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Synovial fluid (SF) is the natural lubricant found in articulated joints, providing unique cartilage surface protecting films under confinement and relative motion. While it is known that the synergistic interactions of the macromolecular constituents provide its unique load-bearing and tribological performance, it is not fully understood how two of the main constituents, glycosaminoglycans (GAGs) and glycoproteins, regulate the formation and mechanics of robust load-bearing films. Here, we present evidence that the load-bearing capabilities, rather than the tribological performance, of the formed SF films depend strongly on its components' integrity. For this purpose, we used a combination of enzymatic treatments, quartz crystal microbalance with dissipation (QCM-D), and the surface forces apparatus (SFA) to characterize the formation and load-bearing capabilities of SF films on model oxide (i.e., silicates) surfaces. We find that, upon cleavage of proteins, the elasticity of the films is reduced and that cleaving GAGs results in irreversible (plastic) molecular re-arrangements of the film constituents when subjected to confinement. Understanding thin film mechanics of SF can provide insight into the progression of diseases, such as arthritis, but may also be applicable to the development of new implant surface treatments or new biomimetic lubricants.

The nature and local environment of Au single atoms supported and stabilized on four different oxides is studied by means of DFT + U calculations using CO as probe molecule and its stretching frequency, ωe, as a fingerprint of the site where the Au atom is bound. Four oxides are considered, anatase TiO2, tetragonal ZrO2, cubic CeO2, and a perovskite LaFeO3. In this latter case a recently reported experimental study has detected a stretching mode for CO adsorbed on Au1/LaFeO3 of 2215 cm−1, with a large blue shift, ∆ω(CO) = 72 cm−1 with respect to free CO. In order to identify the Au adsorption site that can give rise to this large blue-shift we have considered five cases: (a) Au replacing a lattice cation, (Au)subM; (b) Au replacing a lattice O anion, (Au)subO; (c) Au adsorbed on the surface, (Au)ads; (d) Au bound to an extra O atom on the surface, (AuO)ads, or (e) Au bound to two extra O atoms on the surface, (AuO2)ads. It turns out that the correct reproduction of ∆ω for CO adsorbed on positively charged gold, Auδ+, is challenging for DFT. Therefore, we have performed a comparative study of Auδ+-CO molecular compounds for which ωe(CO) is known experimentally using various kinds of DFT functionals and accurate CCSD and CCSD(T) quantum chemistry methods. Also based on this comparison we propose a tentative assignment for the observed frequency of CO adsorbed on Au1/LaFeO3 single atom catalyst. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) and nanoplastics (NPs) attract widespread attention due to their final threats to human health. Here, 50 nm and 500 nm polystyrene particles (PS50 and PS500) were selected as the typical NPs and MPs, respectively. Their aggregation kinetics was monitored, and their deposition was investigated on silica and alumina surfaces using quartz crystal microbalance with dissipation monitoring (QCM-D). PS500 has higher critical coagulation concentration (CCC) values than PS50, because of the weaker Brownian diffusion, less particle number and lower collision chance. PS50 has smaller values of critical deposition concentration (CDC) than PS500, indicating the stronger adsorption on silica. Derjaguin−Landau−Verwey−Overbeek (DLVO) calculations explain that PS500 has weaker attachment on silica and slower deposition rate on alumina than PS50. Our results demonstrate that solution chemistry, particle size and mineral surfaces determine the transport and distribution of plastic particles together. [ABSTRACT FROM AUTHOR]

The activation of molecular oxygen is a fundamental step in almost all catalytic oxidation reactions. We have studied this topic and the role of surface vacancies for Co3O4(100) films with a synergistic combination of experimental and theoretical methods. We show that the as‐prepared surface is B‐layer terminated and that mild reduction produces oxygen single and double vacancies in this layer. Oxygen adsorption experiments clearly reveal different superoxide species below room temperature. The superoxide desorbs below ca. 120 K from a vacancy‐free surface and is not active for CO oxidation while superoxide on a surface with oxygen vacancies is stable up to ca. 270 K and can oxidize CO already at the low temperature of 120 K. The vacancies are not refilled by oxygen from the superoxide, which makes them suitable for long‐term operation. Our joint experimental/theoretical effort highlights the relevance of surface vacancies in catalytic oxidation reactions. [ABSTRACT FROM AUTHOR]

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 V2O3(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 Fe3O4(111) to be Fetet 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. [ABSTRACT FROM AUTHOR]

Acid and basic sites on monoclinic and tetragonal zirconia were investigated at the DFT level by computing IR and NMR properties of adsorbed probe molecules. Regular and stepped ZrO2 surfaces as well as stoichiometric zirconia nanoparticles have been considered. Acidity and basicity were probed by the adsorption of carbon monoxide and pyrrole, respectively. CO adsorption shows a positive shift of the C–O stretching frequency in IR spectra while the C atom of CO is shielded and 13C chemical shifts moves to higher field as a function of the strength of the acid site. For the study of basic sites we used a pyrrole molecule, but the interaction between the pyrrole ring and the surface leads to adsorption modes that cannot be used to titrate the surface basicity. On the other hand, at high coverage the molecule assumes an upright position and the formation of a hydrogen bond of the pyrrole NH group with the oxygen atoms of the surfaces provides a proxy of the basic properties of these sites. In particular, we focus on changes of the N–H IR frequency, 1H, 15N, and 17O NMR chemical shifts and their correlations with the surface basicity. Among the correlations found, that between the N–H stretching frequency of adsorbed pyrrole and the 17O NMR chemical shift of the O ion where the molecule is bound show a nice linear correlation. These two properties can provide useful information about the basic character of various O sites on the surface of zirconia. [ABSTRACT FROM AUTHOR]

Metalation of anchored porphyrins is essential for their functionality at hybrid interfaces. In this work, we have studied the anchoring and metalation of a functionalized porphyrin derivative, 5‐(4‐carboxyphenyl)‐10,15,20‐triphenylporphyrin (MCTPP), on an atomically‐defined CoO(100) film under ultrahigh vacuum (UHV) conditions. We follow both the anchoring to the oxide surface and the self‐metalation by surface Co2+ ions via infrared reflection absorption spectroscopy (IRAS). At 150 K, MCTPP multilayer films adsorb molecularly on CoO(100) without anchoring to the surface. Upon heating to 195 K, the first layer of porphyrin molecules anchors via formation of a bridging surface carboxylate. Above 460 K, the MCTPP multilayer desorbs and only the anchored monolayer resides on the surface up to temperatures of 600 K approximately. The orientation of anchored MCTPP depends on the surface coverage. At low coverage, the MCTPP adopts a nearly flat‐lying geometry, whereas an upright standing film is formed near the multilayer coverage. Self‐metalation of MCTPP depends critically on the surface temperature, the coverage and on the molecular orientation. At 150 K, metalation is largely suppressed, while the degree of metalation increases with increasing temperature and reaches a value of around 60 % in the first monolayer at 450 K. At lower coverage higher metalation fractions (85 % and above) are observed, similar as for increasing temperature. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Porphyrins are large organic molecules that are interesting for different applications, such as photovoltaic cells, gas sensors, or in catalysis. For many of these applications, the interactions between adsorbed molecules and surfaces play a crucial role. Studies of porphyrins on surfaces typically fall into one of two groups: (1) evaporation onto well-defined single-crystal surfaces under well-controlled ultrahigh vacuum conditions or (2) more application-oriented wet chemical deposition onto less well-defined high surface area surfaces under ambient conditions. In this study, we will investigate the wet chemical deposition of 5-(monocarboxyphenyl)-10,15,20-triphenylporphyrin (MCTPP) on well-defined rutile TiO2(110) single crystals under ambient conditions. Prior to deposition, the TiO2(110) crystals were also cleaned wet-chemically under ambient conditions, meaning none of the preparation steps were done in ultrahigh vacuum. However, after each preparation step, the surfaces were characterized in ultrahigh vacuum with X-ray photoelectron spectroscopy (XPS) and the result was compared with porphyrin layers prepared in ultrahigh vacuum (UHV) by evaporation. The differences of both preparations when exposed to zinc ion solutions will also be discussed.

We have studied the adsorption and interfacial reactions of 2H‐tetraphenylporphyrin (2HTPP) with cobalt‐terminated Co3O4(111) and oxygen‐terminated CoO(111) thin films using synchrotron‐radiation X‐ray photoelectron spectroscopy. Already at 275 K, we find evidence for the formation of a metalated species, most likely CoTPP, on both surfaces. The degree of self‐metalation increases with temperature on both surfaces until 475 K, where the metalation is almost complete. At 575 K the porphyrin coverage decreases drastically on the reducible cobalt‐terminated Co3O4(111) surface, while higher temperatures are needed on the non‐reducible oxygen‐terminated CoO(111). The low temperature self‐metalation is similar to that observed on MgO(100) surfaces, but drastically different from that observed on TiO2(110), where no self‐metalation is observed at room temperature. [ABSTRACT FROM AUTHOR]

Abstract Determination of surface structures currently requires careful measurement and computationally expensive methods since, unlike bulk crystals, guiding principles for generating surface structural hypotheses are frequently lacking. Herein, we discuss the applicability of Pauling's rules as a set of guidelines for surface structures. The wealth of solved reconstructions on SrTiO 3 (100), (110), and (111) are considered, as well as nanostructures on these surfaces and a few other ABO 3 oxide materials. These rules are found to explain atomic arrangements for reconstructions and thin films just as they apply to bulk oxide materials. Using this data and Pauling's rules, the fundamental structural units of reconstructions and their arrangement are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Noble metal particles supported on transition metal oxides (TMO) may undergo a so-called strong metal-support interaction via encapsulation. This perspective addresses catalytic properties of the metal catalysts in the SMSI state which can be explained on the basis of complementary studies performed on well-defined, metal-supported TMO films. In particular, the results of low temperature CO oxidation revealed the key role of weakly bound oxygen species provided by a two-dimensional (“monolayer”) oxide film. The binding energy of such oxygen atoms can be used as a descriptor for oxidation activity. Reaction rate enhancement often observed for TMO films partially covering the metal surface is rationalized within a mechanism in which the metal acts as a promoter to create the most active “oxidered/oxideox” interface formed by reduced and oxidized phases in the film. Although only low temperature CO oxidation is considered, it is tempting to generalize these ideas to other oxidation reactions following the Mars-van Krevelen type mechanism. In addition, metal-supported ultrathin TMO films may serve as well-defined model systems to examine different aspects of the “electron theory of catalysis” which was proposed long ago and which is based on electron transfer mechanisms.Graphical Abstract: [ABSTRACT FROM AUTHOR]

The atomic structures of two reconstructions, (√7 × √7)R19.1° and (√13 × √13)R13.9°, on the SrTiO 3 (111) surface were determined using a combination of density functional theory and scanning tunneling microscopy data and APW + lo density functional theory minimizations and simulations. These reconstructions belong to the same structural family made up of an interconnected, single layer of edge-sharing TiO 6 and TiO 5 [] octahedra. This family of reconstructions between 0.5 and 1.5 excess TiO 2, representing the lowest-reported TiO 2 coverages for reconstructions on this surface. This family is found to include the previously-solved (2 × 2)a reconstruction. They all follow a simple rule for surface composition, which serves as a tool for better understanding and predicting the structure of other reconstructions of arbitrary surface unit cell size on SrTiO 3 (111). This reconstruction family and the calculations of surface energies for different hypothesis structures also shed light on the structure of Schottky defects observed on these reconstructed SrTO 3 (111) surfaces. [ABSTRACT FROM AUTHOR]

Controlling the synthesis of nanostructured surfaces is essential to tailor the properties of functional materials such as catalysts. We report on the synthesis of nanocavities of 1-2 nm dimension on planar Si-wafers by sacrificial nanotemplating and atomic layer deposition (ALD). It is shown that the process of nanocavity formation can be directly monitored on a monomolecular level through imaging with an atomic force microscope (AFM). In particular, by employing the AFM peak force tapping mode the simultaneous mapping of surface topography and tip-surface adhesion forces is accessible, which is useful for the assignment of topographical features and determining the orientation of the template molecules on the wafer surface. Detailed analysis based on the three-dimensional AFM topography allows for a quantification of the template and nanocavity surface coverage. The results are of importance for a detailed understanding of the processes underlying template-based nanocavity formation on oxide surfaces. [ABSTRACT FROM AUTHOR]

The novel electronic properties emerging at interfaces between transition metal oxides, and in particular the discovery of conductivity in heterostructures composed of LaAlO 3 (LAO) and SrTiO 3 (STO) band insulators, have generated new challenges and opportunities in condensed matter physics. Although the interface conductivity is stabilized when LAO matches or exceeds a critical thickness of 4 unit cells (uc), other phenomena such as a universal metallic state found on the bare surface of STO single crystals and persistent photon-triggered conductivity in otherwise insulating STO-based interfaces raise important questions about the role of the LAO overlayer and the possible relations between vacuum/STO and LAO/STO interfaces. Here, using angle-resolved photoemission spectroscopy (ARPES) on in situ prepared samples complemented by resonant inelastic X-ray scattering (RIXS), we study how the metallic STO surface state evolves during the growth of a crystalline LAO overlayer. In all the studied samples, the character of the conduction bands, their carrier densities, the Ti 3+ crystal field, and the response to photon irradiation bear strong similarities. Nevertheless, we report here that studied LAO/STO interfaces exhibit an instability toward an apparent 2 × 1 folding of the Fermi surface at and above a 4 uc thickness threshold, which distinguishes these heterostructures from bare STO and sub-critical-thickness LAO/STO. [ABSTRACT FROM AUTHOR]

Understanding how metal atoms are stabilized on metal oxide supports is important for predicting the stability of "single-atom" catalysts. In this study, we use scanning tunnelling microscopy (STM) and x-ray photoelectron spectroscopy (XPS) to investigate four catalytically active metals – platinum, rhodium, nickel and iridium – on the anatase TiO 2 (101) surface. The metals were vapor deposited at room temperature in ultrahigh vacuum (UHV) conditions, and also with a background water pressure of 2 × 10−8 mbar. Pt and Ni exist as a mixture of adatoms and nanoparticles in UHV at low coverage, with the adatoms immobilized at defect sites. Water has no discernible effect on the Pt dispersion, but significantly increases the amount of Ni single atoms. Ir is highly dispersed, but sinters to nanoparticles in the water vapor background leading to the formation of large clusters at step edges. Rh forms clusters on the terrace of anatase TiO 2 (101) irrespective of the environment. We conclude that introducing defect sites into metal oxide supports could be a strategy to aid the dispersion of single atoms on metal-oxide surfaces, and that the presence of water should be taken into account in the modelling of single-atom catalysts. [ABSTRACT FROM AUTHOR]

The ketonization reaction of acetic acid on the (1 0 1) surface of tetragonal zirconia, a process relevant in the catalytic upgrade of cellulosic biomass has been studied by means of DFT+U calculations. The aim was to better understand the role of catalyst pre-reduction. Acetic acid adsorbs strongly on the zirconia surface, and deprotonation to acetate takes place easily. Then, a proton transfer from the methyl group of the acetate ion, CH 3 COO − , to the surface occurs to form an eno-species, CH 2 COO 2− (intermediate 1). In a parallel step, acetate ions convert into acyl fragments, CH 3 CO, by oxygen extraction (intermediate 2). Once formed, the acyl intermediate 2 is able to attack the eno-species intermediate 1, to form a β-keto-acid. On stoichiometric zirconia, the formation of the intermediate 1, CH 2 COO 2− , is unfavorable; oxygen vacancies on the reduced surface stabilize the reaction product and strongly reduce the activation energy. Reduced Zr 3+ centers are essential to stabilize the acyl intermediate 2. The present work shows at an atomistic level the beneficial role of O vacancies and reduced Zr 3+ centers for the ketonization process. [ABSTRACT FROM AUTHOR]

Titanates are salts of polytitanic acid that can be synthesized as nanostructures in a great variety concerning crystallinity, morphology, size, metal content and surface chemistry. Titanate nanotubes (open-ended hollow cylinders measuring up to 200 nm in length and 15 nm in outer diameter) and nanowires (solid, elongated rectangular blocks with length up to 1500 nm and 30–60 nm diameter) are the most widespread representatives of the titanate nanomaterial family. This review covers the properties and applications of these two materials from the surface science point of view. Dielectric, vibrational, electron and X-ray spectroscopic results are comprehensively discussed first, then surface modification methods including covalent functionalization, ion exchange and metal loading are covered. The versatile surface chemistry of one-dimensional titanates renders them excellent candidates for heterogeneous catalytic, photocatalytic, photovoltaic and energy storage applications, therefore, these fields are also reviewed. [ABSTRACT FROM AUTHOR]

We have performed a comparative study of the acid–base characteristics of the surfaces of anatase TiO 2 and tetragonal ZrO 2 . To this end we performed DFT + U calculations on CO and CO 2 probe molecules adsorbed both on terraces and steps of the two oxides. For titania, CO adsorption results in a moderate adsorption energy (about − 0.3 eV) and in a positive shift of the C O stretching frequency (about + 40 cm − 1 ), typical of Lewis acid sites, with no clear difference in the acidity between terraces or steps. For zirconia we found a similar CO binding energy as for titania, and a CO vibrational shift that depends on the location of the Zr cation: negligible on terraces, similar to TiO 2 on steps. We conclude that the acidic properties are similar in the two oxide surfaces. Things are different for CO 2 adsorption. On titania the interaction is weak and surface carbonates compete with physisorbed CO 2 , indicating a weak basic character. On the contrary, on zirconia three types of stable carbonates have been identified. Their vibrational frequencies are consistent with IR measurements reported in the literature. The most stable species forms on steps of the t-ZrO 2 surface and consists of a CO 3 2 − unit which lies flat on the surface with the O atoms pointing towards three Zr ions. The species forms spontaneously by extraction of a lattice oxygen by an incoming CO 2 molecule. The different reactivity points towards a much more pronounced basic character of zirconia compared to titania, at least if measured by CO 2 adsorption. [ABSTRACT FROM AUTHOR]

We chose water-soluble sodium hexanoate as a model organic molecule to study the role of salt ions (Ca 2+ , Na + , Cl − ) in the adsorption of carboxylates to mineral surfaces (silica, alumina, gibbsite) of variable surface charge and chemistry. Quartz crystal microbalance (QCM-D) measurements reveal a qualitatively different dependence of the adsorption behavior on the electrolyte composition for the different surfaces at near neutral pH. Overall, hexanoate adsorption is more pronounced on the positively charged alumina surfaces than on negatively charged silica surfaces. On silica, however, Ca 2+ ions strongly enhance the adsorption of hexanoate, suggesting that the divalent cations act as bridges between carboxylate and deprotonated silanol surface groups. On alumina, hexanoate adsorption is found to depend only weakly on the salt composition, suggesting a direct interaction of the carboxylate group with the surface, consistent with a ligand-exchange mechanism. The adsorption behavior on partially gibbsite-covered silica surfaces is particularly rich and displays a strong non-monotonic dependence on the CaCl 2 concentration. Comparison to earlier work and control experiments suggest an important role of Cl − anions, which compete with the carboxylate group for adsorption sites. [ABSTRACT FROM AUTHOR]

Density functional calculations are employed to simulate the deposition of an isolated Ni atom and a Ni 10 particle on the stoichiometric and reduced anatase TiO 2 (101) and tetragonal ZrO 2 (101) surfaces. The main purpose of this work is to study the modification of the electronic structure of the oxide induced by the metal, aiming at the understanding of the physical properties of new catalysts for biomass conversion. When the adsorption of a Ni atom takes place on stoichiometric surfaces, no major charge transfer is observed. On reduced titania, and more pronouncedly on reduced zirconia, the Ni atom is negatively charged, provided that the vacancy is in direct contact with the adsorbed metal atom. For Ni 10 , on titania the bonding is dominated by the hybridization of the metal and the oxide states but we did not find evidence for a direct reduction of the oxide via formation of Ti 3 + states. For Ni 10 on zirconia, the metal particle is positively charged on the stoichiometric surface and negatively charged on the reduced one but, again, there is no indication of a direct reduction of the oxide. Finally, the reverse oxygen spillover is considered as a possible route to reduce the oxide support. The result is that Ni 10 promotes oxygen spillover on titania almost spontaneously, while on zirconia this process is thermodynamically unfavourable. [ABSTRACT FROM AUTHOR]

Metal–oxide interfaces play a fundamental role in determining the functional properties of artificial layered heterostructures, which are at the root of present and future technological applications. Magnetic exchange and magnetoelectric coupling, spin filtering, metal passivation, catalytic activity of oxide-supported nano-particles are just few examples of physical and chemical processes arising at metal–oxide hybrid systems, readily exploited in working devices. These phenomena are strictly correlated with the chemical and structural characteristics of the metal–oxide interfacial region, making a thorough understanding of the atomistic mechanisms responsible of its formation a prerequisite in order to tailor the device properties. The steep compositional gradient established upon formation of metal–oxide heterostructures drives strong chemical interactions at the interface, making the metal–oxide boundary region a complex system to treat, both from an experimental and a theoretical point of view. However, once properly mastered, interfacial chemical interactions offer a further degree of freedom for tuning the material properties. The goal of the present review is to provide a summary of the latest achievements in the understanding of metal/oxide and oxide/metal layered systems characterized by reactive interfaces. The influence of the interface composition on the structural, electronic and magnetic properties will be highlighted. Particular emphasis will be devoted to the discussion of ultra-thin epitaxial oxides stabilized on highly oxidizable metals, which have been rarely exploited as oxide supports as compared to the much more widespread noble and quasi noble metallic substrates. In this frame, an extensive discussion is devoted to the microscopic characterization of interfaces between epitaxial metal oxides and the Fe(001) substrate, regarded from the one hand as a prototypical ferromagnetic material and from the other hand as a highly oxidizable metal. [ABSTRACT FROM AUTHOR]

Metal-support interactions are frequently invoked to explain the enhanced catalytic activity of metal nanoparticles dispersed over reducible metal oxide supports, yet the atomicscale mechanisms are rarely known. In this report, scanning tunneling microscopy was used to study a Pt1-6/Fe3O4 model catalyst exposed to CO, H2, O2, and mixtures thereof at 550 K. CO extracts lattice oxygen atoms at the cluster perimeter to form CO2, creating large holes in the metal oxide surface. H2 and O2 dissociate on the metal clusters and spill over onto the support. The former creates surface hydroxy groups, which react with the support, ultimately leading to the desorption of water, while oxygen atoms react with Fe from the bulk to create new Fe3O4(001) islands. The presence of the Pt is crucial because it catalyzes reactions that already occur on the bare iron oxide surface, but only at higher temperatures. [ABSTRACT FROM AUTHOR]

An overview of the current research in the field of vanadium oxide (VO x ) monolayer catalysts on oxide supports based on a Surface Science approach applied to model catalysts is reported. These systems are usually prepared in ultra-high-vacuum by depositing the VO x catalysts on planar supports that mimic the oxide supports used in real catalysts. The model catalysts are then characterized by a range of spectroscopic/microscopic tools capable of relating the structure and reactivity of the active sites. Such a methodology also benefits from parallel theoretical investigations that can provide information to interpret the experimental data and vice versa use the experimental data to validate the theoretical models. The systems taken into consideration are VO x /TiO 2 and VO x /CeO 2 , as prototypical examples of catalysts supported on reducible oxides, and VO x /Al 2 O 3 and VO x /SiO 2 for non-reducible supports. Such a methodology allows outlining the existence of several unusual surface stabilized nanostructures, which can be identified as the main players for the specific activities of the VO x monolayer catalysts. Some general trends and basic factors that influence the structure and activity of the VO x catalysts are discussed, i.e. the role of the support, whose interaction with VO x can influence the catalyst reactivity, the vanadia loading, which allows to obtain different nanostructures, and the hybridization at the interface between the oxides, often leading to charge transfer. [ABSTRACT FROM AUTHOR]

This paper describes a 3 × 1 surface reconstruction on the LAO (110) surface and its atomic structure analyzed from experimental electron diffraction data coupled with X-ray photoelectron spectroscopy analysis and reinforced by density functional theory calculations. We construct the multidimensional convex hull for the system with excess Al 2 O 3 and in the presence of water. All the evidence points towards the reconstruction being very similar to the 3 × 1 reconstruction on the SrTiO 3 (110) surface with two hydrogen atoms added for valence neutrality. [ABSTRACT FROM AUTHOR]

The reactivity of MgO(0 0 1) films deposited on Ag(0 0 1) and Mo(0 0 1) in CO oxidation as a function of oxide film thickness was investigated experimentally at ambient pressure reaction conditions. MgO films grown on Mo(0 0 1) were found to be inactive in CO oxidation, whereas activity enhancement with decreasing oxide film thickness was observed for MgO(0 0 1)/Ag(0 0 1). In situ infrared and post-reaction X-ray photoemission data showed that ultra-thin MgO films interact much more strongly with the reactants and residual water than bulk-like MgO. Poisoning of the MgO surfaces by the resultant accumulation of carbonate and hydroxyl species is suggested to inhibit the reactivity in CO oxidation. Detailed investigations of the surface structure of MgO(0 0 1)/Ag(0 0 1) films indicate that silver ad-islands on Ag(0 0 1), which are formed during MgO growth, are responsible for the enhancement of CO oxidation activity over ultrathin MgO(0 0 1)/Ag(0 0 1) films. [ABSTRACT FROM AUTHOR]

Thin oxide films have been used as model supports to unravel the influence of the oxide–metal and oxide–gas interface. We discuss the influence of defects in the oxide lattice and the oxide surface on properties of adsorbed species, in particular the formation of oxide particles from a deposited transition metal onto ceria and of adsorbed oxygen from the gas phase. Here we correlate the structure of the particles, as revealed by a combination of STM and spectroscopic as well as theoretical calculations, with their reactive properties. The nature of the involved defects is characterized by adsorption of Au as a way to correlate the influence of various defects of different structure on the Au charge state. In a second case study, we demonstrate the influence of dopants within the supporting oxide on the adsorption of oxygen on a defect free surface. This is shown to be potentially relevant for the activation of methane in oxidative methane coupling reactions, as recently demonstrated. [ABSTRACT FROM AUTHOR]

Lattice defects are unavoidable structural units in materials and play an important role in determining material properties. Compared with the periodic structure of crystals, the atomic configurations of the lattice defects are determined by the coordinates of a large number of atoms, making it difficult to experimentally investigate them. In computational materials science, multiparameter optimization is also a difficult problem and experimental verification is usually required to determine the possibility of obtaining the structure and properties predicted by calculations. Using our recent studies on oxide surfaces as examples, we introduce the method of integrated aberration-corrected electron microscopy and the first-principles calculations to analyze the atomic structure of lattice defects. The atomic configurations of defects were measured using quantitative high-resolution electron microscopy at subangstrom resolution and picometer precision, and then the electronic structure and dynamic behavior of materials can be studied at the atomic scale using the first-principles calculations. The two methods complement each other and can be combined to increase the understanding of the atomic structure of materials in both the time and space dimensions, which will benefit materials design at the atomic scale. [ABSTRACT FROM AUTHOR]

Discoveries of room-temperature ferromagnetism (RTFM) in semiconductors hold great promise in future spintronics technologies. Unfortunately, this ferromagnetism remains poorly understood and the debate concerning the nature, carrier-mediated versus defect-mediated, of this ferromagnetism in semiconducting oxides is still open. Here, by using X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD), it is demonstrated that the oxygen ions have a ferromagnetic response in different ZnO-based compounds showing RTFM behavior: ZnO nanoparticles capped with organic molecules and ZnO/ZnS heterostructures. These results demonstrate the intrinsic occurrence of RTFM in these systems, and point out that it is not related to the metallic cation but it relays on the conduction band of the semiconductor. [ABSTRACT FROM AUTHOR]

Synovial fluid (SF) is the natural lubricant found in articulated joints, providing unique cartilage surface protecting films under confinement and relative motion. While it is known that the synergistic interactions of the macromolecular constituents provide its unique load-bearing and tribological performance, it is not fully understood how two of the main constituents, glycosaminoglycans (GAGs) and glycoproteins, regulate the formation and mechanics of robust load-bearing films. Here, we present evidence that the load-bearing capabilities, rather than the tribological performance, of the formed SF films depend strongly on its components' integrity. For this purpose, we used a combination of enzymatic treatments, quartz crystal microbalance with dissipation (QCM-D), and the surface forces apparatus (SFA) to characterize the formation and load-bearing capabilities of SF films on model oxide (i.e., silicates) surfaces. We find that, upon cleavage of proteins, the elasticity of the films is reduced and that cleaving GAGs results in irreversible (plastic) molecular re-arrangements of the film constituents when subjected to confinement. Understanding thin film mechanics of SF can provide insight into the progression of diseases, such as arthritis, but may also be applicable to the development of new implant surface treatments or new biomimetic lubricants. [Display omitted] • Synovial fluid nanofilm elasticity is GAGs dependent. • Full nanofilm formation of surfaces is achieved with at least 50% SF concentration. • GAGs and proteins in SF are crucial for the proper load-bearing properties of films. • Healthy (nontreated) SF films are elastic under conditions investigated. [ABSTRACT FROM AUTHOR]