Surface action spectroscopy with rare gas messenger atoms

Models for Reactions in Confined Space: Can Surface Science Contribute? A Review and Perspective

This paper reports and discusses some of our recent advances in surface science research on a silica film supported on a Ru(0001) substrate. This system is unique, as the silica is bound to the metal surface by dispersive forces only, and thus opens the possibility to study reactions in the confined space between the metal substrate and the silica film, acting as a permeable membrane. We demonstrate that this system allows for detailed insights into the complexity of reactions in confined space, including phenomena due to the response of the confined space to the presence of the reactants, and direct comparison to the situation when the same reaction occurs in open space.

Adatom Bonding Sites in a Nickel-Fe3 O4 (001) Single-Atom Model Catalyst and O2 Reactivity Unveiled by Surface Action Spectroscopy with Infrared Free-Electron Laser Light

Single-atom (SA) catalysis presently receives much attention with its promise to decrease the cost of the active material while increasing the catalyst's performance. However, key details such as the exact location of SA species and their stability are often unclear due to a lack of atomic level information. Here, we show how vibrational spectra measured with surface action spectroscopy (SAS) and density functional theory (DFT) simulations can differentiate between different adatom binding sites and determine the location of Ni and Au single atoms on Fe₃ O₄ (001). We reveal that Ni and Au adatoms selectively bind to surface oxygen ions which are octahedrally coordinated to Fe ions. In addition, we find that the Ni adatoms can activate O₂ to superoxide in contrast to the bare surface and Ni in subsurface positions. Overall, we unveil the advantages of combining SAS and DFT for improving the understanding of single-atom catalysts.

Surface Action Spectroscopy: A Review and a Perspective on a New Technique to Study Vibrations at Surfaces

A new vibrational spectroscopy method aimed at the investigation of solid surfaces in ultrahigh vacuum, called "Surface Action Spectroscopy (SAS)", is described and the first results are reviewed. This technique is based on ideas and experiments performed in the gas phase. A surface is exposed to a messenger species at low temperature. This messenger species is desorbed via absorption of tunable infrared light from a free-electron laser and the desorption rate of the messenger species is recorded via mass spectrometry. It is shown that the technique is extremely surface sensitive and we discuss the basic mechanisms of the technique. We show a feasibility study on a V₂ O₃ (0001) surface, where we know the surface structure. We then proceed to the example of iron oxide films to study the surface structure in parallel with calculations of the surface phonons, which allow us to confirm the surface structure of Fe₃ O₄ (111) to be Fe_tet terminated. It also provides evidence for the so-called biphase structure. To conclude, we discuss possibilities to apply the technique to interesting questions in model and real catalysis, since the technique may provide interesting information independent of long-range order of the sample.

Chapter model systems in heterogeneous catalysis at the atomic level: a personal view

The review presents an overview of studies in the surface science of oxide and related surfaces with an emphasis of the studies performed in the authors’ group. Novel instruments and technique developments, as well as their applications are reported, in an attempt to cover studies on model systems of increasing complexity, including some of the key ingredients of an industrially applied heterogeneous catalyst and its fabrication. The review is intended to demonstrate the power of model studies in understanding heterogeneous catalysis at the atomic level. The studies include those on supported nano-particles, both, prepared in vacuum and from solution, interaction of surfaces and the underlying bulk with molecules from the gas phase, strong metal support interaction, as well as the first attempt to include studies on reactions in confined spaces.

Elucidating Surface Structure with Action Spectroscopy

Surface Action Spectroscopy, a vibrational spectroscopy method developed in recent years at the Fritz Haber Institute is employed for structure determination of clean and H₂O-dosed (111) magnetite surfaces. Surface structural information is revealed by using the microscopic surface vibrations as a fingerprint of the surface structure. Such vibrations involve just the topmost atomic layers, and therefore the structural information is truly surface related. Our results strongly support the view that regular Fe₃O₄(111)/Pt(111) is terminated by the so-called Fe_tet1 termination, that the biphase termination of Fe₃O₄(111)/Pt(111) consists of FeO and Fe₃O₄(111) terminated areas, and we show that the method can differentiate between different water structures in H₂O-derived adsorbate layers on Fe₃O₄(111)/Pt(111). With this, we conclude that the method is a capable new member in the set of techniques providing crucial information to elucidate surface structures. The method does not rely on translational symmetry and can therefore also be applied to systems which are not well ordered. Even an application to rough surfaces is possible.

A cryogenic single nanoparticle action spectrometer

A nanoparticle (NP) mass spectrometer designed to perform action spectroscopy on single NPs at cryogenic temperatures is described. NPs from an electrospray ion source with masses ranging from 460 to 740 MDa are injected and trapped in a temperature controllable (8-350 K) split-ring electrode ion-trap characterized by improved optical access and trapping potential. After excess NPs are ejected from the trap, the mass-to-charge ratio and subsequently the absolute mass of the trapped NP are determined nondestructively using Fourier transformation and resonant excitation methods. The setup allows us to monitor the mass variation of a single NP as a function of the ion-trap temperature, collision-gas pressure, and irradiation laser power. Ion-trap temperature controlled N₂ adsorption at cryogenic temperatures onto a single, ∼90 nm diameter SiO₂ NP is demonstrated and characterized. We further show that laser irradiation at 532 nm leads to power-dependent changes in the effective N₂ adsorption rate of the particle, which can be monitored and ultimately exploited to measure absorption spectra of a single NP.