PHOIBOS 150 NAP 1D-DLD

State of the art hemispherical energy analyzer with 1D-DLD detector for photoelectron spectroscopy measurements (XPS and UPS) in the pressure regime from UHV to near ambient pressure (NAP)

The PHOIBOS 150 NAP Analyzer is a true 180° hemispherical energy analyzer with 150 mm mean radius. It consists of a differentially pumped electrostatic pre-lens, with a three-stage differentially pumped PHOIBOS 150 analyzer. Thus, the design concept provides four separate pressure stages separated by apertures. The first pumping stage (pre-lens) is separated from the analytic chamber by a nozzle with a customizable opening at the tip with diameters between 0.3 mm and 1 mm. By using a turbopump on the pre-lens stage, a pressure difference of four orders of magnitude (compared to the analysis chamber) can be achieved.The first and second stages are separated by an aperture. An in-lens gate valve allows a high-vacuum seal between of the PHOIBOS 150 Analyzer and NAP pre-lens and enables venting of the analysis chamber and pre-lens without venting the energy analyzer.

For Imaging NAP-XPS the pre-lens can be equipped with the SPECS NAP-XPS Imaging Lens Module that supports two different operation modes, one optimized for lateral resolution and one for transmission. In the lateral resolving mode the acceptance angle can be freely adjusted between +/- 3° to +/- 8° giving an ultimate lateral resolution of better than 10 µm with an acceptance area of 0.6 mm in diameter.

KEY FEATURES

  • Wide Angle Pre-Lens with 44 ° Acceptance Angle
  • Near Ambient Working Pressures up to 100 mbar (depending on configuration)
  • Large pass energy range
  • Working range up to 3.5 keV (upgradeable to 7 keV with corresponding power supply and detector)
  • High energy and angular resolution
  • High spatial resolution with imaging lens module
  • Ultimate flexibility by switching between high transmission and high lateral resolution mode
  • Fast detectors with high dynamic range for fast real time data acquisition in snapshot mode
  • Pneumatic in-lens gate valve
  • 4 differential pumping stages
  • Full detector flexibility (MCD, 1D-DLD, 2D-DLD, 2D-CCD/-CMOS)

R&D100 in 2010
The PHOIBOS 150 NAP Analyzer won the R&D 100 award for the best 100 products developed in 2010.

MADE FOR THESE METHODS

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RELATED PRODUCTS

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APPLICATION NOTES

XPS of Ag and N2 at 25 mbar
This application note shows near ambient pressure (NAP) measurements performed with the NAP XPS System for the University of Norte Dame, Prof. Franklin Tao.
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Investigation of a Superabsorbent Polymer (SAP) with EnviroESCA
In this study we show how EnviroESCA can be used to analyze the surface of superabsorbent polymers under different environmental conditions. EnviroESCA’s ability to perform X-ray Photoelectron Spectroscopy (XPS) under ambient conditions shows its main advantage when being applied to insulating material that change their surface (chemistry) when they come in contact with different liquids and gases - in this case water. Specimens that tend to charge up under vacuum conditions can be measured with ease.
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XPS surface chemical analysis of aqueous solutions with EnviroESCA
In this study we present the capabilites of EnviroESCA to analyze the surface of various aqueous solutions under near ambient pressure conditions. Such investigations of aqueous solutions are of paramount importance due to the vast number of essential water based processes in nature and industry.
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XPS surface analysis of a human urolith with EnviroESCA
A single human urinary stone (urolith) was characterized using EnviroESCA. The result of surface chemical analysis of the as received samples is presented. Charge neutralization on this insulating material is accomplished by Environmental Charge Compensation.
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XPS surface analysis of human tooth samples with EnviroESCA
Human teeth from an adult and a baby were studied using EnviroESCA. The results of surface chemical analysis of the as-received human tissues samples are presented. Neutralization of the insulating bio-material is accomplished by Environmental Charge Compensation enabling X-ray Photoelectron Spectroscopy (XPS) on tissues as tooth or bone.
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XPS surface analysis of cuttlefish bone samples with EnviroESCA
Biological mineral samples from a cuttlefish (sepia) were studied using EnviroESCA. The results of surface chemical analysis of the native and ion implantation treated samples are presented. Neutralization of the insulating biomaterial is accomplished by Environmental Charge Compensation enabling X-ray Photoelectron Spectroscopy (XPS) on tissue samples.
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XPS surface analysis of V2O5 upon heating with EnviroESCA
This application note presents how EnviroESCA can be used to analyze samples during heating under near ambient pressure conditions using various gas atmospheres. Such investigations of surfaces at elevated temperatures and pressures are of paramount importance for catalysis in nature and industry.
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XPS surface chemical analysis of bacterial samples with EnviroESCA
This application note presents how EnviroESCA can be used to analyze bacterial samples under near ambient pressure conditions in various states of hydration using different levels of humidity. Such investigations of bacterial cell wall surfaces in their hydrated state are essential for studying biological interfaces at work.
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Near-ambient pressure XPS of hydrated Escherichia coli samples with EnviroESCA
This application note presents how EnviroESCA can be used to analyze E. coli biofilms on silicon under near ambient pressure conditions in various states of hydration. Such investigations of the outer bacterial cell surface in their hydrated state are essential for studying biological interfaces at work.
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Gas Cluster Ion Beam (GCIB) sputtering with EnviroESCA
This application note presents how the optional GCIB source at the EnviroESCA can be used to clean samples prior to XPS analysis to get reproducible analytical data and reliable quantification results. Moreover, Argon cluster Arn⁺ (n=500-5000) sputtering and depth profiling of (bio)organic samples is possible which cannot be done when using monoatomic Arn+ sputtering.
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XPS surface analysis of Italian hard cheese with EnviroESCA
This application note presents how EnviroESCA can be used to analyze the surface of food samples, e.g., Italian hard cheese. Due to the advanced vacuum system of EnviroESCA the surface analysis of Food samples even in the presence of fat and oils or volatiles is performed without problems.
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XPS surface analysis of printed paper samples with EnviroESCA
Results of the surface analysis of four paper samples obtained in EnviroESCA are presented. Neutralization of this insulating biopolymer is accomplished by Environmental Charge Compensation enabling X-ray Pho-toelectron Spectroscopy (XPS) on such important natural material with ease.
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XPS surface analysis of sesame seeds with EnviroESCA
Results of the surface analysis of untreated food samples, e.g., sesame seeds, measured with EnviroESCA are presented. High resolution and high quality spectra are recorded using Environmental Charge Compensation even for samples in bulk quantities.
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Investigation of Polymers and Plastics with EnviroESCA
This application note describes how EnviroESCA can be used to analyze the surface of polymers and bulk insulating material. EnviroESCAs ability to perform X-Ray Photoelectron Spectroscopy (XPS) at non vacuum conditions shows its main advantage when being applied to insulating material. Specimens that tend to charge up under vacuum conditions and need to be extensive charge compensated with expensive low energy electron and low energy ion sources can be measured with ease and without the problem of overcompensation.
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Real World Device Inspection Application with EnviroESCA
This application note introduces EnviroESCA as a tool for real world device inspection for microelectronics. A printed circuit board was taken directly from the sales packaging and was investigated with XPS. The measurements concentrate on the crucial parts like contact surfaces and soldering joints. EnviroESCA and near ambient pressure XPS (NAP-XPS) in quality control applications aims to optimize manufacturing processes and device quality in general.
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Investigation of Hydrogel Contact Lenses with EnviroESCA
In this application note we analyze the surface of water filled hydrogels with EnviroESCA, Here, contact lenses serve as an example for medical and biomaterials. The advantage of such investigations under non ultrahigh vacuum conditions is demonstrated and results from wet and dry samples are compared.
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XPS surface analysis of Zeolites with EnviroESCA
In this note we demonstrate how the surface of Clinoptilolite, a natural zeolite, can be analysed with EnviroESCA. It describes how the Environmental Charge Compensation can be used to compensate for charging of the sample surface to be able to measure X-ray Photoelectron Spectra with ease.
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XPS surface analysis of a leaf with EnviroESCA
This application note presents the application of EnviroESCA to the field of biology and surface spectroscopy of biological samples. X-ray Photoelectron Spectroscopy (XPS) measurements on different sites of a leaf will be discussed. It will be shown that XPS is able to detect residues of calcium chloride, being used as a fertilizer, on the leafs surface.
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EnviroESCA and NAP-XPS in the field of Cosmetic Science
This application note presents the application of EnviroESCA to the field of Cosmetic Sciences and Forensic Sciences. Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) measurements on human hair treated with different personal hair care products.
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EnviroESCA applications in Scientific Archaeology
In the present application note EnviroESCA is used for chemical Analysis in the field of Archaeometry. Besides the ability of Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) to analyze the surface composition of metallic and nonmetallic specimens, EnviroESCA allows for a nondestructive analysis of artifacts without special pretreatment procedures.
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XPS surface analysis of a coffee bean with EnviroESCA
The Analysis of food and natural products under environmental conditions is of great importance due to their daily use and direct interaction with humans during consumption. In this study we investigated a roated coffee bean. Charge compensation of this insulating natural product is accomplished by Environmental Charge Compensation enabling X-ray photoelectron spectroscopy on such biological material with ease.
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XPS surface analysis of an ionic liquid with EnviroESCA
This application note presents how EnviroESCA can be used to analyze the surface of ionic liquids in contact with gases under application relevant conditions in the near ambient pressure region.
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Corrosion study of a paper clip in vinegar with EnviroESCA
In this note we present (N)AP XPS results from the first comparative ex-situ and operando corrosion study on the reaction of commercial paper clips in concentrated vinegar solution containing 25% acetic acid.
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PUBLICATIONS

  1. (2018) In-Situ Photoeletron Spectroscopy

    Photoelectron spectroscopy is known for the chemical analysis of surfaces with element specificity. When a material is excited with ultraviolet or X-ray photons, photoelectrons and secondary photons are emitted which carry a kinetic energy and a momentum which reflect the electronic and molecular structure information of the material. The limited mean free path of electrons in matter requires ultrahigh vacuum (UHV) technology warrants that only electrons at or underneath the surface are detected by the instrument. The term surface has different perception and reception in different scientific communities. To the experimental condensed matter physicist, the surface is a two-dimensional system which forms as a result of the cleavage splitting of a three-dimensional body. To a theoretical condensed matter physicist a body may have infinite dimensions, when necessary.The two half bodies respond to such splitting with surface reconstruction, which makes that the crystallographic and electronic structure of a surface differs from the volume. In such case, electronic surface states may evolve which influence the interaction of the body with its environment, be it other solids or fluids. This encyclopedia article features in situ XPS experiments beyond the conventional UHV conditions.



    A. Braun
    Chemistry, Molecular Sciences and Chemical Engineering; Encyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry, pp. 264-279
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  2. (2018) Lab-based ambient pressure X-ray photoelectron spectroscopy from past to present

    Chemical interactions which occur at a heterogeneous interface between a gas and substrate are critical in many technological and natural processes. Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) is a powerful spectroscopy tool that is inherently surface sensitive, elemental and chemical specific, with the ability to probe sample surfaces in the presence of a gas phase. In this review, we discuss the evolution of lab-based AP-XPS instruments, from the first development by Siegbahn and coworkers up through modern day systems. A comprehensive overview is given of heterogeneous experiments investigated to date via lab-based AP-XPS along with the different instrumental metrics that affect the quality of sample probing. We conclude with a discussion of future directions for lab-based AP-XPS, highlighting the efficacy for this in-demand instrument to continue to expand in its ability to significantly advance our understanding of surface chemical processes under in situ conditions in a technologically multidisciplinary setting.



    C. Arble, M. Jia, J. T. Newberg
    Surface Science Reports, 72(2), pp. 37-57
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  3. (2018) Coverage-dependent oxidation and reduction of vanadium supported on anatase TiO2(101)

    Using a multi-technical approach, we studied the oxidation of anatase TiO2(1 0 1)-supported vanadium (V) clusters at room temperature. We found by ex situ XPS that the highest oxidation state is +4 at sub-monolayer coverage regardless of the O2 pressure, and STM studies revealed that the initial oxidation proceeds through oxygen-induced disintegration of V clusters into monomeric VO2 species. By contrast, for ∼2 monolayer V coverage, a partial oxidation to V5+ is achieved. By in situ APXPS measurements, we found that V can be maintained in the V5+ oxidation state irrespective of the coverage; however, in the sub-monolayer range, an O2 pressure of at least ∼1 × 10−5 mbar is needed. Our results suggest an enhanced reducibility of V in direct contact with the TiO2 support compared to V in the 2nd layer, which is in line with the observed optimum V2O5 loading in catalytic applications just slightly below a full monolayer.



    S. Koust, B. N. Reinecke, K. C. Adamsen, I. Beinik, K. Handrup, Z. Li, P. G. Moses, J. Schnadt, J. V. Lauritsen, S. Wendt
    Journal of Catalysis 360, pp. 118-126
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  4. (2017) Probing the effect of the Pt–Ni–Pt(111) bimetallic surface electronic structures on the ammonia decomposition reaction

    We report a detailed investigation of elementary catalytic decomposition of ammonia on the Pt–Ni–Pt(111) bimetallic surface using in situ near ambient pressure X-ray photoelectron spectroscopy. Under the near ambient pressure (0.6 mbar) reaction conditions, a different dehydrogenation pathway with a reduced activation energy barrier for recombinative nitrogen desorption on the Pt–Ni–Pt(111) bimetallic surface is observed. The unique surface catalytic activity is correlated with the downward shift of the Pt 5d band states induced by the Ni subsurface atoms via charge redistribution of the topmost Pt layer. Our results provide a practical understanding of the unique chemistry of bimetallic catalysts for facile ammonia decomposition under realistic reaction conditions.



    J.-Q. Zhong, X. Zhou, K. Yuan, C. A. Wright, A. Tadich, D. Qi, H. X. Li, K. Wu, G. Q. Xua, W. Chen
    Nanoscale 9, pp. 666-672
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  5. (2017) Interfacial charge distributions in carbon-supported palladium catalysts

    Controlling the charge transfer between a semiconducting catalyst carrier and the supported transition metal active phase represents an elite strategy for fine turning the electronic structure of the catalytic centers, hence their activity and selectivity. These phenomena have been theoretically and experimentally elucidated for oxide supports but remain poorly understood for carbons due to their complex nanoscale structure. Here, we combine advanced spectroscopy and microscopy on model Pd/C samples to decouple the electronic and surface chemistry effects on catalytic performance. Our investigations reveal trends between the charge distribution at the palladium–carbon interface and the metal’s selectivity for hydrogenation of multifunctional chemicals. These electronic effects are strong enough to affect the performance of large (~5 nm) Pd particles. Our results also demonstrate how simple thermal treatments can be used to tune the interfacial charge distribution, hereby providing a strategy to rationally design carbon-supported catalysts.



    R. G. Rao, R. Blume, T. W. Hansen, E. Fuentes, K. Dreyer, S. Moldovan, O. Ersen, D. D. Hibbitts, Y. J. Chabal, R. Schlögl, J.-P. Tessonnier
    Nature Communications, 8, Article number: 340
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  6. (2017) Experimental and Theoretical Investigation of the Restructuring Process Induced by CO at Near Ambient Pressure: Pt Nanoclusters on Graphene/Ir(111)

    The adsorption of CO on Pt nanoclusters grown in a regular array on a template provided by the graphene/Ir(111) Moiré was investigated by means of infrared-visible sum frequency generation vibronic spectroscopy, scanning tunneling microscopy, X-ray photoelectron spectroscopy from ultrahigh vacuum to near-ambient pressure, and ab initio simulations. Both terminally and bridge bonded CO species populate nonequivalent sites of the clusters, spanning from first to second-layer terraces to borders and edges, depending on the particle size and morphology and on the adsorption conditions. By combining experimental information and the results of the simulations, we observe a significant restructuring of the clusters. Additionally, above room temperature and at 0.1 mbar, Pt clusters catalyze the spillover of CO to the underlying graphene/Ir(111) interface.



    N. Podda, M. Corva, F. Mohamed, Z. Feng, C. Dri, F. Dvorák, V. Matolin, G. Comelli, M. Peressi, E. Vesselli
    ACS Nano 11 (1), pp. 1041–1053
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  7. (2017) The SPECIES beamline at the MAX IV Laboratory: a facility for soft X-ray RIXS and APXPS

    SPECIES is an undulator-based soft X-ray beamline that replaced the old I511 beamline at the MAX II storage ring. SPECIES is aimed at high-resolution ambient-pressure X-ray photoelectron spectroscopy (APXPS), near-edge X-ray absorption fine-structure (NEXAFS), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) experiments. The beamline has two branches that use a common elliptically polarizing undulator and monochromator. The beam is switched between the two branches by changing the focusing optics after the monochromator. Both branches have separate exit slits, refocusing optics and dedicated permanent endstations. This allows very fast switching between two types of experiments and offers a unique combination of the surface-sensitive XPS and bulk-sensitive RIXS techniques both in UHV and at elevated ambient-pressure conditions on a single beamline. Another unique property of the beamline is that it reaches energies down to approximately 27 eV, which is not obtainable on other current APXPS beamlines. This allows, for instance, valence band studies under ambient-pressure conditions. In this article the main properties and performance of the beamline are presented, together with selected showcase experiments performed on the new setup.



    S. Urpelainen, C. Såthe, W. Grizolli, M. Agåker, A. R. Head, M. Andersson, S.-W. Huang, B. N. Jensen, E. Wallén, H. Tarawneh, R. Sankari, R. Nyholm, M. Lindberg, P. Sjöblom, N. Johansson, B. N. Reinecke, M. A. Arman, L. R. Merte, J. Knudsen, J. Schnadt, J
    J. Synchrotron Rad. 24, pp. 344-353
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  8. (2017) Interfaces in heterogeneous catalytic reactions: Ambient pressure XPS as a tool to unravel surface chemistry

    In this article we provide a summary of the recent development of ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and its application to catalytic surface chemistry. The methodology as well as significant advantages and challenges associated with this novel technique are described. Details about specific examples of using AP-XPS to probe surface chemistry under working reaction conditions for a number of reactions are explained: CO oxidation, water-gas shift (WGS), CO2 hydrogenation, dry reforming of methane (DRM) and ethanol steam reforming (ESR). Finally, we discuss insights into the future development of the AP-XPS technique and its applications.



    R. M. Palomino, R. Hamlyn, Z. Liu, D. C. Grinter, I. Waluyo, J. A. Rodriguez, S. D. Senanayake
    Journal of Electron Spectroscopy and Related Phenomena 221, pp. 28-43
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  9. (2017) The offset droplet: a new methodology for studying the solid/water interface using x-ray photoelectron spectroscopy

    The routine study of the solid-water interface by XPS is potentially revolutionary as this development opens up whole new areas of study for photoelectron spectroscopy. To date this has been realised by only a few groups worldwide and current techniques have significant restrictions on the type of samples which can be studied. Here we present a novel and uniquely flexible approach to the problem. By introducing a thin capillary into the NAP-XPS, a small droplet can be injected onto the sample surface, offset from the analysis area by several mm. By careful control of the droplet size a water layer of controllable thickness can be established in the analysis area—continuous with the bulk droplet. We present results from the solid-water interface on a vacuum prepared TiO2(110) single crystal and demonstrate that the solid/liquid interface is addressable.



    S. G. Booth, A. M. Tripathi, I. Strashnov, R. A. W. Dryfe, A. S. Walton
    J. Phys.: Condens. Matter 29, 45
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  10. (2017) Reversible Bulk Oxidation of Ni Foil During Oscillatory Catalytic Oxidation of Propane: A Novel Type of Spatiotemporal Self-Organization

    A novel type of temporal and spatial self-organization in a heterogeneous catalytic reaction is described for the first time. Using in situ x-ray photoelectron spectroscopy, gas chromatography, and mass spectrometry, we show that, under certain conditions, self-sustained reaction-rate oscillations arise in the oxidation of propane over Ni foil because of reversible bulk oxidation of Ni to NiO, which can be observed even with the naked eye as chemical waves propagating over the catalyst surface.



    V. V. Kaichev, A. A. Saraev, A. Yu. Gladky, I. P. Prosvirin, R. Blume, D. Teschner, M. Hävecker, A. Knop-Gericke, R. Schlögl, V. I. Bukhtiyarov
    Phys. Rev. Lett. 119, 026001
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  11. (2017) Specific cation effects at aqueous solution−vapor interfaces: Surfactant-like behavior of Li+ revealed by experiments and simulations

    It is now well established by numerous experimental and computational studies that the adsorption propensities of inorganic anions conform to the Hofmeister series. The adsorption propensities of inorganic cations, such as the alkali metal cations, have received relatively little attention. Here we use a combination of liquid-jet X-ray photoelectron experiments and molecular dynamics simulations to investigate the behavior of K+ and Li+ ions near the interfaces of their aqueous solutions with halide ions. Both the experiments and the simulations show that Li+ adsorbs to the aqueous solution−vapor interface, while K+ does not. Thus, we provide experimental validation of the “surfactant-like” behavior of Li+ predicted by previous simulation studies. Furthermore, we use our simulations to trace the difference in the adsorption of K+ and Li+ ions to a difference in the resilience of their hydration shells.



    K. A. Perrine, K. M. Parry, A. C. Stern, M. H. C. Van Spyk, M. J. Makowski, J. A. Freites, B. Winter, D. J. Tobias, J. C. Hemminger
    PNAS 114 (51) 13363-13368
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  12. (2017) Surface Chemistry of Perovskite-Type Electrodes During High Temperature CO2 Electrolysis Investigated by Operando Photoelectron Spectroscopy

    Any substantial move of energy sources from fossil fuels to renewable resources requires large scale storage of excess energy, for example, via power to fuel processes. In this respect electrochemical reduction of CO2 may become very important, since it offers a method of sustainable CO production, which is a crucial prerequisite for synthesis of sustainable fuels. Carbon dioxide reduction in solid oxide electrolysis cells (SOECs) is particularly promising owing to the high operating temperature, which leads to both improved thermodynamics and fast kinetics. Additionally, compared to purely chemical CO formation on oxide catalysts, SOECs have the outstanding advantage that the catalytically active oxygen vacancies are continuously formed at the counter electrode, and move to the working electrode where they reactivate the oxide surface without the need of a preceding chemical (e.g., by H2) or thermal reduction step. In the present work, the surface chemistry of (La,Sr)FeO3−δ and (La,Sr)CrO3−δ based perovskite-type electrodes was studied during electrochemical CO2 reduction by means of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at SOEC operating temperatures. These measurements revealed the formation of a carbonate intermediate, which develops on the oxide surface only upon cathodic polarization (i.e., under sufficiently reducing conditions). The amount of this adsorbate increases with increasing oxygen vacancy concentration of the electrode material, thus suggesting vacant oxygen lattice sites as the predominant adsorption sites for carbon dioxide. The correlation of carbonate coverage and cathodic polarization indicates that an electron transfer is required to form the carbonate and thus to activate CO2 on the oxide surface. The results also suggest that acceptor doped oxides with high electron concentration and high oxygen vacancy concentration may be particularly suited for CO2 reduction. In contrast to water splitting, the CO2 electrolysis reaction was not significantly affected by metallic particles, which were exsolved from the perovskite electrodes upon cathodic polarization. Carbon formation on the electrode surface was only observed under very strong cathodic conditions, and the carbon could be easily removed by retracting the applied voltage without damaging the electrode, which is particularly promising from an application point of view.



    A. K. Opitz, A. Nenning, C. Rameshan, M. Kubicek, T. Götsch, R. Blume, M. Hävecker, A. Knop-Gericke, G. Rupprechter, B. Klötzer, J. Fleig
    ACS Appl. Mater. Interfaces 9 (41), pp. 35847–35860
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  13. (2017) CO adsorption on Pd(100) studied by multimodal ambient pressure X-ray photoelectron and infrared reflection absorption spectroscopies

    The adsorption of CO on Pd(100) was investigated using simultaneous ambient pressure X-ray photoelectron spectroscopy (APXPS) and infrared reflection absorption infrared spectroscopy (IRRAS). The measurements were performed as a function of CO partial pressures from ultra-high vacuum to 0.5 Torr. Total CO coverages estimated from the complementary APXPS and IRRAS measurements are in good agreement. A signal for atop CO, which is uncommon for Pd(100), was observed in the IRRAS data and was used to identify the C 1 s binding energy of this species. Discerning this binding configuration of CO on the Pd(100) surface at elevated pressures has significance for catalytic reactions involving CO, where bridging CO is often the only configuration considered. We also detail the combined APXPS/IRRAS instrumentation and discuss ways to improve these multimodal measurements, which should have wide applicability across many areas of surface and interface science.



    A. R. Head, O. Karslıoǧlu, T. Gerber, Y. Yu, L. Trotochaud, J. Raso, P. Kerger, H. Bluhm
    Surface Science 665, pp. 51-55
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  14. (2017) Operando chemistry of catalyst surfaces during catalysis

    Chemistry of a catalyst surface during catalysis is crucial for a fundamental understanding of mechanism of a catalytic reaction performed on the catalyst in the gas or liquid phase. Due to the pressure- or molecular density-dependent entropy contribution of gas or liquid phase of the reactants and the potential formation of a catalyst surface during catalysis different from that observed in an ex situ condition, the characterization of the surface of a catalyst under reaction conditions and during catalysis can be significant and even necessary for understanding the catalytic mechanism at a molecular level. Electron-based analytical techniques are challenging for studying catalyst nanoparticles in the gas or liquid phase although they are necessary techniques to employ. Instrumentation and further development of these electron-based techniques have now made in situ/operando studies of catalysts possible. New insights into the chemistry and structure of catalyst nanoparticles have been uncovered over the last decades. Herein, the origin of the differences between ex situ and in situ/operando studies of catalysts, and the technical challenges faced as well as the corresponding instrumentation and innovations utilized for characterizing catalysts under reaction conditions and during catalysis, are discussed. The restructuring of catalyst surfaces driven by the pressure of reactant(s) around a catalyst, restructuring in reactant(s) driven by reaction temperature and restructuring during catalysis are also reviewed herein. The remaining challenges and possible solutions are briefly discussed.



    J. Dou, Z. Sun, A. A. Opalade, N. Wang, W. Fu, F. Tao
    Chem. Soc. Rev. 46, pp. 2001-2027
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  15. (2017) In Situ Characterization of the Initial Effect of Water on Molecular Interactions at the Interface of Organic/Inorganic Hybrid Systems

    Probing initial interactions at the interface of hybrid systems under humid conditions has the potential to reveal the local chemical environment at solid/solid interfaces under real-world, technologically relevant conditions. Here, we show that ambient pressure X-ray photoelectron spectroscopy (APXPS) with a conventional X-ray source can be used to study the effects of water exposure on the interaction of a nanometer-thin polyacrylic acid (PAA) layer with a native aluminum oxide surface. The formation of a carboxylate ionic bond at the interface is characterized both with APXPS and in situ attenuated total reflectance Fourier transform infrared spectroscopy in the Kretschmann geometry (ATR-FTIR Kretschmann). When water is dosed in the APXPS chamber up to 5 Torr (~28% relative humidity), an increase in the amount of ionic bonds at the interface is observed. To confirm our APXPS interpretation, complementary ATR-FTIR Kretschmann experiments on a similar model system, which is exposed to an aqueous electrolyte, are conducted. These spectra demonstrate that water leads to an increased wet adhesion through increased ionic bond formation.



    S. Pletincx, L. Trotochaud, L.-L. Fockaert, J. M. C. Mol, A.R. Head, O. Karslıoğlu, H. Bluhm, H. Terryn, T. Hauffman
    Scientific Reports 7, Article number: 45123
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  16. (2016) CO Adsorption on Reconstructed Ir(100) Surfaces from UHV to mbar Pressure: A LEED, TPD, and PM-IRAS Study

    Clean and stable surface modifications of an iridium (100) single crystal, i.e., the (1 × 1) phase, the (5 × 1) reconstruction, and the oxygen-terminated (2 × 1)-O surface, were prepared and characterized by low energy electron diffraction (LEED), temperature-programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS) and polarization modulation IRAS (PM-IRAS). The adsorption of CO in UHV and at elevated (mbar) pressure/temperature was followed both ex situ and in situ on all three surface modifications, with a focus on mbar pressures of CO. The Ir(1 × 1) surface exhibited c(4 × 2)/c(2 × 2) and c(6 × 2) CO structures under low pressure conditions, and remained stable up to 100 mbar and 700 K. For the (2 × 1)-O reconstruction CO adsorption induced a structural change from (2 × 1)-O to (1 × 1), as confirmed by LEED, TPD, and IR. For Ir (2 × 1)-O TPD indicated that CO reacted with surface oxygen forming CO2. The (5 × 1) reconstruction featured a reversible and dynamic behavior upon CO adsorption, with a local lifting of the reconstruction to (1 × 1). After CO desorption, the (5 × 1) structure was restored. All three reconstructions exhibited CO adsorption with on-top geometry, as evidenced by IR. With increasing CO exposure the resonances shifted to higher wavenumber, due to adsorbate–adsorbate and adsorbate–substrate interactions. The largest wavenumber shift (from 2057 to 2100 cm–1) was observed for Ir(5 × 1) upon CO dosing from 1 L to 100 mbar.



    K. Anic, A.V. Bukhtiyarov, H. Li, C. Rameshan, G. Rupprechter
    J. Phys. Chem. C 120 (20), pp. 10838–10848
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  17. (2016) Atmospheric pressure X-ray photoelectron spectroscopy apparatus: Bridging the pressure gap

    One of the main goals in catalysis is the characterization of solid/gas interfaces in a reaction environment. The electronic structure and chemical composition of surfaces become heavily influenced by the surrounding environment. However, the lack of surface sensitive techniques that are able to monitor these modifications under high pressure conditions hinders the understanding of such processes. This limitation is known throughout the community as the “pressure gap.” We have developed a novel experimental setup that provides chemical information on a molecular level under atmospheric pressure and in presence of reactive gases and at elevated temperatures. This approach is based on separating the vacuum environment from the high-pressure environment by a silicon nitride grid—that contains an array of micrometer-sized holes—coated with a bilayer of graphene. Using this configuration, we have investigated the local electronic structure of catalysts by means of photoelectron spectroscopy and in presence of gases at 1 atm. The reaction products were monitored online by mass spectrometry and gas chromatography. The successful operation of this setup was demonstrated with three different examples: the oxidation/reduction reaction of iridium (noble metal) and copper (transition metal) nanoparticles and with the hydrogenation of propyne on Pd black catalyst (powder).



    J. J. Velasco-Vélez, V. Pfeifer, M. Hävecker, R. Wang, A. Centeno, A. Zurutuza, G. Algara-Siller, E. Stotz, K. Skorupska, D. Teschner, P. Kube, P. Braeuninger-Weimer, S. Hofmann, R. Schlögl, A. Knop-Gericke
    Review of Scientific Instruments 87, 053121
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  18. (2016) Are Au Nanoparticles on Oxygen-Free Supports Catalytically Active?

    Gold nanoparticles (Au NPs) on oxygen-free supports were examined using near ambient pressure X-ray photoelectron spectroscopy under CO oxidation conditions, and ex situ using scanning electron microscopy and transmission electron microscopy. Our observations demonstrate that Au NPs supported on carbon materials are inactive, regardless of the preparation method. Ozone (O3) treatment of carbon supports leads oxygen-functionalization of the supports. When subsequently exposed to a CO feed, CO is oxidized by the functionalized sites of the carbon support via a stoichiometric pathway. Microscopy reveals that the reaction with CO does not change the morphology of the Au NPs. In situ XPS reveals that the O3 treatment gives rise to additional Au 4f and O 1s peaks at binding energies of 85.25–85.6 and 529.4–530 eV, respectively, which are assigned to the presence of Au oxide. A surface oxide phase is formed during the activation of Au NPs supported on Au foil by O3 treatment. However, this phase decomposes in vacuum and the remaining low-coordinative atoms do not have sufficient catalytic properties to oxidize CO, so the size reduction of Au NPs and/or oxidation of Au NPs is not sufficient to activate Au.



    A. Y. Klyushin, R. Arrigo, Y. Youngmi, Z. Xie, M. Hävecker, A. V. Bukhtiyarov, I. P. Prosvirin, V. I. Bukhtiyarov, A. Knop-Gericke, R. Schlögl
    Topics in Catalysis 59 (5-7), pp. 469-477
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  19. (2016) Liquid-Jet X‑ray Photoelectron Spectra of TiO2 Nanoparticles in an Aqueous Electrolyte Solution

    Titania has attracted significant interest due to its broad catalytic applications, many of which involve titania nanoparticles in contact with aqueous electrolyte solutions. Understanding the titania nanoparticle/electrolyte interface is critical for the rational development of such systems. Here, we have employed liquid-jet ambient pressure X-ray photoelectron spectroscopy (AP-XPS) to investigate the solid/electrolyte interface of 20 nm diameter TiO2 nanoparticles in 0.1 M aqueous nitric acid solution. The Ti 2p line shape and absolute binding energy reflect a fully oxidized stoichiometric titania lattice. Further, by increasing the X-ray excitation energy, the difference in O 1s binding energies between that of liquid water (O 1sliq) and the titania lattice (O 1slat) oxygen was measured as a function of probe depth into the particles. The titania lattice, O 1slat, binding energy decreases by 250 meV when probing from the particle surface into the bulk. This is interpreted as downward band bending at the interface.



    M. J. Makowski, R. P. Galhenage, J. Langford, J. C. Hemminger
    J. Phys. Chem. 7 (9), pp. 1732–1735
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  20. (2016) The Origin of the Catalytic Activity of a Metal Hydride in CO2 Reduction

    Atomic hydrogen on the surface of a metal with high hydrogen solubility is of particular interest for the hydrogenation of carbon dioxide. In a mixture of hydrogen and carbon dioxide, methane was markedly formed on the metal hydride ZrCoHx in the course of the hydrogen desorption and not on the pristine intermetallic. The surface analysis was performed by means of time‐of‐flight secondary ion mass spectroscopy and near‐ambient pressure X‐ray photoelectron spectroscopy, for the in situ analysis. The aim was to elucidate the origin of the catalytic activity of the metal hydride. Since at the initial stage the dissociation of impinging hydrogen molecules is hindered by a high activation barrier of the oxidised surface, the atomic hydrogen flux from the metal hydride is crucial for the reduction of carbon dioxide and surface oxides at interfacial sites.



    S. Kato, S. K. Matam, P. Kerger, L. Bernard, C. Battaglia, D. Vogel, M. Rohwerder, A. Züttel
    Angew. Chem. Int. Ed. 55 (20), 6028-6032
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  21. (2016) Near Ambient Pressure X‑ray Photoelectron Spectroscopy Study of the Atomic Layer Deposition of TiO2 on RuO2(110)

    The atomic layer deposition (ALD) of TiO2 on a RuO2(110) surface from tetrakis(dimethylamido) titanium and water at 110 °C was investigated using near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at precursor pressures up to 0.1 mbar. In addition to the expected cyclic surface species, evidence for side reactions was found. Dimethylamine adsorbs on the surface during the TDMAT half-cycle, and a second species, likely methyl methylenimine, also forms. The removal of the amide ligand and the formation of an alkyammonium species during the water half-cycle were found to be pressure dependent. The O 1s, Ru 3d, and Ti 2p spectra show the formation of the Ru–O–Ti interface, and the binding energies are consistent with formation of TiO2 after one full ALD cycle. Dosing TDMAT on the RuO2(110) surface at room temperature promotes a multilayer formation that begins to desorb at 40 °C. The imine species is not seen until 60 °C. These insights into the ALD mechanism and precursor pressure dependence on reactivity highlight the utility of NAP-XPS in studying ALD processes and interface formation.



    A. R. Head, S. Chaudhary, G. Olivieri, F. Bournel, J. N. Andersen, F. Rochet, J.-J. Gallet, J. Schnadt
    J. Phys. Chem. C, 120 (1), pp. 243–251
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  22. (2016) Graphene Membranes for Atmospheric Pressure Photoelectron Spectroscopy

    Atmospheric pressure X-ray photoelectron spectroscopy (XPS) is demonstrated using single-layer graphene membranes as photoelectron-transparent barriers that sustain pressure differences in excess of 6 orders of magnitude. The graphene serves as a support for catalyst nanoparticles under atmospheric pressure reaction conditions (up to 1.5 bar), where XPS allows the oxidation state of Cu nanoparticles and gas phase species to be simultaneously probed. We thereby observe that the Cu2+ oxidation state is stable in O2 (1 bar) but is spontaneously reduced under vacuum. We further demonstrate the detection of various gas-phase species (Ar, CO, CO2, N2, O2) in the pressure range 10–1500 mbar including species with low photoionization cross sections (He, H2). Pressure-dependent changes in the apparent binding energies of gas-phase species are observed, attributable to changes in work function of the metal-coated grids supporting the graphene. We expect atmospheric pressure XPS based on this graphene membrane approach to be a valuable tool for studying nanoparticle catalysis.



    R. S. Weatherup, B. Eren, Y. Hao, H. Bluhm, M. B. Salmeron
    J. Phys. Chem. Lett. 7 (9), pp. 1622–1627
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  23. (2016) Is Steam an Oxidant or a Reductant for Nickel/Doped-Ceria Cermets?

    Nickel/doped‐ceria composites are promising electrocatalysts for solid‐oxide fuel and electrolysis cells. Very often steam is present in the feedstock of the cells, frequently mixed with other gases, such as hydrogen or CO2. An increase in the steam concentration in the feed mixture is considered accountable for the electrode oxidation and the deactivation of the device. However, direct experimental evidence of the steam interaction with nickel/doped‐ceria composites, with adequate surface specificity, are lacking. Herein we explore in situ the surface state of nickel/gadolinium‐doped ceria (NiGDC) under O2, H2, and H2O environments by using near‐ambient‐pressure X‐ray photoelectron and absorption spectroscopies. Changes in the surface oxidation state and composition of NiGDC in response to the ambient gas are observed. It is revealed that, in the mbar pressure regime and at intermediate temperature conditions (500–700 °C), steam acts as an oxidant for nickel but has a dual oxidant/reductant function for doped ceria.



    V. Papaefthimiou, D. K. Niakolas, F. Paloukis, T. Dintzer, S. Zafeiratos
    ChemPhysChem 18 (1), pp. 164-170
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  24. (2016) Ambient Pressure Photoemission Spectroscopy Reveals the Mechanism of Carbon Soot Oxidation in Ceria-Based Catalysts

    The Front Cover shows a representation of the ALBA synchrotron, where near ambient pressure photoelectron spectroscopy was performed to study the surface/subsurface of ceria and ceria‐zirconia catalysts for removing soot from combustion engines. In their Communication, L. Soler et al. identified two cooperative routes, one occurring at the ceria–soot interface with formation of O vacancies and CeIII, and another at the surface of soot mediated by superoxide species resulting from the reaction between O2 gas and O vacancies (drawing by Javier Sánchez Ríos, javier. sanchezrios.1978@ieee.org). More information can be found in the Communication by L. Soler et al. on page 2748 in Issue 17, 2016 (DOI: 10.1002/cctc.201600615).



    L. Soler, A. Casanovas, C. Escudero, V. Pérez-Dieste, E. Aneggi, A. Trovarelli, J. Llorca
    ChemCatChem 8 (17), pp. 2733-2733
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  25. (2016) Operando Near Ambient Pressure XPS (NAP-XPS) Study of the Pt Electrochemical Oxidation in H2O and H2O/O2 Ambients

    Oxides on the surface of Pt electrodes are largely responsible for the loss of their electrocatalytic activity in the oxygen reduction and oxygen evolution reactions. In this work we apply near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study in operando the electrooxidation of a nanoparticulated Pt electrode integrated in a membrane-electrode assembly of a high temperature proton-exchange membrane under water and water/oxygen ambient. Three types of surface oxides/hydroxides gradually develop on the Pt surface depending on the applied potential at +0.9, + 2.5, and +3.7 eV relative to the 4f peak of metal Pt and were attributed to the formation of adsorbed O/OH, PtO, and PtO2, respectively. The presence of O2 in the gas-phase results in the increase of the extent of surface oxidation, and in the growth of the contribution of the PtO2 oxide. Depth profiling studies, in conjunction with quantitative simulations, allowed us to propose a tentative mechanism of the Pt oxidation at high anodic polarization, consisting of adsorption of O/OH followed by nucleation of PtO/PtO2 oxides and their subsequent three-dimensional growth.



    V. A. Saveleva, V. Papaefthimiou, M. K. Daletou, W. H. Doh, C. Ulhaq-Bouillet, M. Diebold, S. Zafeiratos, E. R. Savinova
    J. Phys. Chem. C, 120 (29), pp. 15930–15940
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  26. (2016) Oxidation of Small Supported Platinum-based Nanoparticles under Near-Ambient Pressure Exposure to Oxygen

    The investigation of nanocatalysts under their working conditions of pressures and temperatures represents a real strategy toward a realistic understanding of their chemical reactivity and related issues. Additionally, the reduction of Pt load in the catalysts while maintaining their optimum performances is essential to large scale practical applications. Here, we show that small PtZn bimetallic nanoparticles (NPs) supported on the rutile and reduced TiO2(110)-(1 × 1) surface can be prepared by a two step consecutive deposition process where Pt was deposited first and followed by Zn. In situ synchrotron-based near ambient pressure photoemission spectroscopy experiments are used to monitor the evolution of the oxidation states and surface elemental composition of pure Pt and PtZn NPs under high exposure to O2 pressure. The formation of stable Pt surface oxide was evidenced for both pure and PtZn NPs. While a sizeable encapsulation of pure Pt NPs by TiOx was seen after annealing at 440 K under 1 mbar of O2, no such effect was noticed for PtZn NPs. The formation of a zinc oxide layer on PtZn NPs enhances the stability of the NPs and induces a partial reduction of the TiO2(110) surface. Spontaneous formation of a Pt–Zn alloy phase at room temperature was seen in PtZn NPs.



    A. Naitabdi, R. Fagiewicz, A. Boucly, G. Olivieri, F. Bournel, H. Tissot, Y. Xu, R. Benbalagh, M. G. Silly, F. Sirotti, J.-J. Gallet, F. Rochet
    Topics in Catalysis 59 (5-7), pp. 550-563
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  27. (2016) Oxidation of Ultrathin FeO(111) Grown on Pt(111): Spectroscopic Evidence for Hydroxylation

    Using high resolution and ambient pressure X-ray photoelectron spectroscopy we show that the catalytically active FeO2 trilayer films grown on Pt(111) are very active for water dissociation, in contrast to inert FeO(111) bilayer films. The FeO2 trilayer is so active for water dissociation that it becomes hydroxylated upon formation, regardless of the applied preparation method. FeO2 trilayers were grown by oxidation of FeO(111) bilayer films either with molecular oxygen in the mbar regime, or by NO2 and atomic oxygen exposures, respectively, in the ultrahigh vacuum regime. Because it was impossible to prepare clean FeO2 without any hydroxyls we propose that catalytically highly active FeO2 trilayer films are generally hydroxylated. In addition, we provide spectroscopic fingerprints both for Pt(111)-supported FeO(111) and FeO2 films that can serve as reference for future in situ studies.



    N. Johansson, L. R. Merte, E. Graånäs, S. Wendt, J. N. Andersen, J. Schnadt, J. Knudsen
    Topics in Catalysis 59 (5-7), pp. 506-515
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  28. (2016) Performance test of new near-ambient-pressure XPS at Korean Basic Science Institute and its application to CO oxidation study on Pt3Ti polycrystalline surface

    A performance test of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at Korean Basic Science Institute (KBSI) in Daejeon, Korea is carried out. The NAP-XPS at KBSI is equipped with SPECS PHOIBOS 150 analyzer and 2-dimensional-delay line detector, which provides improved detection efficiency with 1-dimensional chemical imaging mode. The in-situ gas-pressure cell is designed to operate at pressure up to 25 mbar with differential pumping scheme. A micro-focused AlKα X-ray source is utilized as photon excitation source. The NAP-XPS is composed of two separate chambers, e.g. a main preparation chamber and a measurement chamber, which hold a low energy electron diffraction, a high pressure cell, an ion sputter gun, a multi-cell E-beam evaporators, and a four-axis manipulator with heating and cooling capability. As a test run of NAP-XPS, a CO oxidation experiment is carried out on Pt3Ti polycrystalline surface. During the active phase of CO oxidation, a clear formation of Ti oxide is found on surface, revealing the intriguing role of surface metal oxide in surface chemical reaction.



    C. Jeong, H. Yun, H. Lee, S. Muller, J. Lee, B. S. Mun
    Current Applied Physics 16 (1), pp. 73-78
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  29. (2016) Ambient pressure photoelectron spectroscopy: Practical considerations and experimental frontiers

    Over the past several decades, ambient pressure x-ray photoelectron spectroscopy (APXPS) has emerged as a powerful technique for in situ and operando investigations of chemical reactions under relevant ambient atmospheres far from ultra-high vacuum conditions. This review focuses on exemplary cases of APXPS experiments, giving special consideration to experimental techniques, challenges, and limitations specific to distinct condensed matter interfaces. We discuss APXPS experiments on solid/vapor interfaces, including the special case of 2D films of graphene and hexagonal boron nitride on metal substrates with intercalated gas molecules, liquid/vapor interfaces, and liquid/solid interfaces, which are a relatively new class of interfaces being probed by APXPS. We also provide a critical evaluation of the persistent limitations and challenges of APXPS, as well as the current experimental frontiers.



    L. Trotochaud, A. R. Head, O. Karslıoğlu, L. Kyhl, H. Bluhm
    J. Phys.: Condens. Matter 29 (5)
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  30. (2015) In situ investigation of dissociation and migration phenomena at the Pt/electrolyte interface of an electrochemical cell

    The development of efficient energy conversion systems requires precise engineering of electrochemical interfaces and thus asks for in situ techniques to probe the structure and the composition of the dynamic electrode/electrolyte interfacial region. This work demonstrates the potential of the near ambient pressure X-ray photoelectron spectroscopy (NAPXPS) for in situ studies of processes occurring at the interface between a metal electrode and a liquid electrolyte. By using a model membrane-electrode assembly of a high temperature phosphoric acid-imbibed proton exchange membrane fuel cell, and combining NAPXPS measurements with the density functional theory, it was possible to monitor such fundamental processes as dissociation and migration of the phosphoric acid within a nanostructured Pt electrode under polarization.



    Y. T. Law, S. Zafeiratos, S. G. Neophytides, A. Orfanidi, D. Costa, T. Dintzer, R. Arrigo, A. Knop-Gericke, R. Schlögl, E. R. Savinova
    Chem. Sci. 6 (10) , pp. 5635-5642
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  31. (2015) Understanding complete oxidation of methane on spinel oxides at a molecular level

    It is crucial to develop a catalyst made of earth-abundant elements highly active for a complete oxidation of methane at a relatively low temperature. NiCo2O4 consisting of earth-abundant elements which can completely oxidize methane in the temperature range of 350–550 °C. Being a cost-effective catalyst, NiCo2O4 exhibits activity higher than precious-metal-based catalysts. Here we report that the higher catalytic activity at the relatively low temperature results from the integration of nickel cations, cobalt cations and surface lattice oxygen atoms/oxygen vacancies at the atomic scale. In situ studies of complete oxidation of methane on NiCo2O4 and theoretical simulations show that methane dissociates to methyl on nickel cations and then couple with surface lattice oxygen atoms to form –CH3O with a following dehydrogenation to −CH2O; a following oxidative dehydrogenation forms CHO; CHO is transformed to product molecules through two different sub-pathways including dehydrogenation of OCHO and CO oxidation.



    F. F. Tao, J.-J. Shan, L. Nguyen, Z. Wang, S. Zhang, L. Zhang, Z. Wu, W. Huang, S. Zeng, P. Hu
    Nature Communications 6, Article number: 7798
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  32. (2015) Aqueous solution/metal interfaces investigated in operando by photoelectron spectroscopy

    We describe a new in operando approach for the investigation of heterogeneous processes at solid/liquid interfaces with elemental and chemical specificity which combines the preparation of thin liquid films using the meniscus method with standing wave ambient pressure X-ray photoelectron spectroscopy [Nemšák et al., Nat. Commun., 5, 5441 (2014)]. This technique provides information about the chemical composition across liquid/solid interfaces with sub-nanometer depth resolution and under realistic conditions of solution composition and concentration, pH, as well as electrical bias. In this article, we discuss the basics of the technique and present the first results of measurements on KOH/Ni interfaces.



    O. Karslıoğlu, S. Nemšák, I. Zegkinoglou, A. Shavorskiy, M. Hartl, F. Salmassi, E. M. Gullikson, M. L. Ng, Ch. Rameshan, B. Rude, D. Bianculli, A. A. Cordones, S. Axnanda, E. J. Crumlin, P. N. Ross, C. M. Schneider, Z. Hussain, Z. Liu, C. S. Fadley, H. Bl
    Faraday Discuss. 180, pp. 35-53
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  33. (2015) Catalysis on singly dispersed bimetallic sites

    A catalytic site typically consists of one or more atoms of a catalyst surface that arrange into a configuration offering a specific electronic structure for adsorbing or dissociating reactant molecules. The catalytic activity of adjacent bimetallic sites of metallic nanoparticles has been studied previously. An isolated bimetallic site supported on a non-metallic surface could exhibit a distinctly different catalytic performance owing to the cationic state of the singly dispersed bimetallic site and the minimized choices of binding configurations of a reactant molecule compared with continuously packed bimetallic sites. Here we report that isolated Rh1Co3 bimetallic sites exhibit a distinctly different catalytic performance in reduction of nitric oxide with carbon monoxide at low temperature, resulting from strong adsorption of two nitric oxide molecules and a nitrous oxide intermediate on Rh1Co3 sites and following a low-barrier pathway dissociation to dinitrogen and an oxygen atom. This observation suggests a method to develop catalysts with high selectivity.



    S. Zhang, L. Nguyen, J.-X. Liang, J. Shan, J. Liu, A.I. Frenkel, A. Patlolla, W. Huang, J. Li, F. Tao
    Nature Communications 6, Article number: 7938
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  34. (2015) Synthesis and Structural Evolution of Nickel–Cobalt Nanoparticles Under H2 and CO2

    Bimetallic nanoparticle (NP) catalysts are interesting for the development of selective catalysts in reactions such as the reduction of CO2 by H2 to form hydrocarbons. Here the synthesis of Ni–Co NPs is studied, and the morphological and structural changes resulting from their activation (via oxidation/reduction cycles), and from their operation under reaction conditions, are presented. Using ambient‐pressure X‐ray photoelectron spectroscopy, X‐ray absorption spectroscopy, and transmission electron microscopy, it is found that the initial core–shell structure evolves to form a surface alloy due to nickel migration from the core. Interestingly, the core consists of a Ni‐rich single crystal and a void with sharp interfaces. Residual phosphorous species, coming from the ligands used for synthesis, are found initially concentrated in the NP core, which later diffuse to the surface.



    S. Carenco, C.‐H. Wu, A. Shavorskiy, S. Alayoglu, G. A. Somorjai, H. Bluhm, M. Salmeron
    Small 11 (25), pp. 3045-3053
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  35. (2015) The Electronic Structure of Saturated NaCl and NaI Solutions in Contact with a Gold Substrate

    The near ambient pressure X-ray photoelectron spectroscopy set up installed recently at SOLEIL synchrotron facility is used to study the electronic structure of NaCl and NaI saturated solutions formed on a gold substrate. The binding energies of the solution constituents are measured with respect to the Fermi level of the gold substrate. The C1s binding energy of the aliphatic contaminant floating at the surface of the solution is an evidence that the Fermi level in the metal and in the solution are aligned. The use of the Fermi level common energy reference is an added value with respect to previous works realized with micro-jets that were calibrated in energy with respect to vacuum level. We observe that the water valence molecular levels binding energies, and hence the Fermi positioning in the gap of the liquid, the Na+ 2s binding energy and even the work function are independent of the nature of the anions. The secondary electron energy distribution curves show that the work functions of the two solutions are equal within experimental uncertainty. We discuss this point considering the different ion distributions at the surface (related to the different size and polarizability of the anions), and the possible contribution of carbon contaminants. We compare the WF values extracted from the secondary electron edges to alternative measurements using the binding energy of the gas phase O1s or 1b1 spectra (referenced to the gold Fermi level). The ionization energies (referenced to the vacuum level), that we obtain by adding the work function to the measured binding energies, are in good accord with previously published works using micro-jets, obtained, however, at much lower solute concentration. Finally we discuss the origin of the Fermi level pinning in the liquid band gap and consider the possibility that the H+/H2 redox level is aligned with the metal Fermi level.



    H. Tissot, J.-J. Gallet, F. Bournel, G. Olivieri, M. G. Silly, F. Sirotti, A. Boucly, F. Rochet
    Topics in Catalysis 59 (5-7), pp. 605-620
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  36. (2015) A Comparative Ambient Pressure X-ray Photoelectron and Absorption Spectroscopy Study of Various Cobalt-Based Catalysts in Reactive Atmospheres

    The oxidation state of cobalt in various forms (single crystal, nanopowder, deposited on CeO2 and ZnO supports) was investigated in situ under O2, H2 and ethanol steam reforming (ESR) conditions (C2H6O:H2O = 1:3) by using ambient pressure X-ray photoelectron and absorption spectroscopies. In O2 atmosphere single crystalline, nanopowder and CeO2-supported cobalt is readily oxidized into a spinel Co3O4 phase, while over the ZnO a mixed Zn1−xCoxO oxide is formed. In H2 and ESR atmospheres, Co3O4 oxide reduces to the metallic state, with an evident effect of the gas atmosphere and the sample type in this process. On the other hand the Zn1−xCoxO oxide proved to be extremely stable in reductive conditions. Finally, under the ESR atmosphere the amount of carbon deposition and the type of the adsorbed oxygen species considerably varies between supported and single crystalline/nanopowder cobalt catalysts.



    S. Turczyniak, W. Luo, V. Papaefthimiou, N. S. Ramgir, M. Haevecker, A. Machocki, S. Zafeiratos
    Topics in Catalysis 59 (5-7), pp. 532-542
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  37. (2014) Synchrotron-based Ambient Pressure X-ray Photoelectron Spectroscopy

    Solid/vapor and liquid/vapor interfaces govern many processes in the environment and atmosphere, energy generation, and electrochemical devices as well as heterogeneous catalysis. Examples include catalytic converters in automobiles , solid oxide fuel cells, cloud droplet nucleation on atmospheric aerosol particles, as well as the interaction of trace gases with polar snow packs. A fundamental understanding of the molecular processes at these interfaces requires experimental methods that allow the investigation of samples under as close to operating conditions as possible. This kind of investigation has become increasingly important over the last few decades, leading to the development of a number of surface-sensitive, in-situ spectroscopies and microscopies, including infrared spectroscopy (IR); vibrational sum-frequency generation (VSFG); X-ray emission spectroscopy (XES); surface X-ray diffraction (SXRD); scanning force microscopy (SFM) in both contact and non-contact modes; scanning tunneling microscopy (STM); as well as transmission electron microscopy and scanning electron microscopy.



    A. Shavorskiy, O. Karslioglu, I. Zegkinoglou, H. Bluhm
    Synchrotron Radiation News 27 (2), pp. 14-23
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  38. (2014) Influence of the support on surface rearrangements of bimetallic nanoparticles in real catalysts

    Catalysts used for heterogeneous processes are usually composed of metal nanoparticles dispersed over a high–surface-area support. In recent years, near-ambient pressure techniques have allowed catalyst characterization under operating conditions, overcoming the pressure gap effect. However, the use of model systems may not truly represent the changes that occur in real catalysts (the so-called material gap effect). Supports can play an important role in the catalytic process by providing new active sites and may strongly affect both the physical and chemical properties of metal nanoparticles. We used near-ambient pressure x-ray photoelectron spectroscopy to show that the surface rearrangement of bimetallic (rhodium-palladium) nanoparticles under working conditions for ethanol steam reforming with real catalysts is strongly influenced by the presence of a reducible ceria support.



    N. J. Divins, I. Angurell, C. Escudero, V. Pérez-Dieste, J. Llorca
    Science 346 (6209), pp. 620-623
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  39. (2014) Sub-nanosecond time-resolved ambient-pressure X-ray photoelectron spectroscopy setup for pulsed and constant wave X-ray light sources

    An apparatus for sub-nanosecond time-resolved ambient-pressure X-ray photoelectron spectroscopy studies with pulsed and constant wave X-ray light sources is presented. A differentially pumped hemispherical electron analyzer is equipped with a delay-line detector that simultaneously records the position and arrival time of every single electron at the exit aperture of the hemisphere with ∼0.1 mm spatial resolution and ∼150 ps temporal accuracy. The kinetic energies of the photoelectrons are encoded in the hit positions along the dispersive axis of the two-dimensional detector. Pump-probe time-delays are provided by the electron arrival times relative to the pump pulse timing. An average time-resolution of (780 ± 20) ps (FWHM) is demonstrated for a hemisphere pass energy Ep = 150 eV and an electron kinetic energy range KE = 503–508 eV. The time-resolution of the setup is limited by the electron time-of-flight (TOF) spread related to the electron trajectory distribution within the analyzer hemisphere and within the electrostatic lens system that images the interaction volume onto the hemisphere entrance slit. The TOF spread for electrons with KE = 430 eV varies between ∼9 ns at a pass energy of 50 eV and ∼1 ns at pass energies between 200 eV and 400 eV. The correlation between the retarding ratio and the TOF spread is evaluated by means of both analytical descriptions of the electron trajectories within the analyzer hemisphere and computer simulations of the entire trajectories including the electrostatic lens system. In agreement with previous studies, we find that the by far dominant contribution to the TOF spread is acquired within the hemisphere. However, both experiment and computer simulations show that the lens system indirectly affects the time resolution of the setup to a significant extent by inducing a strong dependence of the angular spread of electron trajectories entering the hemisphere on the retarding ratio. The scaling of the angular spread with the retarding ratio can be well approximated by applying Liouville's theorem of constant emittance to the electron trajectories inside the lens system. The performance of the setup is demonstrated by characterizing the laser fluence-dependent transient surface photovoltage response of a laser-excited Si(100) sample.



    A. Shavorskiy, S. Neppl, D.S. Slaughter, J. P. Cryan, K. R. Siefermann, F. Weise, M.-F. Lin, C. Bacellar, M. P. Ziemkiewicz, I. Zegkinoglou, M. W. Fraund, C. Khurmi, M. P. Hertlein, T. W. Wright, N. Huse, R. W. Schoenlein, T. Tyliszczak, G. Coslovich, J.
    Review of Scientific Instruments 85, 093102
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  40. (2013) Investigation of solid/vapor interfaces using ambient pressure X-ray photoelectron spectroscopy

    Heterogeneous chemical reactions at vapor/solid interfaces play an important role in many processes in the environment and technology. Ambient pressure X-ray photoelectron spectroscopy (APXPS) is a valuable tool to investigate the elemental composition and chemical specificity of surfaces and adsorbates on the molecular scale at pressures of up to 130 mbar. In this review we summarize the historical development of APXPS since its introduction over forty years ago, discuss different approaches to minimize scattering of electrons by gas molecules, and give a comprehensive overview about the experimental systems (vapor/solid interfaces) that have been studied so far. We also present several examples for the application of APXPS to environmental science, heterogeneous catalysis, and electrochemistry.



    D. E. Starr, Z. Liu, M. Hävecker, A. Knop-Gerickec, H. Bluhm
    Chem. Soc. Rev. 42, pp. 5833-5857
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  41. (2013) Physics and chemistry of material surfaces under ambient conditions of gases and liquids: What’s new?

    The atoms at the surfaces of materials represent the frontier separating the bulk from the surrounding medium. Over the last decades, scientists have intensely studied the structure and properties of surfaces with the goal of understanding and improving the electronic and chemical properties of materials. The surface–medium interaction determines wetting, friction, chemical, biological, and electronic properties. The activity of catalysts, phenomena occurring in water droplets and particles in the atmosphere, and the electronic properties of semiconductor devices are direct consequences of surface-environment interactions. While the need to pursue studies in the normal environment that surrounds a material has always been recognized, the techniques used in the past have only partially fulfilled this need, as most of them work best under high vacuum conditions. My research over the last 10 years has focused on discovering the structure of a surface and its dynamics in real life—in everyday environments. This required the development of new techniques and methods. I present some of the new tools developed in my laboratory and new properties that were discovered by their application in the areas of environmental science, surface chemistry, and catalysis.



    M. Salmeron
    Surface-enhanced Raman spectroscopy: Substrates and materials 38 (8), pp. 650-657
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  42. (2012) The new ambient-pressure X-ray photoelectron spectroscopy instrument at MAX-lab

    The new instrument for near-ambient-pressure X-ray photoelectron spectroscopy which has been installed at the MAX II ring of the Swedish synchrotron radiation facility MAX IV Laboratory in Lund is presented. The new instrument, which is based on a SPECS PHOIBOS 150 NAP analyser, is the first to feature the use of retractable and exchangeable high-pressure cells. This implies that clean vacuum conditions are retained in the instrument's analysis chamber and that it is possible to swiftly change between near-ambient and ultrahigh-vacuum conditions. In this way the instrument implements a direct link between ultrahigh-vacuum and in situ studies, and the entire pressure range from ultrahigh-vacuum to near-ambient conditions is available to the user. Measurements at pressures up to 10-5 mbar are carried out in the ultrahigh-vacuum analysis chamber, while measurements at higher pressures are performed in the high-pressure cell. The installation of a mass spectrometer on the exhaust line of the reaction cell offers the users the additional dimension of simultaneous reaction data monitoring. Moreover, the chosen design approach allows the use of dedicated cells for different sample environments, rendering the Swedish ambient-pressure X-ray photoelectron spectroscopy instrument a highly versatile and flexible tool.



    J. Schnadt, J. Knudsen, J. N. Andersen, H. Siegbahn, A. Pietzsch, F. Hennies, N. Johansson, N. Mårtensson, G. Öhrwall, S. Bahr, S. Mähl, O. Schaff
    J. Synchrotron Rad. 19, pp. 701-704
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  43. (2012) Operando Studies of Catalyst Surfaces during Catalysis and under Reaction Conditions: Ambient Pressure X-Ray Photoelectron Spectroscopy with a Flow-Cell Reactor

    We present the development and performance of a new, reactor‐like, in‐house ambient pressure X‐ray photoelectron spectrometer (AP‐XPS) using Al Kα, which can study material surfaces, particularly surfaces of catalysts during catalysis and under reaction conditions. This ambient pressure X‐ray photoelectron spectroscopy technique uses an affordable bench‐top X‐ray source, monochromated Al Kα, making it available for research groups on any campus. A unique feature of this in‐house AP‐XPS is the integration of a micro ambient pressure reaction cell working in either flowing or batch mode into a monochromatic Al Kα source and an ambient pressure energy analyzer. This integration allows XPS studying surfaces of materials while they functionalize in a flowing gaseous environment. Another feature is the integration of characterization of surfaces of catalysts into simultaneous measurements of catalytic performance by using on‐line, quadrupole mass spectrometry and gas chromatography. Performance tests of this in‐house AP‐XPS have demonstrated that it can study material surfaces at temperatures up to 500–550 °C in a gaseous environment with pressures up to 25–50 Torr. This design has successfully brought the synchrotron‐based AP‐XPS technique to research groups on campuses.



    F. Tao
    ChemCatChem 4 (5), pp. 583-590
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Article No.
 
DN40CF 4-fold SMB Feedthrough for DLD

Spare electrical feedthrough for all DLD detectors. Connection flange for the ACU unit

2100011768
Cu gasket for PHOIBOS 150

PHOIBOS 150 analyzer main flange gasket for Releases R5, R6, R7

2074050088
Nozzle 0,3 mm, double coated

Nozzle 0,3 mm for 7 kV PHOIBOS 150 Backfilling Pre-Lens

2055020988
Nozzle 1,0 mm, double coated

Nozzle 1,0 mm for 7 kV PHOIBOS 150 Backfilling Pre-Lens

2055022579
Rotary feedthrough for IRIS

Replacement feedthrough for PHOIBOS Release R5 & R6 iris mechanism

2060001175
Spindle with Spur and Bevel Gear for Iris

Replacement spindle for PHOIBOS Release R5 & R6 iris mechanism

2055021656
Tubus 3 with Iris

Replacement iris mechanism for PHOIBOS Release R5 & R6

2079150291