| 1. |
- Temperton, Robert H., et al.
(författare)
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Dip-and-pull ambient pressure photoelectron spectroscopy as a spectroelectrochemistry tool for probing molecular redox processes
- 2022
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 157:24
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Tidskriftsartikel (refereegranskat)abstract
- Ambient pressure x-ray photoelectron spectroscopy (APXPS) can provide a compelling platform for studying an analyte's oxidation and reduction reactions in solutions. This paper presents proof-of-principle operando measurements of a model organometallic complex, iron hexacyanide, in an aqueous solution using the dip-and-pull technique. The data demonstrates that the electrochemically active liquid meniscuses on the working electrodes can undergo controlled redox reactions which were observed using APXPS. A detailed discussion of several critical experimental considerations is included as guidance for anyone undertaking comparable experiments.
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| 2. |
- Temperton, Robert H., et al.
(författare)
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Spin propensity in resonant photoemission of transition metal complexes
- 2021
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Ingår i: Physical Review Research. - 2643-1564. ; 3:3
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Tidskriftsartikel (refereegranskat)abstract
- Resonant photoelectron spectroscopy (RPES) has been used to probe electronic structure properties of the closed-shell [FeII(CN)6]4− and open-shell [FeIII(CN)6]3− prototype transition metal complexes in aqueous solution. Site-selective Fe 2p (L-edge) RPES mapsprovide new insight into spin-coupling processes at the core-excited metal centers, with autoionization of [FeIII(CN)6]3− showing a dramatic (∼4×) singlet versus triplet final-state enhancement. This shows that RPES provides unique opportunities to study spin-dependent electronic properties in transition metal based functional materials.
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| 3. |
- Chen, Heyin, et al.
(författare)
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Investigating Surface Reactivity of a Ni-Rich Cathode Material toward CO2, H2O, and O2 Using Ambient Pressure X-ray Photoelectron Spectroscopy
- 2023
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 6:22, s. 11458-11467
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Tidskriftsartikel (refereegranskat)abstract
- Layered Ni-rich transition metal oxide materials are considered the most promising cathodes for use in commercial Li-ion batteries. Due to their instability in air, an impurity layer forms during storage under ambient conditions, and this layer increases electrochemical polarization during charging and discharging, which ultimately leads to a lower cycling capacity. In this work, we found that storage of the LiNi0.8Mn0.1Co0.1O2 (NMC 811) material in ultrahigh vacuum (UHV) can restore the surface by reducing the amount of native carbonate species in the impurity layer. In this work, in situ soft X-ray ambient pressure photoelectron spectroscopy is used to directly follow the interaction between common gases found in air and the NMC 811 surface. During gas exposure of the NMC 811 surface to pure CO2, O2, and a mixture of both pure gases, surface-adsorbed CO2 or/and O2 were detected; however, permanent changes could not be identified under UHV after the gas exposure. In contrast, a permanent increase in metal hydroxide species was observed on the sample surface following H2O vapor exposure, and an increased intensity in the carboxylate peak was observed after exposure to a mixture of CO2/O2/H2O. Thus, the irreversible degradation reaction with CO2 is triggered in the presence of H2O (on relevant time scales defined by the experiment). Additional measurements revealed that X-ray irradiation induces the formation of metal carbonate species on the NMC 811 surface under CO2 and H2O vapor pressure.
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| 4. |
- Gericke, Sabrina Maria, et al.
(författare)
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In Situ H2 Reduction of Al2O3-Supported Ni- and Mo-Based Catalysts
- 2022
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Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 12:7
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Tidskriftsartikel (refereegranskat)abstract
- Nickel (Ni)-promoted Molybdenum (Mo)-based catalysts are used for hydrotreatment processes in the chemical industry where the catalysts are exposed to high-pressure H2 at elevated temperature. In this environment, the catalyst transforms into the active phase, which involves the reduction of the oxide. Here, we report on the first in situ study on the reduction of alumina supported Ni- and Mo-based catalysts in 1 mbar H2 using ambient-pressure X-ray photoelectron spectroscopy (APXPS). The study confirms that mixing Ni and Mo lowers the reduction temperature of both Ni- and Mo-oxide as compared to the monometallic catalysts and shows that the MoO3 reduction starts at a lower temperature than the reduction of NiO in NiMo/Al2O3 catalysts. Additionally, the reduction of Ni and Mo foil was directly compared to the reduction of the Al2O3-supported catalysts and it was observed that the reduction of the supported catalysts is more gradual than the reduction of the foils, indicating a strong interaction between the Ni/Mo and the alumina support. © 2022 by the authors.
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| 5. |
- Gibson, Andrew J., et al.
(författare)
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Resonant core spectroscopies of the charge transfer interactions between C60 and the surfaces of Au(111), Ag(111), Cu(111) and Pt(111)
- 2017
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028. ; 657, s. 69-78
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Tidskriftsartikel (refereegranskat)abstract
- Charge transfer interactions between C60 and the metal surfaces of Ag(111), Cu(111), Au(111) and Pt(111) have been studied using synchrotron-based photoemission, resonant photoemission and X-ray absorption spectroscopies. By placing the X-ray absorption and valence band spectra on a common binding energy scale, the energetic overlap of the unoccupied molecular orbitals with the density of states of the underlying metal surface have been assessed in the context of possible charge transfer pathways. Resonant photoemission and resonant Auger data, measuring the valence region as a function of photon energy for C60 adsorbed on Au(111) reveals three constant high kinetic energy features associated with Auger-like core-hole decay involving an electron transferred from the surface to the LUMO of the molecule and electrons from the three highest occupied molecular orbitals, respectively and in the presence of ultra-fast charge transfer of the originally photoexcited molecule to the surface. Data for the C60/Ag(111) surface reveals an additional Auger-like feature arising from a core-hole decay process involving more than one electron transferred from the surface into the LUMO. An analysis of the relative abundance of these core-hole decay channels estimates that on average 2.4 ± 0.3 electrons are transferred from the Ag(111) surface into the LUMO. A core-hole clock analysis has also been applied to assess the charge transfer coupling in the other direction, from the molecule to the Au(111) and Ag(111) surfaces. Resonant photoemission and resonant Auger data for C60 molecules adsorbed on the Pt(111) and Cu(111) surfaces are shown to exhibit no super-Auger features, which is attributed to the strong modification of the unoccupied molecular orbitals arising from stronger chemical coupling of the molecule to the surface.
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| 6. |
- O'Shea, James N., et al.
(författare)
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Exploring ultra-fast charge transfer and vibronic coupling with N 1s RIXS maps of an aromatic molecule coupled to a semiconductor
- 2017
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 147:13
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Tidskriftsartikel (refereegranskat)abstract
- We present for the first time two-dimensional resonant inelastic x-ray scattering (RIXS) maps of multilayer and monolayer bi-isonicotinic acid adsorbed on the rutile TiO2(110) single crystal surface. This enables the elastic channel to be followed over the lowest unoccupied molecular orbitals resonantly excited at the N 1s absorption edge. The data also reveal ultra-fast intramolecular vibronic coupling, particularly during excitation into the lowest unoccupied molecular orbital-derived resonance. Both elastic scattering and the vibronic coupling loss features are expected to contain the channel in which the originally excited electron is directly involved in the core-hole decay process. This allows RIXS data for a molecule coupled to a wide bandgap semiconductor to be considered in the same way as the core-hole clock implementation of resonant photoemission spectroscopy (RPES). However, contrary to RPES measurements, we find no evidence for the depletion of the participator channel under the conditions of ultra-fast charge transfer from the molecule to the substrate densities of states, on the time scale of the core-hole lifetime. These results suggest that the radiative core-hole decay processes in RIXS are not significantly modified by charge transfer on the femtosecond time scale in this system.
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| 7. |
- O'Shea, James N., et al.
(författare)
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Ultra-fast intramolecular vibronic coupling revealed by RIXS and RPES maps of an aromatic adsorbate on TiO2(110)
- 2018
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 148:20
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Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional resonant inelastic x-ray scattering (RIXS) and resonant photoelectron spectroscopy (RPES) maps are presented for multilayer and monolayer coverages of an aromatic molecule (bi-isonicotinic acid) on the rutile TiO2(110) single crystal surface. The data reveal ultra-fast intramolecular vibronic coupling upon core excitation from the N 1s orbital into the lowest unoccupied molecular orbital (LUMO) derived resonance. In the RIXS measurements, this results in the splitting of the participator decay channel into a purely elastic line which disperses linearly with excitation energy and a vibronic coupling channel at constant emission energy. In the RPES measurements, the vibronic coupling results in a linear shift in binding energy of the participator channel as the excitation is tuned over the LUMO-derived resonance. Localisation of the vibrations on the molecule on the femtosecond time scale results in predominantly inelastic scattering from the core-excited state in both the physisorbed multilayer and the chemisorbed monolayer.
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| 8. |
- Shavorskiy, Andrey, et al.
(författare)
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Gas Pulse-X-Ray Probe Ambient Pressure Photoelectron Spectroscopy with Submillisecond Time Resolution
- 2021
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:40, s. 47629-47641
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Tidskriftsartikel (refereegranskat)abstract
- A setup capable of conducting gas pulse-X-ray probe ambient pressure photoelectron spectroscopy with high time resolution is presented. The setup makes use of a fast valve that creates gas pulses with an internal pressure in the mbar range and a rising edge of few hundreds of microseconds. A gated detector based on a fast camera is synchronized with the valve operation to measure X-ray photoemission spectra with up to 20 μs time resolution. The setup is characterized in several experiments in which the N2 gas is pulsed either into vacuum or a constant flow of another gas. The observed width of the pulse rising edge is 80 μs, and the maximum internal pulse pressure is ∼1 mbar. The CO oxidation reaction over Pt (111) was used to demonstrate the capability of the setup to correlate the gas phase composition with that of the surface during transient supply of CO gas into an O2 stream. Thus, formation of both chemisorbed and oxide oxygen species was observed prior to CO gas perturbation. Also, the data indicated that both the Langmuir-Hinshelwood and Mars-van-Krevelen mechanisms play an important role in the oxidation of carbon monoxide under ambient conditions.
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| 9. |
- Spadetto, Clément, et al.
(författare)
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Electrocatalytic Hydrogenation of Furfural with Improved Activity and Selectivity at the Surface of Structured Copper Electrodes
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Ingår i: ACS Catalysis. - 2155-5435. ; , s. 4489-4500
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Tidskriftsartikel (refereegranskat)abstract
- Furfural is a pivotal renewable platform molecule obtained from the chemical breakdown of hemicellulose. While it has traditionally been valorized to value-added chemicals through catalytic hydrogenation in biorefineries, its direct electrocatalytic hydrogenation presents attractive advantages. This article describes the significant improvements brought by the structuring of copper cathodes applied to this process in terms of activity and selectivity. We show that structured electrodes are capable of converting furfural to furfuryl alcohol with 100% selectivity at potentials as high as −0.2 V vs the reversible hydrogen electrode (RHE) in neutral conditions (pH 7.0). Moreover, the same electrode can selectively generate either furfuryl alcohol or 2-methylfuran in acidic conditions (pH 1.0), depending on the applied potential and temperature. We further show the existence of optimal voltage-temperature conditions for the efficient conversion of furfural to furfuryl alcohol or 2-methylfuran, highlighting the delicate influence of operating conditions on the selectivity of furfural reduction, in competition with the hydrogen evolution reaction in aqueous electrolytes. These performances are attributed to the resilience of Cu(I) species under operating conditions and their likely contribution to the electrocatalytic active site, as revealed by quasi-in situ photoelectron spectroscopy.
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| 10. |
- Temperton, Robert H., et al.
(författare)
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A soft x-ray probe of a titania photoelectrode sensitized with a triphenylamine dye
- 2021
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 154:23
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Tidskriftsartikel (refereegranskat)abstract
- We present a thorough soft x-ray photoelectron spectroscopy (XPS) study of a mesoporous titanium dioxide electrode sensitized with the dye 4-(diphenylamino)phenylcyanoacrylic acid, referred to as “L0.” Supported by calculations, the suite of XPS, x-ray absorption spectroscopy, and resonant photoelectron spectroscopy allows us to examine bonding interactions between the dye and the surface and the frontier electronic structure at the molecule-oxide interface. While placing these measurements in the context of existing literature, this paper is intended as a useful reference for further studies of more complex triphenylamine based sensitizers.
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| 11. |
- Temperton, Robert H., et al.
(författare)
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Adsorption and charge transfer interactions of bi-isonicotinic acid on Ag(111)
- 2017
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 147:5
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption and charge transfer dynamics of the organic molecule bi-isonicotinic acid (4,4-dicarboxy-2,2-bipyridine) on single crystal Ag(111) has been studied using synchrotron radiation-based photoemission, x-ray absorption, and resonant core spectroscopies. Measurements for multilayer and monolayer coverage are used to determine the nature of the molecule-surface interactions and the molecular orientation. An experimental density of states for the monolayer with respect to the underlying metal surface is obtained by combining x-ray absorption spectroscopy at the N 1s edge and valence photoemission to measure the unoccupied and occupied valence states, respectively. This shows that the lowest unoccupied molecular orbital in the core-excited state lies energetically below the Fermi level of the surface allowing charge transfer from the metal into this orbital. Resonant photoelectron spectroscopy was used to probe this charge transfer in the context of super-spectator and super-Auger electron transitions. The results presented provide a novel interpretation of resonant core-level spectroscopy to explore ultra-fast charge transfer between an adsorbed organic molecule and a metal surface through the observation of electrons from the metal surface playing a direct role in the core-hole decay of the core-excited molecule.
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| 12. |
- Temperton, Robert H., et al.
(författare)
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Resonant inelastic X-ray scattering of a Ru photosensitizer : Insights from individual ligands to the electronic structure of the complete molecule
- 2019
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 151:7
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Tidskriftsartikel (refereegranskat)abstract
- N 1s Resonant Inelastic X-ray Scattering (RIXS) was used to probe the molecular electronic structure of the ruthenium photosensitizer complex cis-bis(isothiocyanato) bis(2,2′-bipyridyl-4,4′-dicarboxylato) ruthenium(II), known as "N3." In order to interpret these data, crystalline powder samples of the bipyridine-dicarboxylic acid ligand ("bi-isonicotinic acid") and the single ring analog "isonicotinic acid" were studied separately using the same method. Clear evidence for intermolecular hydrogen bonding is observed for each of these crystalline powders, along with clear vibronic coupling features. For bi-isonicotinic acid, these results are compared to those of a physisorbed multilayer, where no hydrogen bonding is observed. The RIXS of the "N3" dye, again prepared as a bulk powder sample, is interpreted in terms of the orbital contributions of the bi-isonicotinic acid and thiocyanate ligands by considering the two different nitrogen species. This allows direct comparison with the isolated ligand molecules where we highlight the impact of the central Ru atom on the electronic structure of the ligand. Further interpretation is provided through complementary resonant photoemission spectroscopy and density functional theory calculations. This combination of techniques allows us to confirm the localization and relative coupling of the frontier orbitals and associated vibrational losses.
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| 13. |
- Temperton, Robert H., et al.
(författare)
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Resonant X-ray photo-oxidation of light-harvesting iron (II/III) N-heterocyclic carbene complexes
- 2021
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Two photoactive iron N-heterocyclic carbene complexes [FeII(btz)2(bpy)]2+ and [FeIII(btz)3]3+, where btz is 3,3’-dimethyl-1,1’-bis(p-tolyl)-4,4’-bis(1,2,3-triazol-5-ylidene) and bpy is 2,2’-bipyridine, have been investigated by Resonant Photoelectron Spectroscopy (RPES). Tuning the incident X-ray photon energy to match core-valence excitations provides a site specific probe of the electronic structure properties and ligand-field interactions, as well as information about the resonantly photo-oxidised final states. Comparing measurements of the Fe centre and the surrounding ligands demonstrate strong mixing of the Fe t 2 g levels with occupied ligand π orbitals but weak mixing with the corresponding unoccupied ligand orbitals. This highlights the importance of π-accepting and -donating considerations in ligand design strategies for photofunctional iron carbene complexes. Spin-propensity is also observed as a final-state effect in the RPES measurements of the open-shell Fe III complex. Vibronic coupling is evident in both complexes, where the energy dispersion hints at a vibrationally hot final state. The results demonstrate the significant impact of the iron oxidation state on the frontier electronic structure and highlights the differences between the emerging class of Fe III photosensitizers from those of more traditional Fe II complexes.
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| 14. |
- Temperton, Robert H., et al.
(författare)
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Site-Selective Orbital Interactions in an Ultrathin Iron-Carbene Photosensitizer Film
- 2020
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 124:8, s. 1603-1609
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Tidskriftsartikel (refereegranskat)abstract
- We present the first experimental study of the frontier orbitals in an ultrathin film of the novel hexa-carbene photosensitizer [Fe(btz)3]3+, where btz is 3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene). Resonant photoelectron spectroscopy (RPES) was used to probe the electronic structure of films where the molecular and oxidative integrities had been confirmed with optical and X-ray spectroscopies. In combination with density functional theory calculations, RPES measurements provided direct and site-selective information about localization and interactions of occupied and unoccupied molecular orbitals. Fe 2p, N 1s, and C 1s measurements selectively probed the metal, carbene, and side-group contributions revealing strong metal-ligand orbital mixing of the frontier orbitals. This helps explain the remarkable photophysical properties of iron-carbenes in terms of unconventional electronic structure properties and favorable metal-ligand bonding interactions - important for the continued development of these type of complexes toward light-harvesting and light-emitting applications.
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| 15. |
- Temperton, Robert H., et al.
(författare)
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Ultra-fast charge transfer between fullerenes and a gold surface, as prepared by electrospray deposition
- 2020
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 747
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Tidskriftsartikel (refereegranskat)abstract
- Monolayers of C60 and the functionalised fullerene phenyl-C61-butyric acid methyl ester (PCBM) have been prepared on Au(1 1 1) by in situ electrospray deposition. The observation of super-spectator/super-Auger decay in resonant photoemission spectroscopy (RPES) of C60 confirms monolayers prepared using electrospray undergo ultra-fast charge transfer as per previous studies of C60 monolayers on Au(1 1 1) prepared by sublimation. For PCBM, X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) show the lowest unoccupied molecular orbital (LUMO) of the molecule overlaps the Fermi-level of the metal surface. Despite this, no evidence of ultra-fast charge transfer is observed in the RPES of PCBM.
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| 16. |
- Zhu, Suyun, et al.
(författare)
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HIPPIE : a new platform for ambient-pressure X-ray photoelectron spectroscopy at the MAX IV Laboratory
- 2021
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Ingår i: Journal of Synchrotron Radiation. - : INT UNION CRYSTALLOGRAPHY. - 1600-5775 .- 0909-0495. ; 28, s. 624-636
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Tidskriftsartikel (refereegranskat)abstract
- HIPPIE is a soft X-ray beamline on the 3 GeV electron storage ring of the MAX IV Laboratory, equipped with a novel ambient-pressure X-ray photoelectron spectroscopy (APXPS) instrument. The endstation is dedicated to performing in situ and operando X-ray photoelectron spectroscopy experiments in the presence of a controlled gaseous atmosphere at pressures up to 30 mbar [1 mbar = 100 Pa] as well as under ultra-high-vacuum conditions. The photon energy range is 250 to 2200 eV in planar polarization and with photon fluxes >1012 photons s-1 (500 mA ring current) at a resolving power of greater than 10000 and up to a maximum of 32000. The endstation currently provides two sample environments: a catalysis cell and an electrochemical/liquid cell. The former allows APXPS measurements of solid samples in the presence of a gaseous atmosphere (with a mixture of up to eight gases and a vapour of a liquid) and simultaneous analysis of the inlet/outlet gas composition by online mass spectrometry. The latter is a more versatile setup primarily designed for APXPS at the solid-liquid (dip-and-pull setup) or liquid-gas (liquid microjet) interfaces under full electrochemical control, and it can also be used as an open port for ad hoc-designed non-standard APXPS experiments with different sample environments. The catalysis cell can be further equipped with an IR reflection-absorption spectrometer, allowing for simultaneous APXPS and IR spectroscopy of the samples. The endstation is set up to easily accommodate further sample environments.
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