The interaction of oxygen with gold adsorbed on Ti(0001) was studied by synchrotron radiation photoelectron spectroscopy. Two kinds of surfaces were explored: as-deposited 0.38, 1.16 and 1.85 monolayer (ML) thick Au overlayers on the Ti(0001) surface, and the same samples after thermal treatment, which resulted in the formation of Au-Ti intermetallic surfaces. The Ti 3p core level was strongly affected by reaction with oxygen, while the Au 4f core level showed only minor changes other than a decrease in intensity. The Ti 3p peak was fitted with several components which were identified as Ti atoms in different oxidation states, namely TiO, Ti(2)O(3), TiO(2) and Ti-OH. Titanium oxide phase formation is accompanied by Au-Ti bond dissociation and outward diffusion of Ti. The presence of an Au-Ti intermetallic phase on the Ti(0001) surface promotes oxidation of the Ti atoms.

We present the results of scanning tunneling microscopy (STM) and photoemission spectroscopy (PES) of the Ta/Si(111)-7×7 system after deposition of Ta at substrate temperatures from 300 to 1250K. The coverage of Ta varied from 0.05 up to 2.5 of a monolayer (ML). STM shows that at 300K and coverage less than 1 ML, a disordered chemisorbed phase is formed. Deposition on a hot surface (above 500K) produces round 3D clusters randomly distributed on the surface. Cluster height and their diameter are found to change drastically with annealing temperature and the Ta coverage. Analysis of photoemission data of the Si 2p core levels shows that at room temperature and at coverage ⩽1ML core level binding energy shifts and intensity variations of Si surface related components are observed, which clearly indicate that the reaction starts already at 300K. Shifts in the binding energy, changes of the peak shapes and intensity of the Ta 4f doublet at higher temperatures can be explained by the formation of stable silicide on the surface.

The reaction of oxygen at low pressure with the Sn/Pd(110) system has been examined by photoelectron spectroscopy using synchrotron radiation. The c(2 x 2) and (3 x 1) reconstructions of the Sn/Pd(110) surface at 0.5 and 0.7 monolayers (ML) Sn coverage and a 1.75 ML Sn overlayer on the Pd(110) surface after flashing to 470 K were studied. The Sn 4d core level is strongly affected by O-2 adsorption while the Pd 3d core level shows very little change other than a decrease in intensity. Starting with a 10 L dose of oxygen, prominent changes in the spectra were observed for all Sn/Pd(110) surface alloys. Analysis of the Sn 4d core levels indicates that oxidation proceeds with the formation of well-defined states of Sn, which were identified as a Pd-Sn-O interface layer, SnO and SnO2 oxides. The valence band spectra confirm this assignment. The Sn2+ and Sn4+ component signals originate from the topmost surface layer, i.e. tin atoms in more highly oxidized states constitute the topmost surface layer on top of the Pd-Sn-O interface. The presence of a sub-surface PdSn intermetallic alloy facilitates the tin oxide formation; the Sn-O phase formation is accompanied by Pd-Sn bond dissociation.

Lead submonolayers on the Si(111) surface in ordered structures of symmetry (3×3)R30° were studied with photoelectron diffraction and ab initio calculations. At 1/3 monolayer coverage Pb atoms flip between up and down positions. This fluctuating geometry is connected with the charge redistribution in the basic triangular bipyramid formed by an adsorbed Pb atom and its four closest Si neighbors. The dynamic balance is reflected in the switching of bipyramids from semiconductor to metal character as a result of the interaction between an unsaturated Pb atom in the T4 position and a saturated Si atom beneath. Substitution of a Pb atom in the 1/3 monolayer coverage with a Si atom results in stabilisation of the neighboring Pb atoms in the up position which is characteristic for Pb atoms in the 1/6 monolayer mosaic phase.

We have studied the adsorption of Pb on the Rh(1 0 0) and (1 1 0) surfaces by photoemission and low energy electron diffraction (LEED), and tested the chemical properties by adsorption of CO. Pb forms two distinct c(2 × 2) phases on Rh(1 0 0), according to the temperature of the substrate. The phase formed below about 570–620 K, denoted α-c(2 × 2), reduces the coverage of adsorbed CO but does not affect the valence band spectrum of the molecule. The phase formed above this temperature, denoted β-c(2 × 2), also reduces the coverage of adsorbed CO but the valence band spectrum of the adsorbed CO is strongly affected. The two phases are also characterised by a slightly different binding energy of the Pb 5d5/2 level, 17.54 eV for the α phase and 17.70 for the β phase. The Pb/Rh(1 1 0) surface shows two ordered Pb induced phases, c(2 × 2) and p(3 × 1). CO adsorbs on the first with reduced heat of adsorption and with a valence band spectrum that is strongly altered with respect to CO adsorbed on clean Rh(1 1 0), but does not adsorb on the p(3 × 1) structure at 300 K. We compare the present results with previous results from related systems.

Enhancement of surface state peaks in angle resolved ultraviolet photoelectron spectra (ARUPS) from the Al(111) surface is studied experimentally and theoretically within the one-step model of photoemission. The resonant enhancement of the surface state emission is explained by the crucial role of elastic scattering of the outgoing electron. Dipole transitions to evanescent states in the final bands of the crystal are shown to determine photoemission at the resonant photon energy. The band structure based explanation is confirmed by the measurements of electron reflectivity and of the fine structure of valence band spectra. The surface sensitivity of ARUPS is shown to depend strongly on the complex band structure of the crystal and to be finely tunable by the choice of photoemitted electron energy.

The Au/Ti(0001) adsorption system was studied by low energy electron diffraction (LEED) and photoemission spectroscopy with synchrotron radiation after step-wise Au evaporation onto the Ti(0001) surface. For adsorption of Au at 300K, no additional superstructures were observed and the (1×1) pattern of the clean surface simply became diffuse. Annealing of gold layers more than 1ML thick resulted in the formation of an ordered Au–Ti surface alloy. Depending on the temperature and annealing time, three surface reconstructions were observed by LEED: (√3×√3) R30°, (2×2) and a one-dimensional incommensurate (√3×√3) rectangular pattern. The Au 4f core level and valence band photoemission spectra provided evidence of a strong chemical interaction between gold and titanium. The data indicated formation of an intermetallic interface and associated valence orbital hybridization, together with diffusion of gold into the bulk. Au core-level shifts were found to be dependent on the surface alloy stoichiometry.

A new way of imaging the local density of states has been devised through a combination of the constant-height scanning tunnelling microscopy operational mode and lock-in techniques. We have obtained Current images simultaneously with real space dynamical conductance maps (dI /dV) for energies around the Fermi level, on the Si(111)-(7 x 7) surface. We reconstructed the normalized dynamical conductance spectra-(dI/dV)/(I/V). Since the (dl/dV)/(I/V) curves are closely related to the local densities of states, we compared their sum over the unit cell to photoelectron spectra and theoretical calculations. We find that the results are in good agreement. Consequently, the extent of localization of surface electronic states at lattice positions was determined.

The surface segregation of a Fe94Si6 and Fe76Si24 alloys was studied using high resolution photoemission spectroscopy with synchrotron radiation at 150-166 eV photon beam energy. During Ar+ ion sputtering and following heat treatment, a SiO2 layer and segregation of Si atoms in three clearly resolved phases occurred. This indicates formation of silicides, mainly Fe3Si and cubic FeSi superstructures. The photoemission measurements were complemented by Fe-57 Mossbauer spectroscopy in different modes which gave information about deeper surface layers (approximately 10-30000 nm) of the samples. The results derived from the Mossbauer spectra support the conclusions concerning phase composition of the surface deduced from photoemission spectroscopy. (c) 2006 Elsevier B.V. All rights reserved.

We have studied adsorption of water on the Zr(0001) surface at sub-monolayer coverage by means of LEED and photoemission spectroscopy. An ordered (2×2) structure is formed after adsorption of 0.6–1.4 Langmuirs at 473K. The sharpest LEED pattern was observed at an exposure of 1.2L implying a coverage of 0.5ML of oxygen. The same exposure at 293K gives only a weak and diffuse (2×2) pattern. In addition, the sharp (2×2) pattern obtained at 473K can be reversibly weakened by cooling to 293K and subsequently sharpened by heating. For the sharp (2×2) structure, valence band spectra indicated dissociation of water and showed a peak composed mainly of O 2p derived states with two components at 6.0eV and 6.6eV binding energy. On cooling to 293K, the O 2p peak became narrower and a new state appeared at 7.9eV. Two components of the O 1s core level were resolved for the (2×2) structure, assigned to oxide and hydroxyl groups. The hydrogen on the surface of Zr(0001) resulting from the dissociation of water and from bulk segregation strongly influenced the formation of the (2×2) structure of oxygen, and caused a temperature instability of the structure.

$\mathrm{Pb}∕\mathrm{Ni}\phantom{\rule{0.3em}{0ex}}(111)$ surface phases were investigated by synchrotron radiation photoemission and low-energy electron diffraction. For room temperature deposition of Pb, two surface ordered layers, $(3\ifmmode\times\else\texttimes\fi{}3)$ and $(4\ifmmode\times\else\texttimes\fi{}4)$, were observed. The $\mathrm{Pb}\phantom{\rule{0.3em}{0ex}}5d$ and $\mathrm{Pb}\phantom{\rule{0.3em}{0ex}}4f$ core levels as well as valence band spectra indicated a weak chemical interaction between Pb and Ni, and the formation of a close-packed overlayer with Pb atoms in two different adsorption sites. Annealing of the $\mathrm{Pb}∕\mathrm{Ni}\phantom{\rule{0.3em}{0ex}}(111)$ surface led to the formation of the $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ reconstruction, characterized by a topmost layer consisting of a substitutional alloy. The transformation to the $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ structure was accompanied by the appearance of a strong photoelectron diffraction effect, confirming embedding of Pb atoms in the $\mathrm{Ni}(111)$ first surface layer. $\mathrm{CO}$ adsorption results showed that lead simply blocked the $\mathrm{CO}$ adsorption sites for the unannealed surface while the surface alloy exhibited a chemical effect of weakening of the $\mathrm{CO}\text{\ensuremath{-}}\mathrm{Ni}$ bond. The $\mathrm{Pb}\phantom{\rule{0.3em}{0ex}}5d$ core-level shift indicated charge transfer from Pb to the surface, particularly for $(4\ifmmode\times\else\texttimes\fi{}4)$ and $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ structures.

Zr–V alloy getter films were prepared on stainless steel substrates by magnetron sputtering. The thermal activation behavior of these getters was investigated by synchrotron radiation photoelectron spectroscopy using photon excitation energies of 600, 250 and 73eV. Depth resolved results were compared to the results of the SIMS profiling. The measurements confirmed the disappearance of the superficial oxide layer covering the air-exposed Zr–V surfaces via its progressive reduction during the thermal activation. The depth sensitive results showed that the activated getter surface is covered by a residual zirconium sub-oxide.

The surface segregation on the Fe-3wt.%Si alloy was studied using X-ray Photoelectron Spectroscopy (XPS) with synchrotron radiation at 150 eV photon beam energy (Si 2p). A silicon oxide layer and also segregation of Si atoms in three clearly resolved phases occurred during heat treatment. A formation of silicides mainly with the Fe3Si superstructure was observed. A silicon nitride layer was created by nitrogen ion implantation. The structure and atomic ordering in a surface layer of the samples (approx. 300 nm thick) was checked by Conversion Electron Mössbauer Spectroscopy (CEMS). Simultaneously emission Mössbauer spectroscopy was used for the investigation of the Si concentration and atomic ordering at grain boundaries.

We have studied the Sn/Pd(110) adsorption system by synchrotron radiation photoelectron spectroscopy and low-energy electron diffraction (LEED). For room temperature evaporation, two surface reconstructions were observed: c(2×2) and (3×1), corresponding to about 0.5ML and 0.75ML of Sn adlayer coverage. The Pd 3d and Sn 4d core levels as well as valence band spectra indicate a strong chemical interaction between Sn and Pd, and the formation of an intermetallic interface. Structural models are proposed for both of these phases based on the photoemission and CO adsorption results. We show that at coverage higher than 0.7ML, tin is alloyed with the Pd crystal forming a subsurface layer of Pd–Sn intermetallic compound of stoichiometry which varies with tin coverage. CO adsorption occurs only at low temperature (120K) and depends on the Sn coverage and reconstruction of the Pd(110) surface. We estimate the CO adsorption energy for the c(2×2)- and (3×1)-Sn/Pd(110) surfaces to be reduced by 40% compared to the clean palladium (110) surface.

We have investigated the 1/3 monolayer root3xroot3-Pb/Si(111) system with core level photoemission at temperatures of 300 and 120 K. At both temperatures the Pb 5d(5/2) and 5d(3/2) core levels are split into two states with an intensity ratio of 2:1, as in the related Sn/Ge(111) and Sn/Si(111) systems. On doping the surface with Cs (an electron donor) or oxygen (an electron acceptor) the ratio of the intensities of the two states change strongly, suggesting the states have filled or empty dangling bonds. The results are interpreted in terms of charge fluctuations with one third of Pb atoms acting as charge donors and two thirds as acceptors in the undoped phase. Four chemically shifted Si 2p core level peaks are found whose energies are almost constant for the doped and undoped surfaces, and whose relative intensities change significantly on doping. These states of Si are assigned to two distinct kinds of atoms bonded to the two states of Pb, and to deeper Si atoms. The shifts are explained in the framework of the charge fluctuation model [M. Gothelid, M. Bjorkvist, T. M. Grehk, G. Le Lay, and U. O. Karlsson, Phys. Rev. B 52, R14 352 (1995)], and the integer pseudo charge model [G. Ballabio, G. Profeta, S. de Gironcoli, S. Scandolo, G. E. Santoro, and E. Tosatti, Phys. Rev. Lett. 89, 126803 (2002)]. Within the family of group IV metals adsorbed on group IV (111) semiconductor surfaces, Pb/Si(111) is similar to Pb/Ge(111) and Sn/Ge(111) with Sn/Si(111) being the exceptional case.

The adsorption of Pb on Pd(110) and co-adsorption with CO have been studied by photoemission spectroscopy and low energy electron diffraction. Two ordered structures are formed at sub-monolayer coverages of Pb with symmetry c(2×2) and (3×1). The valence band and Pd 3d core level spectra indicate a strong chemical interaction between Pb and Pd, and the formation of intermetallic bonds with both the first and second layer of Pd. The heat of CO adsorption on the c(2×2) phase is reduced to about half of the value on clean Pd, and even less on the (3×1) structure so that CO does not adsorb at a temperature of 120 K. Structural models are proposed for both of these phases based on the photoemission and co-adsorption results. The results confirm that the de-activation by Pb of Pd as a CO oxidation catalyst is due to the formation of an intermetallic compound, which drastically lowers the adsorption energy. However even the formation of a sub-monolayer phase is sufficient to radically alter the catalytic properties, and the formation of a bulk intermetallic is not necessary.

We have investigated the 1/3 monolayer $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\text{\ensuremath{-}}\mathrm{Pb}∕\mathrm{Si}(111)$ system with core level photoemission at temperatures of 300 and $120\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. At both temperatures the $\mathrm{Pb}\phantom{\rule{0.3em}{0ex}}5{d}_{5∕2}$ and $5{d}_{3∕2}$ core levels are split into two states with an intensity ratio of 2:1, as in the related $\mathrm{Sn}∕\mathrm{Ge}(111)$ and $\mathrm{Sn}∕\mathrm{Si}(111)$ systems. On doping the surface with $\mathrm{Cs}$ (an electron donor) or oxygen (an electron acceptor) the ratio of the intensities of the two states change strongly, suggesting the states have filled or empty dangling bonds. The results are interpreted in terms of charge fluctuations with one third of $\mathrm{Pb}$ atoms acting as charge donors and two thirds as acceptors in the undoped phase. Four chemically shifted $\mathrm{Si}\phantom{\rule{0.3em}{0ex}}2p$ core level peaks are found whose energies are almost constant for the doped and undoped surfaces, and whose relative intensities change significantly on doping. These states of $\mathrm{Si}$ are assigned to two distinct kinds of atoms bonded to the two states of $\mathrm{Pb}$, and to deeper $\mathrm{Si}$ atoms. The shifts are explained in the framework of the charge fluctuation model [M. G\"othelid, M. Bj\"orkvist, T. M. Grehk, G. Le Lay, and U. O. Karlsson, Phys. Rev. B 52, R14 352 (1995)], and the integer pseudo charge model [G. Ballabio, G. Profeta, S. de Gironcoli, S. Scandolo, G. E. Santoro, and E. Tosatti, Phys. Rev. Lett. 89, 126803 (2002)]. Within the family of group IV metals adsorbed on group IV (111) semiconductor surfaces, $\mathrm{Pb}∕\mathrm{Si}(111)$ is similar to $\mathrm{Pb}∕\mathrm{Ge}(111)$ and $\mathrm{Sn}∕\mathrm{Ge}(111)$ with $\mathrm{Sn}∕\mathrm{Si}(111)$ being the exceptional case.

Zr–V alloy getter films were prepared on stainless steel substrates by magnetron sputtering. The thermal activation behavior of these getters was investigated by photoelectron spectroscopy using two photon excitation energies of 600 eV (synchrotron light) and 1253.6 eV (MgKα laboratory source). During the activation by heating from 120 to 320 °C, the adsorbed carbon was transformed to metal carbides and diffused to the subsurface region.