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WOS: 000312762900007, PubMed ID: 26291100, The knowledge of the catalyst active phase on the atomic scale under realistic working conditions is the key for designing new and more efficient materials. In this context, the investigation of CO oxidation on the bimetallic Pt3Sn(111) surfaces by near-ambient-pressure X-ray photoelectron spectroscopy and density functional theory calculations illustrates how combining advanced methodologies allows the determination of the nature of the active phase. Starting from 300 K and 500 mTorr of oxygen, the progressive formation of surface oxides is observed with increasing temperature: SnO, PtO units first, and SnO2, PtO2 units afterward. For CO oxidation on the (2 X 2) surface, the activity gain is assigned to the build-up of ultrathin domains composed of SnO and SnO2 units. The formation of these early stage surface oxides is entirely supported by a density functional theory analysis. More generally, this study demonstrates how the catalyst surface oxidation and transformation can be better controlled by a relevant choice of environmental conditions., Office of Science, Office of Basic Energy Sciences, U.S. Department of Energy [DE-AC02-05CH11231]; Agence Nationale de la Recherche (ANR) [ANR-08-BLAN-0096-03], This research was partially carried out at the Advanced Light Source supported by the Director, Office of Science, Office of Basic Energy Sciences, U.S. Department of Energy under contract DE-AC02-05CH11231. Y.J. acknowledges U. Bardi (Firenze University) for providing the Pt3Sn(111) sample and the Agence Nationale de la Recherche (ANR) for financial support (ANR-08-BLAN-0096-03). D.L., C.D., and F.D. thank IDRIS, Orsay, CINES, Montpellier and PSMN, Lyon for CPU time and assistance.

SSCI-VIDE+ATARI+MAA:EEH:YJU:JBE; International audience; With the combination of various in-situ surface science tools, surface chemical and structural properties of bimetallic AuPd(1 1 0) alloys arecharacterized under elevated CO pressure. Under 1 Torr of CO gaspressure, STM images show the formation of nano-sized surfacerice-grains along the index direction of [1-10] while PM-IRRAS shows newCO vibrational band. This new vibrational band of PM-IRRAS is confirmedas the CO molecules attached to atop site of Pd with the results ofambient pressure XPS. In the case of adsorption of CO on AuPd(1 1 0)alloys, the so-called "pressure gap" exists and the surface morphologyand its chemical states change at elevated pressure conditions. (C) 2015Elsevier B.V. All rights reserved.

The reactivity of Pt3Sn(111) has been tested in the 1,3-butadiene hydrogenation reaction and compared to that of Pt(111) by a combination of polarization modulation absorption reflection infrared spectroscopy, mass spectroscopy and gas phase chromatography techniques. Pt3Sn(111) is less active than Pt(111) by one order of magnitude but it is more selective into butenes whatever the initial surface structure p ( 2 × 2 ) or ( 3 × 3 ).

Bond-order conservation-Morse potential (BOC-MP) model has been used to study the energetics of acrolein hydrogenation on Pt(1 1 1) and Ag(1 1 1) surfaces. For hydrogenation at low coverage of acrolein (θ=1/9), the model predicts an overall low activity for acrolein conversion and a lower selectivity for the formation of allyl alcohol. At higher acrolein coverage (θ=1/4), however, the total activity increases and the selectivity for the allyl alcohol is improved compared to its magnitude at low coverage. The results are in qualitative agreement with the experimental results on hydrogenation of similar α,β-unsaturated aldehyde on Pt surfaces indicating steric hindrance for the CC bond hydrogenation at higher coverages. As for hydrogenation on Ag(1 1 1) surface, the energetics predict relatively higher selectivity for allyl alcohol compared to the selectivity on Pt(1 1 1) surface. The predictions are critically discussed with reference to the available experimental results.

SAMs (self-assembled monolayers) of alkanethiols functionalized by α-terthienyl (3T-SAMs) and α-quaterthienyl (4T-SAMs) were formed on a gold surface presenting (111) terraces and studied by high-resolution electron energy loss spectroscopy (HREELS). The angular width of the elastic peak leads to a domain size of ca. 90 A, comparable to that of the Au(111) terraces of the substrate. Enhancement of the spectral resolution by using a new generation spectrometer enables the improvement of the spectral analysis in the energy range of the vibrational losses. A detailed analysis of the differential cross sections of the different vibrational peaks indicates the nature of their mechanisms: impact mechanisms show that the extreme surface of the monolayers is mainly constituted by thienyl moieties with the thienyl density in 3T-SAMs higher than that in 4T-SAMs; dipolar mechanisms show that molecules are standing up slightly tilted on the substrate; a resonance via a negative ion formation was detected around 4.5 ...

The adsorption and dissociation of trichloroethene (TCE) on PdCu(1 1 0) have been investigated under the view of high resolution electron energy loss spectroscopy (HREELS) and first-principle quantum chemical calculations. At 180 K and after an exposure of 10 L, TCE is physisorbed on the surface. The HREELS spectrum is similar to the gas-phase one, measured by infrared spectroscopy. There are small shifts in the bands of the HREELS spectrum, which also indicate a weak interaction between the molecule and the surface. The chemistry of the TCE dissociation on PdCu(1 1 0) is more complex than the one on Cu(1 1 0). By increasing the surface temperature, a great variety of surface species occurs, as shown by the experimental spectra and confirmed by the calculations. This reaction seems to occur relatively early, at 200 K. At 280 K most of the CCl bonds have been already broken. The decrease of the intensity of the ν CCl stretching vibration and the increase of the intensity of the metalCl vibration are shown to be fingerprints of this process.

Spectra of polystyrene film surfaces achieving a resolution of 2.55 meV (20.4 cm−1) were recorded using new generation high resolution electron energy loss spectroscopy spectrometers. Spectra show a high number of characteristic energy losses corresponding to infrared- and Raman-active modes. Mechanisms involved in the electron interaction with the film surface were unraveled through their energy dependence. Impact is the predominant mechanism revealing an analysis depth of some angstroms. Absence of dipole mechanisms is related to a surface conformation where phenyl rings are mostly perpendicular to the substrate.

Two reactions, the hydrogenation of buta-1,3-diene on a Pd8Ni92(1 1 1) alloy and the hydrogenation of benzene on Pt(1 1 1), have been investigated under catalytic conditions by reflection absorption infrared spectroscopy (RAIRS). The purpose of this study was to use infrared spectroscopy to observe both the consumption/production of the different reactants/products and the adsorbed species present during the reaction. On Pd8Ni92(1 1 1), only butenes were produced during the buta-1,3-diene hydrogenation reaction up to the quasi-complete conversion of the diene, with a high rate of reaction. This alloy is therefore, active and very selective for such a reaction. In this case, no absorption bands corresponding to surface species were observed. Ad-species were observed during the benzene hydrogenation reaction on Pt(1 1 1); they cannot be attributed to chemisorbed molecular benzene, but are more probably due to partially hydrogenated intermediates, such as cyclohexadiene and/or cyclohexene.

The decomposition of trichloroethene, C2HCl3, on Cu(110) has been investigated as a function of temperature by RAIRS, HREELS and TPD. This has provided a detailed identification of intermediate surface species involved in the dechlorination reaction. Multilayers form readily at 85 K, desorbing at 140 K. A weakly perturbed molecular species exists at 150 K that is converted, with increasing temperature, to a CCH intermediate at the surface. This ethynyl intermediate subsequently disproportionates to produce C2H2 and a carbon deposit at the surface. At T>300 K, C2H2 desorption competes with the trimerisation reaction that leads to benzene evolution at 370 K. Cl atoms are retained at the surface up to high temperatures.

The chemisorption and reaction of trans-dichloroethene on Cu(110) have been investigated by high-resolution electron-energy-loss spectroscopy (HREELS) as a function of coverage and temperature. At 135 K, both physisorbed and chemisorbed trans-dichloroethene are present. Heating to 200 K leads to the formation of acetylene and of a partially dehalogenated intermediate species. By 300 K, the acetylene trimerises to form adsorbed benzene at the surface. Adsorption of trans-dichloroethene at 300 K produces benzene directly. Evidence of C–Cl cleavage at temperature as low as 220 K is clearly marked by the emergence of very intense Cu–Cl stretching vibrations which remain even after further heating up to 570 K.

The catalytic properties of (111) and (110) Pd50Cu50 single-crystal surfaces have been tested for the 1,3-butadiene hydrogenation reaction, and compared to those of pure Pd having the same surface orientations. The Pd50Cu50(111) single crystal has the highest activity; it is also more effective than the corresponding pure Pd face. The activity of the Pd50Cu50(110) is less; nevertheless, it is practically as effective as the Pd(110) crystal, which is itself more effective than the (111) oriented Pd sample. The results are discussed in terms of both geometric and electronic effects. They are associated on one side to the dilution by the inactive Cu surface atoms, and on the other side to the electronic interaction between the outer Pd surface atoms and the surrounding Cu atoms.

Pd deposits on Ni(110) have been studied by low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), low-energy ion scattering spectroscopy (LEIS), and X-ray photoelectron spectroscopy techniques and their catalytic properties tested by the butadiene hydrogenation reaction at room temperature. Their catalytic activity is greatly enhanced by appropriate annealings. Superstructure indicative of a long range ordering of Pd atoms on Ni is evidenced for low Pd coverages neither before nor after annealing. For higher coverages, a LEED superstructure appears after annealing. AES and LEIS studies reveal a sharp Pd depth profile and the existence of a Pd–Ni surface alloy even at room temperature. The Pd 3d core level binding energy is shifted upwards by at least 0.4 eV with respect to pure Pd surface atoms and remains unchanged in the course of annealings. Hence geometrical rearrangements have to be taken into consideration to explain the activity enhancement.

The adsorption of 1,3-butadiene and 1-butene on Pt(111), and Pd(111) was studied by near edge X-ray absorption fine structure (NEXAFS). It is found that at 95 K, 1-butene is π-bonded to Pd(111), while it is di-σ bonded to Pt(111). At 95 K, 1,3-butadiene is loosely bonded on both Pd(111) and Pt(111). However, at 300 K, 1,3-butadiene adsorption differs, depending on the substrate. A di-σ bonding is observed on Pd(111) while on Pt(111), a di-σ interaction, keeping one central carbon-carbon double bond, is proposed. In the butadiene molecule half of the carbon atoms undergo a large rehybridization from sp 2 to sp 3 , as evidenced by high resolution electron energy loss spectroscopy (HREELS). These differences between 1,3-butadiene adsorption on Pt(111) and Pd(111) are discussed in terms of differences in catalytic activities and selectivities in the 1,3-butadiene hydrogenation reaction.

An upward shift of 0.8 ±0.1 eV is measured on the Pd 3d core levels of Pd atoms deposited on Ni(110) with respect to pure Pd surface atoms. These electronic properties are found to be unchanged in the course of a 475 K thermal treatment whereas the activity of the annealed deposit towards the butadiene hydrogenation reaction is largely enhanced. Consequently, electronic effects are not sufficient to explain the activity enhancement. The LEIS technique reveals that the Pd atoms remain at the very surface of the sample, the Pd concentration being roughly 48 at%. Therefore, some geometric effects have to be taken into consideration. The annealing would lead to a particular arrangement and would generate more effective catalytic sites.

Graphite powder electrodes bonded by polymerized LaPO4 have been investigated for the first time by atomic force microscopy (AFM). The interest in investigating this material stems from the fact that graphite electrodes intercalated, or not, with various metals and bonded with LaPO4 have shown very good mechanical and electrochemical stability during the hydrogen evolution reaction (HER) in 1 M KOH aqueous solutions. Examination of their surfaces by scanning electron microscopy has revealed that these electrodes are very porous. AFM furnishes additional data about the surface and can therefore be considered a powerful tool for surface characterization.

Poly(tetrafluoroethylene) (PTFE) films and fibres were surface modified by different methods (chemical and plasma treatments) to improve their wetting and adhesion properties. Both chemical and, to a lesser extent, ammonia and hydrogen plasma treatments have been shown to greatly enhance the adhesion between PTFE and an epoxy resin. In the last case (ammonia and hydrogen plasma treatments), the adhesion increase has been reiated to the degree of defluorination rather than to the presence of polar functions at the surface. In the case of the chemical treatment, in addition to the defluorination, the incorporation of a large amount of oxygen moieties can play an important role in adhesive properties. In all cases the failure zones, observed by X-ray photoelectron spectroscopy after pull-off tests, are characteristic of a cohesive failure. The differences between the chemical and the plasma treatments have been attributed to the modified depth, which is more important in the former case. Fibre wettability is enhanced by a previous ammonia plasma treatment making easier the formation of an epoxy microdroplet for microbond tests. For ammonia-plasma-treated PTFE fibres the ultimate load increases; this cannot be attributed to a debonding process since either the droplet or the fibre breaks.

13 Haubrich, J. Loffreda, D. Delbecq, F. Sautet, P. Jugnet, Y. Krupski, A. Becker, C. Wandelt, K.; The prediction of a reaction mechanism and the identification of the corresponding chemical intermediates is a major challenge in surface science and heterogeneous catalysis, due to a complex network of elementary steps and surface species. Here we demonstrate how to overcome this difficulty by tracking the temperature dependent formation of the initial reaction intermediates and identifying the decomposition pathways in the case of prenal, an alpha,beta-unsaturated aldehyde, on the Pt(111) model catalyst surface by combining vibrational spectroscopy, thermal reaction/desorption spectroscopy (TPRS) experiments and detailed theoretical analysis. TPRS characterization of this reaction up to 600 K shows a series of desorption states of H-2 (similar to 280 K, 410 K and 473 K) and CO (similar to 414 K), giving valuable insights into the sequence of elementary steps suggesting that the loss of hydrogen and the carbonyl functions are among the first elementary steps. HREELS experiments recorded after annealing to specific temperatures result in complex spectra, which can be assigned to several subsequently formed and transformed surface intermediates. Starting from stable prenal adsorption structures, complementary DFT calculations allow the determination of the most likely reaction pathway for the initial decomposition steps and the identification of the corresponding intermediates by comparison with HREELS. The decomposition occurs from the strongly bonded prenal adsorption structures via a dehydro-eta(3)-tri sigma(CCC)-H1 intermediate to the highly stable eta(1)-isobutylidyne species at high temperatures.

2 Dupont, C. Delbecq, F. Loffreda, D. Jugnet, Y.; An experimental evaluation, under realistic conditions, of the catalytic properties of a Pt3Sn(1 1 1) model catalyst in CO oxidation under excess of hydrogen is reported in this study. From a structural point of view, two different surface terminations are available in this alloy, viz. (2 x 2) and (root 3 x root 3)R30 degrees, differing by their tin concentration and Pt-Sn local structural arrangements in the uppermost layers, thus offering specific active sites for the reaction to proceed. In this study, mass spectrometry and polarization modulation infrared reflection absorption spectroscopy measurements (PM-IRRAS) have been performed at near ambient pressure on both surfaces of the alloy and compared to those obtained on Pt(1 1 1) used as a reference. The presence of hydrogen promotes the rate of CO oxidation on the three surfaces. The influence of tin is remarkable, increasing the catalytic activity of Pt atoms by one order of magnitude. With the exception of CO, no other species such as formyls or carbonates are observed on the surface by IR spectroscopy in the range of temperature (293-425 K) investigated. (C) 2010 Elsevier Inc. All rights reserved.

The gas phase selective hydrogenation of 1,3-butadiene was studied over Pd and Pd–Sn supported on mixed phase θ/α-(MA) and pure α-alumina (AA). The catalysts were characterized by XRD, XPS, TEM, and FTIR spectroscopy of adsorbed CO. A remarkable improvement in terms of activity and selectivity in the selective hydrogenation of 1,3-butadiene was achieved over Pd–Sn on the mixed phase alumina support in which butane formation and isomerization of 1-butene were suppressed. Nevertheless, Pd–Sn/AA showed much lower activity than Pd–Sn/MA due to lower metal dispersion.

Dupont, Celine Jugnet, Yvette Delbecq, Francoise Loffreda, David; The activation of oxygen reduction reaction fascinates numerous scientists in the fields of heterogeneous catalysis, electrochemistry and surface science. Indeed, oxygen dissociation is considered usually as the rate determining step of several reactions on conventional platinum catalysts. From combined experimental and theoretical approaches, we demonstrate comprehensively how tailored platinum-tin alloy surfaces allow to go beyond this chemical limitation. Near-ambient pressure kinetic measurements show the outstanding capacity of the Pt3Sn(111) single-crystal surfaces for carbon monoxide oxidation. The apparent activation energy is almost twice lower on the platinum-tin surface than on pure platinum catalyst. The theoretical analysis based on density functional theory calculations supports the idea that oxygen dissociation is never the rate determining step on these alloy surfaces since the corresponding rates calculated at room temperature always outstrip those of carbon monoxide oxidation. The influence of surface tin content and oxygen coverage on the activity is addressed in details. The mediatory role of tin in the alloy is elucidated on the basis of a charge transfer analysis. (C) 2010 Elsevier Inc. All rights reserved.

Elevated pressure in situ STM studies were crucial to show that CO adsorption on gold surfaces strongly modifies their surface structures [1–3]. However oxygen dissociation does not occur spontaneously on such surfaces preventing efficient CO oxidation. The addition of an oxygen-dissociative metal (such as Pd) to gold may overcome this difficulty. In this work we present results concerning the behaviour of Pd70Au30(110) under elevated pressures of CO and O2 and compare them to the results obtained on Au(110) under similar conditions.

The surface restructuring of Pt(3)Sn(111) induced by oxygen chemisorption is examined by means of density-functional theory calculations. Molecular and atomic oxygen chemisorption is investigated on the two available terminations of the bulk alloy--(2 x 2) and (square root(3) x square root(3))R30 degrees--these two surfaces differing by the tin content and the nature of chemical sites. An extensive geometric, energetic, and vibrational analysis is performed including the influence of oxygen coverage in the case of atomic adsorption. For molecular adsorption, regular structures have been obtained for both surfaces with a clear effect of tin on the stability of the adsorption forms. In contrast, for atomic adsorption, two oxygen chemical states are found. In particular, a peculiar surface restructuring, involving the formation of a network of SnO(2) species, appears for large oxygen coverage. However the two terminations present discrepancies for the restructuring mechanism all along the oxygen coverage increase. All these results are supported by a systematic vibrational analysis.

For the first time, a clean metal surface reconstruction, viz. Pt(110)(2 × 1), is investigated using X-ray photoelectron diffraction (XPD). Comparison of the obtained experimental XPD azimuthal and polar curves with quasidynamical calculations reveals that the Pt(110)(2 × 1) reconstruction is, as expected, of the “missing row model” type and, furthermore, presents a first layer contraction estimated to be around 30%. The result is compared with previous LEED results.

The adsorption and thermal decomposition of the α,β-unsaturated aldehyde prenal (3-methyl-2-butenal) have been studied on Pt(111), the Pt3Sn/Pt(111) and Pt2Sn/Pt(111) surface alloys, and the corresponding terminations of the Pt3Sn(111) bulk alloy by means of high-resolution electron energy loss spectroscopy (HREELS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED). By comparing the experimental results with extensive theoretical calculations of the multitude of possible adsorption configurations of prenal using density functional theory (DFT), the adsorption configurations actually present on all model catalysts have been identified. This approach, thus, reveals a new way to identify complex, multifunctional molecules adsorbed on model catalyst surfaces. On Pt(111), prenal is strongly adsorbed and decomposes at approximately 300 K. By the aid of density functional theory (DFT), five flat-lying adsorption structures of η2, η3, and η4 hapticity, which exhibit similar adso...

International audience; We present results from high-resolution electron energy loss spectroscopy (HREELS) and XPS studies of self-assembled monolayers of DNA. The monolayers are well-organized and display sharp vibrational peaks in the HREEL spectra. The electrons interact mainly with the backbone of the DNA. The XPS results indicate that, in most of the samples studied, the phosphates on the DNA are not charged.

International audience; The adsorption of CO on the two terminations, p(2 × 2) and (√3 × √3) R30°, of the bulk Pt3Sn(111) alloy is studied by high pressure polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). The influence of O2 is also investigated. While no differences are observed when CO is chemisorbed alone, the behavior of the two terminations clearly differs in presence of O2. The presence of oxygen induces modifications on the (√3 × √3)R30° surface. Finally we study how the interaction between O2 and the surface modifies the reactivity. Hence we show that the p(2 × 2) termination is more efficient than the (√3 × √3) R30° for CO oxidation. However this termination remains more efficient than pure platinum.

Ce cristal massif n'est termine que par une seule couche Si, en opposition aux films CoSi 2 deposes epitaxialement sur Si(100) qui peuvent presenter des surfaces a une ou plus couche Si selon les conditions de croissance epitaxiale

International audience; Vibrational insights into the CO adsorption states on the (2 x 2) surface of the Pt3Sn(111) bulk alloy are reported for the first time by a systematic comparison between high-resolution electron energy loss spectroscopy (HREELS) measurements and density functional theory (DFT) anharmonic frequency calculations. CO adsorbs preferentially in top configuration on Pt atoms. In contrast with Pt(111), CO multifold sites are observed only at low coverage. This difference is interpreted on the basis of the relative stability between top and threefold hollow sites on Pt3Sn(111) compared to Pt(111). The evolution of the CO vibrational bands as a function of temperature shows that CO adsorption is weakened by the presence of tin; this result is confirmed by DFT calculations.

The efficiency of PtSn alloy surfaces toward CO oxidation is demonstrated from first-principles theory. Oxidation kinetics based on atomistic density-functional theory calculations shows that the Pt3Sn surface alloy exhibits a promising catalytic activity for fuel cells. At room temperature, the corresponding rate outstrips the activity of Pt(111) by several orders of magnitude. According to the oxidation pathways, the activation barriers are actually lower on Pt3Sn(111) and Pt3Sn/Pt(111) surfaces than on Pt(111). A generalization of Hammer's model is proposed to elucidate the key role of tin on the lowering of the barriers. Among the energy contributions, a correlation is evidenced between the decrease of the barrier and the strengthening of the attractive interaction energy between CO and O moieties. The presence of tin modifies also the symmetry of the transition states which are composed of a CO adsorbate on a Pt near-top position and an atomic O adsorption on an asymmetric mixed PtSn bridge site. Along the reaction pathways, a CO2 chemisorbed surface intermediate is obtained on all the surfaces. These results are supported by a thorough vibrational analysis including the coupling with the surface phonons which reveals the existence of a stretching frequency between the metal substrate and the CO2 molecule.

International audience; The (Nx1) reconstruction (N = 5-6) of the clean Pd8Ni92(110) surface has been investigated by surface X-ray diffraction. A good fit with experimental data collected under UHV conditions is obtained when introducing undulations in the outer dense rows, constituted mainly of Pd atoms which strongly segregate to the surface. This reconstruction can be regarded as a way to relax the strains induced on the bigger Pd surface atoms, at least partially. The modifications of the surface were studied under butadiene then hydrogen as well as during butadiene hydrogenation at elevated pressure at 300 K and the (Nx1) reconstruction was found to be still present. The main changes are observed under pure hydrogen and during butadiene hydrogenation.

A combination of GGA total-energy calculations and vibrational spectra simulations with HREELS experiments is reported to obtain new insights in the stable adsorption modes of the acrolein molecule on the Pt(111) surface. The simulations of the EELS spectra have allowed us to interpret the evolution of the experimental spectra, as a function of gas exposure. A strongly bound and coverage dependent chemisorption structure is shown. The 1 L spectrum has been assigned to a low coverage η3-cis and η4-trans mixed phase, with the molecule lying flat on the surface and interacting by both CC and CO bonds. The modified spectrum for an exposure of 2 L is associated with a change in the molecule adsorption structure toward a high coverage η2-cis and η2-trans form on the surface in complete agreement with the DFT total energy results.

The adsorption of carbon monoxide on the Au(1 1 1) single-crystal surface has been investigated in the [10 � 3 –10 3 Torr] range at room temperature (RT). Using scanning tunneling microscopy (STM), a CO-induced modification of the surface morphology (step edge roughening) and terrace structure (22 � p 3 ! 1 � 1 transition) is evidenced. Reflection absorption infrared spectroscopy (RAIRS) experiments suggest that CO molecules are linearly chemisorbed on top of gold atoms and that adsorption occurs only above � 1 Torr CO pressure at RT. Density functional theory (DFT) calculations, through consideration of perfect, stepped or kinked surfaces support these results and give additional evidence of strong structure sensitivity for CO adsorption on gold. � 2004 Elsevier B.V. All rights reserved.

Self assembled monolayers (SAMs) of thiols functionalised with oligothiophene functions were used as models for polymer surfaces. Thienyl functionalisation simulates the surface region and demonstrates that the analysed depth is of the order of 10 A. Spectra of polystyrene (PS) films were recorded and show that impact mechanism dominates, which corroborates the high sensitivity of HREELS applied to polymer surfaces. Different orientation of phenyl groups is unravel for PS films deposited on platinum and silicon substrates, which is here related to a different conformation of the PS chains in the surface region of the film. To illustrate the state of the art of HREELS applied to organic films, spectra were recorded with old and new generation spectrometers.

CO chemisorption on Au(1 1 0) at 300 K is observed under pressures in the range 10 −1 –10 +2 Torr. This is identified by an infrared band at 2110 cm −1 , whose intensity depends on the pressure. Scanning tunneling microscopy reveals deep restructuring of the surface.

Pd 8 Ni 92 (111) and (110) surfaces have been investigated using X-ray photoelectron spectroscopy and low energy ion scattering. As expected, a high rate of Pd segregation is observed on both faces leading to Pd surface concentrations of 76 and 81 at.% on the (111) and (110) surfaces, respectively. The catalytic performances of these surfaces have been studied for the 1,3-butadiene hydrogenation reaction. The catalytic activity of these alloys is greatly enhanced relative to that of the pure Pd(111) and (110) surfaces.

The growth of Cu and Al films thermally evaporated onto polyethylene (PE) and polyethyleneterephthalate (PET) surfaces is followed in situ by XPS (X-ray Photoelectron Spectroscopy) and XAES (X-ray Auger Electron Spectroscopy) from the early submonolayer stages up to the completion of a metallic film. PE and PET surfaces were metallized first without any preliminary treatment. A second series of metallization experiments were run on the polymer surfaces but pretreated by a remote O2 microwave plasma (2.45 GHz). These metal films have also been investigated by AFM (Atomic Force Microscopy) in air. Both metals are shown not to undergo chemical interaction with low surface energy polyolefin such as PE. While an abrupt interface is seen with A1, a diffusion of Cu into the bulk of the polymer is demonstrated. Large size clusters are evidenced by AFM in the initial steps of deposition. Cu and A1 are both shown to react with PET, but not in the same way. In the case of A1, the chemical interaction across the meta...

The surface modification of polytetrafluoroethylene (PTFE) by microwave plasma treatment was investigated by means of contact angle measurement and e.s.c.a. studies. Various gases (e.g. O 2 , O 2 N 2 , NH 3 ) were used. The influence of the various plasma parameters, such as power, gas flow, distance between the sample and the centre of the discharge, treatment time, etc., has been evaluated. No modification was induced by O 2 and O 2 N 2 treatment, whatever the treatment conditions. NH 3 plasma irradiation, however, rendered the PTFE surfaces more hydrophilic, leading to an increase of the polar component of the surface energy from 4.5 to ∼ 57 mJ m −2 under optimized treatment conditions. NH 3 treatment led to defluorination, crosslinking, hydrocarbon (CC,CH) bond formation, and incorporation of nitrogen-containing groups, as confirmed by e.s.c.a. Oxygen was also detected at the surface of treated PTFE. Correlations between the contact angle, defluorination rate, and surface nitrogen and oxygen contents, have been established. Optimization of operational NH 3 plasma parameters, leading to the best wettability of the treated samples, is also reported.

The chemical interactions of thermally evaporated gold and aluminium with several polymer substrates: polyethylene, polystyrene, polypropylene, polydimethylsiloxane, silicone, poly(ethyleneterephthalate), poly(ether ether ketone) and polyvinylalcohol have been investigated “in-situ” by X-ray Photoelectron Spectroscopy (XPS). From XPS core level shifts and intensity measurements a mechanism of adsorption of metal atoms on specific acidic sites present on polymer surfaces is evidenced, with the formation of a charge transfer complex without surface bond breaking. The detailed mechanism as well as the interface morphology and growth mechanism are governed by the balance between metal-metal and metal-polymer interactions. A trend in the strength of evaporated Al - polymer interaction can be monitored by XPS shifts correlated with an electron transfer from Al to the acidic sites on polymer.

The chemisorption of both buta-1,3-diene and but-1-ene on Pt(111), Pd(111), Pd(110) and Pd50Cu50(111) samples has been characterized by near-edge X-ray absorption fine structure (NEXAFS), ultraviolet photoelectron spectroscopy (UPS) and high-resolution electron energy loss spectroscopy (HREELS). The buta-1,3-diene hydrogenation reaction, investigated on the same surfaces of Pd(111), Pd(110) and Pd50Cu50(111), displays a very good selectivity in butenes and a higher activity compared to Pt(111). Furthermore, the Pd activity greatly depends on the surface crystalline orientation and is also influenced by alloying effects. The origin of these effects has been sought in differences of chemisorption modes of buta-1,3-diene and but-1-ene on the various surfaces: at 95 K, buta-1,3-diene and but-1-ene are physisorbed on the different Pd-based single crystals. On Pt(111), buta-1,3-diene is π-bonded when but-1-ene is di-σ-bonded. At 300 K, buta-1-diene either dehydrogenates into butadiene on Pd(110) and Pd50Cu50(111) or very probably transforms into butylidyne on Pt(111) and on Pd(111) by analogy to ethene adsorbed on these (111) surfaces. Buta-1,3-diene leads to a di-σ mode on Pt(111) and to a di-π one on the different Pd surfaces. Moreover, the NEXAFS esperiments reveal that the π*1–π*2 splitting variations [2.0 eV on Pd(111), ca. 2.4 eV on Pd(110) and Pd50Cu50(111), cf. 2.7 eV on the condensed multilayer] agree with a decrease of the hydrocarbon–substrate interaction according to the sequence: Pd(111) > Pd(110) Pd50Cu50(111). The activity would therefore obey the reverse sequence in agreement with the reactivity results.

A toroidal grating monochromator (TGM) has been tested at the VUV ring of the NSLS at Brookhaven National Laboratory. The instrument combines three 6 m (entrance-to-exit-slit distance) and three 10 m gratings with 10 and 4° angles of incidence, respectively. The optics is designed for high resolution from 5 to 700 eV photon energy, e.g. 7, 25, 80 and 130 meV at 25, 70, 300 and 500 eV according to ray tracings for a grating illumination of 3 rad × 15 mrad (1.5 mrad × 3.75 mrad) for the 6 m (10 m) gratings. The usable photon energy range (limited by stray light) was found to extend up to 1300 eV. Photon fluxes of about 10 11 photons/s in a 1 eV window have been observed for the 10 m TGM. A resolution of better than 0.17 eV has been observed at the C(1s) level.

This paper combines some aspects of the theory of level splitting and of the theory of photoemission intensity and thus provides a unified framework for a quantitative interpretation of the valence band photoemission spectra of 3dN ions in complexes and/or solids. The approach to the position of the photoemission peaks lies on a simplified LCAO–MO model, namely, the Koide–Pryce model involving e2 terms. Two mechanisms are proposed for the intensity of the photopeaks : Both of them take configuration interaction into account but they differ in that one of them includes additional interference processes between the ejection of t2 and e photoelectrons and the other one does not. The formalism is applied to FeO, CoO, and NiO.

The authors present new experimental XPS spectra of 4f7/2 levels of tungsten in the W(110)-O system and a theoretical model in which the change of the binding energy of core levels of W atoms bound to O is due to a small charge transfer from these atoms towards oxygen. The same analysis is done for a Ta(110)-O system. Finally, using thermodynamical arguments, they link the displacements of core levels to the variation of the binding energy of O along the transition series and show that they always correspond to larger binding energy.

We have studied the actinide superconductor U${\mathrm{Be}}_{13}$ with resonant photoemission using synchrotron radiation $30l~h\ensuremath{\nu}l~120$ eV. In agreement with the anomalously high $\ensuremath{\gamma}$ value of 1.1 J/mole ${\mathrm{K}}^{2}$, we find a high density of $5f$ states at the Fermi level ${E}_{F}$. Uranium $6d$ electrons are not present at ${E}_{F}$ as can be derived from the zero intensity at ${E}_{F}$ in the off-resonance spectrum. The close resemblance of this off-resonance curve to a photoemission spectrum of pure Be suggests that the hybridization of U $5f$ electrons with Be $s,p$ electrons is small. Indeed, the U${\mathrm{Be}}_{13}$ photoemission curves look like a superposition of U and Be curves. By using photoemission results from U${\mathrm{O}}_{2}$ as a reference, we find that the valence-band emission contains about one $5f$ electron. The present results on U${\mathrm{Be}}_{13}$ are compared with those of Ce${\mathrm{Cu}}_{2}$${\mathrm{Si}}_{2}$, another member of the family of exotic superconductors.

The object of this paper is to provide a formalism for the interpretation of the core-level photoemission spectra of $3{d}^{N}$ ions embedded in a cubic environment. The formalism is first developed in the general case of the photoemission of a ${n}^{\ensuremath{'}}{l}^{\ensuremath{'}}$ electron from an inner shell of a $n{l}^{N}$ ion in arbitrary symmetry $G$. This general formalism may be thought of as a coherent combination of the theory of level splitting (for the determination of the position of the core photo-peaks) and of the theory of the photoemission intensity (for the determination of the intensity of the core photopeaks). The interactions taken into consideration here are the Coulomb, the spin-orbit, and the crystal-field interactions both for the photoemission initial Hamiltonian and the photoemission final Hamiltonian. General formulas for the matrix elements of the involved interactions are given for the initial configuration $n{l}^{N}$ and the final configuration ${n}^{\ensuremath{'}}{l}^{\ensuremath{'}4{l}^{\ensuremath{'}}+1}n{l}^{N}$ in a weak-field basis adapted to the group $G$. The determination of the photopeak position follows from the diagonalization of the final Hamiltonian within the entire ${n}^{\ensuremath{'}}{l}^{\ensuremath{'}4{l}^{\ensuremath{'}}+1}n{l}^{N}$ manifold. The determination of the photopeak intensity requires the knowledge of the ground-state eigenvector of the initial Hamiltonian and of (all) the eigenvectors of the final Hamiltonian. General formulas are given for the intensity of the transitions $n{l}^{N}\ensuremath{\rightarrow}{n}^{\ensuremath{'}}{l}^{\ensuremath{'}4{l}^{\ensuremath{'}}+1}n{l}^{N}$ in a weak-field basis adapted to the group $G$. Finally, the general formalism is particularized to the case of iron-group ions ($\mathrm{nl}\ensuremath{\equiv}3d$) in octahedral symmetry ($G\ensuremath{\equiv}O$). Only those particular points which are specific to the case of $3{d}^{N}$ ions in octahedral symmetry are examined. In particular, the ejection process may concern the shells ${n}^{\ensuremath{'}}{l}^{\ensuremath{'}}\ensuremath{\equiv}{n}^{\ensuremath{'}}p$ or ${n}^{\ensuremath{'}}{l}^{\ensuremath{'}}\ensuremath{\equiv}{n}^{\ensuremath{'}}s$.