| 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
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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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