A5007675692- Atomic and Molecular Physics
- Advanced Chemical Physics Studies
- Mass Spectrometry Techniques and Applications
- Catalytic Processes in Materials Science
- Ion-surface interactions and analysis
- Cold Atom Physics and Bose-Einstein Condensates
- X-ray Spectroscopy and Fluorescence Analysis
- Electronic and Structural Properties of Oxides
- Advanced Photocatalysis Techniques
- Photoreceptor and optogenetics research
- Quantum, superfluid, helium dynamics
- Spectroscopy and Laser Applications
- Surface Chemistry and Catalysis
- Surface and Thin Film Phenomena
- Particle accelerators and beam dynamics
- Atomic and Subatomic Physics Research
- Catalysts for Methane Reforming
- Astro and Planetary Science
- Advanced Fluorescence Microscopy Techniques
- Electrocatalysts for Energy Conversion
- Astrophysics and Star Formation Studies
- Advanced X-ray Imaging Techniques
- Laser-induced spectroscopy and plasma
- TiO2 Photocatalysis and Solar Cells
- Photochromic and Fluorescence Chemistry
Aarhus University
2014-2024
MAX IV Laboratory
2016
Ikerbasque
2016
CIC nanoGUNE
2016
Lund University
2016
Max Planck Institute for Nuclear Physics
2002-2011
Max Planck Society
2002-2010
University of Copenhagen
2006
Heidelberg University
2001
Abstract Transition metal oxides show great promise as Earth-abundant catalysts for the oxygen evolution reaction in electrochemical water splitting. However, progress development of highly active oxide nanostructures is hampered by a lack knowledge location and nature sites. Here we show, through atom-resolved scanning tunnelling microscopy, X-ray spectroscopy computational modelling, how hydroxyls form from dissociation at under coordinated cobalt edge sites nanoislands. Surprisingly, find...
Within the area of surface science, one "holy grails" is to directly visualize a chemical reaction at atomic scale. Whereas this goal has been reached by high-resolution scanning tunneling microscopy (STM) in number cases for reactions occurring flat surfaces, such direct view often inhibited steps and interfaces. Here we have studied CO oxidation interface between ultrathin FeO islands Pt(111) support situ STM density functional theory (DFT) calculations. Time-lapsed imaging on inverse...
Band gap engineering in hydrogen functionalized graphene is demonstrated by changing the symmetry of functionalization structures. Small differences adsorbate binding energies on Ir(111) allow tailoring highly periodic structures favoring one distinct region moiré supercell. Scanning tunneling microscopy and X-ray photoelectron spectroscopy measurements show that a sheet can thus be prepared controlling sample temperature (Ts) during functionalization. At deposition temperatures Ts = 645 K...
With the purpose of investigating reactivity Fe carbide as an active phase in Fischer–Tropsch catalysis, we studied formation a well-defined surface structure resulting from carbon exposure film on Au(111). Using two different sources (C), namely atomic and ethylene gas, used synchrotron X-ray photoelectron spectroscopy (XPS) to show that 6 ML readily converts into thermodynamically stable phase. Scanning tunneling microscopy (STM) showed is crystalline dominated by Fe(110)-like facets...
Abstract Methanol formation over Cu/ZnO catalysts is linked with a catalytically active phase created by contact between Cu nanoparticles and Zn species whose chemical structural state depends on reaction conditions. Herein, we use variable-temperature scanning tunneling microscopy at elevated pressure conditions combined X-ray photoelectron spectroscopy measurements to investigate the surface structures states that evolve when CuZn/Cu(111) alloy exposed gas mixtures. In CO 2 hydrogenation...
We demonstrate that the dissociative recombination of ${\mathrm{D}}_{2}{\mathrm{H}}^{+}$ with low-energy electrons depends on rotational energy molecular ion such highly excited ions have a larger rate coefficient than colder ones. Observations an beam continuously interacting at low relative velocity indicate levels are preferentially depleted which, in competition radiative heating due to blackbody radiation, provides opportunity for controlling temperature stored molecules.
The energy-resolved rate coefficient for the dissociative recombination (DR) of $\mathrm{H}_{3}{}^{+}$ with slow electrons has been measured by storage-ring method using an ion beam produced from a radiofrequency multipole trap, employing buffer-gas cooling at 13 K. electron energy spread merged-beams measurement is reduced to $500\text{ }\text{ }\ensuremath{\mu}\mathrm{eV}$ cryogenic GaAs photocathode. This and previous cold-$\mathrm{H}_{3}{}^{+}$ jointly confirm capability storage rings,...
Photoabsorption studies of 11-cis and all-trans Schiff-base retinal chromophore cations in the gas phase have been performed at electrostatic ion storage ring Aarhus. A broad absorption band due to optically allowed excitation first electronically excited singlet state (${S}_{1}$) is observed around 600 nm. second ``dark'' (${S}_{2}$) just below 400 nm reported for time. It located $\ensuremath{\sim}1.2\text{ }\text{ }\mathrm{eV}$ above ${S}_{1}$ both chromophores. The ${S}_{2}$ was not...
Monolayer thin FeO(111) films were grown on Pd(111) and oxidized by atomic oxygen (O). The stoichiometric studied in detail scanning tunneling microscopy (STM) density functional theory (DFT) calculations. Compared to the previously FeO(111)/Pt(111) system, small structural differences observed for FeO monolayer films. Upon O exposure, film reconstructs, leading formation of new O-rich structures incorporating increasing amounts additional atoms. At low exposures, STM images exhibit bright...
Abstract Finding the active sites of catalysts and photo-catalysts is crucial for an improved fundamental understanding development efficient catalytic systems. Here we have studied photo-activated dehydrogenation ethanol on reduced oxidized rutile TiO 2 (110) in ultrahigh vacuum conditions. Utilizing scanning tunnelling microscopy, various spectroscopic techniques theoretical calculations found that photo-reaction proceeds most efficiently when reactants are adsorbed regular Ti surface...
Fragmentation patterns for dissociative recombination of the triatomic hydrogen molecular ion H(3)(+) in vibrational ground state have been measured using storage ring technique and fragment imaging. A broad distribution states H(2) after two-body dissociation a large predominance nearly linear momentum geometries three-body are found. The fragmentation results directly contrasted with Coulomb explosion imaging data on initial geometry, compared to existing wave-packet calculations,...
We used high-resolution scanning tunneling microscopy to study the structure of ultrathin FeO islands grown on Pt(111). Our focus is particularly edges that are important in heterogeneous catalysis, as they host active sites inversed catalysts. To imitate various reaction environments we studied pristine, oxidized, and reduced islands. Oxidation by O2 exposure led formation two types O adatom dislocations a restructuring islands, creating long O-rich few short Fe-terminated edges. In...
The vibrational relaxation of ${\mathrm{H}}_{3}^{+}$ molecules from a conventional plasma ion source is studied performing Coulomb explosion imaging on the ions extracted storage ring after variable times storage. Storage for 2 s found sufficient radiative breathing excitation and fragment velocity distribution in coordinate then agrees well with simulations based calculated ground-state wave function. decay two lowest pure levels ${(1,0}^{0})$ ${(2,0}^{0})$ seen to be considerably faster...
The breakup dynamics of ${\mathrm{H}}_{3}^{+}$ and ${\mathrm{D}}_{3}^{+}$ following dissociative recombination is studied using the combination two-dimensional imaging storage ring techniques. vibrational distributions molecular ${\mathrm{H}}_{2}$ ${\mathrm{D}}_{2}$ fragments produced in two body fragmentation channel were measured, as well kinematical correlation between hydrogen or deuterium atoms three channel. For latter, we find predominantly linear dissociation geometries. data also...
The dissociative recombination (DR) of $^{3}\mathrm{He}\phantom{\rule{0.2em}{0ex}}^{4}\mathrm{He}^{+}$ has been investigated at the heavy-ion Test Storage Ring (TSR) in Heidelberg by observing neutral products from electron-ion collisions a merged beams configuration relative energies near-zero (thermal electron energy about 10 meV) up to 40 eV. After storage and cooling for 35 s, an effective DR rate coefficient...
The lifetime of the ${\mathrm{SF}}_{6}$ anion was measured at electrostatic ion storage ring ELISA, where decays in time span from $100\text{ }\ensuremath{\mu}\mathrm{s}$ to a few seconds were recorded. We find nonexponential decay with an approximate ${t}^{\ensuremath{-}1.5}$ power-law dependence. observed rate is accounted for by model thermionic emission that takes into account initial energy spread molecule prior electron capture as well some kinetic captured applied plasma-ion source....
The nucleation and growth of Pt nanoparticles (NP’s) on rutile TiO2 (110) surfaces with O on-top atoms (oxidized TiO2), surface vacancies, H adatoms, respectively (reduced was studied by means scanning tunneling microscopy (STM) experiments density functional theory calculations. At room temperature, found to be trapped at leading rather small NP’s. In contrast, adatoms the mobility much larger. As a result, large NP's were temperature adatoms. However, ∼150 K diffusion kinetically hindered...
The photofragmentation of the water cation H${}_{2}$O${}^{+}$ through dicationic states has been studied at $35.0\ifmmode\pm\else\textpm\fi{}0.2$ nm ($35.4\ifmmode\pm\else\textpm\fi{}0.3$ eV) and $21.8\ifmmode\pm\else\textpm\fi{}0.2$ ($56.8\ifmmode\pm\else\textpm\fi{}0.5$ with a crossed ion-photon beams experiment free electron laser FLASH. dissociation dications is found to be similar two wavelengths proceed into ${\mathrm{O}}^{0}+2{\mathrm{H}}^{+}$, ${\mathrm{OH}}^{+}+{\mathrm{H}}^{+}$,...
By means of scanning tunneling microscopy (STM) measurements, we studied in situ the oxidation and reduction FeO bilayer islands on Au(111) by oxygen (O2) hydrogen (H2), respectively. The respond very dynamically toward O2, with coordinatively unsaturated ferrous (CUF) sites at island edges being essential for O2 dissociation O atom incorporation. An STM movie obtained during reveals how further molecules can dissociate after consumption all initially existing CUF through formation new...
We combined scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) to study the molecular electronic structure of submonolayer tungsten oxide supported on anatase TiO2(101), −(001), rutile TiO2(110) surfaces. found that monomeric species form all three TiO2 surfaces upon mild annealing at 400 K, with a geometry depending supporting facet. At ∼600 surface diffusion monomers sets in, but remain without diffusing into bulk even higher temperatures. As-deposited monolayer...
Merging an HD+ beam with velocity matched electrons in a heavy ion storage ring we observed rapid cooling of the rotational excitations ions by superelastic collisions (SEC) electrons. The process is well described using theoretical SEC rate coefficients obtained combining molecular R-matrix approach adiabatic nuclei rotation approximation. We verify DeltaJ=-2 coefficients, which are predicted to be dominant as opposed DeltaJ=-1 rates and amount (1-2)x10;{-6} cm;{3} s;{-1} for initial...
By means of scanning tunnelling microscopy (STM) the nucleation, growth and sintering platinum nanoparticles (Pt NP's) was studied on vicinal flat rutile titanium dioxide (TiO2) surfaces. Utilising physical vapour deposition, nucleation Pt NP's TiO2 surfaces at room temperature (RT) found to be random invariant towards different surface morphologies reduction states. Thus, RT is rather insensitive structure defects. Vacuum-annealing 600 K, 700 K 800 respectively, led lower densities as a...
We describe the design of and first commissioning experiments with a newly constructed electrostatic storage ring named SAPHIRA (Storage Ring in Aarhus for PHoton-Ion Reaction Analysis). With an intense beam Cu(-) at 4 keV, is characterized terms stored ion decay rate, longitudinal spreading injected bunch, as well direct measurements transverse spatial distributions under different conditions storage. The stability was investigated systematically selected region its electrical configuration space.