissociating States in Oxygen
- 2011
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 106, s. 153004-153008
-
Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic soft x-ray scattering (RIXS) spectra excited at the 1σg→3σu resonance in gas-phase O2 show excitations due to the nuclear degrees of freedom with up to 35 well-resolved discrete vibronic states and a continuum due to the kinetic energy distribution of the separated atoms. The RIXS profile demonstrates spatial quantum beats caused by two interfering wave packets with different momenta as the atoms separate. Thomson scattering strongly affects both the spectral profile and the scattering anisotropy.
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| 34. |
- Rubensson, Jan-Erik, et al.
(författare)
-
High-resolution resonant inelastic soft X-ray scattering applied to liquids
- 2013
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 188, s. 79-83
-
Tidskriftsartikel (refereegranskat)abstract
- The brilliance of modern synchrotron radiation sources and capabilities of new instrumentation facilitate resonant inelastic soft X-ray scattering of liquids and molecular materials with high spectral quality. Especially, when the energy resolution approaches the natural line widths a detailed analysis provides information about local potential surfaces, dynamic coupling between nuclear and electronic degrees of freedom, and intermolecular interactions. After briefly commenting on various sample handling systems we review the recent high-resolution RIXS results on liquid acetone. The experimental RIXS spectra excited at the 0 K edge demonstrate that the CO stretching mode dominates the vibrational progressions, and that softer modes are little affected by the nuclear dynamics in the intermediate state. It is shown that intermolecular coupling can be neglected in this specific case, and it is predicted that such interaction significantly broadens spectral features in liquids with larger dipole-dipole interaction. Analysis of the data further shows that initial state thermal excitations at room temperature have a noticeable influence on the spectral features. (C) 2013 Elsevier B.V. All rights reserved.
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| 35. |
- Rubensson, Jan-Erik, et al.
(författare)
-
Rydberg-Resolved Resonant Inelastic Soft X-Ray Scattering: Dynamics at Core Ionization Thresholds
- 2015
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 114:13
-
Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic x-ray scattering spectra excited in the immediate vicinity of the core-level ionization thresholds of N-2 have been recorded. Final states of well-resolved symmetry-selected Rydberg series converging to valence-level ionization thresholds with vibrational excitations are observed. The results are well described by a quasi-two-step model which assumes that the excited electron is unaffected by the radiative decay. This threshold dynamics simplifies the interpretation of resonant inelastic x-ray scattering spectra considerably and facilitates characterization of low-energy excited final states in molecular systems.
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| 36. |
- Rubensson, Jan-Erik, et al.
(författare)
-
Vibrationally resolved resonant inelastic soft X-ray scattering spectra of free molecules
- 2012
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 185:8-9, s. 294-300
-
Tidskriftsartikel (refereegranskat)abstract
- The brilliance of modern synchrotron radiation sources and capabilities of new instrumentation facilitate molecular resonant inelastic soft X-ray scattering with high spectral quality. Especially, energy resolution of vibrational fine structure allows for a detailed analysis, providing information about the dynamic coupling between nuclear and electronic degrees of freedom. After a brief historical account and a short qualitative comparison between the radiative and non-radiative decay channels we review the recent results for the oxygen molecule. Nuclear wavepacket dynamics in bound and unbound states is studied, and in the latter case spatial quantum beats are observed as the dissociation proceeds via two different electronic states. A new internal spin-coupling conservation rule is established, whereas a commonly accepted selection rule based on orbital symmetry is violated. (C) 2012 Elsevier B.V. All rights reserved.
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| 37. |
- Schnadt, Joachim, et al.
(författare)
-
The new ambient-pressure X-ray photoelectron spectroscopy instrument at MAX-lab
- 2012
-
Ingår i: Journal of Synchrotron Radiation. - 0909-0495 .- 1600-5775. ; 19, s. 701-704
-
Tidskriftsartikel (refereegranskat)abstract
- The new instrument for near-ambient-pressure X-ray photoelectron spectroscopy which has been installed at the MAX II ring of the Swedish synchrotron radiation facility MAX IV Laboratory in Lund is presented. The new instrument, which is based on a SPECS PHOIBOS 150 NAP analyser, is the first to feature the use of retractable and exchangeable high-pressure cells. This implies that clean vacuum conditions are retained in the instrument's analysis chamber and that it is possible to swiftly change between near-ambient and ultrahigh-vacuum conditions. In this way the instrument implements a direct link between ultrahigh-vacuum and in situ studies, and the entire pressure range from ultrahigh-vacuum to near-ambient conditions is available to the user. Measurements at pressures up to 10(-5) mbar are carried out in the ultrahigh-vacuum analysis chamber, while measurements at higher pressures are performed in the high-pressure cell. The installation of a mass spectrometer on the exhaust line of the reaction cell offers the users the additional dimension of simultaneous reaction data monitoring. Moreover, the chosen design approach allows the use of dedicated cells for different sample environments, rendering the Swedish ambient-pressure X-ray photoelectron spectroscopy instrument a highly versatile and flexible tool.
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| 38. |
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| 39. |
- Schreck, Simon, et al.
(författare)
-
Ground state potential energy surfaces around selected atoms from resonant inelastic x-ray scattering.
- 2016
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- Thermally driven chemistry as well as materials' functionality are determined by the potential energy surface of a systems electronic ground state. This makes the potential energy surface a central and powerful concept in physics, chemistry and materials science. However, direct experimental access to the potential energy surface locally around atomic centers and to its long-range structure are lacking. Here we demonstrate how sub-natural linewidth resonant inelastic soft x-ray scattering at vibrational resolution is utilized to determine ground state potential energy surfaces locally and detect long-range changes of the potentials that are driven by local modifications. We show how the general concept is applicable not only to small isolated molecules such as O2 but also to strongly interacting systems such as the hydrogen bond network in liquid water. The weak perturbation to the potential energy surface through hydrogen bonding is observed as a trend towards softening of the ground state potential around the coordinating atom. The instrumental developments in high resolution resonant inelastic soft x-ray scattering are currently accelerating and will enable broad application of the presented approach. With this multidimensional potential energy surfaces that characterize collective phenomena such as (bio)molecular function or high-temperature superconductivity will become accessible in near future.
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| 40. |
- Sun, Yuping, et al.
(författare)
-
Intramolecular soft modes and intermolecular interactions in liquid acetone
- 2011
-
Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 84:13
-
Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic x-ray scattering spectra excited at the O1s−1π* resonance of liquid acetone are presented. Scattering to the electronic ground state shows a resolved vibrational progression where the dominant contribution is due to the C-O stretching mode, thus demonstrating a unique sensitivity of the method to the local potential energy surface in complex molecular systems. For scattering to electronically excited states, soft vibrational modes and, to a smaller extent, intermolecular interactions give a broadening, which blurs the vibrational fine structure. It is predicted that environmental broadening is dominant in aqueous acetone.
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| 41. |
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| 42. |
- Sun, Yu-Ping, et al.
(författare)
-
Interference between Resonant and Nonresonant Inelastic X-Ray Scattering
- 2013
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 110:22, s. 223001-
-
Tidskriftsartikel (refereegranskat)abstract
- A detailed study of inelastic x-ray scattering from the ground state to the Σg3(3σg-13sg1) state of the O2 molecule is presented. The observed angular anisotropy shows that the vibrational excitations within this final state are strongly dependent on the polarization of the incident radiation. The analysis demonstrates that this is a manifestation of interference between resonant and direct nonresonant inelastic x-ray scattering. This interference provides a new tool to monitor nuclear dynamics by relative rotation of the polarization vectors of the incident and scattered photons.
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| 43. |
- Sun, Yu-Ping, et al.
(författare)
-
Internal symmetry and selection rules in resonant inelastic soft x-ray scattering
- 2011
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 44:16, s. 161002-
-
Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic soft x-ray scattering spectra excited at the dissociative 1 sigma(g) -> 3 sigma(u) resonance in gas-phase O(2) are presented and discussed in terms of state-of-the-art molecular theory. A new selection rule due to internal spin coupling is established, facilitating a deep analysis of the valence excited final states. Furthermore, it is found that a commonly accepted symmetry selection rule due to orbital parity breaks down, as the core hole and excited electron swap parity, thereby opening the symmetry forbidden 3 sigma(g) decay channel.
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| 44. |
- Söderström, Johan, 1978-, et al.
(författare)
-
Resonant inelastic x-ray scattering on CO2 : Parity conservation in inversion-symmetric polyatomics
- 2020
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 101:6
-
Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic x-ray scattering (RIXS) spectra excited at the oxygen K edge of CO2 are presented and discussed. Although excitation from a gerade initial state to the intermediate 1s-1π* state breaks the inversion symmetry due to strong vibronic coupling, RIXS excited at the corresponding resonance exclusively populates gerade vibrations in the gerade electronic ground state. This observation constitutes an experimental confirmation of the prediction that the parity selection rule applies in RIXS on an inversion-symmetric polyatomic system, provided that the total electronic-vibronic wave function is considered. Parity selectivity is used for assigning spectra to the population of electronically excited final states, a procedure hampered only when symmetry-breaking vibronic coupling in the final states is prominent. A RIXS spectrum excited in the Rydberg region is tentatively assigned using a simplified quasi-two-step model in which it is assumed that the electron in the Rydberg orbital excited in the first step remains as a spectator during the second decay step.
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| 45. |
- Urpelainen, Samuli, et al.
(författare)
-
The SPECIES beamline at the MAX IV Laboratory : A facility for soft X-ray RIXS and APXPS
- 2017
-
Ingår i: Journal of Synchrotron Radiation. - 1600-5775 .- 0909-0495. ; 24:1, s. 344-353
-
Tidskriftsartikel (refereegranskat)abstract
- SPECIES is an undulator-based soft X-ray beamline that replaced the old I511 beamline at the MAX II storage ring. SPECIES is aimed at high-resolution ambient-pressure X-ray photoelectron spectroscopy (APXPS), near-edge X-ray absorption fine-structure (NEXAFS), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) experiments. The beamline has two branches that use a common elliptically polarizing undulator and monochromator. The beam is switched between the two branches by changing the focusing optics after the monochromator. Both branches have separate exit slits, refocusing optics and dedicated permanent endstations. This allows very fast switching between two types of experiments and offers a unique combination of the surface-sensitive XPS and bulk-sensitive RIXS techniques both in UHV and at elevated ambient-pressure conditions on a single beamline. Another unique property of the beamline is that it reaches energies down to approximately 27 eV, which is not obtainable on other current APXPS beamlines. This allows, for instance, valence band studies under ambient-pressure conditions. In this article the main properties and performance of the beamline are presented, together with selected showcase experiments performed on the new setup.
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| 46. |
- Ursby, Thomas, et al.
(författare)
-
BioMAX the first macromolecular crystallography beamline at MAX IV Laboratory
- 2020
-
Ingår i: Journal of Synchrotron Radiation. - Chichester : Wiley-Blackwell. - 0909-0495 .- 1600-5775. ; 27, s. 1415-1429
-
Tidskriftsartikel (refereegranskat)abstract
- BioMAX is the first macromolecular crystallography beamline at the MAX IV Laboratory 3 GeV storage ring, which is the first operational multi-bend achromat storage ring. Due to the low-emittance storage ring, BioMAX has a parallel, high-intensity X-ray beam, even when focused down to 20 μm × 5 μm using the bendable focusing mirrors. The beam is tunable in the energy range 5-25 keV using the in-vacuum undulator and the horizontally deflecting double-crystal monochromator. BioMAX is equipped with an MD3 diffractometer, an ISARA high-capacity sample changer and an EIGER 16M hybrid pixel detector. Data collection at BioMAX is controlled using the newly developed MXCuBE3 graphical user interface, and sample tracking is handled by ISPyB. The computing infrastructure includes data storage and processing both at MAX IV and the Lund University supercomputing center LUNARC. With state-of-the-art instrumentation, a high degree of automation, a user-friendly control system interface and remote operation, BioMAX provides an excellent facility for most macromolecular crystallography experiments. Serial crystallography using either a high-viscosity extruder injector or the MD3 as a fixed-target scanner is already implemented. The serial crystallography activities at MAX IV Laboratory will be further developed at the microfocus beamline MicroMAX, when it comes into operation in 2022. MicroMAX will have a 1 μm × 1 μm beam focus and a flux up to 1015 photons s with main applications in serial crystallography, room-temperature structure determinations and time-resolved experiments.
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| 47. |
- Wang, Qi, et al.
(författare)
-
Synthesis of water-dispersible photoluminescent silicon nanoparticles and their use in biological fluorescent imaging
- 2011
-
Ingår i: Journal of Nanoparticle Research. - : Springer Science and Business Media LLC. - 1572-896X .- 1388-0764. ; 13:1, s. 405-413
-
Tidskriftsartikel (refereegranskat)abstract
- Water-dispersible silicon nanoparticles (Si-NPs) are desirable for applications in biological techniques. A simplified method to synthesize such particles is reported here. The resulting Si-NPs are water-dispersible and luminescent. Under the excitation of UV light, the Si-NPs emit strong red light with a peak maximum at 606 nm and a quantum yield of 6%. They are highly stable, and remain so over several weeks. Fourier Transform Infrared (FTIR) spectroscopy shows a visible Si-CH2 scissoring vibration mode. Furthermore, the surface chemical bondings were confirmed by X-ray photoelectron spectroscopy (XPS). In the Si2p and C1s core levels, Si-C components are observed. The diameters of the synthesized Si-NPS as measured by atomic force microscope (AFM) are approximately 5 nm. Furthermore, the nanoparticles can be taken up by cultured cells. Fluorescence images of Si-NPs within MCF-7 human breast cancer cells show they are distributed throughout the cell tissue.
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| 48. |
- Wernet, Philippe, 1971-, et al.
(författare)
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Orbital-specific mapping of the ligand exchange dynamics of Fe(CO)5 in solution
- 2015
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 520:7545, s. 78-81
-
Tidskriftsartikel (refereegranskat)abstract
- Transition-metal complexes have long attracted interest for fundamental chemical reactivity studies and possible use in solar energy conversion. Electronic excitation, ligand loss from the metal centre, or a combination of both, creates changes in charge and spin density at the metal site that need to be controlled to optimize complexes for photocatalytic hydrogen production and selective carbon-hydrogen bond activation. An understanding at the molecular level of how transition-metal complexes catalyse reactions, and in particular of the role of the short-lived and reactive intermediate states involved, will be critical for such optimization. However, suitable methods for detailed characterization of electronic excited states have been lacking. Here we show, with the use of X-ray laser-based femtosecond resolution spectroscopy and advanced quantum chemical theory to probe the reaction dynamics of the benchmark transition-metal complex Fe(CO)5 insolution, that the photoinduced removal of CO generates the 16-electron Fe(CO)4 species, a homogeneous catalyst with an electron deficiency at the Fe centre, in a hitherto unreported excited singlet state that either converts to the triplet ground state or combines with a CO or solvent molecule to regenerate a penta-coordinated Fe species on a sub-picosecond timescale. This finding, which resolves the debate about the relative importance of different spin channels in the photochemistry of Fe(CO)5 (refs 4, 16,17,18,19 and 20), was made possible by the ability of femtosecond X-ray spectroscopy to probe frontier-orbital interactions with atom specificity. We expect the method to be broadly applicable in the chemical sciences, and to complement approaches that probe structural dynamics in ultrafast processes.
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| 49. |
- Yu, Shun, et al.
(författare)
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4-tert-Butyl Pyridine Bond Site and Band Bending on TiO2(110)
- 2010
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:5, s. 2315-2320
-
Tidskriftsartikel (refereegranskat)abstract
- In the present work, we study the bonding of 4-tert-butyl pyridine (4TBP) to the TiO2(110) surface using photoelectron spectroscopy (PES) and density functional theory (DFT) calculations. The results show that at low coverage, 4TBP adsorbs preferentially on oxygen vacancies. The calculated adsorption energy at the vacancies is 120 kJ/mol larger than that oil the five-fold-coordinated Ti4+ sites located in the rows on the TiO2 surface. The vacancy is "healed" by 4TBP, and the related gap state is strongly reduced through charge transfer into empty pi* orbitals on the pyridine ring. This leads to a change in surface band bending by 0.2 eV toward lower binding energies. The band bending does not change with further 4TBP deposition when saturating the surface to monolayer coverage, where the TiO2 surface is effectively protected against further adsorption by the dense 4TBP layer.
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| 50. |
- Yu, Shun, et al.
(författare)
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Adsorption geometry, molecular interaction, and charge transfer of triphenylamine-based dye on rutile TiO2(110)
- 2010
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 133:22, s. 224704-
-
Tidskriftsartikel (refereegranskat)abstract
- The fast development of new organic sensitizers leads to the need for a better understanding of the complexity and significance of their adsorption processes on TiO2 surfaces. We have investigated a prototype of the triphenylamine-cyanoacrylic acid (donor-acceptor) on rutile TiO2 (110) surface with special attention on the monolayer region. This molecule belongs to the type of dye, some of which so far has delivered the record efficiency of 10%-10.3% for pure organic sensitizers [W. Zeng, Y. Cao, Y. Bai, Y. Wang, Y. Shi, M. Zhang, F. Wang, C. Pan, and P. Wang, Chem. Mater. 22, 1915 (2010)]. The molecular configuration of this dye on the TiO2 surface was found to vary with coverage and adopt gradually an upright geometry, as determined from near edge x-ray absorption fine structure spectroscopy. Due to the molecular interaction within the increasingly dense packed layer, the molecular electronic structure changes systematically: all energy levels shift to higher binding energies, as shown by photoelectron spectroscopy. Furthermore, the investigation of charge delocalization within the molecule was carried out by means of resonant photoelectron spectroscopy. A fast delocalization (similar to 1.8 fs) occurs at the donor part while a competing process between delocalization and localization takes place at the acceptor part. This depicts the "push-pull" concept in donor-acceptor molecular system in time scale. (C) 2010 American Institute of Physics. [doi:10.1063/1.3509389]
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