Changes in chemical and physical properties resulting from water adsorption play an important role in the characterization and performance of device-relevant materials. Studies of model oxides with well-characterized surfaces can provide detailed information that is vital for a general understanding of water–oxide interactions. In this work, we study single crystals of indium oxide, the prototypical transparent contact material that is heavily used in a wide range of applications and most prominently in optoelectronic technologies. Water adsorbs dissociatively already at temperatures as low as 100 K, as confirmed by scanning tunneling microscopy (STM), photoelectron spectroscopy, and density functional theory. This dissociation takes place on lattice sites of the defect-free surface. While the In2O3(111)-(1 × 1) surface offers four types of surface oxygen atoms (12 atoms per unit cell in total), water dissociation happens exclusively at one of them together with a neighboring pair of 5-fold coordinated In atoms. These O–In groups are symmetrically arranged around the 6-fold coordinated In atoms at the surface. At room temperature, the In2O3(111) surface thus saturates at three dissociated water molecules per unit cell, leading to a well-ordered hydroxylated surface with (1 × 1) symmetry, where the three water OWH groups plus the surface OSH groups are imaged together as one bright triangle in STM. Manipulations with the STM tip by means of voltage pulses preferentially remove the H atom of one surface OSH group per triangle. The change in contrast due to strong local band bending provides insights into the internal structure of these bright triangles. The experimental results are further confirmed by quantitative simulations of the STM image corrugation.

Oxygen vacancies in five-monolayer-thick tetragonal ZrO2 films can cause core level binding energies up to 1.8 eV higher than in the (near-stoichiometric) monoclinic phase. The vacancies can be healed by oxygen spillover from a metal catalyst.

Starting from subsurface Zr0-doped “inverse” Pd and bulk-intermetallic Pd0Zr0 model catalyst precursors, we investigated the dry reforming reaction of methane (DRM) using synchrotron-based near ambient pressure in-situ X-ray photoelectron spectroscopy (NAP-XPS), in-situ X-ray diffraction and catalytic testing in an ultrahigh-vacuum-compatible recirculating batch reactor cell. Both intermetallic precursors develop a Pd0–ZrO2 phase boundary under realistic DRM conditions, whereby the oxidative segregation of ZrO2 from bulk intermetallic PdxZry leads to a highly active composite layer of carbide-modified Pd0 metal nanoparticles in contact with tetragonal ZrO2. This active state exhibits reaction rates exceeding those of a conventional supported Pd–ZrO2 reference catalyst and its high activity is unambiguously linked to the fast conversion of the highly reactive carbidic/dissolved C-species inside Pd0 toward CO at the Pd/ZrO2 phase boundary, which serves the role of providing efficient CO2 activation sites. In contrast, the near-surface intermetallic precursor decomposes toward ZrO2 islands at the surface of a quasi-infinite Pd0 metal bulk. Strongly delayed Pd carbide accumulation and thus carbon resegregation under reaction conditions leads to a much less active interfacial ZrO2–Pd0 state.

We have studied zirconia films on a Rh(111) substrate with thicknesses in the range of 2-10 monolayers (ML) using scanning tunneling microscopy (STM) and lowenergy electron diffraction (LEED). Zirconia was deposited using a UHV-compatible sputter source, resulting in layer-by-layer growth and good uniformity of the films. For thicknesses of 2-4 ML, a layer-dependent influence of the substrate on the structure of the thin films is observed. Beyond this thickness, films show a (2 × 1) or a distorted (2 × 2) surface structure with respect to cubic ZrO 2 (111); these structures correspond to tetragonal and monoclinic zirconia, respectively. The tetragonal phase occurs for annealing temperatures of up to 730 °C; transformation to the thermodynamically stable monoclinic phase occurs after annealing at 850 °C or above. High-temperature annealing also breaks up the films and exposes the Rh(111) substrate. We argue that the tetragonal films are stabilized by oxygen deficiency, while the monoclinic films are only weakly defective and show band bending at defects and grain boundaries. This observation is in agreement with positive charge being responsible for the grain-boundary blocking effect in zirconia-based solid electrolytes. Our work introduces the tetragonal and monoclinic 5 ML-thick ZrO 2 films on Rh(111) as well-suited model system for surface-science studies on ZrO 2 as they do not exhibit the charging problems of thicker films or the bulk material and show better homogeneity and stability than the previously-studied ZrO 2 /Pt(111) system.

A comprehensive study of water adsorption and desorption on an ultrathin trilayer zirconia film by experimental and computational methods shows good agreement with data for H2O/ZrO2 powder material.

A sputter deposition source for the use in ultrahigh vacuum (UHV) is described, and some properties of the source are analyzed. The operating principle is based on the design developed by Mayr et al. [Rev. Sci. Instrum. 84, 094103 (2013)], where electrons emitted from a filament ionize argon gas and the Ar ions are accelerated to the target. In contrast to the original design, two grids are used to direct a large fraction of the Ar ions to the target, and the source has a housing cooled by liquid nitrogen to reduce contaminations. The source has been used for the deposition of zirconium, a material that is difficult to evaporate in standard UHV evaporators. At an Ar pressure of 9×10 mbar in the UHV chamber and moderate emission current, a highly reproducible deposition rate of ≈1 ML in 250 s was achieved at the substrate (at a distance of ≈50 mm from the target). Higher deposition rates are easily possible. X-ray photoelectron spectroscopy shows a high purity of the deposited films. Depending on the grid voltages, the substrate gets mildly sputtered by Ar ions; in addition, the substrate is also reached by electrons from the negatively biased sputter target.

The strong metal-support interaction (SMSI) leads to substantial changes of the properties of an oxide-supported catalyst after annealing under reducing conditions. The common explanation is the formation of heavily reduced, ultrathin oxide films covering metal particles. This is typically encountered for reducible oxides such as TiO 2 or Fe 3 O 4 . Zirconia (ZrO 2 ), a typical catalyst support, is difficult to reduce and therefore no obvious candidate for the SMSI effect. In this work, we use inverse model systems with Rh(111), Pt(111), and Ru(0001) as supports. Contrary to expectations, we show that SMSI is encountered for zirconia. Upon annealing in ultra-high vacuum, oxygen-deficient ultrathin zirconia films (≈ZrO 1.5 ) form on all three substrates. However, Zr remains in its preferred charge state of 4+, as electrons are transferred to the underlying metal. At high temperatures, the stability of the ultrathin zirconia films depends on whether alloying of Zr and the substrate metal occurs. The SMSI effect is reversible; the ultrathin suboxide films can be removed by annealing in oxygen.

The structure of the Fe3O4(110)-(1×3) surface was studied with scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and reflection high energy electron diffraction (RHEED). The so-called one-dimensional reconstruction is characterised by bright rows that extend hundreds of nanometers in the [1 � 10] direction and have a periodicity of 2.52 nm in [001] in STM. It is concluded that this reconstruction is the result of a periodic faceting to expose {111}-type planes with a lower surface energy. Main TextMagnetite (Fe3O4) is a common material in the Earth's crust and plays an important role in geochemistry and corrosion [1; 2]. At room temperature Fe3O4 crystallizes in the inverse-spinel structure, and Fe cations occupy tetrahedrally (Fetet) and octahedrally (Feoct) coordinated interstices within a face-centred cubic lattice of O 2anions. Natural single crystals are typically octahedrally shaped and expose {111} facets, consistent with density functional theory (DFT)-based calculations that find (111) to be the most stable low-index surface [3; 4]. In recent years however, advances in synthesis have allowed the size and shape of Fe3O4 nanomaterial to be tailored with a view to enhancing performance in applications such as groundwater remediation, biomedicine, and heterogeneous catalysis [1; 5], and nanocubes and nanorods exposing {100} surfaces have been reported [6; 7]. To date, there have been no reports of Fe3O4 nanomaterial exhibiting {110} surfaces.