A5041603922- Catalytic Processes in Materials Science
- Iron oxide chemistry and applications
- Electrocatalysts for Energy Conversion
- Magnetic Properties and Synthesis of Ferrites
- Electronic and Structural Properties of Oxides
- Catalysis and Oxidation Reactions
- Nanomaterials for catalytic reactions
- Surface and Thin Film Phenomena
- Advanced Chemical Physics Studies
- Magnetic properties of thin films
- Copper-based nanomaterials and applications
- Minerals Flotation and Separation Techniques
- Surface Chemistry and Catalysis
- Catalysts for Methane Reforming
- Advanced Photocatalysis Techniques
- Advanced Condensed Matter Physics
- X-ray Diffraction in Crystallography
- Electron and X-Ray Spectroscopy Techniques
- nanoparticles nucleation surface interactions
- Molecular Junctions and Nanostructures
- Graphene research and applications
- X-ray Spectroscopy and Fluorescence Analysis
- Environmental remediation with nanomaterials
- Electrochemical Analysis and Applications
- Mine drainage and remediation techniques
TU Wien
2016-2025
Institut für Technische und Angewandte Physik (Germany)
2024
University of Vienna
2020
Austrian Economics Center
2017-2020
University of Warwick
2005-2012
Institute of Applied Physics
2012
Pacific Northwest National Laboratory
2009-2010
Tulane University
2010
Iron oxides play an increasingly prominent role in heterogeneous catalysis, hydrogen production, spintronics, and drug delivery. The surface or material interface can be performance-limiting these applications, so it is vital to determine accurate atomic-scale structures for iron understand why they form. Using a combination of quantitative low-energy electron diffraction, scanning tunneling microscopy, density functional theory calculations, we show that ordered array subsurface vacancies...
Understanding how the local environment of a "single-atom" catalyst affects stability and reactivity remains challenge. We present an in-depth study copper1, silver1, gold1, nickel1, palladium1, platinum1, rhodium1, iridium1 species on Fe3O4(001), model support in which all metals occupy same twofold-coordinated adsorption site upon deposition at room temperature. Surface science techniques revealed that CO strength single metal sites differs from respective surfaces supported clusters....
An array of surface science measurements has revealed novel water adsorption behavior at the Fe(3)O(4)(001) surface. Following room temperature exposure to water, a low coverage hydrogen atoms is observed, with no associated hydroxyl group. Mild annealing hydrogenated leads desorption via abstraction oxygen atoms, leading reduction These results point an irreversible splitting molecule. The observed phenomena are discussed in context recent DFT calculations (Mulakaluri, N.; Pentcheva, R.;...
Significance The catalytic activity of metal particles is highly size-dependent in the subnanometer regime, which makes understanding how and why particle sizes change reactive atmospheres particularly important. Here, we show that carbon monoxide plays a dual role coarsening otherwise stable Pt atoms on an Fe 3 O 4 (001) support: CO adsorption weakens adatom–support interaction inducing mobility, stabilizes dimer against decay into two adatoms. Our results illustrate molecules modify...
We present a Scanning Tunneling Microscopy (STM) investigation of gold deposited at the magnetite Fe3O4(001) surface room temperature. This forms reconstruction with (\surd2\times\surd2)R45{\deg} symmetry, where pairs Fe and neighboring O ions are slightly displaced laterally, forming undulating rows 'narrow' 'wide' adsorption sites. At fractional monolayer coverages, single Au adatoms adsorb exclusively narrow sites, no significant sintering up to annealing temperatures 400 {\deg}C. The...
The photoactivity of methanol adsorbed on the anatase TiO
The α-Fe2O3(11̅02) surface (also known as the hematite r-cut or (012) surface) was studied using low-energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS), ultraviolet (UPS), scanning tunneling microscopy (STM), noncontact atomic force (nc-AFM), and ab initio density functional theory (DFT)+U calculations. Two structures are stable under ultrahigh vacuum (UHV) conditions; a stoichiometric (1 × 1) can be prepared by annealing at 450 °C in ≈10–6 mbar O2, reduced (2...
A combination of Photoemission, Atomic Force and Scanning Tunneling Microscopy/Spectroscopy measurements shows that excess electrons in TiO2 anatase (101) surface are trapped at step edges. Consequently, steps act as preferred adsorption sites for O2. In Density Functional Theory calculations localize clean edges, this tendency is enhanced by O vacancies hydroxylation. The results show the importance defects wide-ranging applications titania.
It now seems clear that supported metal adatoms can be effective catalysts for some reactions, but how to make best use of this phenomenon remains an open question. Most studies date have focussed on synthesizing stable "single-atom" variants functioning nanoparticle systems, there is mounting evidence the properties do not scale from those larger nanoparticles in a simple way. The sensitivity adsorption charge state and coordination environment adatom has led researchers dream single atom...
Significance Determining the structure of water on metal oxide surfaces is a key step toward molecular-level understanding dissolution, corrosion, geochemistry, and catalysis, but hydrogen bonding large, complex unit cells present major challenge to modern theory. Here, we utilize state-of-the-art experimental techniques guide density functional theory (DFT)-based search for minimum-energy configurations Fe 3 O 4 (001). A subsurface reconstruction dominates adsorption at all coverages. An...
The adsorption of H on the magnetite (001) surface was studied with photoemission spectroscopies, scanning tunneling microscopy, and density-functional theory. At saturation coverage insulating $(\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2})R45\ifmmode^\circ\else\textdegree\fi{}$ reconstruction is lifted undergoes a semiconductor--half metal transition. This transition involves subtle changes in local geometric structure linked to an enrichment ${\text{Fe}}^{2+}$ cations at surface....
The adsorption of Ni, Co, Mn, Ti, and Zr at the $(\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2})\text{R}{45}^{\ensuremath{\circ}}$-reconstructed ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}(001)$ surface was studied by scanning tunneling microscopy, x-ray ultraviolet photoelectron spectroscopy, low-energy electron diffraction (LEED), density functional theory (DFT). Following deposition room temperature, metals are either adsorbed as isolated adatoms or fill subsurface cation vacancy sites...
Significance Molecular oxygen is an inert species, unable to enter chemical reactions. Activation occurs through the acceptance of extra electron; this catalytic step plays a major role in applications such as heterogeneous catalysis and fuel cells. It also used by all living organisms. We show that two different charge states O 2 can be easily distinguished atomic force microscopy (AFM). directly injected or removed electrons into/from molecule AFM tip, switching reactivity. These results...
Graphene has a close lattice match to the Ni(111) surface, resulting in preference for 1 × configurations. We have investigated graphene grown by chemical vapor deposition (CVD) on nickel carbide (Ni(2)C) reconstruction of with scanning tunneling microscopy (STM). The presence excess carbon, form Ni(2)C, prevents from adopting preferred configuration and leads grain rotation. STM measurements show that residual Ni(2)C domains are present under rotated graphene. Nickel vacancy islands...
Metal-support interactions are frequently invoked to explain the enhanced catalytic activity of metal nanoparticles dispersed over reducible metal-oxide supports, yet atomic scale mechanisms rarely known. Here, we use scanning tunneling microscopy study a Pt1-6/Fe3O4 model catalyst exposed CO, H2, O2, and mixtures thereof, at 550 K. CO extracts lattice oxygen cluster perimeter form CO2, creating large holes in surface. H2 O2 dissociate on clusters spill onto support. The former creates...
Reduced terminations of the Fe${}_{3}$O${}_{4}$(001) surface were studied using scanning tunneling microscopy, x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). Fe atoms, deposited onto thermodynamically stable, distorted B-layer termination at room temperature (RT), occupy one two available tetrahedrally coordinated sites per ($\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}$)$R$45\ifmmode^\circ\else\textdegree\fi{} unit cell. Further RT deposition results in...
The high specific activity and cost-effectiveness of single-atom catalysts (SACs) hold great promise for numerous catalytic chemistries. In hydrogenation reactions, the mechanisms critical steps such as hydrogen activation spillover are far from understood. Here, we employ a combination scanning tunneling microscopy density functional theory to demonstrate that on model SAC comprised single Pd atoms Fe3O4(001), H2 dissociates heterolytically between surface oxygen. efficient allows...
The adsorption of carbon monoxide on the anatase TiO2 (101) surface was studied with infrared reflection absorption spectroscopy (IRRAS), temperature-programmed desorption (TPD), X-ray photoelectron (XPS), scanning tunneling microscopy (STM), and density functional theory (DFT). IRRAS data reveal only one CO band at ∼2181 cm–1 for both stoichiometric reduced surfaces. From TPD, an energy 0.37 ± 0.03 eV is estimated isolated molecule, which shifts to slightly smaller values higher coverages....
A Gaussian Approximation Potential (GAP) was trained using density-functional theory data to enable a global geometry optimization of low-index rutile IrO2 facets through simulated annealing. Ab initio thermodynamics identifies (101) and (111) (1x1)-terminations competitive with (110) in reducing environments. Experiments on single crystals find that dominate, exhibit the theoretically predicted (1x1) periodicity X-ray photoelectron spectroscopy (XPS) core level shifts. The obtained...
The structural evolution of graphene on Ni(111) is investigated as a function growth temperature by scanning tunneling microscopy (STM). Low (400–500 °C) results in continuous but highly defective film with small ordered domains and disordered composed Stone–Wales (SW)-like defects. As the increased, shrink leaving clusters defects alongside epitaxially matched graphene. Density functional theory (DFT) calculations indicate crucial role metallic support for healing SW defects, interaction...