The XPS of pyridine: A combined theoretical and experimental analysis.

A detailed analysis of the N(1s) and C(1s) X-Ray Photoelectron Spectroscopy (XPS) is made, where the measured XPS is compared with theoretical Sudden Approximation (SA) intensities and theoretical XPS Binding Energies (BEs). There is remarkably good agreement between the theoretical predictions and the measured XPS; in particular, the different full width at half maximum values for the C(1s) and N(1s) BEs are explained in terms of unresolved C(1s) BEs for the different C atoms in pyridine. This work demonstrates that the combination of theory and XPS measurements can extract analysis of the XPS relevant to the molecular electronic structure.

Direct Anchoring of Molybdenum Sulfide Molecular Catalysts on Antimony Selenide Photocathodes for Solar Hydrogen Production.

Molybdenum sulfide serves as an effective nonprecious metal catalyst for hydrogen evolution, primarily active at edge sites with unsaturated molybdenum sites or terminal disulfides. To improve the activity at a low loading density, two molybdenum sulfide clusters, [MoS] and [MoS], were investigated. The MoS molecular catalysts were heterogenized on SbSe with a simple soaking treatment, resulting in a thin catalyst layer of only a few nanometers that gave up to 20 mA cm under one sun illumination.

Hydrogen evolution with hot electrons on a plasmonic-molecular catalyst hybrid system.

Plasmonic systems convert light into electrical charges and heat, mediating catalytic transformations. However, there is ongoing controversy regarding the involvement of hot carriers in the catalytic process. In this study, we demonstrate the direct utilisation of plasmon hot electrons in the hydrogen evolution reaction with visible light.

Stability of Iridium Single Atoms on FeO(001) in the mbar Pressure Range.

Stable single metal adatoms on oxide surfaces are of great interest for future applications in the field of catalysis. We studied iridium single atoms (Ir) supported on a FeO(001) single crystal, a model system previously only studied in ultra-high vacuum, to explore their behavior upon exposure to several gases in the millibar range (up to 20 mbar) utilizing ambient-pressure X-ray photoelectron spectroscopy. The Ir single adatoms appear stable upon exposure to a variety of common gases at room temperature, including oxygen (O), hydrogen (H), nitrogen (N), carbon monoxide (CO), argon (Ar), and water vapor.

Solution phase treatments of SbSe heterojunction photocathodes for improved water splitting performance.

Antimony selenide (SbSe) is an auspicious material for solar energy conversion that has seen rapid improvement over the past ten years, but the photovoltage deficit remains a challenge. Here, simple and low-temperature treatments of the p-n heterojunction interface of SbSe/TiO-based photocathodes for photoelectrochemical water splitting were explored to address this challenge. The FTO/Ti/Au/SbSe (substrate configuration) stack was treated with (NH)S as an etching solution, followed by CuCl treatment prior to deposition of the TiO by atomic layer deposition.

Dynamic Equilibrium at the HCOOH-Saturated TiO(110)-Water Interface.

Carboxylic acids bind to titanium dioxide (TiO) dissociatively, forming surface superstructures that give rise to a (2 × 1) pattern detected by low-energy electron diffraction. Exposing this system to water, however, leads to a loss of the highly ordered surface structure. The formate-covered surface was investigated by a combination of diffraction and spectroscopy techniques, together with static and dynamic ab initio simulations, with the conclusion that a dynamic equilibrium exists between adsorbed formic acid and water molecules.

Influence of surface defect density on the ultrafast hot carrier relaxation and transport in photoelectrodes.

Cuprous oxide () is a promising material for photoelectrochemical energy conversion due to its small direct band gap, high absorbance, and its Earth-abundant constituents. High conversion efficiencies require transport of photoexcited charges to the interface without energy loss. We studied the electron dynamics in (111) by time-resolved two-photon photoemission for different surface defect densities in order to elucidate the influence on charge carrier transport.

Kinetics of the Thermal Oxidation of Ir(100) toward IrO Studied by Ambient-Pressure X-ray Photoelectron Spectroscopy.

Using time-lapsed ambient-pressure X-ray photoelectron spectroscopy, we investigate the thermal oxidation of single-crystalline Ir(100) films toward rutile IrO(110) in situ. We initially observe the formation of a carbon-free surface covered with a complete monolayer of oxygen, based on the binding energies of the Ir 4f and O 1s core level peaks. During a rather long induction period with nearly constant oxygen coverage, the work function of the surface changes continuously as sensed by the gas phase O 1s signal.

Probing the solid-liquid interface with tender x rays: A new ambient-pressure x-ray photoelectron spectroscopy endstation at the Swiss Light Source.

A new endstation to perform operando chemical analysis at solid-liquid interfaces by means of ambient pressure x-ray photoelectron spectroscopy (APXPS) is presented. The endstation is located at the Swiss Light Source and can be attached to the soft x-ray in situ spectroscopy beamline (X07DB) for solid-gas type experiments and to a tender x-ray beamline (PHOENIX I) for solid-liquid interface experiments. The setup consists of three interconnected ultrahigh vacuum chambers: one for sample preparation using surface science techniques, the analysis chamber for APXPS experiments, and an entry-lock chamber for sample transfer across the two pressure regimes.

Dynamic Role of Cluster Cocatalysts on Molecular Photoanodes for Water Oxidation.

While loading of cocatalysts is one of the most widely investigated strategies to promote the efficiency of photoelectrodes, the understanding of their functionality remains controversial. We established new hybrid molecular photoanodes with cobalt-based molecular cubane cocatalysts on hematite as a model system. Photoelectrochemical and rate law analyses revealed an interesting functionality transition of the {Co(II)O}-type cocatalysts.

Functionalization and passivation of ultrathin alumina films of defined sub-nanometer thickness with self-assembled monolayers.

Instability of ultrathin surface oxides on alloys under environmental conditions can limit the opportunities for applications of these systems when the thickness control of the insulating oxide film is crucial for device performance. A procedure is developed to directly deposit self-assembled monolayers (SAM) from solvent onto substrates prepared under ultra-high vacuum conditions without exposure to air. As an example, rhenium photosensitizers functionalized with carboxyl linker groups are attached to ultrathin alumina grown on NiAl(1 1 0).

Formation of Supported Graphene Oxide: Evidence for Enolate Species.

Graphene oxides are promising materials for novel electronic devices or anchoring of the active sites for catalytic applications. Here we focus on understanding the atomic oxygen (AO) binding and mobility on different regions of graphene (Gr) on Ru(0001). Differences in the Gr/Ru lattices result in the superstructure, which offers an array of distinct adsorption sites.

Adsorption of CO on the FeO(001) Surface.

The interaction of CO with the FeO(001)-(√2 × √2)R45° surface was studied using temperature-programmed desorption (TPD), scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS), the latter both under ultrahigh vacuum (UHV) conditions and in CO pressures up to 1 mbar. In general, the CO-FeO interaction is found to be weak. The strongest adsorption occurs at surface defects, leading to small TPD peaks at 115, 130, and 190 K.

Growth and Stability of Titanium Dioxide Nanoclusters on Graphene/Ru(0001).

Titanium dioxide/graphene composites have recently been demonstrated to improve the photocatalytic activity of TiO in visible light. To better understand the interactions of TiO with graphene we have investigated the growth of TiO nanoclusters on single-layer graphene/Ru(0001) using scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). Deposition of Ti in the O background at 300 K resulted in the formation of nanoclusters nucleating on intrinsic defects in the graphene (Gr) layer.

Cerium Oxide Nanoclusters on Graphene/Ru(0001): Intercalation of Oxygen via Spillover.

Cerium oxide is an important catalytic material known for its ability to store and release oxygen, and as such, it has been used in a range of applications, both as an active catalyst and as a catalyst support. Using scanning tunneling microscopy and Auger electron spectroscopy, we investigated oxygen interactions with CeOx nanoclusters on a complete graphene monolayer-covered Ru(0001) surface at elevated temperatures (600-725 K). Under oxidizing conditions (PO2 = 1 × 10(-7) Torr), oxygen intercalation under the graphene layer is observed.

Cluster nucleation and growth from a highly supersaturated adatom phase: silver on magnetite.

The atomic-scale mechanisms underlying the growth of Ag on the (√2×√2)R45°-Fe3O4(001) surface were studied using scanning tunneling microscopy and density functional theory based calculations. For coverages up to 0.5 ML, Ag adatoms populate the surface exclusively; agglomeration into nanoparticles occurs only with the lifting of the reconstruction at 720 K.

Charge trapping at the step edges of TiO(2) anatase (101).

A combination of photoemission, atomic force, and scanning tunneling microscopy/spectroscopy measurements shows that excess electrons in the TiO2 anatase (101) surface are trapped at step edges. Consequently, steps act as preferred adsorption sites for O2 . In density functional theory calculations electrons localize at clean step edges, this tendency is enhanced by O vacancies and hydroxylation.

Water Adsorption at the Tetrahedral Titania Surface Layer of SrTiO(110)-(4 × 1).

The interaction of water with oxide surfaces is of great interest for both fundamental science and applications. We present a combined theoretical (density functional theory (DFT)) and experimental (scanning tunneling microscopy (STM) and photoemission spectroscopy (PES)) study of water interaction with the two-dimensional titania overlayer that terminates the SrTiO(110)-(4 × 1) surface and consists of TiO tetrahedra. STM and core-level and valence band PES show that HO neither adsorbs nor dissociates on the stoichiometric surface at room temperature, whereas it does dissociate at oxygen vacancies.

Carbon monoxide-induced adatom sintering in a Pd-Fe3O4 model catalyst.

The coarsening of catalytically active metal clusters is often accelerated by the presence of gases, but the role played by gas molecules is difficult to ascertain and varies from system to system. We use scanning tunnelling microscopy to follow the CO-induced coalescence of Pd adatoms supported on the Fe3O4(001) surface at room temperature, and find Pd-carbonyl species to be responsible for mobility in this system. Once these reach a critical density, clusters nucleate; subsequent coarsening occurs through cluster diffusion and coalescence.

Ordered array of single adatoms with remarkable thermal stability: Au/Fe3O4(001).

Gold deposited on the Fe3O4(001) surface at room temperature was studied using scanning tunneling microscopy (STM) and x-ray photoelectron spectroscopy (XPS). This surface forms a (√2 × √2)R45° reconstruction, where pairs of Fe and neighboring O ions are slightly displaced laterally producing undulating rows with "narrow" and "wide" hollow sites. At low coverages, single Au adatoms adsorb exclusively at the narrow sites, with no significant sintering up to annealing temperatures of 400 °C.

Room temperature water splitting at the surface of magnetite.

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 of hydrogen atoms is observed, with no associated water hydroxyl group. Mild annealing of the hydrogenated surface leads to desorption of water via abstraction of surface oxygen atoms, leading to a reduction of the surface.