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| 2. |
- Céolin, D., et al.
(författare)
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Ultrafast Charge Transfer Processes Accompanying KLL Auger Decay in Aqueous KCl Solution
- 2017
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Ingår i: Physical Review Letters. - 0031-9007. ; 119:26
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Tidskriftsartikel (refereegranskat)abstract
- X-ray photoelectron and KLL Auger spectra were measured for the K+ and Cl- ions in aqueous KCl solution. While the XPS spectra of these ions have similar structures, both exhibiting only weak satellites near the main line, the Auger spectra differ dramatically. Contrary to the chloride case, a very strong extra peak was found in the Auger spectrum of K+ at the low kinetic energy side of the D1 state. Using the equivalent core model and ab initio calculations this spectral feature was assigned to electron transfer processes from solvent water molecules to the solvated cation. The observed charge transfer processes are suggested to play an important role in charge redistribution following single and multiple core-hole creation in atoms and molecules placed into environment.
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| 3. |
- Conlon, C. S., et al.
(författare)
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Hard x-ray standing-wave photoemission insights into the structure of an epitaxial Fe/MgO multilayer magnetic tunnel junction
- 2019
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 126:7
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Tidskriftsartikel (refereegranskat)abstract
- The Fe/MgO magnetic tunnel junction is a classic spintronic system, with current importance technologically and interest for future innovation. The key magnetic properties are linked directly to the structure of hard-to-access buried interfaces, and the Fe and MgO components near the surface are unstable when exposed to air, making a deeper probing, nondestructive, in-situ measurement ideal for this system. We have thus applied hard x-ray photoemission spectroscopy (HXPS) and standing-wave (SW) HXPS in the few kilo-electron-volt energy range to probe the structure of an epitaxially grown MgO/Fe superlattice. The superlattice consists of 9 repeats of MgO grown on Fe by magnetron sputtering on an MgO(001) substrate, with a protective Al2O3 capping layer. We determine through SW-HXPS that 8 of the 9 repeats are similar and ordered, with a period of 33 +/- 4 angstrom, with the minor presence of FeO at the interfaces and a significantly distorted top bilayer with ca. 3 times the oxidation of the lower layers at the top MgO/Fe interface. There is evidence of asymmetrical oxidation on the top and bottom of the Fe layers. We find agreement with dark-field scanning transmission electron microscope (STEM) and x-ray reflectivity measurements. Through the STEM measurements, we confirm an overall epitaxial stack with dislocations and warping at the interfaces of ca. 5 angstrom. We also note a distinct difference in the top bilayer, especially MgO, with possible Fe inclusions. We thus demonstrate that SW-HXPS can be used to probe deep buried interfaces of novel magnetic devices with few-angstrom precision.
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| 4. |
- Keqi, A., et al.
(författare)
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Electronic structure of the dilute magnetic semiconductor Ga1-xMnxP from hard x-ray photoelectron spectroscopy and angle-resolved photoemission
- 2018
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Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 97:15
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the electronic structure of the dilute magnetic semiconductor (DMS) Ga0.98Mn0.02P and compared it to that of an undoped GaP reference sample, using hard x-ray photoelectron spectroscopy (HXPS) and hard x-ray angle-resolved photoemission spectroscopy (HARPES) at energies of about 3 keV. We present experimental data, as well as theoretical calculations, to understand the role of the Mn dopant in the emergence of ferromagnetism in this material. Both core-level spectra and angle-resolved or angle-integrated valence spectra are discussed. In particular, the HARPES experimental data are compared to free-electron final-state model calculations and to more accurate one-step photoemission theory. The experimental results show differences between Ga0.98Mn0.02P and GaP in both angle-resolved and angle-integrated valence spectra. The Ga0.98Mn0.02P bands are broadened due to the presence of Mn impurities that disturb the long-range translational order of the host GaP crystal. Mn-induced changes of the electronic structure are observed over the entire valence band range, including the presence of a distinct impurity band close to the valence-band maximum of the DMS. These experimental results are in good agreement with the one-step photoemission calculations and a prior HARPES study of Ga0.97Mn0.03As and GaAs [Gray et al., Nat. Mater. 11, 957 (2012)], demonstrating the strong similarity between these two materials. The Mn 2p and 3s core-level spectra also reveal an essentially identical state in doping both GaAs and GaP.
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| 5. |
- Capone, F. G., et al.
(författare)
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Operando observation of the dynamic SEI formation on a carbonaceous electrode by near-ambient pressure XPS
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Ingår i: Energy and Environmental Science. - 1754-5692.
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic formation of chemical species composing the solid electrolyte interphase (SEI) layer at the surface of a carbonaceous electrode in a carbonate-based liquid electrolyte was observed in real-time using operando near-ambient pressure XPS (NAP-XPS). The potential of the glassy carbon electrode vs. metallic lithium was controlled during the XPS experiment. By following the binding energy shifts as a function of applied potential, we could identify the main SEI species and observe their deposition on the electrode surface during the formation of the SEI. These results demonstrate that NAP-XPS is a powerful tool to investigate the SEI formation and stability in Li- and post-Li-ion batteries, paving the way for future studies on the effect of electrolyte additives and solvent mixtures on battery performance.
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| 6. |
- Céolin, D., et al.
(författare)
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Far-Zone Resonant Energy Transfer in X-ray Photoemission as a Structure Determination Tool
- 2017
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185 .- 1948-7185. ; 8:12, s. 2730-2734
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Tidskriftsartikel (refereegranskat)abstract
- Near-zone Förster resonant energy transfer is the main effect responsible for excitation energy flow in the optical region and is frequently used to obtain structural information. In the hard X-ray region, the Förster law is inadequate because the wavelength is generally shorter than the distance between donors and acceptors; hence, far-zone resonant energy transfer (FZRET) becomes dominant. We demonstrate the characteristics of X-ray FZRET and its fundamental differences with the ordinary near-zone resonant energy-transfer process in the optical region by recording and analyzing two qualitatively different systems: high-density CuO polycrystalline powder and SF6 diluted gas. We suggest a method to estimate geometrical structure using X-ray FZRET employing as a ruler the distance-dependent shift of the acceptor core ionization potential induced by the Coulomb field of the core-ionized donor.
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| 7. |
- Ismail, I., et al.
(författare)
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Experimental setup for the study of resonant inelastic X-ray scattering of organometallic complexes in gas phase
- 2018
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Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 89:6
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Tidskriftsartikel (refereegranskat)abstract
- A new setup has been designed and built to study organometallic complexes in gas phase at the third-generation Synchrotron radiation sources. This setup consists of a new homemade computer-controlled gas cell that allows us to sublimate solid samples by accurately controlling the temperature. This cell has been developed to be a part of the high-resolution X-ray emission spectrometer permanently installed at the GALAXIES beamline of the French National Synchrotron Facility SOLEIL. To illustrate the capabilities of the setup, the cell has been successfully used to record high-resolution K alpha emission spectra of gas-phase ferrocene Fe(C5H5)(2) and to characterize their dependence with the excitation energy. This will allow to extend resonant X-ray emission to different organometallic molecules.
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| 8. |
- Kukk, E., et al.
(författare)
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Unified treatment of recoil and Doppler broadening in molecular high-energy photoemission
- 2021
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Ingår i: New Journal of Physics. - : Institute of Physics Publishing (IOPP). - 1367-2630. ; 23:6
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Tidskriftsartikel (refereegranskat)abstract
- Doppler and recoil effects are an integral part of the photoemission process at the high kinetic energies reached in hard x-ray photo-electron spectroscopy (HAXPES) and have a major effect on the observed lineshape, resulting in broadening, energy losses and discrete excitations. These effects can be modeled with a high degree of detail for small systems like diatomic molecules, for larger systems such treatment is often superfluous as the fine spectral features are not observable. We present a united description of the Doppler and recoil effects for arbitrary polyatomic systems and offer an approximate description of the recoil- and Doppler-modified photoemission spectral lineshape as a practical tool in the analysis of HAXPES spectra of core-level photoemission. The approach is tested on the examples of carbon dioxide and pentane molecules. The C and O 1s photoelectron spectra of CO2 in gas phase were also measured at 2.3 and 7.0 keV photon energy at Synchrotron SOLEIL and the spectra were analyzed using the model description. The limitations and applicability of the approach to adsorbates, interfaces and solids is briefly discussed.
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| 9. |
- Ceolin, D., et al.
(författare)
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Auger resonant-Raman study at the Ar K edge as probe of electronic-state-lifetime interferences
- 2015
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 91:2
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Tidskriftsartikel (refereegranskat)abstract
- The resonant-Auger decay in argon following Ar 1s - np excitations was studied under resonant-Raman conditions, i.e., with a total instrumental bandwidth much narrower than the natural linewidth of the absorption features. These state-of-the-art experiments are combined with a radiationless resonant-Raman scattering theory. The main results include identification of the energy position of some high-lying Rydberg states previously masked by insufficient resolution and clear evidence of electronic-state-lifetime interference phenomena.
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| 10. |
- Dallera, C., et al.
(författare)
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Understanding mixed valent materials : Effects of dynamical core-hole screening in high-pressure x-ray spectroscopy
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:8, s. 081101-
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Tidskriftsartikel (refereegranskat)abstract
- Changes in the electronic structure of Yb, a material whose valence is modified under pressure, are observed with remarkable detail in x-ray absorption and emission data measured between ambient conditions and 20 GPa. These changes are reproduced by a theory that essentially does not rely on experimental parameters, and includes dynamical core-hole screening. From the combined experimental and theoretical data we can firmly establish on a quantitative level how the valency of an intermediate valence material is modified by pressure. In metallic Yb it increases from 2 to 2.55 +/- 0.05 between 0 and 20 GPa.
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