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The surface work function (WF) and substrate temperature dependence of the NaCl thin-film growth on Ag(001) have been studied by noncontact atomic force microscopy and Kelvin probe force microscopy. In the sub-monolayer range, the NaCl film is composed of large crystalline islands, which decrease in density and increase in size with increasing temperature during deposition. Each island is composed of a large base island 2 monolayers (ML) thick (for T > 343 K), which collects impinging NaCl molecules that form adislands on top. Kelvin probe force microscopy (KPFM) measurements show a reduction of the silver WF by Δφ = φAg -φNaCl/Ag = 0.69±0.03 eV with no dependence on the film thickness (1-6 ML), in agreement with recent theoretical calculations. The previously observed nanometer-sized moiré pattern on islands that are 45° rotated with respect to the silver lattice could be observed in the scanning tunneling microscopy mode. However, no contrast could be obtained in KPFM images. [ABSTRACT FROM AUTHOR]

Thanks to a dedicated modelling of intensities, the depth sensitivity of X-ray photoemission is used to probe the segregation profile of aluminium at the (110), (100) and (111) low index surfaces of the body-centred Fe 0.85 Al 0.15 random alloy. Sputtered surface composition is close to the nominal bulk one, thus excluding preferential sputtering. Surface enrichment in aluminium upon annealing starts at around 700 K before reaching a stationary state above 1000 K. The average surface composition is close to Fe 0.5 Al 0.5 , corresponding to the B 2 CsCl structure of the phase diagram. The impacted depth, that is in the range of 2.5–3.5 nm, is quite significant. Although not evidenced previously in surface science conditions at FeAl single crystal surfaces, it is qualitatively in agreement with the segregation at grain boundaries and shear planes of Al-alloyed steels. This segregation tendency is rationalized through ab initio calculations. Unlabelled Image • Severe aluminium segregation above 700 K at the surfaces of bcc Fe 0.85 Al 0.15 • Photoemission determination of the concentration profile in a random alloy • Nanometer deep impacted layer with a Fe 0.5 Al 0.5 composition • Ab initio modelling of segregation trends [ABSTRACT FROM AUTHOR]

By combining Scanning Tunnelling Microscopy, Low Energy Electron Diffraction and X-ray Photoelectron Spectroscopy, it was found that the surface of A 2 random alloy Fe 0.85 Al 0.15 (1 1 0) is significantly influenced by the segregation of aluminium but also of carbon bulk impurities. Below ∼ 900  K, carbon segregates in the form of self-organized protruding stripes separated by ∼ 5  nm that run along the [ 0 0 1 ] B bulk direction and cover up to 34% of the surface. Their C 1s spectroscopic signature that is dominated by graphitic carbon peaks around 900 K. Above this temperature, the surface carbon concentration decays by redissolution in the bulk, whereas an intense aluminium segregation is observed giving rise to a hexagonal superstructure. The present findings is interpreted by a competitive segregation between the two elements. [ABSTRACT FROM AUTHOR]

Oxygen vacancies on metal oxide surfaces have long been thought to play a key role in the surface chemistry. Such processes have been directly visualized in the case of the model photocatalyst surface TiO2(110) in reactions with water and molecular oxygen. These vacancies have been assumed to be neutral in calculations of the surface properties. However, by comparing experimental and simulated scanning tunneling microscopy images and spectra, we show that oxygen vacancies act as trapping centers and are negatively charged. We demonstrate that charging the defect significantly affects the reactivity by following the reaction of molecular oxygen with surface hydroxyl formed by water dissociation at the vacancies. Calculations with electronically charged hydroxyl favor a condensation reaction forming water and surface oxygen adatoms, in line with experimental observations. This contrasts with simulations using neutral hydroxyl where hydrogen peroxide is found to be the most stable product. [ABSTRACT FROM AUTHOR]

• Similar aluminium segregation deep profile at the surfaces of bcc Fe 0.85 Al 0.15. • Orientation (1 1 0)/(1 0 0)/(1 1 1) dependent surface structures. • Al-rich long-range nanometer size surface reconstruction at (1 1 0) surface. • Pronounced nano-faceting at (1 1 1) surface. Based on previous photoemission findings, the influence of newly observed aluminum surface segregation at the low (1 1 0), (1 0 0) and (1 1 1) index surfaces of the A 2 body-centered Fe 0.85 Al 0.15 random alloy is explored. Scanning Tunneling Microscopy, Low-Energy Electron Diffraction and Grazing-Incidence X-ray Diffraction are combined to explore surface structures and topographies. The formation of a surface composition close to the B 2 Fe 0.5 Al 0.5 occurs with the appearance of (i) a long-range pseudo-hexagonal incommensurate superstructure with a periodicity of ~ 18 Å on the (1 1 0) surface, (ii) a (1 × 1) termination on the (1 0 0) surface and (iii) a intense vicinal faceting of the (1 1 1) surface in the form of triangular pits. [ABSTRACT FROM AUTHOR]

Surface x-ray diffraction has been used to determine the quantitative structure of the (101) termination of anatase TiO2. The atomic displacements from the bulk-terminated structure are significantly different from those previously calculated with density functional theory (DFT) methods with discrepancies for the Ti displacements in the [101] direction of up to 0.3Å. DFT calculations carried out as part of the current paper provide a much better agreement through improved accuracy and thicker slab models. [ABSTRACT FROM AUTHOR]