| 1. |
- Kyhl, Line, et al.
(författare)
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Exciting H2 Molecules for Graphene Functionalization
- 2017
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851.
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen functionalization of graphene by exposure to vibrationally excited H2 molecules is investigated by combined scanning tunneling microscopy, high-resolution electron energy loss spectroscopy, X-ray photoelectron spectroscopy measurements, and density functional theory calculations. The measurements reveal that vibrationally excited H2 molecules dissociatively adsorb on graphene on Ir(111) resulting in nanopatterned hydrogen functionalization structures. Calculations demonstrate that the presence of the Ir surface below the graphene lowers the H2 dissociative adsorption barrier and allows for the adsorption reaction at energies well below the dissociation threshold of the H–H bond. The first reacting H2 molecule must contain considerable vibrational energy to overcome the dissociative adsorption barrier. However, this initial adsorption further activates the surface resulting in reduced barriers for dissociative adsorption of subsequent H2 molecules. This enables functionalization by H2 molecules with lower vibrational energy, yielding an avalanche effect for the hydrogenation reaction. These results provide an example of a catalytically active graphene-coated surface and additionally set the stage for a re-interpretation of previous experimental work involving elevated H2 background gas pressures in the presence of hot filaments.
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| 2. |
- Maibach, Julia, et al.
(författare)
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Probing a battery electrolyte drop with ambient pressure photoelectron spectroscopy
- 2019
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Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Operando ambient pressure photoelectron spectroscopy in realistic battery environments is a key development towards probing the functionality of the electrode/electrolyte interface in lithium-ion batteries that is not possible with conventional photoelectron spectroscopy. Here, we present the ambient pressure photoelectron spectroscopy characterization of a model electrolyte based on 1M bis(trifluoromethane)sulfonimide lithium salt in propylene carbonate. For the first time, we show ambient pressure photoelectron spectroscopy data of propylene carbonate in the liquid phase by using solvent vapor as the stabilizing environment. This enables us to separate effects from salt and solvent, and to characterize changes in electrolyte composition as a function of probing depth. While the bulk electrolyte meets the expected composition, clear accumulation of ionic species is found at the electrolyte surface. Our results show that it is possible to measure directly complex liquids such as battery electrolytes, which is an important accomplishment towards true operando studies.
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| 3. |
- Nurk, Gunnar, et al.
(författare)
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Near ambient pressure X-ray photoelectron - and impedance spectroscopy study of NiO - Ce 0.9 Gd 0.1 O 2-δ anode reduction using a novel dual-chamber spectroelectrochemical cell
- 2018
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 378, s. 589-596
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports an experimental study, where the reduction of NiO-GDC to Ni-GDC is monitored using high temperature (HT) near ambient pressure (NAP) X-ray photoelectron spectroscopy (XPS) in combination with simultaneous impedance spectroscopy (IS). The experiment is carried out using a dual chamber (DC)-HT-NAP-XPS cell designed for membrane electrode studies. The dual chamber measurement cell enables adequate electrochemical feedback, i.e. the possibility of measuring the working electrode potential against a Pt reference electrode in a well-known environment (pO2 = 0.2 bar) and of monitoring the pO2 value on the studied electrode through open circuit voltage (OCV) measurements. Simultaneous changes of electrode impedance and O 1s, Ce 4d and Ni 3p electron binding energies are observed and discussed. The shape of the O 1s photoelectron peak is significantly influenced by the equilibria of Ce4+ ↔ Ce3+ and Ni2+ ↔ Ni0, influenced by pO2, in analysis chamber.
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| 4. |
- Shayesteh, Payam, et al.
(författare)
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Experimental and theoretical gas phase electronic structure study of tetrakis(dimethylamino) complexes of Ti(IV) and Hf(IV)
- 2019
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 234, s. 80-85
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Tidskriftsartikel (refereegranskat)abstract
- The gas phase electronic structure of two transition metal alkylamino complexes, M(N(CH3)2)4, where M = Ti, Hf, was studied using photoelectron spectroscopy and density functional theory (DFT). These studies are a first step for predicting atomic layer and chemical vapor deposition reactions on surfaces, which are common applications of these molecules. The valence photoemission spectra of these two complexes were collected with 50 and 150 eV photon energies. Comparison of calculated ionization energies and our experiments yielded good agreement. Analysis of calculated molecular orbitals provides insight into the π-donation interaction between the lone pair of electrons on the amino ligands and the empty metal orbitals. In addition to the valence structure, the core level photoemission spectra were analyzed. The π-interaction was found to influence core level ionization energies. Vibrational structure in the C 1s spectra are reported with insight from DFT calculations. The comprehensive experimental and theoretical characterization of the electronic structure of these complexes provide a robust foundation to progress to detailed spectroscopic studies of the interactions between these molecules and surfaces.
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| 5. |
- Sjöblom, Peter, et al.
(författare)
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Motion control system of MAX IV Laboratory soft x-ray beamlines
- 2016
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Ingår i: Proceedings of the 12th International Conference on Synchrotron Radiation Instrumentation, SRI 2015. - : Author(s). - 9780735413986 ; 1741
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Konferensbidrag (refereegranskat)abstract
- At the MAX IV Laboratory, five new soft x-ray beamlines are under development. The first is Species and it will be used to develop and set the standard of the control system, which will be common across the facility. All motion axes at MAX IV will be motorized using stepper motors steered by the IcePAP motion controller and a mixture of absolute and incremental encoders following a predefined coordinate system. The control system software is built in Tango and uses the Python-based Sardana framework. The user controls the entire beamline through a synoptic overview and Sardana is used to run the scans.
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| 6. |
- Timm, Rainer, et al.
(författare)
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Self-cleaning and surface chemical reactions during hafnium dioxide atomic layer deposition on indium arsenide
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Atomic layer deposition (ALD) enables the ultrathin high-quality oxide layers that are central to all modern metal-oxide-semiconductor circuits. Crucial to achieving superior device performance are the chemical reactions during the first deposition cycle, which could ultimately result in atomic-scale perfection of the semiconductor-oxide interface. Here, we directly observe the chemical reactions at the surface during the first cycle of hafnium dioxide deposition on indium arsenide under realistic synthesis conditions using photoelectron spectroscopy. We find that the widely used ligand exchange model of the ALD process for the removal of native oxide on the semiconductor and the simultaneous formation of the first hafnium dioxide layer must be significantly revised. Our study provides substantial evidence that the efficiency of the self-cleaning process and the quality of the resulting semiconductor-oxide interface can be controlled by the molecular adsorption process of the ALD precursors, rather than the subsequent oxide formation.
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| 7. |
- Urpelainen, Samuli, et al.
(författare)
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The SPECIES beamline at the MAX IV Laboratory : A facility for soft X-ray RIXS and APXPS
- 2017
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Ingår i: Journal of Synchrotron Radiation. - 1600-5775 .- 0909-0495. ; 24:1, s. 344-353
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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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