60 results on '"Baran Eren"'
Search Results
2. Electrochemically controlled solid liquid interfaces probed with lab-based X-ray photoelectron spectroscopy
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Bat-Or Shalom, Miguel A. Andrés, Youngseok Yu, Ashley R. Head, and Baran Eren
- Subjects
In-situ spectroscopy ,Redox ,Copper ,Solid–liquid interfaces ,APXPS ,Graphene ,Industrial electrochemistry ,TP250-261 ,Chemistry ,QD1-999 - Abstract
A micro-electrochemical cell is sealed with 2–5 layers of graphene to monitor the changing oxidation state of Cu nanoparticles (NPs) with X-ray photoelectron spectroscopy (XPS) in a mildly alkaline aqueous solution under electrochemical control. The main role of graphene is to ensure an abrupt change between the liquid and vacuum environments, where the latter is required for conducting XPS experiments. Decent transparency to the generated photoelectrons with a kinetic energy of few hundred eV is another requirement that graphene fulfils for performing such experiments. Graphene also acts as an electrically conducting support material for Cu NPs, ensuring that a bias can be applied to them. The proof-of-concept measurements presented in this work show that relatively lower flux X-ray sources, such as those with Al-Kα emission that are commonly used in laboratories, are sufficient for probing the solid–liquid interfaces with this approach.
- Published
- 2022
- Full Text
- View/download PDF
3. Pure hydrogen low-temperature plasma exposure of HOPG and graphene: Graphane formation?
- Author
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Baran Eren, Dorothée Hug, Laurent Marot, Rémy Pawlak, Marcin Kisiel, Roland Steiner, Dominik M. Zumbühl, and Ernst Meyer
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graphane ,HOPG ,hydrogenation ,plasma ,Technology ,Chemical technology ,TP1-1185 ,Science ,Physics ,QC1-999 - Abstract
Single- and multilayer graphene and highly ordered pyrolytic graphite (HOPG) were exposed to a pure hydrogen low-temperature plasma (LTP). Characterizations include various experimental techniques such as photoelectron spectroscopy, Raman spectroscopy and scanning probe microscopy. Our photoemission measurement shows that hydrogen LTP exposed HOPG has a diamond-like valence-band structure, which suggests double-sided hydrogenation. With the scanning tunneling microscopy technique, various atomic-scale charge-density patterns were observed, which may be associated with different C–H conformers. Hydrogen-LTP-exposed graphene on SiO2 has a Raman spectrum in which the D peak to G peak ratio is over 4, associated with hydrogenation on both sides. A very low defect density was observed in the scanning probe microscopy measurements, which enables a reverse transformation to graphene. Hydrogen-LTP-exposed HOPG possesses a high thermal stability, and therefore, this transformation requires annealing at over 1000 °C.
- Published
- 2012
- Full Text
- View/download PDF
4. Ambient Pressure Spectroscopy in Complex Chemical Environments
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Ashley R. Head, Slavomír Nemšák, Baran Eren, David E. Starr, Ashley R. Head, Clemens Richter, Rémi Dupuy, Hendrik Bluhm, Yifan Ye, Zhi Liu, Juan J. Velasco-Vélez, Verena Pramhaas, Günther Rupprechter, Shahar Dery, Elad Gross, Elizabeth S. Jones, Jack E. N. Swallow, Robert S. Weatherup, Andrey Shavor and Ashley R. Head, Slavomír Nemšák, Baran Eren, David E. Starr, Ashley R. Head, Clemens Richter, Rémi Dupuy, Hendrik Bluhm, Yifan Ye, Zhi Liu, Juan J. Velasco-Vélez, Verena Pramhaas, Günther Rupprechter, Shahar Dery, Elad Gross, Elizabeth S. Jones, Jack E. N. Swallow, Robert S. Weatherup, Andrey Shavor
- Published
- 2021
5. Hydrogen Exchange through Hydrogen Bonding between Methanol and Water in the Adsorbed State on Cu(111)
- Author
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Roey Ben David, Adva Ben Yaacov, and Baran Eren
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General Materials Science ,Physical and Theoretical Chemistry - Published
- 2023
6. Revealing the role of CO during CO2 hydrogenation on Cu surfaces with in situ soft X-ray spectroscopy
- Author
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Jack E. N. Swallow, Elizabeth S. Jones, Ashley R. Head, Joshua S. Gibson, Roey Ben David, Michael W. Fraser, Matthijs A. van Spronsen, Shaojun Xu, Georg Held, Baran Eren, and Robert S. Weatherup
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Oxygen ,Colloid and Surface Chemistry ,Catalysts ,Alcohols ,Mixtures ,General Chemistry ,Biochemistry ,Catalysis ,Dissociation - Abstract
The reactions of H2, CO2, and CO gas mixtures on the surface of Cu at 200 °C, relevant for industrial methanol synthesis, are investigated using a combination of ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and atmospheric-pressure near edge X-ray absorption fine structure (AtmP-NEXAFS) spectroscopy bridging pressures from 0.1 mbar to 1 bar. We find that the order of gas dosing can critically affect the catalyst chemical state, with the Cu catalyst maintained in a metallic state when H2 is introduced prior to the addition of CO2. Only on increasing the CO2 partial pressure is CuO formation observed that coexists with metallic Cu. When only CO2 is present, the surface oxidizes to Cu2O and CuO, and the subsequent addition of H2 partially reduces the surface to Cu2O without recovering metallic Cu, consistent with a high kinetic barrier to H2 dissociation on Cu2O. The addition of CO to the gas mixture is found to play a key role in removing adsorbed oxygen that otherwise passivates the Cu surface, making metallic Cu surface sites available for CO2 activation and subsequent conversion to CH3OH. These findings are corroborated by mass spectrometry measurements, which show increased H2O formation when H2 is dosed before rather than after CO2. The importance of maintaining metallic Cu sites during the methanol synthesis reaction is thereby highlighted, with the inclusion of CO in the gas feed helping to achieve this even in the absence of ZnO as the catalyst support.
- Published
- 2023
7. Water Vapor and Alcohol Vapor Induced Healing of the Nanostructured KBr Surface
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Santanu Parida, Jesús S. Lacasa, and Baran Eren
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General Energy ,Physical and Theoretical Chemistry ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
Using atomic force microscopy in the pressure range of 10
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- 2022
8. Methanol Decomposition on Copper Surfaces under Ambient Conditions: Mechanism, Surface Kinetics, and Structure Sensitivity
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Roey Ben David, Adva Ben Yaacov, Ashley R. Head, and Baran Eren
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General Chemistry ,Catalysis - Published
- 2022
9. Identification of Adsorbed Species and Surface Chemical State on Ag(111) in the Presence of Ethylene and Oxygen Studied with Infrared and X-ray Spectroscopies
- Author
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Roey Ben David, Baran Eren, Adva Ben Yaacov, David C. Grinter, and Georg Held
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Chemistry ,Ag(111) ,Inorganic chemistry ,Physical and theoretical chemistry ,QD450-801 ,Infrared spectroscopy ,chemistry.chemical_element ,x-ray photoelectron spectroscopy ,Oxygen ,Redox ,PM-IRRAS ,chemistry.chemical_compound ,Chemical state ,Adsorption ,X-ray photoelectron spectroscopy ,Carbonate ,ethylene oxidation ,AP-XPS ,Total pressure ,infrared spectroscopy - Abstract
Using a combination of two surface-sensitive spectroscopy techniques, the chemical state of the Ag(111) surface and the nature of the adsorbed species in the presence of ethylene and oxygen gases are identified. In the 10 mbar pressure range and 25–200 °C studied here, Ag(111) remains largely metallic even in O2-rich conditions. The only adsorbed molecular species with a low but discernible coverage is surface carbonate, which forms due to further oxidation of produced CO2, in a similar manner to its formation in ambient air on Ag surfaces. Its formation is also pressure-dependent, for instance, it is not observed when the total pressure is in the 1 mbar pressure range. Production of carbonate, along with carbon dioxide and water vapor as the main gas-phase products, suggests that an unpromoted Ag(111) surface catalyzes mainly the undesired full oxidation reaction.
- Published
- 2021
10. Effect of Surface Orientation on Methanol Adsorption and Thermally Induced Structural Transformations on Copper Surfaces
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Roey Ben David, Baran Eren, and Adva Ben Yaacov
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Materials science ,Infrared ,Analytical chemistry ,Thermal desorption ,chemistry.chemical_element ,Atmospheric temperature range ,Orientation (graph theory) ,Copper ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,General Energy ,Adsorption ,chemistry ,Methanol ,Physical and Theoretical Chemistry ,Spectroscopy - Abstract
Molecular adsorption of methanol on Cu(111), Cu(100), and Cu(110) surfaces in the 90–200 K temperature range is studied by a combination of infrared (IR) spectroscopy, thermal desorption analysis, ...
- Published
- 2021
11. CO Oxidation Mechanisms on CoOx-Pt Thin Films
- Author
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Zahra Hooshmand, Baran Eren, Miquel Salmeron, Gabor A. Somorjai, Duy Le, Cheng Hao Wu, George Yan, Adrian Hunt, Talat S. Rahman, Slavomír Nemšák, Heath Kersell, Philippe Sautet, Huy Nguyen, and Iradwikanari Waluyo
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Chemistry ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Biochemistry ,Oxygen ,Catalysis ,0104 chemical sciences ,law.invention ,Colloid and Surface Chemistry ,Adsorption ,X-ray photoelectron spectroscopy ,law ,Torr ,Density functional theory ,Scanning tunneling microscope ,Thin film ,Ambient pressure - Abstract
The reaction of CO and O2 with submonolayer and multilayer CoOx films on Pt(111), to produce CO2, was investigated at room temperature in the mTorr pressure regime. Using operando ambient pressure X-ray photoelectron spectroscopy and high pressure scanning tunneling microscopy, as well as density functional theory calculations, we found that the presence of oxygen vacancies in partially oxidized CoOx films significantly enhances the CO oxidation activity to form CO2 upon exposure to mTorr pressures of CO at room temperature. In contrast, CoO films without O-vacancies are much less active for CO2 formation at RT, and CO only adsorbed in the form of carbonate species that are stable up to 260 °C. On submonolayer CoOx islands, the carbonates form preferentially at island edges, deactivating the edge sites for CO2 formation, even while the reaction proceeds inside the islands. These results provide a detailed understanding of CO oxidation pathways on systems where noble metals such as Pt interact with reducible oxides.
- Published
- 2020
12. Carbon Monoxide Adsorption on Manganese Oxide/Cobalt: an Ambient Pressure X-ray Photoelectron Spectroscopy Study
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Baran Eren and Ashley R. Head
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Inorganic chemistry ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Manganese oxide ,01 natural sciences ,Methane ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,chemistry.chemical_compound ,General Energy ,X-ray photoelectron spectroscopy ,chemistry ,Carbon monoxide adsorption ,Physical and Theoretical Chemistry ,0210 nano-technology ,Selectivity ,Cobalt ,Ambient pressure - Abstract
MnOx enhances the catalytic activity of Co during Fischer–Tropsch synthesis, increases selectivity toward C5+ products, and decreases methane formation. These desired traits are thought to result f...
- Published
- 2020
13. Beam-Induced Effects in Ambient Pressure Experiments with X-rays
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Baran Eren and Miquel Salmeron
- Published
- 2021
14. Contamination Issues in Ambient Pressure Experiments
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Baran Eren, Roey Ben David, and Andrey Shavorskiy
- Published
- 2021
15. Electronic interactions and stability issues at the copper-graphene interface in air and in alkaline solution under electrochemical control
- Author
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Salma Khatun, Miguel A. Andrés, Sidney R. Cohen, Ifat Kaplan-Ashiri, Olga Brontvein, Irit Rosenhek-Goldian, Robert S. Weatherup, and Baran Eren
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History ,Polymers and Plastics ,General Chemical Engineering ,Electrochemistry ,Business and International Management ,Industrial and Manufacturing Engineering - Abstract
A micro-electrochemical cell is sealed with a polymer-free single-layer graphene (SLG) membrane to monitor the stability of Cu nanoparticles (NPs) attached to SLG, as well as the interfacial electronic interactions between Cu NPs and SLG both in air and in a mildly alkaline aqueous solution under electrochemical control. A combination of techniques, including in-situ Kelvin probe force microscopy (KPFM) and ex-situ electron microscopy, are applied. When Cu NPs are metallic at cathodic potentials, there is a relatively bias-independent offset in the SLG work function due to charge transfer at the Cu-SLG contact. When Cu NPs are oxidized at anodic potentials, on the other hand, the work function of SLG also depends on the applied bias in a quasi-linear fashion due to electrochemical gating, in addition to charge transfer at the CuOx-SLG contact. Furthermore, Cu NPs were found to oxidize and detach from SLG when kept under anodic potentials for a few hours, whereas they remain adhered to SLG at cathodic potentials. This is attributed to water intercalation at the CuO-SLG interface associated with the enhanced hydrophilicity of positively polarized graphene, as supported by the absence of Cu detachment following oxidation by galvanic corrosion in air.
- Published
- 2022
16. Observing electrochemical reactions on suspended graphene: an operando Kelvin probe force microscopy approach
- Author
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Robert S. Weatherup, Sidney R. Cohen, Salma Khatun, Sa'ar Shor Peled, Baran Eren, and Irit Rosenhek-Goldian
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Kelvin probe force microscope ,Working electrode ,Materials science ,Graphene ,Mechanical Engineering ,Doping ,Oxygen evolution ,Context (language use) ,Electrochemistry ,law.invention ,Chemical engineering ,Mechanics of Materials ,law ,Work function - Abstract
An electrochemical micro-reactor sealed with a single-layer graphene (SLG) membrane is demonstrated that allows straightforward measurement with established scanning probe microscopies. SLG serves as a working electrode which separates the liquid electrochemical environment from the ambient to enable direct energy-level determination. Kelvin probe force microscopy (KPFM) thereby reveals the shifts in Fermi-level of suspended SLG under electrochemical reaction conditions in aqueous alkaline media. Polymer-free transfer to create suspended SLG minimizes contributions to doping related to any support or contaminants, such that changes in work function (WF) relate predominantly to the electrochemical system under study. These WF changes are rationalized in the context of a simple model of electrochemical gating, providing insight into the interplay between electronic and electrochemical doping (through redox of water) of suspended graphene. Further changes in WF are attributable to the reversible functionalization of graphene during the oxygen evolution reaction. Mechanical changes in the suspended graphene in the form of bulging also occur, which are attributed to electro-wetting of graphene induced by charge-carrier doping.
- Published
- 2021
17. Operando STM study of the interaction of imidazolium-based ionic liquid with graphite
- Author
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Hai-Tao Fang, Yibo Hao, Bingmei Feng, Miquel Salmeron, Huixin Wang, Baran Eren, and Cheng Hao Wu
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Materials science ,Intercalation (chemistry) ,Energy Engineering and Power Technology ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,law.invention ,symbols.namesake ,chemistry.chemical_compound ,Highly oriented pyrolytic graphite ,law ,General Materials Science ,Graphite ,Alkyl ,chemistry.chemical_classification ,Renewable Energy, Sustainability and the Environment ,Graphene ,021001 nanoscience & nanotechnology ,Exfoliation joint ,0104 chemical sciences ,chemistry ,Chemical engineering ,Ionic liquid ,symbols ,van der Waals force ,0210 nano-technology - Abstract
Understanding interactions at the interfaces of carbon with ionic liquids (ILs) is crucially beneficial for the diagnostics and performance improvement of electrochemical devices containing carbon as active materials or conductive additives in electrodes and ILs as solvents or additives in electrolytes. The interfacial interactions of three typical imidazolium-based ILs, 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (AMImTFSI) ILs having ethyl (C2), butyl (C4) and octyl (C8) chains in their cations, with highly oriented pyrolytic graphite (HOPG) were studied in-situ by electrochemical scanning tunneling microscopy (EC-STM). The etching of HOPG surface and the exfoliation of graphite/graphene flakes as well as cation intercalation were observed at the HOPG/C2MImTFSI interface. The etching also takes place in C4MImTFSI at −1.5 V vs Pt but only at step edges with a much slower rate, whereas C8MIm+ cations adsorbs strongly on the HOPG surface under similar conditions with no observable etching or intercalation. The EC-STM observations can be explained by the increase in van der Waals interaction between the cations and the graphite surface with increasing length of alkyl chains.
- Published
- 2019
18. Preface
- Author
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Ashley R. Head, Slavomír Nemšák, and Baran Eren
- Published
- 2021
19. Bimetallic synergy in cobalt–palladium nanocatalysts for CO oxidation
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Huolin L. Xin, Cheng Hao Wu, Dong Su, Christopher B. Murray, Chang Liu, Miquel Salmeron, Baran Eren, Sen Zhang, and Hai-Tao Fang
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Materials science ,010405 organic chemistry ,Process Chemistry and Technology ,chemistry.chemical_element ,Nanoparticle ,Bioengineering ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,Nanomaterial-based catalyst ,0104 chemical sciences ,chemistry ,Chemical engineering ,X-ray photoelectron spectroscopy ,Selectivity ,Cobalt ,Bimetallic strip ,Palladium - Abstract
Bimetallic and multi-component catalysts typically exhibit composition-dependent activity and selectivity, and when optimized often outperform single-component catalysts. Here we used ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and in situ and ex situ transmission electron microscopy (TEM) to elucidate the origin of composition dependence observed in the catalytic activities of monodisperse CoPd bimetallic nanocatalysts for CO oxidation. We found that the catalysis process induced a reconstruction of the catalysts, leaving CoOx on the nanoparticle surface. The synergy between Pd and CoOx coexisting on the surface promotes the catalytic activity of the bimetallic catalysts. This synergistic effect can be optimized by tuning the Co/Pd ratios in the nanoparticle synthesis, and it reaches a maximum at compositions near Co0.24Pd0.76, which achieves complete CO conversion at the lowest temperature. Our combined AP-XPS and TEM studies provide direct observation of the surface evolution of the bimetallic nanoparticles under catalytic conditions and show how this evolution correlates with catalytic properties.
- Published
- 2018
20. High-Pressure Scanning Tunneling Microscopy
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Miquel Salmeron and Baran Eren
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Surface (mathematics) ,Range (particle radiation) ,Atmospheric pressure ,010405 organic chemistry ,Chemistry ,General Chemistry ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Characterization (materials science) ,law.invention ,Chemical physics ,law ,Torr ,Diffusion (business) ,Scanning tunneling microscope ,Ambient pressure - Abstract
This is a Review of recent studies on surface structures of crystalline materials in the presence of gases in the mTorr to atmospheric pressure range, which brings surface science into a brand new direction. Surface structure is not only a property of the material but also depends on the environment surrounding it. This Review emphasizes that high/ambient pressure goes hand-in-hand with ambient temperature, because weakly interacting species can be densely covering surfaces at room temperature only when in equilibrium with a sufficiently high gas pressure. At the same time, ambient temperatures help overcome activation barriers that impede diffusion and reactions. Even species with weak binding energy can have residence lifetimes on the surface that allow them to trigger reconstructions of the atomic structure. The consequences of this are far from trivial because under ambient conditions the structure of the surface dynamically adapts to its environment and as a result completely new structures are often formed. This new era of surface science emerged and spread rapidly after the retooling of characterization techniques that happened in the last two decades. This Review is focused on the new surface structures enabled particularly by one of the new tools: high-pressure scanning tunneling microscopy. We will cover several important surfaces that have been intensely scrutinized, including transition metals, oxides, and alloys.
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- 2020
21. Role of vacancies in CO oxidation by CoOx-Pt catalysts: A spectroscopic, structural, and theoretical approach
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Slavomir Nemsak, Miquel Salmeron, Talat Rahman, Heath Kersell, Baran Eren, Adrian Hunt, and Iradwikanari Waluyo
- Published
- 2020
22. CO Oxidation Mechanisms on CoO
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Heath, Kersell, Zahra, Hooshmand, George, Yan, Duy, Le, Huy, Nguyen, Baran, Eren, Cheng Hao, Wu, Iradwikanari, Waluyo, Adrian, Hunt, Slavomír, Nemšák, Gabor, Somorjai, Talat S, Rahman, Philippe, Sautet, and Miquel, Salmeron
- Abstract
The reaction of CO and O
- Published
- 2020
23. Predicting Surface Clustering at Ambient Conditions from Thermodynamic Data
- Author
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Baran Eren and Miquel Salmeron
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Surface (mathematics) ,Materials science ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Nanoclusters ,law.invention ,Gas phase ,Crystal ,General Energy ,Transition metal ,law ,Chemical physics ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,0210 nano-technology ,Cluster analysis ,Adsorption energy - Abstract
Scanning tunneling microscopy (STM) has proved to be a prime tool to characterize the atomic structure of crystal surfaces under UHV conditions. With the development of high-pressure scanning tunneling microscopy (HP-STM), the scope of this technique has been largely extended, as new structures were found to occur under gas phase chemical potentials achieved under ambient conditions. Particularly interesting is the substantial restructuring of initially flat and stable surfaces into new orientations by formation of nanoclusters. Here we discuss the possible generality of this phenomenon by analyzing cases where atomically flat surfaces of certain transition metals undergo such changes in the presence of CO at room temperature (RT) while some remain unchanged. From our analysis we argue that such changes can be predicted from thermodynamic data published in the literature, particularly from the difference in adsorption energy on low- and high-coordination sites, like terrace and step sites, which can be ob...
- Published
- 2018
24. Structure of Copper–Cobalt Surface Alloys in Equilibrium with Carbon Monoxide Gas
- Author
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Baran Eren, Cheng Hao Wu, Dario Stacchiola, Hendrik Bluhm, Zongyuan Liu, Gabor A. Somorjai, Osman Karslıoğlu, Daniel Torres, and Miquel Salmeron
- Subjects
Absorption spectroscopy ,Chemistry ,Binding energy ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Adsorption ,law ,Atom ,Physical chemistry ,Density functional theory ,Scanning tunneling microscope ,0210 nano-technology ,Cobalt ,Carbon monoxide - Abstract
We studied the structure of the copper-cobalt (CuCo) surface alloy, formed by Co deposition on Cu(110), in dynamic equilibrium with CO. Using scanning tunneling microscopy (STM), we found that, in vacuum at room temperature and at low Co coverage, clusters of a few Co atoms substituting Cu atoms form at the surface. At CO pressures in the Torr range, we found that up to 2.5 CO molecules can bind on a single Co atom, in carbonyl-like configurations. Based on high-resolution STM images, together with density functional theory calculations, we determined the most stable CuCo cluster structures formed with bound CO. Such carbonyl-like formation manifests in shifts in the binding energy of the Co core-level peaks in X-ray photoelectron spectra, as well as shifts in the vibrational modes of adsorbed CO in infrared reflection absorption spectra. The multiple CO adsorption on a Co site weakens the Co-CO bond and thus reduces the C-O bond scission probability. Our results may explain the different product distribution, including higher selectivity toward alcohol formation, when bimetallic CuCo catalysts are used compared to pure Co.
- Published
- 2018
25. Ambient-Pressure X-ray Photoelectron Spectroscopy Study of Cobalt Foil Model Catalyst under CO, H2, and Their Mixtures
- Author
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Miquel Salmeron, Cheng Hao Wu, Baran Eren, and Hendrik Bluhm
- Subjects
Chemistry ,Inorganic chemistry ,Analytical chemistry ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Catalysis ,Dissociation (chemistry) ,0104 chemical sciences ,Carbide ,X-ray photoelectron spectroscopy ,Impurity ,0210 nano-technology ,Cobalt ,FOIL method ,Ambient pressure - Abstract
Ambient-pressure X-ray photoelectron spectroscopy (XPS) was used to investigate the reactions of CO, H2, and their mixtures on Co foils. We found that CO adsorbs molecularly on the clean Co surface and desorbs intact in vacuum with increasing rate until ∼90 °C where all CO desorbs in seconds. In equilibrium with 100 mTorr gas, CO dissociates above 120 °C, leaving carbide species on the surface but no oxides, because CO efficiently reduces the oxides at temperatures ∼100 °C lower than H2. Water as impurities or produced by reaction of CO and H2 efficiently oxidizes Co even at room temperature. Under 97:3 CO/H2 mixture and with increasing temperatures, the Co surface becomes more oxidized and covered by hydroxyl groups until ∼150 °C where surface starts to get reduced, accompanied by carbide accumulation indicative of CO dissociation. A similar trend was observed for 9:1 and 1:1 mixtures, but surface reduction begins at higher temperatures.
- Published
- 2017
26. Nanostructuring of an alkali halide surface by low temperature plasma exposure
- Author
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Baran Eren, Res Jöhr, Ernst Meyer, Roland Steiner, Sara Freund, Thilo Glatzel, Antoine Hinaut, Shigeki Kawai, and Laurent Marot
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Materials science ,Annealing (metallurgy) ,General Physics and Astronomy ,Nanoparticle ,Halide ,02 engineering and technology ,Plasma ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic mass ,Ion ,Adsorption ,Chemical physics ,0103 physical sciences ,Irradiation ,Physical and Theoretical Chemistry ,010306 general physics ,0210 nano-technology - Abstract
Templating insulating surfaces at the nanoscale is an interesting prospect for applications that involve the adsorption of molecules or nanoparticles where electronic decoupling of the adsorbed species from the substrate is needed. In this study, we present a method to structure alkali halide surfaces at the nanoscale using a combination of low temperature plasma exposure and annealing, and characterize the surfaces by atomic force microscopy. We find that nanostructurating can be controlled by the duration of the exposure, the atomic mass of the plasma gas and the subsequent step-by-step annealing process. In contrast to previous studies with electron or high energy (few keV) ion irradiation, our approach of employing moderate particle energy (10–15 eV Ar+ or He+ ions) results in fine nanostructuring at length scales of nanometers and even single atom vacancies.
- Published
- 2017
27. A study of the O/Ag(111) system with scanning tunneling microscopy and x-ray photoelectron spectroscopy at ambient pressures
- Author
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Baran Eren, Barbara A. J. Lechner, Christian Heine, and Miquel Salmeron
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Analytical chemistry ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,Surfaces and Interfaces ,Atmospheric temperature range ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Oxygen ,0104 chemical sciences ,Surfaces, Coatings and Films ,law.invention ,Chemical state ,chemistry.chemical_compound ,X-ray photoelectron spectroscopy ,chemistry ,law ,Phase (matter) ,Materials Chemistry ,Scanning tunneling microscope ,0210 nano-technology ,Ambient pressure - Abstract
The interaction of O 2 with the Ag(111) surface was studied with scanning tunneling microscopy (STM) in the pressure range from 10 − 9 Torr to 1 atm at room temperature and with X-ray photoelectron spectroscopy (XPS) up to 0.3 Torr O 2 in the temperature range from RT to 413 K. STM images show that the Ag(111) surface topography is little affected in regions with large flat terraces, except for the appearance of mobile features due to oxygen atoms at pressures above 0.01 Torr. In regions where the step density is high, the surface became rough under 0.01 Torr of O 2 , due to the local oxidation of Ag. Various chemical states of oxygen due to chemisorbed, oxide and subsurface species were identified by XPS as a function of pressure and temperature. The findings from the STM images and XPS measurements indicate that formation of an oxide phase, the thermodynamically stable form at room temperature under ambient O 2 pressure, is kinetically hindered in the flat terrace areas but proceeds readily in regions with high-step density.
- Published
- 2016
28. Structural Changes of Cu(110) and Cu(110)-(2 × 1)-O Surfaces under Carbon Monoxide in the Torr Pressure Range Studied with Scanning Tunneling Microscopy and Infrared Reflection Absorption Spectroscopy
- Author
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Dario Stacchiola, Zongyuan Liu, Miquel Salmeron, Baran Eren, and Gabor A. Somorjai
- Subjects
Absorption spectroscopy ,Infrared ,Chemistry ,Analytical chemistry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,chemistry.chemical_compound ,General Energy ,Adsorption ,law ,Torr ,Molecule ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,0210 nano-technology ,Spectroscopy ,Carbon monoxide - Abstract
The atomic structure of the clean Cu(110) and the oxygen covered Cu(110) surfaces in the presence of carbon monoxide (CO) gas in the Torr pressure range at 298 K is studied using scanning tunneling microscopy (STM) and infrared reflection adsorption spectroscopy (IRRAS). We found that the initially clean surface reconstructs to form short rows of Cu atoms along the [1–10] direction separated by missing rows. The adsorbed CO molecules show two different C–O stretch vibration modes originating from molecules bound to Cu atoms with different coordination numbers, in the middle and at the end of the atomic rows. On the oxygen covered p(2 × 1) surface, adsorbed CO is observed only after removal of surface O atoms by reaction with CO. In the presence of 1:5 and 1:1 mixtures of O2 and CO at 298 K, the p(2 × 1)-O reconstructed surface transforms into Cu2O, instead of reducing to metallic Cu.
- Published
- 2016
29. Structure and Dynamics of Reactant Coadsorption on Single Crystal Model Catalysts by HP-STM and AP-XPS: A Mini Review
- Author
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Baran Eren, Cheng Hao Wu, and Miquel Salmeron
- Subjects
Reaction mechanism ,Chemistry ,Nanotechnology ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Electron spectroscopy ,Catalysis ,0104 chemical sciences ,Mini review ,law.invention ,Adsorption ,X-ray photoelectron spectroscopy ,Chemical engineering ,law ,Scanning tunneling microscope ,0210 nano-technology ,Single crystal - Abstract
Understanding the reaction mechanism of various heterogeneous catalytic reactions is of fundamental importance in catalysis science. In the past, scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) have proved to be powerful surface-sensitive techniques to characterize surface reactions on model catalysts under UHV conditions. The recent development of high-pressure scanning tunneling microscopy (HP-STM) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) has largely extended the application of these two excellent surface-sensitive imaging and electron spectroscopy techniques to a variety of catalytic systems under realistic conditions. In this mini review, we will review a series of catalytic systems studied by HP-STM and AP-XPS, including reactant coadsorption systems, coadsorption + reaction systems, and poisoned reaction systems. We will also illustrate one of the main difficulties in the practical execution of experiments where the initial surface cleanliness is easily compromised by the adsorption of adventitious contaminants. All of these examples will demonstrate that the combined use of HP-STM and AP-XPS can provide a deeper understanding of the structure and dynamics of reactant coadsorption on model catalysts, although great care has to been taken to maintain the cleanness of the in situ instrumentation.
- Published
- 2016
30. Surface Structure and Modifications Under Ambient Pressure: A Case Study With Copper Surfaces
- Author
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Baran Eren
- Subjects
Materials science ,Absorption spectroscopy ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,law.invention ,Nanoclusters ,Adsorption ,X-ray photoelectron spectroscopy ,law ,Chemical physics ,Density functional theory ,Scanning tunneling microscope ,0210 nano-technology ,Spectroscopy ,Ambient pressure - Abstract
Low Miller-index copper surfaces break up into nanoclusters in the presence of reactant gases such as CO or CO 2 in the Torr pressure range at room temperature. Such an atomistic phenomenon has a great significance in heterogeneous catalysis as it directly affects the electronic structure and thereby the chemical properties of the surface. The reason behind clustering of such compact surfaces is the high difference in adsorption energy at the low-coordinated Cu atoms (steps, kinks) and high-coordinated Cu atoms (terraces). Unlike CO and CO 2 , gas-phase methanol does not break up Cu into clusters because methoxy can already adsorb strongly on Cu terraces. These observations were made possible by the recent developments of high-pressure scanning tunneling microscopy and complementary spectroscopy techniques like ambient pressure X-ray photoelectron spectroscopy and infrared reflection absorption spectroscopy. This article provides scanning tunneling microscope images, corroborating spectra, and density functional theory calculations to summarize all the recent findings in this field.
- Published
- 2018
31. Catalyst Chemical State during CO Oxidation Reaction on Cu(111) Studied with Ambient-Pressure X-ray Photoelectron Spectroscopy and Near Edge X-ray Adsorption Fine Structure Spectroscopy
- Author
-
Baran Eren, Miquel Salmeron, Gabor A. Somorjai, Hendrik Bluhm, and Christian Heine
- Subjects
Chemistry ,Analytical chemistry ,General Chemistry ,Partial pressure ,Reaction intermediate ,Biochemistry ,Catalysis ,XANES ,Chemical state ,Colloid and Surface Chemistry ,Adsorption ,X-ray photoelectron spectroscopy ,Spectroscopy - Abstract
The chemical structure of a Cu(111) model catalyst during the CO oxidation reaction in the CO+O2 pressure range of 10-300 mTorr at 298-413 K was studied in situ using surface sensitive X-ray photoelectron and adsorption spectroscopy techniques [X-ray photoelectron spectroscopy (XPS) and near edge X-ray adsorption fine structure spectroscopy (NEXAFS)]. For O2:CO partial pressure ratios below 1:3, the surface is covered by chemisorbed O and by a thin (∼1 nm) Cu2O layer, which covers completely the surface for ratios above 1:3 between 333 and 413 K. The Cu2O film increases in thickness and exceeds the escape depth (∼3-4 nm) of the XPS and NEXAFS photoelectrons used for analysis at 413 K. No CuO formation was detected under the reaction conditions used in this work. The main reaction intermediate was found to be CO2(δ-), with a coverage that correlates with the amount of Cu2O, suggesting that this phase is the most active for CO oxidation.
- Published
- 2015
32. Reaction of CO with Preadsorbed Oxygen on Low-Index Copper Surfaces: An Ambient Pressure X-ray Photoelectron Spectroscopy and Scanning Tunneling Microscopy Study
- Author
-
Baran Eren, Gabor A. Somorjai, Leonid Lichtenstein, Cheng Hao Wu, Miquel Salmeron, and Hendrik Bluhm
- Subjects
Oxide ,Analytical chemistry ,chemistry.chemical_element ,Atmospheric temperature range ,7. Clean energy ,Copper ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Reaction rate ,chemistry.chemical_compound ,General Energy ,chemistry ,X-ray photoelectron spectroscopy ,law ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,Oxygen binding ,Ambient pressure - Abstract
The reaction of CO with chemisorbed oxygen on three low-index faces of copper was studied using ambient pressure X-ray photoelectron spectroscopy (XPS) and high-pressure scanning tunneling microscopy. At room temperature, the chemisorbed oxide can be removed by reaction with gas-phase CO in the 0.01–0.20 Torr pressure range. The reaction rates were determined by measuring the XPS peak intensities of O and CO as a function of time, pressure, and temperature. On Cu(111) the rate was found to be one order of magnitude faster than that on Cu(100) and two orders of magnitude faster than that on Cu(110). The apparent activation energies for CO oxidation were measured as 0.24 eV for O/Cu(111), 0.29 eV for O/Cu(100), and 0.51 eV for O/Cu(110) in the temperature range between 298 and 473 K. These energies are correlated to the oxygen binding energies on each surface.
- Published
- 2015
33. Carbon nanotube growth on AlN support: Comparison between Ni and Fe chemical states and morphology
- Author
-
Marcel Düggelin, Kenneth N. Goldie, Daniel Mathys, Vesna Olivieri, Laurent Marot, Roland Steiner, Teresa de los Arcos, Ernst Meyer, and Baran Eren
- Subjects
Materials science ,Morphology (linguistics) ,General Physics and Astronomy ,Nanoparticle ,Nanotechnology ,Carbon nanotube ,Thermal treatment ,Catalysis ,law.invention ,Metal ,Chemical state ,Chemical engineering ,law ,visual_art ,visual_art.visual_art_medium ,Dewetting ,Physical and Theoretical Chemistry - Abstract
In this work, carbon nanotubes (CNTs) are grown from Ni and Fe nanoparticles supported on a rough AlN surface. Although, identical experimental parameters are used during dewetting (island formation) via thermal treatment, Ni particles appear metallic and larger, whereas Fe particles are smaller and slightly oxidized. This difference in the nanoparticle chemical state and morphology reflects to CNTs during catalytic chemical vapor deposition in terms of their CNT growth mode and size: tip-growth mode for Ni catalyst with CNT diameters of up to 40 nm, whereas base-growth mode for Fe with CNT diameters typically less than 10 nm are observed.
- Published
- 2014
34. Morphological Changes of Tungsten Surfaces by Low-Flux Helium Plasma Treatment and Helium Incorporation via Magnetron Sputtering
- Author
-
Baran Eren, Santhosh Iyyakkunnel, Laurent Marot, Ernst Meyer, Patrick Chapon, Marcel Düggelin, L. Moser, Daniel Mathys, and Roland Steiner
- Subjects
Argon ,Materials science ,chemistry ,Vacancy defect ,Analytical chemistry ,chemistry.chemical_element ,General Materials Science ,Partial pressure ,Sputter deposition ,Tungsten ,Microstructure ,Helium ,Nanocrystalline material - Abstract
The effect of helium on the tungsten microstructure was investigated first by exposure to a radio frequency driven helium plasma with fluxes of the order of 1 × 10(19) m(-2) s(-1) and second by helium incorporation via magnetron sputtering. Roughening of the surface and the creation of pinholes were observed when exposing poly- and nanocrystalline tungsten samples to low-flux plasma. A coating process using an excess of helium besides argon in the process gas mixture leads to a porous thin film and a granular surface structure whereas gas mixture ratios of up to 50% He/Ar (in terms of their partial pressures) lead to a dense structure. The presence of helium in the deposited film was confirmed with glow-discharge optical emission spectroscopy and thermal desorption measurements. Latter revealed that the highest fraction of the embedded helium atoms desorb at approximately 1500 K. Identical plasma treatments at various temperatures showed strongest modifications of the surface at 1500 K, which is attributed to the massive activation of helium singly bond to a single vacancy inside the film. Thus, an efficient way of preparing nanostructured tungsten surfaces and porous tungsten films at low fluxes was found.
- Published
- 2014
35. Graphene Synthesis via Thermal Polymerization of Aromatic Quinone Molecules
- Author
-
Laurent Marot, Baran Eren, Shigeki Kawai, and Ernst Meyer
- Subjects
Materials science ,Hydrogen bond ,Graphene ,General Engineering ,General Physics and Astronomy ,Nanotechnology ,Thermal treatment ,Photochemistry ,law.invention ,Pentacene ,chemistry.chemical_compound ,chemistry ,Polymerization ,Covalent bond ,law ,Molecular film ,Molecule ,General Materials Science - Abstract
Graphene was synthesized from pentacenequinone molecules on a Cu(111) surface using a three-step thermal treatment process: (1) self-assembly of a single layer molecular film at 190 °C, (2) formation of covalent bonding between adjacent molecules at intermediate temperatures, (3) thermal dehydrogenation and in-plane carbon diffusion at 600 °C. Transformation of the surface conformation was monitored with bimodal atomic force microscopy at the atomic scale and was corroborated with core-level X-ray photoelectron spectroscopy. A strong C═O···H-C hydrogen bonding involving the quinone moiety plays a key role in graphene growth, whereas conventional pentacene simply desorbs from the substrate during the same process. The most significant achievement of this proposed technique is obtaining graphene a couple of hundred degrees lower than standard techniques. Intrinsic defects due to carbon deficiency and the defects intentionally introduced by the microscope tip were also investigated with atomic-scale imaging.
- Published
- 2014
36. Author Correction: Bimetallic synergy in cobalt–palladium nanocatalysts for CO oxidation
- Author
-
Miquel Salmeron, Chang Liu, Baran Eren, Sen Zhang, Christopher B. Murray, Huolin L. Xin, Cheng Hao Wu, Dong Su, and Hai-Tao Fang
- Subjects
Engineering ,ComputerSystemsOrganization_COMPUTERSYSTEMIMPLEMENTATION ,business.industry ,Process Chemistry and Technology ,Metallurgy ,chemistry.chemical_element ,Bioengineering ,Biochemistry ,Catalysis ,Nanomaterial-based catalyst ,chemistry ,business ,National laboratory ,Bimetallic strip ,Cobalt ,Palladium - Abstract
In the version of this Article originally published, the author Baran Eren was mistakenly affiliated with the Harbin Institute of Technology, China; it has now been corrected to Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
- Published
- 2019
37. Can aluminium or magnesium be a surrogate for beryllium: A critical investigation of their chemistry
- Author
-
Christian Linsmeier, Baran Eren, Laurent Marot, Roland Steiner, Ernst Meyer, and L. Moser
- Subjects
Work (thermodynamics) ,Hydride ,Magnesium ,Mechanical Engineering ,Metallurgy ,chemistry.chemical_element ,Tungsten ,Electronegativity ,Nuclear Energy and Engineering ,chemistry ,Aluminium ,General Materials Science ,Beryllium ,Carbon ,Civil and Structural Engineering - Abstract
The use of beryllium is still an existing question according to the studies concerning the plasma–wall interactions which are expected to occur in ITER. Prediction of erosion and co-deposition processes for ITER is necessary for the design and the material choice of the first wall. In the current configuration, it is expected that co-deposited layers containing Be, tungsten and possibly carbon will be formed. However, the toxicity of Be limits its use in many experimental facilities around the world. Using aluminium or magnesium as Be replacements in laboratory experiments would solve this problem of toxicity and handling of Be mixed materials. A critical question which automatically arises is the relevance to use Al or Mg regarding the physical and chemical properties of both elements in comparison to the co-deposited layers expected in ITER. This work provides a review of the chemical and physical properties of Al and Mg, in the respect of comparing these properties to those of Be. Thanks to the similarity of its electronegativity to Be, Al can successfully resemble Be in terms of formation of compounds, especially the oxides and possibly the hydrides. However, due to the difference in the nature of the bonding, Mg cannot be a replacement for a possible hydride deposit formation.
- Published
- 2013
38. In situ evaluation of the reflectivity of molybdenum and rhodium coatings in an ITER-like mixed environment
- Author
-
Jean-Marcel Travère, M. Wisse, Laurent Marot, Maryline Joanny, Roland Steiner, Daniel Mathys, Baran Eren, and Ernst Meyer
- Subjects
Nuclear and High Energy Physics ,Materials science ,Metallurgy ,chemistry.chemical_element ,Tungsten ,Rhodium ,Amorphous solid ,Nuclear Energy and Engineering ,chemistry ,X-ray photoelectron spectroscopy ,Molybdenum ,Impurity ,Aluminium ,General Materials Science ,Beryllium - Abstract
Molybdenum and rhodium are foreseen to be utilized in ITER for the light reflecting, plasma facing components called first mirrors (FMs). In this work, the plasma and impurity conditions which FMs are expected to be subjected to were simulated experimentally, while monitoring their reflectivity. Experiments include deuterium plasma exposure with tungsten–carbon and tungsten–aluminum impurities, where aluminum was employed as a proxy for beryllium. The surface composition and morphology of the mirrors were characterized with XPS and SEM. When carbon was present in the plasma, the molybdenum surface became carbidized, while this effect was not observed for rhodium. Aluminum impurities were deposited as oxides, whereas tungsten was either oxidized or carbidized depending on the presence of carbon in the plasma. SEM results show the deposits to be amorphous. The mirrors in erosion conditions showed no critical decrease in the reflectivity, whereas the degradation was severe in net deposition conditions involving carbon. Cleaning techniques have to be developed for mirrors in deposition conditions, which should be part of ITER’s routine operation.
- Published
- 2013
39. Deuterium plasma exposure on rhodium: Reflectivity monitoring and evidence of subsurface deuteride formation
- Author
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Ernst Meyer, Laurent Marot, Roland Steiner, Baran Eren, and M. Wisse
- Subjects
Hydride ,Chemistry ,Ultra-high vacuum ,Fermi level ,technology, industry, and agriculture ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Rhodium ,symbols.namesake ,Deuterium ,Electrical resistivity and conductivity ,symbols ,Work function ,Ultraviolet photoelectron spectroscopy - Abstract
The effects of low flux, low temperature deuterium plasma (LTP) exposure on nanocrystalline rhodium (Rh) films are investigated. The exposures do not cause any surface damage on the nanoscale and the specific electrical resistivity of the films remains invariant during exposures. However, the spectral reflectivity of Rh decreases during exposure and recovers very slowly during subsequent storage in high vacuum. This drop in the reflectivity can be associated with a formation of a subsurface rhodium deuteride (RhD x , x ≤ 2), which has optical constants different to those of Rh. After air storage of the exposed samples, the Rh surface gets depopulated of deuterium adsorbates due to a catalytic reaction taking place between oxygen and deuterium, which results in a diffusion of the incorporated deuterium first to the surface and then into the air. Consequently, the reflectivity is rapidly recovered. Comparison of the ultraviolet photoelectron spectroscopy (UPS) measurements performed before and after plasma exposure reveals an increase in the work function which is attributed to deuterium adsorbates on the surface. Changes in the valence band structure were also observed with UPS measurements, lending support to the suggestion of subsurface RhD x formation. Deuterium atoms in Rh are electron donors filling the 4d states above the Fermi level, thus reducing optical transitions.
- Published
- 2013
40. Pure hydrogen low-temperature plasma exposure of HOPG and graphene: Graphane formation?
- Author
-
Laurent Marot, Rémy Pawlak, Dorothée Hug, Baran Eren, Ernst Meyer, Marcin Kisiel, Dominik M. Zumbühl, and Roland Steiner
- Subjects
Materials science ,Hydrogen ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,lcsh:Chemical technology ,lcsh:Technology ,01 natural sciences ,Full Research Paper ,law.invention ,chemistry.chemical_compound ,symbols.namesake ,Scanning probe microscopy ,X-ray photoelectron spectroscopy ,law ,0103 physical sciences ,Graphane ,lcsh:TP1-1185 ,General Materials Science ,Pyrolytic carbon ,Electrical and Electronic Engineering ,lcsh:Science ,010306 general physics ,plasma ,graphane ,lcsh:T ,Graphene ,021001 nanoscience & nanotechnology ,lcsh:QC1-999 ,Nanoscience ,chemistry ,HOPG ,symbols ,lcsh:Q ,hydrogenation ,Scanning tunneling microscope ,0210 nano-technology ,Raman spectroscopy ,lcsh:Physics - Abstract
Single- and multilayer graphene and highly ordered pyrolytic graphite (HOPG) were exposed to a pure hydrogen low-temperature plasma (LTP). Characterizations include various experimental techniques such as photoelectron spectroscopy, Raman spectroscopy and scanning probe microscopy. Our photoemission measurement shows that hydrogen LTP exposed HOPG has a diamond-like valence-band structure, which suggests double-sided hydrogenation. With the scanning tunneling microscopy technique, various atomic-scale charge-density patterns were observed, which may be associated with different C–H conformers. Hydrogen-LTP-exposed graphene on SiO2 has a Raman spectrum in which the D peak to G peak ratio is over 4, associated with hydrogenation on both sides. A very low defect density was observed in the scanning probe microscopy measurements, which enables a reverse transformation to graphene. Hydrogen-LTP-exposed HOPG possesses a high thermal stability, and therefore, this transformation requires annealing at over 1000 °C.
- Published
- 2012
41. Dissociative Carbon Dioxide Adsorption and Morphological Changes on Cu(100) and Cu(111) at Ambient Pressures
- Author
-
Baran Eren, Miquel Salmeron, Nikos Liakakos, Robert S. Weatherup, and Gabor A. Somorjai
- Subjects
Chemistry ,Inorganic chemistry ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Biochemistry ,Catalysis ,Dissociation (chemistry) ,0104 chemical sciences ,Nanoclusters ,law.invention ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Adsorption ,X-ray photoelectron spectroscopy ,law ,Torr ,Methanol ,Scanning tunneling microscope ,0210 nano-technology - Abstract
Ambient-pressure X-ray photoelectron spectroscopy (APXPS) and high-pressure scanning tunneling microscopy (HPSTM) were used to study the structure and chemistry of model Cu(100) and Cu(111) catalyst surfaces in the adsorption and dissociation of CO2. It was found that the (100) face is more active in dissociating CO2 than the (111) face. Atomic oxygen formed after the dissociation of CO2 poisons the surface by blocking further adsorption of CO2. This "self-poisoning" mechanism explains the need to mix CO into the industrial feed for methanol production from CO2, as it scavenges the chemisorbed O. The HPSTM images show that the (100) surface breaks up into nanoclusters in the presence of CO2 at 20 Torr and above, producing active kink and step sites. If the surface is precovered with atomic oxygen, no such nanoclustering occurs.
- Published
- 2016
42. Graphene Membranes for Atmospheric Pressure Photoelectron Spectroscopy
- Author
-
Yibo Hao, Robert S. Weatherup, Miquel Salmeron, Baran Eren, and Hendrik Bluhm
- Subjects
Surface Properties ,Analytical chemistry ,02 engineering and technology ,Photoionization ,010402 general chemistry ,7. Clean energy ,01 natural sciences ,law.invention ,X-ray photoelectron spectroscopy ,Oxidation state ,law ,General Materials Science ,Work function ,Physical and Theoretical Chemistry ,Particle Size ,Atmospheric pressure ,Chemistry ,Graphene ,Photoelectron Spectroscopy ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Membrane ,Atmospheric Pressure ,Physical Sciences ,Chemical Sciences ,Graphite ,0210 nano-technology ,Bar (unit) - Abstract
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 Cu(2+) 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.
- Published
- 2016
43. One-dimensional nanoclustering of the Cu(100) surface under CO gas in the mbar pressure range
- Author
-
Baran Eren, Miquel Salmeron, Gabor A. Somorjai, Yibo Hao, Danylo Zherebetskyy, Lin-Wang Wang, Laerte L. Patera, Eren, Baran, Zherebetskyy, Danylo, Hao, Yibo, Patera, LAERTE LUIGI, Wang, Lin Wang, Somorjai, Gabor A., and Salmeron, Miquel
- Subjects
Surface (mathematics) ,Cu(100) ,Materials Chemistry2506 Metals and Alloys ,Materials science ,Analytical chemistry ,Surfaces, Coatings and Film ,Nanotechnology ,02 engineering and technology ,Condensed Matter Physic ,010402 general chemistry ,01 natural sciences ,DFT ,law.invention ,Nanoclusters ,Pressure range ,Coatings and Films ,chemistry.chemical_compound ,HPSTM ,law ,Atom ,Materials Chemistry ,Nanoclustering ,Carbon monoxide ,Range (particle radiation) ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,Surfaces, Coatings and Films ,Surfaces ,chemistry ,Density functional theory ,Scanning tunneling microscope ,0210 nano-technology ,Surfaces and Interface - Abstract
The bulk terminated Cu(100) surface becomes unstable in the presence of CO at room temperature when the pressure reaches the mbar range. Scanning tunneling microscopy images show that above 0.25 mbar the surface forms nanoclusters with CO attached to peripheral Cu atoms. At 20 mbar and above 3-atom wide one-dimensional nanoclusters parallel to directions cover the surface, with CO on every Cu atom, increasing in density up to 115 mbar. Density functional theory explains the findings as a result of the detachment of Cu atoms from step edges caused by the stronger binding of CO relative to that on flat terraces.
- Published
- 2016
44. Activation of Cu(111) surface by decomposition into nanoclusters driven by CO adsorption
- Author
-
Cristina Africh, Baran Eren, Lin-Wang Wang, Hendrik Bluhm, Miquel Salmeron, Gabor A. Somorjai, Danylo Zherebetskyy, Laerte L. Patera, Cheng Hao Wu, Eren, Baran, Zherebetskyy, Danylo, Patera, LAERTE LUIGI, Wu, Cheng Hao, Bluhm, Hendrik, Africh, Cristina, Wang, Lin Wang, Somorjai, Gabor A., and Salmeron, Miquel
- Subjects
General Science & Technology ,Analytical chemistry ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,carbon monoxide ,Dissociation (chemistry) ,Water-gas shift reaction ,Nanoclusters ,law.invention ,chemistry.chemical_compound ,catalysis, high-pressure scanning probe microscopy, ambient pressure X-ray photo-emission spectroscopy ,Adsorption ,law ,Cluster (physics) ,high-pressure scanning probe microscopy ,ambient pressure X-ray photo-emission spectroscopy ,Multidisciplinary ,catalysis ,copper nanoparticles ,scanning tunnelling microscopy ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,chemistry ,Torr ,Scanning tunneling microscope ,0210 nano-technology ,Carbon monoxide - Abstract
Nanoclusters just by adding CO The most closely packed surfaces of transition metals are usually stable under vacuum, but during catalytic reactions, energetic changes that result from adsorbing molecules could change the surface structure. Eren et al. present an extreme example for carbon monoxide (CO) adsorption on the (111) surface of copper at very low partial pressures. The surface decomposed into small nanoclusters (most containing 3 or 19 atoms). The surface was more reactive than the original and, for example, could dissociate adsorbed water at room temperature. Science , this issue p. 475
- Published
- 2016
45. Reflective metallic coatings for first mirrors on ITER
- Author
-
Andrey Litnovsky, Laurent Marot, Valentin Emberger, Daniel Mathys, M. Wisse, Baran Eren, Roland Steiner, M. Matveeva, Ernst Meyer, and G. Covarel
- Subjects
Materials science ,business.industry ,Mechanical Engineering ,chemistry.chemical_element ,Substrate (electronics) ,Sputter deposition ,Evaporation (deposition) ,Nuclear Energy and Engineering ,chemistry ,Molybdenum ,Impurity ,Surface roughness ,Optoelectronics ,Deposition (phase transition) ,General Materials Science ,Crystallite ,business ,Civil and Structural Engineering - Abstract
Metallic mirrors are foreseen to play a crucial role for all optical diagnostics in ITER. Therefore, the development of reliable techniques for the production of mirrors which are able to maintain their optical properties in the harsh ITER environment is highly important. By applying magnetron sputtering and evaporation techniques, rhodium and molybdenum films have been prepared for tokamak tests. The films were characterised in terms of chemical composition, surface roughness, crystallite structure, reflectivity and adhesion. No impurities were detected on the surface after deposition. The effects of deposition parameters and substrate temperature on the resulting crystallite structure, surface roughness and hence on the reflectivity, were investigated. The films are found to exhibit nanometric crystallites with a dense columnar structure. Open boundaries between the crystallite columns, which are sometimes present after evaporation, are found to reduce the reflectivity as compared to rhodium or molybdenum references.
- Published
- 2011
46. Influence of Step Geometry on the Reconstruction of Stepped Platinum Surfaces under Coadsorption of Ethylene and CO
- Author
-
Zhi Liu, Baran Eren, Norbert Kruse, Zhongwei Zhu, Gabor A. Somorjai, Baohua Mao, Miquel Salmeron, Cédric Barroo, Thierry Visart de Bocarmé, Cheng Hao Wu, and Leonid Lichtenstein
- Subjects
Analytical chemistry ,chemistry.chemical_element ,Partial pressure ,law.invention ,Crystallography ,Adsorption ,X-ray photoelectron spectroscopy ,chemistry ,law ,Torr ,Cluster (physics) ,General Materials Science ,Physical and Theoretical Chemistry ,Scanning tunneling microscope ,Platinum ,Surface reconstruction - Abstract
We demonstrate the critical role of the specific atomic arrangement at step sites in the restructuring processes of low-coordinated surface atoms at high adsorbate coverage. By using high-pressure scanning tunneling microscopy (HP-STM) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), we have investigated the reconstruction of Pt(332) (with (111)-oriented triangular steps) and Pt(557) surfaces (with (100)-oriented square steps) in the mixture of CO and C2H4 in the Torr pressure range at room temperature. CO creates Pt clusters at the step edges on both surfaces, although the clusters have different shapes and densities. A subsequent exposure to a similar partial pressure of C2H4 partially reverts the clusters on Pt(332). In contrast, the cluster structure is barely changed on Pt(557). These different reconstruction phenomena are attributed to the fact that the 3-fold (111)-step sites on Pt(332) allows for adsorption of ethylidyne-a strong adsorbate formed from ethylene-that does not form on the 4-fold (100)-step sites on Pt(557).
- Published
- 2015
47. Towards plasma cleaning of ITER first mirrors
- Author
-
L. Moser, Frank Leipold, Roland Steiner, Laurent Marot, Daniel Mathys, Baran Eren, R. Reichle, and Ernst Meyer
- Subjects
Nuclear and High Energy Physics ,Materials science ,Plasma cleaning ,business.industry ,chemistry.chemical_element ,Plasma ,Tungsten ,Condensed Matter Physics ,Secondary ion mass spectrometry ,Optics ,X-ray photoelectron spectroscopy ,chemistry ,Sputtering ,Aluminium ,Specular reflection ,business - Abstract
To avoid reflectivity losses in ITER’s optical diagnostic systems, on-site cleaning of metallic first mirrors via plasma sputtering is foreseen to remove deposit build-ups migrating from the main wall. In this work, the influence of aluminium and tungsten deposits on the reflectivity of molybdenum mirrors as well as the possibility to clean them with plasma exposure is investigated. Porous ITER-like deposits are grown to mimic the edge conditions expected in ITER, and a severe degradation in the specular reflectivity is observed as these deposits build up on the mirror surface. In addition, dense oxide films are produced for comparisonswithporousfilms. Thecomposition,morphologyandcrystalstructureofseveralfilmswerecharacterizedbymeans of scanning electron microscopy, x-ray photoelectron spectroscopy, x-ray diffraction and secondary ion mass spectrometry. The cleaning of the deposits and the restoration of the mirrors’ optical properties are possible either with a Kaufman source or radio frequency directly applied to the mirror (or radio frequency plasma generated directly around the mirror surface). Accelerating ions of an external plasma source through a direct current applied onto the mirror does not remove deposits composed of oxides. A possible implementation of plasma cleaning in ITER is addressed.
- Published
- 2015
- Full Text
- View/download PDF
48. Spectroscopic ellipsometry on Si/SiO2/graphene tri-layer system exposed to downstream hydrogen plasma: Effects of hydrogenation and chemical sputtering
- Author
-
Ernst Meyer, Wangyang Fu, Laurent Marot, Michel Calame, Baran Eren, and Roland Steiner
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,Hydrogen ,Graphene ,Analytical chemistry ,chemistry.chemical_element ,Plasma ,law.invention ,symbols.namesake ,chemistry ,Sputtering ,law ,Ellipsometry ,symbols ,sense organs ,Raman spectroscopy ,Graphene nanoribbons ,Graphene oxide paper - Abstract
In this work, the optical response of graphene to hydrogen plasma treatment is investigated with spectroscopic ellipsometry measurements. Although the electronic transport properties and Raman spectrum of graphene change after plasma hydrogenation, ellipsometric parameters of the Si/SiO2/graphene tri-layer system do not change. This is attributed to plasma hydrogenated graphene still being electrically conductive, since the light absorption of conducting 2D materials does not depend on the electronic band structure. A change in the light transmission can only be observed when higher energy hydrogen ions (30 eV) are employed, which chemically sputter the graphene layer. An optical contrast is still apparent after sputtering due to the remaining traces of graphene and hydrocarbons on the surface. In brief, plasma treatment does not change the light transmission of graphene; and when it does, this is actually due to plasma damage rather than plasma hydrogenation. (C) 2015 AIP Publishing LLC.
- Published
- 2015
- Full Text
- View/download PDF
49. Laser damage thresholds of ITER mirror materials and first results on in situ laser cleaning of stainless steel mirrors
- Author
-
Ernst Meyer, Baran Eren, Roland Steiner, Laurent Marot, M. Wisse, and Daniel Mathys
- Subjects
Materials science ,Laser ablation ,Physics - Instrumentation and Detectors ,Mechanical Engineering ,chemistry.chemical_element ,FOS: Physical sciences ,Instrumentation and Detectors (physics.ins-det) ,Sputter deposition ,engineering.material ,Tungsten ,Laser ,Nanocrystalline material ,Physics - Plasma Physics ,law.invention ,Plasma Physics (physics.plasm-ph) ,Nuclear Energy and Engineering ,chemistry ,Coating ,X-ray photoelectron spectroscopy ,Molybdenum ,law ,engineering ,General Materials Science ,Composite material ,Civil and Structural Engineering - Abstract
A laser ablation system has been constructed and used to determine the damage threshold of stainless steel, rhodium and single-, poly- and nanocrystalline molybdenum in vacuum, at a number of wavelengths between 220 and 1064 nm using 5 ns pulses. All materials show an increase of the damage threshold with decreasing wavelength below 400 nm. Tests in a nitrogen atmosphere showed a decrease of the damage threshold by a factor of two to three. Cleaning tests have been performed in vacuum on stainless steel samples after applying mixed Al/W/C/D coatings using magnetron sputtering. In situ XPS analysis during the cleaning process as well ex situ reflectivity measurements demonstrate near complete removal of the coating and a substantial recovery of the reflectivity. The first results also show that the reflectivity obtained through cleaning at 532 nm may be further increased by additional exposure to UV light, in this case 230 nm, an effect which is attributed to the removal of tungsten dust from the surface., 19 pages, 16 figures
- Published
- 2012
50. Work function of few layer graphene covered nickel thin films measured with Kelvin probe force microscopy
- Author
-
Laurent Marot, Urs Gysin, Roland Steiner, Th-H. Glatzel, Baran Eren, and Ernst Meyer
- Subjects
Kelvin probe force microscope ,Materials science ,Physics and Astronomy (miscellaneous) ,Graphene ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,law.invention ,Nickel ,chemistry ,law ,0103 physical sciences ,Microscopy ,Work function ,Graphite ,Composite material ,Thin film ,010306 general physics ,0210 nano-technology ,Graphene oxide paper - Abstract
Few layer graphene and graphite are simultaneously grown on a similar to 100 nm thick polycrystalline nickel film. The work function of few layer graphene/Ni is found to be 4.15 eV with a variation of 50 meV by local measurements with Kelvin probe force microscopy. This value is lower than the work function of free standing graphene due to peculiar electronic structure resulting from metal 3d-carbon 2p(pi) hybridization. (C) 2016 AIP Publishing LLC.
- Published
- 2016
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