1
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Presel F, Kern CS, Boné TG, Schwarz F, Puschnig P, Ramsey MG, Sterrer M. Charge and adsorption height dependence of the self-metalation of porphyrins on ultrathin MgO(001) films. Phys Chem Chem Phys 2022; 24:28540-28547. [PMID: 36411984 PMCID: PMC9710497 DOI: 10.1039/d2cp04688a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2022] [Accepted: 11/16/2022] [Indexed: 12/07/2023]
Abstract
We have experimentally determined the adsorption structure, charge state, and metalation state of porphin, the fundamental building block of porphyrins, on ultrathin Ag(001)-supported MgO(001) films by scanning tunneling microscopy and photoemission spectroscopy, supported by calculations based on density functional theory. By tuning the substrate work function to values below and above the critical work function for charging, we succeeded in the preparation of 2H-P monolayers which contain negatively charged and uncharged molecules. It is shown that the porphin molecules self-metalate at room temperature, forming the corresponding Mg-porphin, irrespective of their charge state. This is in contrast to self-metalation of tetraphenyl porphyrin (TPP), which occurs on planar MgO(001) only if the molecules are negatively charged. The different reactivity is explained by the reduced molecule-substrate distance of the planar porphin molecule compared to the bulkier TPP. The results of this study shed light on the mechanism of porphyrin self-metalation on oxides and highlight the role of the adsorption geometry on the chemical reactivity.
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Affiliation(s)
- Francesco Presel
- Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, A-8010 Graz, Austria.
| | - Christian S Kern
- Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, A-8010 Graz, Austria.
| | - Thomas G Boné
- Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, A-8010 Graz, Austria.
| | - Florian Schwarz
- Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, A-8010 Graz, Austria.
| | - Peter Puschnig
- Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, A-8010 Graz, Austria.
| | - Michael G Ramsey
- Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, A-8010 Graz, Austria.
| | - Martin Sterrer
- Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, A-8010 Graz, Austria.
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2
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Hurdax P, Kern CS, Boné TG, Haags A, Hollerer M, Egger L, Yang X, Kirschner H, Gottwald A, Richter M, Bocquet F, Soubatch S, Koller G, Tautz FS, Sterrer M, Puschnig P, Ramsey MG. Large Distortion of Fused Aromatics on Dielectric Interlayers Quantified by Photoemission Orbital Tomography. ACS NANO 2022; 16:17435-17443. [PMID: 36239301 PMCID: PMC9620409 DOI: 10.1021/acsnano.2c08631] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Accepted: 10/12/2022] [Indexed: 06/16/2023]
Abstract
Polycyclic aromatic compounds with fused benzene rings offer an extraordinary versatility as next-generation organic semiconducting materials for nanoelectronics and optoelectronics due to their tunable characteristics, including charge-carrier mobility and optical absorption. Nonplanarity can be an additional parameter to customize their electronic and optical properties without changing the aromatic core. In this work, we report a combined experimental and theoretical study in which we directly observe large, geometry-induced modifications in the frontier orbitals of a prototypical dye molecule when adsorbed on an atomically thin dielectric interlayer on a metallic substrate. Experimentally, we employ angle-resolved photoemission experiments, interpreted in the framework of the photoemission orbital tomography technique. We demonstrate its sensitivity to detect geometrical bends in adsorbed molecules and highlight the role of the photon energy used in experiment for detecting such geometrical distortions. Theoretically, we conduct density functional calculations to determine the geometric and electronic structure of the adsorbed molecule and simulate the photoemission angular distribution patterns. While we found an overall good agreement between experimental and theoretical data, our results also unveil limitations in current van der Waals corrected density functional approaches for such organic/dielectric interfaces. Hence, photoemission orbital tomography provides a vital experimental benchmark for such systems. By comparison with the state of the same molecule on a metallic substrate, we also offer an explanation why the adsorption on the dielectric induces such large bends in the molecule.
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Affiliation(s)
- Philipp Hurdax
- Institute
of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010Graz, Austria
| | - Christian S. Kern
- Institute
of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010Graz, Austria
| | - Thomas Georg Boné
- Institute
of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010Graz, Austria
| | - Anja Haags
- Peter
Grünberg Institute (PGI-3), Forschungszentrum
Jülich, 52425Jülich, Germany
- Jülich
Aachen Research Alliance (JARA), Fundamentals
of Future Information Technology, 52425Jülich, Germany
- Experimentalphysik
IV A, RWTH Aachen University, 52074Aachen, Germany
| | - Michael Hollerer
- Institute
of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010Graz, Austria
| | - Larissa Egger
- Institute
of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010Graz, Austria
| | - Xiaosheng Yang
- Peter
Grünberg Institute (PGI-3), Forschungszentrum
Jülich, 52425Jülich, Germany
- Jülich
Aachen Research Alliance (JARA), Fundamentals
of Future Information Technology, 52425Jülich, Germany
- Experimentalphysik
IV A, RWTH Aachen University, 52074Aachen, Germany
| | - Hans Kirschner
- Physikalisch-Technische
Bundesanstalt (PTB), 10587Berlin, Germany
| | | | - Mathias Richter
- Physikalisch-Technische
Bundesanstalt (PTB), 10587Berlin, Germany
| | - François
C. Bocquet
- Peter
Grünberg Institute (PGI-3), Forschungszentrum
Jülich, 52425Jülich, Germany
- Jülich
Aachen Research Alliance (JARA), Fundamentals
of Future Information Technology, 52425Jülich, Germany
| | - Serguei Soubatch
- Peter
Grünberg Institute (PGI-3), Forschungszentrum
Jülich, 52425Jülich, Germany
- Jülich
Aachen Research Alliance (JARA), Fundamentals
of Future Information Technology, 52425Jülich, Germany
| | - Georg Koller
- Institute
of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010Graz, Austria
| | - Frank Stefan Tautz
- Peter
Grünberg Institute (PGI-3), Forschungszentrum
Jülich, 52425Jülich, Germany
- Jülich
Aachen Research Alliance (JARA), Fundamentals
of Future Information Technology, 52425Jülich, Germany
- Experimentalphysik
IV A, RWTH Aachen University, 52074Aachen, Germany
| | - Martin Sterrer
- Institute
of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010Graz, Austria
| | - Peter Puschnig
- Institute
of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010Graz, Austria
| | - Michael G. Ramsey
- Institute
of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010Graz, Austria
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3
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Richter NF, Risse T. Defects of thin CaO(001) on Mo(001): an EPR spectroscopic perspective. Phys Chem Chem Phys 2022; 24:7732-7738. [PMID: 35293416 DOI: 10.1039/d2cp00389a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Paramagnetic defects of thin CaO(001) films grown on Mo(001) are characterized using electron paramagnetic resonance (EPR) spectroscopy under ultrahigh vacuum conditions. A variety of paramagnetic centers located in the volume of the films are identified whose speciation as well as relative abundance was found to depend on the growth rate of the films. Pristine films prepared at a lower growth rate exhibited a larger number and a different speciation of paramagnetic defects than films grown at a higher rate. Annealing of the films to 1030 K, which improves their long-range order, results in quenching of most of the paramagnetic species observed for the pristine film; however, films prepared at a lower growth rate exhibit new paramagnetic signals upon annealing, which are absent in films prepared at a higher growth rate. The signals can be assigned to paramagnetic Mo ions previously shown to diffuse into these films. These results indicate that the amount and speciation of the transition metal ions depend on the preparation conditions which in turn can also affect the surface chemistry of these systems.
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Affiliation(s)
- Nina F Richter
- Institut für Chemie und Biochemie, Freie Universität Berlin, Arnimallee 22, 14195 Berlin, Germany.
| | - Thomas Risse
- Institut für Chemie und Biochemie, Freie Universität Berlin, Arnimallee 22, 14195 Berlin, Germany.
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4
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Chen Y, Bae Y, Heinrich AJ. Harnessing the Quantum Behavior of Spins on Surfaces. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2022:e2107534. [PMID: 34994026 DOI: 10.1002/adma.202107534] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Revised: 12/28/2021] [Indexed: 06/14/2023]
Abstract
The desire to control and measure individual quantum systems such as atoms and ions in a vacuum has led to significant scientific and engineering developments in the past decades that form the basis of today's quantum information science. Single atoms and molecules on surfaces, on the other hand, are heavily investigated by physicists, chemists, and material scientists in search of novel electronic and magnetic functionalities. These two paths crossed in 2015 when it was first clearly demonstrated that individual spins on a surface can be coherently controlled and read out in an all-electrical fashion. The enabling technique is a combination of scanning tunneling microscopy (STM) and electron spin resonance, which offers unprecedented coherent controllability at the Angstrom length scale. This review aims to illustrate the essential ingredients that allow the quantum operations of single spins on surfaces. Three domains of applications of surface spins, namely quantum sensing, quantum control, and quantum simulation, are discussed with physical principles explained and examples presented. Enabled by the atomically-precise fabrication capability of STM, single spins on surfaces might one day lead to the realization of quantum nanodevices and artificial quantum materials at the atomic scale.
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Affiliation(s)
- Yi Chen
- Center for Quantum Nanoscience, Institute for Basic Science (IBS), Seoul, 03760, Korea
- Department of Physics, Ewha Womans University, Seoul, 03760, Korea
| | - Yujeong Bae
- Center for Quantum Nanoscience, Institute for Basic Science (IBS), Seoul, 03760, Korea
- Department of Physics, Ewha Womans University, Seoul, 03760, Korea
| | - Andreas J Heinrich
- Center for Quantum Nanoscience, Institute for Basic Science (IBS), Seoul, 03760, Korea
- Department of Physics, Ewha Womans University, Seoul, 03760, Korea
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5
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Helmreich R, Classen A, Fauster T. Negative electron affinity opens quantum well in MgO layers on Ag(100). JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 34:045001. [PMID: 34670197 DOI: 10.1088/1361-648x/ac316c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2021] [Accepted: 10/20/2021] [Indexed: 06/13/2023]
Abstract
Epitaxial MgO films on Ag(100) were studied by photoelectron spectroscopy. From the low-energy part of the spectra we obtain a negative electron affinity of about -0.9 eV. Even though electrons in the lowest conduction band are not confined by a potential barrier at the surface, quantum-well resonances are observed. The dispersion of the conduction band is determined in good agreement with theoretical calculations. Aspects of observing image-potential states predicted by theory on MgO films are discussed.
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Affiliation(s)
- Rebecca Helmreich
- Lehrstuhl für Festkörperphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstraße 7, 91058 Erlangen, Germany
| | - Andrej Classen
- Lehrstuhl für Festkörperphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstraße 7, 91058 Erlangen, Germany
| | - Thomas Fauster
- Lehrstuhl für Festkörperphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstraße 7, 91058 Erlangen, Germany
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6
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De Santis M, Langlais V, Schneider K, Torrelles X. Growth-mode and interface structure of epitaxial ultrathin MgO/Ag(001) films. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:265002. [PMID: 33902021 DOI: 10.1088/1361-648x/abfb8e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Accepted: 04/26/2021] [Indexed: 06/12/2023]
Abstract
MgO ultrathin films are of great technological importance as electron tunneling barrier in electronics and spintronics, and as template for metallic clusters in catalysis and for molecular networks for 2D electronics. The wide band-gap of MgO allows for a very effective decoupling from the substrate. The films morphology and the detailed structure of the interface are crucial for applications, controlling the electronic transfer. Using surface x-ray diffraction, we studied the growth-mode and the structure of MgO/Ag(001) ultrathin films elaborated by reactive molecular beam epitaxy as function of the substrate temperature. We observed that deposition of about 1 monolayer results in an MgO(001) film in coherent epitaxy, with the oxygen atoms on top of silver as predicted by DFT calculations, and an interlayer distance at the interface of about 270 pm. Under well-defined conditions, a sharp MgO bilayer is formed covering a fraction of the substrate surface.
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Affiliation(s)
- M De Santis
- Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 38042 Grenoble, France
| | - V Langlais
- CEMES, UPR8011, CNRS, Université de Toulouse, 29 rue Jeanne Marvig, B.P. 94347, 31055 Toulouse cedex 4, France
| | - K Schneider
- CEMES, UPR8011, CNRS, Université de Toulouse, 29 rue Jeanne Marvig, B.P. 94347, 31055 Toulouse cedex 4, France
| | - X Torrelles
- Institut de Ciència de Materials de Barcelona (ICMAB), CSIC, Bellaterra, 08193 Barcelona, Spain
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7
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Gogate MR. New perspectives on the nature and imaging of active site in small metallic particles: II. Electronic effects. CHEM ENG COMMUN 2021. [DOI: 10.1080/00986445.2020.1719078] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
- Makarand R. Gogate
- Independent Consultant for ChE Education and Research, Aurangabad, Maharashtra, India
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8
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Ninova S, Malcıoğlu OB, Auburger P, Franke M, Lytken O, Steinrück HP, Bockstedte M. Morphology dependent interaction between Co(II)-tetraphenylporphyrin and the MgO(100) surface. Phys Chem Chem Phys 2021; 23:2105-2116. [PMID: 33437981 PMCID: PMC8431532 DOI: 10.1039/d0cp04859c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Porphyrins are key elements in organic–inorganic hybrid systems for a wide range of applications. Understanding their interaction with the substrate gives a handle on structural and electronic device properties. Here we investigate a single transition-metal porphyrin, namely Co(ii)-tetraphenylporphyrin (CoTPP), on the MgO(100) surface and the effect of multilayer film formation within hybrid density-functional theory and many-body perturbation theory. We focus on the relevant adsorption sites, simulate their photoemission spectra as a key fingerprint and compare with experiments on MgO(100) films on Ag(100). While we find only weak interaction between the cobalt centre and terrace sites on the MgO(100) surface, a strong interaction manifests itself with the low-coordinated sites. This leads to distinct features in both the valence and core-level regions of the electronic structure, as observed in the ultraviolet and X-ray photoemission spectra, corroborated by simulated spectra and calculated cobalt core-level shifts. Our work thus demonstrates the relevance of morphology-related low-coordinated sites and their properties in the adsorption of CoTPP on the MgO(100) surface. The adsorption of Co-tetraphenylporphyrin at relevant low-coordinated sites on MgO(100) shows distinct features from terrace-site and multilayer films in the near-valence and corelevel regions of the electronic structure.![]()
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Affiliation(s)
- Silviya Ninova
- Chemistry and Physics of Materials, Paris-Lodron University Salzburg, Jakob-Haringer-Str. 2a, A-5020 Salzburg, Austria.
| | - Osman Barış Malcıoğlu
- Chemistry and Physics of Materials, Paris-Lodron University Salzburg, Jakob-Haringer-Str. 2a, A-5020 Salzburg, Austria.
| | - Philipp Auburger
- Theoretische Festkörperphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstr. 7B2, D-91058 Erlangen, Germany
| | - Matthias Franke
- Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 3, D-91058 Erlangen, Germany
| | - Ole Lytken
- Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 3, D-91058 Erlangen, Germany
| | - Hans-Peter Steinrück
- Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstr. 3, D-91058 Erlangen, Germany
| | - Michel Bockstedte
- Chemistry and Physics of Materials, Paris-Lodron University Salzburg, Jakob-Haringer-Str. 2a, A-5020 Salzburg, Austria. .,Theoretische Festkörperphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstr. 7B2, D-91058 Erlangen, Germany.,Institut für Theoretische Physik, Johannes-Kepler-Universität Linz, Altenberger Str. 68, A-4040 Linz, Austria
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9
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Biswas A, Swarnkar A, Pandey P, Kour P, Parmar S, Ogale S. Dynamics of Photo-Generated Carriers across the Interface between CsPbBr 3 Nanocrystals and Au-Ag Nanostructured Film, and Its Control via Ultrathin MgO Interface Layer. ACS OMEGA 2020; 5:11915-11922. [PMID: 32548370 PMCID: PMC7271035 DOI: 10.1021/acsomega.9b03817] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/10/2019] [Accepted: 05/05/2020] [Indexed: 06/11/2023]
Abstract
The dynamics and control of charge transfer between optoelectronically interesting and size-tunable halide perovskite quantum dots and other juxtaposed functional electronic materials are important issues for the emergent device interest involving such a family of materials in heterostructure configurations. Herein, we have grown bimetallic Au-Ag thin films on glass by pulsed laser deposition at room temperature, which bear nanoparticulate character, and the corresponding optical absorption spectra reveal the expected surface plasmon resonance signature(s). Subsequently, spin-coated CsPbBr3 nanoparticle films onto the bimetallic Au-Ag films exhibit surface-enhanced Raman scattering as well as strong photoluminescence quenching, the latter reflecting highly efficient transfer of photo-generated carriers across the CsPbBr3/Au-Ag interface. Surprisingly, when an ultrathin MgO (insulating) layer of optimum thickness is introduced between the CsPbBr3 and Au-Ag films, the charge transfer is further facilitated with the average lifetime of carriers becoming even shorter. By changing the thickness of the thin MgO layer, the carrier lifetime can in fact be tuned; with the charge transfer getting fully blocked for thick enough MgO layers, as expected. Our study thus throws light on the charge-carrier dynamics in halide perovskites, which is of importance to emergent optoelectronic applications.
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Affiliation(s)
- Abhijit Biswas
- Department
of Physics and Centre for Energy Science, Indian Institute of Science Education and Research (IISER), Pune, Pune, Maharashtra 411008, India
| | - Abhishek Swarnkar
- Department
of Physics and Centre for Energy Science, Indian Institute of Science Education and Research (IISER), Pune, Pune, Maharashtra 411008, India
| | - Padmini Pandey
- Department
of Physics and Centre for Energy Science, Indian Institute of Science Education and Research (IISER), Pune, Pune, Maharashtra 411008, India
| | - Prachi Kour
- Department
of Physics and Centre for Energy Science, Indian Institute of Science Education and Research (IISER), Pune, Pune, Maharashtra 411008, India
| | - Swati Parmar
- Department
of Physics and Centre for Energy Science, Indian Institute of Science Education and Research (IISER), Pune, Pune, Maharashtra 411008, India
| | - Satishchandra Ogale
- Department
of Physics and Centre for Energy Science, Indian Institute of Science Education and Research (IISER), Pune, Pune, Maharashtra 411008, India
- Research
Institute for Sustainable Energy (RISE), TCG Centres for Research and Education in Science and Technology
(TCG-CREST), Kolkata 700091, India
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10
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Freund HJ, Heyde M, Kuhlenbeck H, Nilius N, Risse T, Schmidt T, Shaikhutdinov S, Sterrer M. Chapter model systems in heterogeneous catalysis at the atomic level: a personal view. Sci China Chem 2020. [DOI: 10.1007/s11426-019-9671-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
AbstractThe review presents an overview of studies in the surface science of oxide and related surfaces with an emphasis of the studies performed in the authors’ group. Novel instruments and technique developments, as well as their applications are reported, in an attempt to cover studies on model systems of increasing complexity, including some of the key ingredients of an industrially applied heterogeneous catalyst and its fabrication. The review is intended to demonstrate the power of model studies in understanding heterogeneous catalysis at the atomic level. The studies include those on supported nano-particles, both, prepared in vacuum and from solution, interaction of surfaces and the underlying bulk with molecules from the gas phase, strong metal support interaction, as well as the first attempt to include studies on reactions in confined spaces.
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11
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Kremer G, Alvarez Quiceno JC, Lisi S, Pierron T, González C, Sicot M, Kierren B, Malterre D, Rault JE, Le Fèvre P, Bertran F, Dappe YJ, Coraux J, Pochet P, Fagot-Revurat Y. Electronic Band Structure of Ultimately Thin Silicon Oxide on Ru(0001). ACS NANO 2019; 13:4720-4730. [PMID: 30916924 DOI: 10.1021/acsnano.9b01028] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Silicon oxide can be formed in a crystalline form, when prepared on a metallic substrate. It is a candidate support catalyst and possibly the ultimately thin version of a dielectric host material for two-dimensional materials and heterostructures. We determine the atomic structure and chemical bonding of the ultimately thin version of the oxide, epitaxially grown on Ru(0001). In particular, we establish the existence of two sublattices defined by metal-oxygen-silicon bridges involving inequivalent substrate sites. We further discover four electronic bands below the Fermi level, at high binding energy, two of them having a linear dispersion at their crossing K point (Dirac cones) and two others forming semiflat bands. While the latter two correspond to hybridized states between the oxide and the metal, the former relate to the topmost silicon-oxygen plane, which is not directly coupled to the substrate. Our analysis is based on high-resolution X-ray photoelectron spectroscopy, angle-resolved photoemission spectroscopy, scanning tunneling microscopy, and density functional theory calculations.
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Affiliation(s)
- Geoffroy Kremer
- Institut Jean Lamour , UMR 7198, CNRS-Université de Lorraine, Campus ARTEM, 2 Allée André Guinier , BP 50840, 54011 Nancy , France
| | | | - Simone Lisi
- Univ. Grenoble Alpes, CNRS, Grenoble INP, Institut Néel , 38000 Grenoble , France
| | - Thomas Pierron
- Institut Jean Lamour , UMR 7198, CNRS-Université de Lorraine, Campus ARTEM, 2 Allée André Guinier , BP 50840, 54011 Nancy , France
| | - César González
- Departamento de Física Teórica de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias , Universidad Autónoma de Madrid , E-28049 Madrid , Spain
| | - Muriel Sicot
- Institut Jean Lamour , UMR 7198, CNRS-Université de Lorraine, Campus ARTEM, 2 Allée André Guinier , BP 50840, 54011 Nancy , France
| | - Bertrand Kierren
- Institut Jean Lamour , UMR 7198, CNRS-Université de Lorraine, Campus ARTEM, 2 Allée André Guinier , BP 50840, 54011 Nancy , France
| | - Daniel Malterre
- Institut Jean Lamour , UMR 7198, CNRS-Université de Lorraine, Campus ARTEM, 2 Allée André Guinier , BP 50840, 54011 Nancy , France
| | - Julien E Rault
- Synchrotron SOLEIL , Saint-Aubin , BP 48, F-91192 Gif-sur-Yvette Cedex, France
| | - Patrick Le Fèvre
- Synchrotron SOLEIL , Saint-Aubin , BP 48, F-91192 Gif-sur-Yvette Cedex, France
| | - François Bertran
- Synchrotron SOLEIL , Saint-Aubin , BP 48, F-91192 Gif-sur-Yvette Cedex, France
| | - Yannick J Dappe
- SPEC, CEA, CNRS , Université Paris-Saclay , CEA Saclay, 91191 Gif-sur-Yvette Cedex, France
| | - Johann Coraux
- Univ. Grenoble Alpes, CNRS, Grenoble INP, Institut Néel , 38000 Grenoble , France
| | - Pascal Pochet
- Laboratoire de Simulation Atomistique , Univ. Grenoble Alpes & CEA , 38054 Grenoble , France
| | - Yannick Fagot-Revurat
- Institut Jean Lamour , UMR 7198, CNRS-Université de Lorraine, Campus ARTEM, 2 Allée André Guinier , BP 50840, 54011 Nancy , France
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12
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Barcaro G, Fortunelli A. 2D oxides on metal materials: concepts, status, and perspectives. Phys Chem Chem Phys 2019; 21:11510-11536. [DOI: 10.1039/c9cp00972h] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Two-dimensional oxide-on-metal materials: concepts, methods, and link to technological applications, with 5 subtopics: structural motifs, robustness, catalysis, ternaries, and nanopatterning.
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13
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Blades WH, Reinke P. From Alloy to Oxide: Capturing the Early Stages of Oxidation on Ni-Cr(100) Alloys. ACS APPLIED MATERIALS & INTERFACES 2018; 10:43219-43229. [PMID: 30452217 DOI: 10.1021/acsami.8b15210] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The interaction of oxygen with Ni-Cr(100) alloy surfaces is studied using scanning tunneling microscopy (STM) and spectroscopy (STS) to observe the initial steps of oxidation and formation of the alloy-oxide interface. The progression of oxidation was observed for Ni(100) and Ni-Cr(100) thin films including Ni-8 wt % Cr(100) and Ni-12 wt % Cr(100), which were grown on MgO(100) in situ. These surfaces were exposed to between 1 and 150 L O2 at 500 °C, and additional annealing steps were performed at 500 and 600 °C. Each oxidation and annealing step was studied with STM and STS, and differential conductance maps delivered spatially resolved information on doping and band gap distributions. Initial NiO nucleation and growth begins along the step edges of the Ni-Cr alloy accompanied by the formation of small oxide particles on the terraces. The incubation period known in oxidation of Ni(100) is absent on Ni-Cr alloy surfaces illustrating the significant changes in surface chemistry triggered by Cr-alloying. Step edge faceting is initiated by oxide decoration along the step edges and is expressed as moiré patterns in the STM images. The surface oxide can be characterized by NiONi(6 × 7) and NiO-Ni(7 × 8) coincidence lattices, which have a cube-on-cube epitaxial relationship. Small patches of NiO are susceptible to reduction during annealing; however, additional oxide coverage stabilizes the NiO. NiO regions are interspersed with areas covered predominantly with a novel cross-type reconstruction, which is interpreted tentatively as a Cr-rich, phase-separated region. Statistical analysis of the geometric features of the surface oxide including step edge heights, and NiO wedge angles illustrates the layer-by-layer growth mode of NiO in this pre-Cabrera-Mott regime, and the restructuring of the alloy-oxide interface during the oxidation process. This experimental approach has offered greater insight into the progression of oxide growth in Ni-Cr thin films and underscores the dramatic impact of alloying on oxidation process in the pre-Cabrera-Mott regime.
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Affiliation(s)
- William H Blades
- Department of Materials Science and Engineering , University of Virginia , Charlottesville , Virginia 22904 , United States
| | - Petra Reinke
- Department of Materials Science and Engineering , University of Virginia , Charlottesville , Virginia 22904 , United States
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Di Filippo G, Classen A, Pöschel R, Fauster T. Interaction of free-base tetraphenylporphyrin with magnesium oxide: Influence of MgO morphology on metalation. J Chem Phys 2018; 146:064702. [PMID: 28201886 DOI: 10.1063/1.4975229] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Using x-ray photoemission spectroscopy, we investigated the self-metalation of free-base tetraphenylporphyrin (2HTPP) on thin MgO(100) films on Ag(100). The deposition of one monolayer 2HTPP on MgO results in the formation of magnesium(ii) tetraphenylporphyrin (MgTPP) at room temperature. We demonstrate that the efficiency of the reaction drastically depends on the morphology of the oxide layers. The latter is changed by varying the substrate temperature during the oxide growth. We observe the complete metalation of the 2HTPP monolayer when the MgO films are grown at 393 K. The increase of the growth temperature to 573 K leads to the reduction of the percentage of metalated molecules to ∼50%. We ascribe these results to the fact that MgTPP formation takes place through the hydroxilation of steps and defects on the MgO surface, which leads to an increase of the OH component in the O 1s line.
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Affiliation(s)
- Gianluca Di Filippo
- Lehrstuhl für Festkörperphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstraße 7, 91058 Erlangen, Germany
| | - Andrej Classen
- Lehrstuhl für Festkörperphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstraße 7, 91058 Erlangen, Germany
| | - Rebecca Pöschel
- Lehrstuhl für Festkörperphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstraße 7, 91058 Erlangen, Germany
| | - Thomas Fauster
- Lehrstuhl für Festkörperphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstraße 7, 91058 Erlangen, Germany
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15
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Yildirim H, Pachter R. Mechanistic Analysis of Oxygen Vacancy-Driven Conductive Filament Formation in Resistive Random Access Memory Metal/NiO/Metal Structures. ACS APPLIED MATERIALS & INTERFACES 2018; 10:9802-9816. [PMID: 29488379 DOI: 10.1021/acsami.7b17645] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Electrically switchable resistive random access memories have drawn much interest as nonvolatile memory device candidates based on metal-insulator-metal (MIM) structure concepts. However, atomic level mechanisms that lead to conductive filament (CF) formation in MIM structures are often lacking, such as for the system with NiO as the oxide layer, which was found promising for resistive random access memory (RRAM) device applications. In this work, using density functional theory with a Hubbard-type on-site Coulomb correction, which we carefully benchmarked, we analyzed the intrinsic propensity toward CF formation in NiO upon introduction of oxygen vacancies, including interfacial effects of Ag or Pt electrodes. First, for stoichiometric MIM structural models, contributions from metal-induced gap states to the electronic density of states (DOS) were identified, accommodating oxygen vacancy states and showing that the interface region is reduced more easily than the bulklike region, for example, for the Ag/NiO/Ag structure. Moreover, a tendency toward oxygen vacancy clustering was demonstrated, important for CF formation. Indeed, by introducing ordered oxygen vacancies into the oxide layer for both MIM models, several extended defect states within the forbidden gap have resulted, which lead to defect-assisted transport. These were shown to be influenced by the spatial distribution and number of oxygen vacancies in the filament, where the degree of reduction of Ni atoms changes based on the immediate surroundings. Projected electronic DOS for individual Ni atoms in regions near and away from oxygen vacancies indicated that those Ni close to oxygen vacancies contribute most to the conductivity. Interestingly, based on charge analyses, these atoms are revealed to undergo significant reduction, generating a locally conductive region in the oxide layer that consists of metallic/near-metallic Ni (Ni0), formed through local reduction.
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Affiliation(s)
- Handan Yildirim
- Air Force Research Laboratory, Materials and Manufacturing Directorate , Wright-Patterson Air Force Base , Dayton , Ohio 45433 , United States
| | - Ruth Pachter
- Air Force Research Laboratory, Materials and Manufacturing Directorate , Wright-Patterson Air Force Base , Dayton , Ohio 45433 , United States
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16
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Katsube D, Yamashita H, Abo S, Abe M. Combined pulsed laser deposition and non-contact atomic force microscopy system for studies of insulator metal oxide thin films. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2018; 9:686-692. [PMID: 29527442 PMCID: PMC5827635 DOI: 10.3762/bjnano.9.63] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Accepted: 01/26/2018] [Indexed: 06/09/2023]
Abstract
We have designed and developed a combined system of pulsed laser deposition (PLD) and non-contact atomic force microscopy (NC-AFM) for observations of insulator metal oxide surfaces. With this system, the long-period iterations of sputtering and annealing used in conventional methods for preparing a metal oxide film surface are not required. The performance of the combined system is demonstrated for the preparation and high-resolution NC-AFM imaging of atomically flat thin films of anatase TiO2(001) and LaAlO3(100).
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Affiliation(s)
- Daiki Katsube
- Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan
| | - Hayato Yamashita
- Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan
- also at PRESTO, JST, 4-1-8, Honcho, Kawaguchi, Saitama. 332-0012, Japan
| | - Satoshi Abo
- Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan
| | - Masayuki Abe
- Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan
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17
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Pacchioni G, Freund HJ. Controlling the charge state of supported nanoparticles in catalysis: lessons from model systems. Chem Soc Rev 2018; 47:8474-8502. [DOI: 10.1039/c8cs00152a] [Citation(s) in RCA: 110] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Model systems are very important to identify the working principles of real catalysts, and to develop concepts that can be used in the design of new catalytic materials.
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Affiliation(s)
| | - Hans-Joachim Freund
- Fritz-Haber-Institut der Max-Planck-Gesellschaft
- Department of Chemical Physics
- 14195 Berlin
- Germany
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18
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Schneider WD, Heyde M, Freund HJ. Charge Control in Model Catalysis: The Decisive Role of the Oxide-Nanoparticle Interface. Chemistry 2017; 24:2317-2327. [PMID: 28857287 DOI: 10.1002/chem.201703169] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2017] [Indexed: 11/06/2022]
Abstract
In chemistry and physics the electronic charge on a species or material is one important determinant of its properties. In the present Minireview, the essential requirements for a model catalyst system suitable to study charge control are discussed. The ideal model catalyst for this purpose consists of a material system, which comprises a single crystal metal support, covered by an epitaxially grown ultrathin oxide film, and flat, two-dimensional nanoparticles residing on this film. Several examples from the literature are selected and presented, which illustrate various aspects of electron transport from the support to the nanoparticle and vice versa. Key experiments demonstrate charge control within such model catalysts and give direct evidence for a chemical reaction at the perimeter of Au nanoparticles. The concepts derived from these studies are then taken a step further to see how they may be applied for bulk powder oxide supported nanoparticles as they are frequently found in catalytically active materials.
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Affiliation(s)
- Wolf-Dieter Schneider
- Department of Chemical Physics, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195, Berlin, Germany
| | - Markus Heyde
- Department of Chemical Physics, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195, Berlin, Germany
| | - Hans-Joachim Freund
- Department of Chemical Physics, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195, Berlin, Germany
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19
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Vaida ME, Bernhardt TM. Tuning the ultrafast photodissociation dynamics of CH 3 Br on ultrathin MgO films by reducing the layer thickness to the 2D limit. Chem Phys Lett 2017. [DOI: 10.1016/j.cplett.2017.09.019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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20
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Chan WY, Lu SM, Su WB, Liao CC, Hoffmann G, Tsai TR, Chang CS. Sharpness-induced energy shifts of quantum well states in Pb islands on Cu(111). NANOTECHNOLOGY 2017; 28:095706. [PMID: 28135205 DOI: 10.1088/1361-6528/aa583a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We elucidate that the tip sharpness in scanning tunneling microscopy (STM) can be characterized through the number of field-emission (FE) resonances. A higher number of FE resonances indicates higher sharpness. We observe empty quantum well (QW) states in Pb islands on Cu(111) under different tip sharpness levels. We found that QW states observed by sharper tips always had lower energies, revealing negative energy shifts. This sharpness-induced energy shift originates from an inhomogeneous electric field in the STM gap. An increase in sharpness increases the electric field inhomogeneity, that is, enhances the electric field near the tip apex, but weakens the electric field near the sample. As a result, higher sharpness can increase the electronic phase in vacuum, causing the lowering of QW state energies. Moreover, the behaviors of negative energy shift as a function of state energy are entirely different for Pb islands with a thickness of two and nine atomic layers. This thickness-dependent behavior results from the electrostatic force in the STM gap decreasing with increasing tip sharpness. The variation of the phase contributed from the expansion deformation induced by the electrostatic force in a nine-layer Pb island is significantly greater, sufficient to effectively negate the increase of electronic phase in vacuum.
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Affiliation(s)
- Wen-Yuan Chan
- Institute of Physics, Academia Sinica, Nankang, Taipei 11529, Taiwan, Republic of China
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21
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Franke M, Wechsler D, Tariq Q, Röckert M, Zhang L, Kumar Thakur P, Tsud N, Bercha S, Prince K, Lee TL, Steinrück HP, Lytken O. Interfacial interactions between CoTPP molecules and MgO(100) thin films. Phys Chem Chem Phys 2017; 19:11549-11553. [PMID: 28425530 DOI: 10.1039/c7cp00442g] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We have investigated the interactions between cobalt(ii)-tetraphenylporphyrin molecules and MgO(100) thin films on Ag(100) by means of synchrotron radiation X-ray and ultra-violet photoelectron spectroscopy.
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22
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Kumagai T, Liu S, Shiotari A, Baugh D, Shaikhutdinov S, Wolf M. Local electronic structure, work function, and line defect dynamics of ultrathin epitaxial ZnO layers on a Ag(1 1 1) surface. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:494003. [PMID: 27731306 DOI: 10.1088/0953-8984/28/49/494003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Using combined low-temperature scanning tunneling microscopy and Kelvin probe force microscopy we studied the local electronic structure and work function change of the (0 0 0 1)-oriented epitaxial ZnO layers on a Ag(1 1 1) substrate. Scanning tunneling spectroscopy (STS) revealed that the conduction band minimum monotonically downshifts as the number of the ZnO layers increases up to 4 monolayers (ML). However, it was found by field emission resonance (FER) spectroscopy that the local work function of Ag(1 1 1) slightly decreases for 2 ML thick ZnO but it dramatically changes and drops by about 1.2 eV between 2 and 3 ML, suggesting a structural transformation of the ZnO layer. The spatial variation of the conduction band minimum and the local work function change were visualized at the nanometer scale by mapping the STS and FER intensities. Furthermore, we found that the ZnO layers contained line defects with a few tens of nm long, which can be removed by the injection of a tunneling electron into the conduction band.
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23
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Töpfer K, Tremblay JC. How surface reparation prevents catalytic oxidation of carbon monoxide on atomic gold at defective magnesium oxide surfaces. Phys Chem Chem Phys 2016; 18:18590-7. [PMID: 27345190 DOI: 10.1039/c6cp02339h] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this contribution, we study using first principles the co-adsorption and catalytic behaviors of CO and O2 on a single gold atom deposited at defective magnesium oxide surfaces. Using cluster models and point charge embedding within a density functional theory framework, we simulate the CO oxidation reaction for Au1 on differently charged oxygen vacancies of MgO(001) to rationalize its experimentally observed lack of catalytic activity. Our results show that: (1) co-adsorption is weakly supported at F(0) and F(2+) defects but not at F(1+) sites, (2) electron redistribution from the F(0) vacancy via the Au1 cluster to the adsorbed molecular oxygen weakens the O2 bond, as required for a sustainable catalytic cycle, (3) a metastable carbonate intermediate can form on defects of the F(0) type, (4) only a small activation barrier exists for the highly favorable dissociation of CO2 from F(0), and (5) the moderate adsorption energy of the gold atom on the F(0) defect cannot prevent insertion of molecular oxygen inside the defect. Due to the lack of protection of the color centers, the surface becomes invariably repaired by the surrounding oxygen and the catalytic cycle is irreversibly broken in the first oxidation step.
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Affiliation(s)
- Kai Töpfer
- Freie Universität Berlin, Takustraße 3, 14195 Berlin, Germany.
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24
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Wäckerlin C, Donati F, Singha A, Baltic R, Rusponi S, Diller K, Patthey F, Pivetta M, Lan Y, Klyatskaya S, Ruben M, Brune H, Dreiser J. Giant Hysteresis of Single-Molecule Magnets Adsorbed on a Nonmagnetic Insulator. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2016; 28:5195-5199. [PMID: 27159732 DOI: 10.1002/adma.201506305] [Citation(s) in RCA: 89] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Revised: 04/02/2016] [Indexed: 06/05/2023]
Abstract
TbPc2 single-molecule magnets adsorbed on a magnesium oxide tunnel barrier exhibit record magnetic remanence, record hysteresis opening, perfect out-of-plane alignment of the magnetic easy axes, and self-assembly into a well-ordered layer.
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Affiliation(s)
- Christian Wäckerlin
- Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Lausanne, Switzerland
| | - Fabio Donati
- Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Lausanne, Switzerland
| | - Aparajita Singha
- Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Lausanne, Switzerland
| | - Romana Baltic
- Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Lausanne, Switzerland
| | - Stefano Rusponi
- Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Lausanne, Switzerland
| | - Katharina Diller
- Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Lausanne, Switzerland
| | - François Patthey
- Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Lausanne, Switzerland
| | - Marina Pivetta
- Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Lausanne, Switzerland
| | - Yanhua Lan
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76344, Eggenstein-Leopoldshafen, Germany
| | - Svetlana Klyatskaya
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76344, Eggenstein-Leopoldshafen, Germany
| | - Mario Ruben
- Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), D-76344, Eggenstein-Leopoldshafen, Germany
- Institut de Physique et Chimie des Matériaux (IPCMS), Université de Strasbourg, F-67034, Strasbourg, France
| | - Harald Brune
- Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Lausanne, Switzerland
| | - Jan Dreiser
- Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015, Lausanne, Switzerland
- Swiss Light Source, Paul Scherrer Institut (PSI), CH-5232, Villigen, Switzerland
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25
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Su WB, Lin CL, Chan WY, Lu SM, Chang CS. Field enhancement factors and self-focus functions manifesting in field emission resonances in scanning tunneling microscopy. NANOTECHNOLOGY 2016; 27:175705. [PMID: 26983371 DOI: 10.1088/0957-4484/27/17/175705] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Field emission (FE) resonance (or Gundlach oscillation) in scanning tunneling microscopy (STM) is a phenomenon in which the FE electrons emitted from the microscope tip couple into the quantized standing-wave states within the STM tunneling gap. Although the occurrence of FE resonance peaks can be semi-quantitatively described using the triangular potential well model, it cannot explain the experimental observation that the number of resonance peaks may change under the same emission current. This study demonstrates that the aforementioned variation can be adequately explained by introducing a field enhancement factor that is related to the local electric field at the tip apex. The peak number of FE resonances increases with the field enhancement factor. The peak intensity of the FE resonance on the reconstructed Au(111) surface varies in the face-center cubic, hexagonal-close-packed, and ridge regions, thus providing the contrast in the mapping through FE resonances. The mapping contrast is demonstrated to be nearly independent of the tip-sample distance, implying that the FE electron beam is not divergent because of a self-focus function intrinsically involved in the STM configuration.
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Affiliation(s)
- Wei-Bin Su
- Institute of Physics, Academia Sinica, Nankang, Taipei 11529, Taiwan
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26
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Baumann S, Donati F, Stepanow S, Rusponi S, Paul W, Gangopadhyay S, Rau IG, Pacchioni GE, Gragnaniello L, Pivetta M, Dreiser J, Piamonteze C, Lutz CP, Macfarlane RM, Jones BA, Gambardella P, Heinrich AJ, Brune H. Origin of Perpendicular Magnetic Anisotropy and Large Orbital Moment in Fe Atoms on MgO. PHYSICAL REVIEW LETTERS 2015; 115:237202. [PMID: 26684139 DOI: 10.1103/physrevlett.115.237202] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2015] [Indexed: 06/05/2023]
Abstract
We report on the magnetic properties of individual Fe atoms deposited on MgO(100) thin films probed by x-ray magnetic circular dichroism and scanning tunneling spectroscopy. We show that the Fe atoms have strong perpendicular magnetic anisotropy with a zero-field splitting of 14.0±0.3 meV/atom. This is a factor of 10 larger than the interface anisotropy of epitaxial Fe layers on MgO and the largest value reported for Fe atoms adsorbed on surfaces. The interplay between the ligand field at the O adsorption sites and spin-orbit coupling is analyzed by density functional theory and multiplet calculations, providing a comprehensive model of the magnetic properties of Fe atoms in a low-symmetry bonding environment.
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Affiliation(s)
- S Baumann
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
- Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - F Donati
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - S Stepanow
- Department of Materials, ETH Zürich, Hönggerbergring 64, CH-8093 Zürich, Switzerland
| | - S Rusponi
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - W Paul
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
| | - S Gangopadhyay
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
- Department of Physics, University of California, Davis, California 95616, USA
| | - I G Rau
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
| | - G E Pacchioni
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - L Gragnaniello
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - M Pivetta
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - J Dreiser
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
- Swiss Light Source (SLS), Paul Scherrer Institute (PSI), CH-5232 Villigen PSI, Switzerland
| | - C Piamonteze
- Swiss Light Source (SLS), Paul Scherrer Institute (PSI), CH-5232 Villigen PSI, Switzerland
| | - C P Lutz
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
| | - R M Macfarlane
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
| | - B A Jones
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
| | - P Gambardella
- Department of Materials, ETH Zürich, Hönggerbergring 64, CH-8093 Zürich, Switzerland
| | - A J Heinrich
- IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120, USA
| | - H Brune
- Institute of Condensed Matter Physics, École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
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28
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Smerieri M, Pal J, Savio L, Vattuone L, Ferrando R, Tosoni S, Giordano L, Pacchioni G, Rocca M. Spontaneous Oxidation of Ni Nanoclusters on MgO Monolayers Induced by Segregation of Interfacial Oxygen. J Phys Chem Lett 2015; 6:3104-3109. [PMID: 26267209 DOI: 10.1021/acs.jpclett.5b01362] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We report the study of Ni nanoclusters deposited on MgO/Ag(100) ultrathin films (one monolayer) at T = 200 K. We show by STM analysis and DFT calculations that in the limit of low Ni coverage the formation of nanoclusters of four to six atoms occurs and that these aggregates are flat rather than 3D, as expected for Ni tetramers, pentamers, or hexamers. Both the shape of the clusters and the interatomic distance between neighboring Ni atoms are indicative that the nanoparticles do not consist of pure metal atoms but that a NiyOx structure has formed thanks to the availability of atomic oxygen accumulated at the MgO/Ag interface, with Ni clusters acting as oxygen pumps. Besides being of relevance in view of the use of metal nanoclusters in catalysis and other applications, this finding gives a further proof of the peculiar behavior of ultrathin oxide films.
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Affiliation(s)
- M Smerieri
- †IMEM-CNR, U.O.S. Genova, Via Dodecaneso 33, 16146 Genova, Italy
| | - J Pal
- †IMEM-CNR, U.O.S. Genova, Via Dodecaneso 33, 16146 Genova, Italy
- ‡Dipartimento di Fisica, Università di Genova, Via Dodecaneso 33, 16146 Genova, Italy
| | - L Savio
- †IMEM-CNR, U.O.S. Genova, Via Dodecaneso 33, 16146 Genova, Italy
| | - L Vattuone
- †IMEM-CNR, U.O.S. Genova, Via Dodecaneso 33, 16146 Genova, Italy
- ‡Dipartimento di Fisica, Università di Genova, Via Dodecaneso 33, 16146 Genova, Italy
| | - R Ferrando
- †IMEM-CNR, U.O.S. Genova, Via Dodecaneso 33, 16146 Genova, Italy
- §Dipartimento di Chimica e Chimica Industriale, Università di Genova, Via Dodecaneso 31, 16146 Genova, Italy
| | - S Tosoni
- ∥Dipartimento di Scienza dei Materiali, Università Milano Bicocca, via R. Cozzi 55, 20125 Milano, Italy
| | - L Giordano
- ∥Dipartimento di Scienza dei Materiali, Università Milano Bicocca, via R. Cozzi 55, 20125 Milano, Italy
| | - G Pacchioni
- ∥Dipartimento di Scienza dei Materiali, Università Milano Bicocca, via R. Cozzi 55, 20125 Milano, Italy
| | - M Rocca
- †IMEM-CNR, U.O.S. Genova, Via Dodecaneso 33, 16146 Genova, Italy
- ‡Dipartimento di Fisica, Università di Genova, Via Dodecaneso 33, 16146 Genova, Italy
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Stiehler C, Calaza F, Schneider WD, Nilius N, Freund HJ. Molecular Adsorption Changes the Quantum Structure of Oxide-Supported Gold Nanoparticles: Chemisorption versus Physisorption. PHYSICAL REVIEW LETTERS 2015; 115:036804. [PMID: 26230817 DOI: 10.1103/physrevlett.115.036804] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Indexed: 06/04/2023]
Abstract
STM conductance spectroscopy and mapping has been used to analyze the impact of molecular adsorption on the quantized electronic structure of individual metal nanoparticles. For this purpose, isophorone and CO2, as prototype molecules for physisorptive and chemisorptive binding, were dosed onto monolayer Au islands grown on MgO thin films. The molecules attach exclusively to the metal-oxide boundary, while the interior of the islands remains pristine. The Au quantum well states are perturbed due to the adsorption process and increase their mutual energy spacing in the CO2 case but move together in isophorone-covered islands. The shifts disclose the nature of the molecule-Au interaction, which relies on electron exchange for the CO2 ligands but on dispersive forces for the organic species. Our experiments reveal how molecular adsorption affects individual quantum systems, a topic of utmost relevance for heterogeneous catalysis.
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Affiliation(s)
| | - Florencia Calaza
- Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin, Germany
| | - Wolf-Dieter Schneider
- Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin, Germany
- Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
| | - Niklas Nilius
- Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin, Germany
- Carl von Ossietzky Universität, 26111 Oldenburg, Germany
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30
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Korabel’nikov DV, Zhuravlev YN. Structure and electronic properties of Na2O2/NaClO4(001), K2O/KClO3(001) systems. J STRUCT CHEM+ 2015. [DOI: 10.1134/s0022476615020018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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31
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D’Addato S, Pinotti D, Spadaro MC, Paolicelli G, Grillo V, Valeri S, Pasquali L, Bergamini L, Corni S. Influence of size, shape and core-shell interface on surface plasmon resonance in Ag and Ag@MgO nanoparticle films deposited on Si/SiO x. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2015; 6:404-413. [PMID: 25821680 PMCID: PMC4362337 DOI: 10.3762/bjnano.6.40] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2014] [Accepted: 01/12/2015] [Indexed: 05/31/2023]
Abstract
Ag and Ag@MgO core-shell nanoparticles (NPs) with a diameter of d = 3-10 nm were obtained by physical synthesis methods and deposited on Si with its native ultrathin oxide layer SiO x (Si/SiO x ). Scanning electron microscopy and transmission electron microscopy (TEM) images of bare Ag NPs revealed the presence of small NP aggregates caused by diffusion on the surface and agglomeration. Atomic resolution TEM gave evidence of the presence of crystalline multidomains in the NPs, which were due to aggregation and multitwinning occurring during NP growth in the nanocluster source. Co-deposition of Ag NPs and Mg atoms in an oxygen atmosphere gave rise to formation of a MgO shell matrix surrounding the Ag NPs. The behaviour of the surface plasmon resonance (SPR) excitation in surface differential reflectivity (SDR) spectra with p-polarised light was investigated for bare Ag and Ag@MgO NPs. It was shown that the presence of MgO around the Ag NPs caused a red shift of the plasmon excitation, and served to preserve its existence after prolonged (five months) exposure to air, realizing the possibility of technological applications in plasmonic devices. The Ag NP and Ag@MgO NP film features in the SDR spectra could be reproduced by classical electrodynamics simulations by treating the NP-containing layer as an effective Maxwell Garnett medium. The simulations gave results in agreement with the experiments when accounting for the experimentally observed aggregation.
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Affiliation(s)
- Sergio D’Addato
- CNR-NANO, S3, via G. Campi 213/a, 41125 Modena, Italy
- Dipartimento FIM, Università di Modena e Reggio Emilia, via G. Campi 213/a, 41125 Modena, Italy
- Centro Interdipartimentale En&TECH, Università di Modena e Reggio Emilia, via G. Campi 213/a, 41125 Modena, Italy
| | - Daniele Pinotti
- Dipartimento FIM, Università di Modena e Reggio Emilia, via G. Campi 213/a, 41125 Modena, Italy
| | - Maria Chiara Spadaro
- CNR-NANO, S3, via G. Campi 213/a, 41125 Modena, Italy
- Dipartimento FIM, Università di Modena e Reggio Emilia, via G. Campi 213/a, 41125 Modena, Italy
| | | | - Vincenzo Grillo
- CNR-NANO, S3, via G. Campi 213/a, 41125 Modena, Italy
- CNR-IMEM, Parco Area delle Scienze 37/A, 43100 Parma, Italy
| | - Sergio Valeri
- CNR-NANO, S3, via G. Campi 213/a, 41125 Modena, Italy
- Dipartimento FIM, Università di Modena e Reggio Emilia, via G. Campi 213/a, 41125 Modena, Italy
| | - Luca Pasquali
- Dipartimento di Ingegneria “Enzo Ferrari”, Università di Modena e Reggio Emilia, via Vignolese 905, 41125 Modena, Italy
| | - Luca Bergamini
- CNR-NANO, S3, via G. Campi 213/a, 41125 Modena, Italy
- Dipartimento FIM, Università di Modena e Reggio Emilia, via G. Campi 213/a, 41125 Modena, Italy
- Department of Electricity and Electronics, Faculty of Science and Technology, UPV/EHU, 48080 Bilbao, Spain
- Materials Physics Center CSIC-UPV/EHU and Donostia International Physics Center DIPC, Paseo Manuel Lardizabal 4, 20018 Donostia-San Sebastian, Spain
| | - Stefano Corni
- CNR-NANO, S3, via G. Campi 213/a, 41125 Modena, Italy
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Ringleb F, Fujimori Y, Brown MA, Kaden WE, Calaza F, Kuhlenbeck H, Sterrer M, Freund HJ. The role of exposed silver in CO oxidation over MgO(0 0 1)/Ag(0 0 1) thin films. Catal Today 2015. [DOI: 10.1016/j.cattod.2014.04.025] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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33
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Pacchioni G. Two-Dimensional Oxides and Their Role in Electron Transfer Mechanisms with Adsorbed Species. CHEM REC 2014; 14:910-22. [DOI: 10.1002/tcr.201402002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Indexed: 01/24/2023]
Affiliation(s)
- Gianfranco Pacchioni
- Dipartimento di Scienza dei Materiali; Università di Milano-Bicocca; via Cozzi 55 20125 Milano Italy
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34
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Rau IG, Baumann S, Rusponi S, Donati F, Stepanow S, Gragnaniello L, Dreiser J, Piamonteze C, Nolting F, Gangopadhyay S, Albertini OR, Macfarlane RM, Lutz CP, Jones BA, Gambardella P, Heinrich AJ, Brune H. Reaching the magnetic anisotropy limit of a 3d metal atom. Science 2014; 344:988-92. [PMID: 24812206 DOI: 10.1126/science.1252841] [Citation(s) in RCA: 269] [Impact Index Per Article: 26.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Designing systems with large magnetic anisotropy is critical to realize nanoscopic magnets. Thus far, the magnetic anisotropy energy per atom in single-molecule magnets and ferromagnetic films remains typically one to two orders of magnitude below the theoretical limit imposed by the atomic spin-orbit interaction. We realized the maximum magnetic anisotropy for a 3d transition metal atom by coordinating a single Co atom to the O site of an MgO(100) surface. Scanning tunneling spectroscopy reveals a record-high zero-field splitting of 58 millielectron volts as well as slow relaxation of the Co atom's magnetization. This striking behavior originates from the dominating axial ligand field at the O adsorption site, which leads to out-of-plane uniaxial anisotropy while preserving the gas-phase orbital moment of Co, as observed with x-ray magnetic circular dichroism.
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Affiliation(s)
- Ileana G Rau
- IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA
| | - Susanne Baumann
- IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA. Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland
| | - Stefano Rusponi
- Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - Fabio Donati
- Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - Sebastian Stepanow
- Department of Materials, Eidgenössische Technische Hochschule (ETH) Zürich, Hönggerbergring 64, CH-8093 Zürich, Switzerland
| | - Luca Gragnaniello
- Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
| | - Jan Dreiser
- Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland. Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
| | - Cinthia Piamonteze
- Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
| | - Frithjof Nolting
- Swiss Light Source, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
| | | | - Oliver R Albertini
- IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA. Department of Physics, Georgetown University, 3700 O Street NW, Washington, DC 20057, USA
| | | | | | - Barbara A Jones
- IBM Almaden Research Center, 650 Harry Road, San Jose, CA 95120, USA
| | - Pietro Gambardella
- Department of Materials, Eidgenössische Technische Hochschule (ETH) Zürich, Hönggerbergring 64, CH-8093 Zürich, Switzerland.
| | | | - Harald Brune
- Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland.
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35
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Taleatu BA, Omotoso E, Lal C, Makinde WO, Ogundele KT, Ajenifuja E, Lasisi AR, Eleruja MA, Mola GT. XPS and some surface characterizations of electrodeposited MgO nanostructure. SURF INTERFACE ANAL 2014. [DOI: 10.1002/sia.5425] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- B. A. Taleatu
- Department of Physics; Obafemi Awolowo University; Ile-Ife 220005 Nigeria
- International Centre for Theoretical Physics Strada Costiera 11; 34151 Trieste Italy
- School of Chemistry and Physics; University of KwaZulu Natal Pietermaritzburg; P Bag X01 Scottsville 3209 South Africa
| | - E. Omotoso
- Department of Physics; Obafemi Awolowo University; Ile-Ife 220005 Nigeria
| | - C. Lal
- International Centre for Theoretical Physics Strada Costiera 11; 34151 Trieste Italy
- Centre for Non-Conventional Energy Resources 14-Vigyan Bhawan; University of Rajasthan; Jaipur-04 India
| | - W. O. Makinde
- Centre for Energy research and Development; O.A.U; Ile-Ife 220005 Nigeria
| | - K. T. Ogundele
- Centre for Energy research and Development; O.A.U; Ile-Ife 220005 Nigeria
| | - E. Ajenifuja
- Centre for Energy research and Development; O.A.U; Ile-Ife 220005 Nigeria
| | - A. R. Lasisi
- Federal College of Education Kotangora; Niger State Nigeria
| | - M. A. Eleruja
- Department of Physics; Obafemi Awolowo University; Ile-Ife 220005 Nigeria
| | - G. T. Mola
- School of Chemistry and Physics; University of KwaZulu Natal Pietermaritzburg; P Bag X01 Scottsville 3209 South Africa
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36
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Pal J, Smerieri M, Celasco E, Savio L, Vattuone L, Rocca M. Morphology of monolayer MgO films on Ag(100): switching from corrugated islands to extended flat terraces. PHYSICAL REVIEW LETTERS 2014; 112:126102. [PMID: 24724662 DOI: 10.1103/physrevlett.112.126102] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Indexed: 05/28/2023]
Abstract
The ability to engineer nearly perfect ultrathin oxide layers, up to the limit of monolayer thickness, is a key issue for nanotechnological applications. Here we face the difficult and important case of ultrathin MgO films on Ag(100), for which no extended and well-ordered layers could thus far be produced in the monolayer limit. We demonstrate that their final morphology depends not only on the usual growth parameters (crystal temperature, metal flux, and oxygen partial pressure), but also on aftergrowth treatments controlling so far neglected thermodynamics constraints. We thus succeed in tuning the shape of the oxide films from irregular, nanometer-sized, monolayer-thick islands to slightly larger, perfectly squared, bilayer islands, to extended monolayers limited apparently only by substrate steps.
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Affiliation(s)
- Jagriti Pal
- IMEM-CNR, UOS Genova, Via Dodecaneso 33, 16146 Genova, Italy and Dipartimento di Fisica, Università di Genova, Via Dodecaneso 33, 16146 Genova, Italy
| | - Marco Smerieri
- IMEM-CNR, UOS Genova, Via Dodecaneso 33, 16146 Genova, Italy
| | - Edvige Celasco
- IMEM-CNR, UOS Genova, Via Dodecaneso 33, 16146 Genova, Italy and Dipartimento di Fisica, Università di Genova, Via Dodecaneso 33, 16146 Genova, Italy
| | - Letizia Savio
- IMEM-CNR, UOS Genova, Via Dodecaneso 33, 16146 Genova, Italy
| | - Luca Vattuone
- IMEM-CNR, UOS Genova, Via Dodecaneso 33, 16146 Genova, Italy and Dipartimento di Fisica, Università di Genova, Via Dodecaneso 33, 16146 Genova, Italy
| | - Mario Rocca
- IMEM-CNR, UOS Genova, Via Dodecaneso 33, 16146 Genova, Italy and Dipartimento di Fisica, Università di Genova, Via Dodecaneso 33, 16146 Genova, Italy
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37
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Baumann S, Rau IG, Loth S, Lutz CP, Heinrich AJ. Measuring the three-dimensional structure of ultrathin insulating films at the atomic scale. ACS NANO 2014; 8:1739-1744. [PMID: 24377286 DOI: 10.1021/nn4061034] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The increasing technological importance of thin insulating layers calls for a thorough understanding of their structure. Here we apply scanning probe methods to investigate the structure of ultrathin magnesium oxide (MgO) which is the insulating material of choice in spintronic applications. A combination of force and current measurements gives high spatial resolution maps of the local three-dimensional insulator structure. When force measurements are not available, a lower spatial resolution can be obtained from tunneling images at different voltages. These broadly applicable techniques reveal a previously unknown complexity in the structure of MgO on Ag(001), such as steps in the insulator-metal interface.
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Affiliation(s)
- Susanne Baumann
- IBM Almaden Research Center , 650 Harry Road, San Jose, California 95120, United States
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38
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Droubay TC, Chambers SA, Joly AG, Hess WP, Németh K, Harkay KC, Spentzouris L. Metal-insulator photocathode heterojunction for directed electron emission. PHYSICAL REVIEW LETTERS 2014; 112:067601. [PMID: 24580707 DOI: 10.1103/physrevlett.112.067601] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2013] [Indexed: 06/03/2023]
Abstract
We use angle-resolved photoemission under ultraviolet laser excitation to demonstrate that the electron emission properties of Ag(001) can be markedly enhanced and redirected along the surface normal by the deposition of a few monolayers of epitaxial MgO. We observe new low-binding energy states with small spreads in their surface parallel momenta as a result of MgO/Ag(001) interface formation. Under 4.66 eV laser excitation, the quantum efficiency of MgO/Ag(001) is a factor of 7 greater than that of clean Ag(001), revealing the utility of such heterojunctions as advanced photocathodes.
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Affiliation(s)
- Timothy C Droubay
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA
| | - Scott A Chambers
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA
| | - Alan G Joly
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA
| | - Wayne P Hess
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA
| | - Karoly Németh
- Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA and Department of Physics, Illinois Institute of Technology, Chicago, Illinois 60616, USA
| | - Katherine C Harkay
- Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
| | - Linda Spentzouris
- Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA and Department of Physics, Illinois Institute of Technology, Chicago, Illinois 60616, USA
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39
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Krupski A. Growth morphology of thin films on metallic and oxide surfaces. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2014; 26:053001. [PMID: 24445588 DOI: 10.1088/0953-8984/26/5/053001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In this work we briefly review recent investigations concerning the growth morphology of thin metallic films on the Mo(110) and Ni3Al(111) surfaces, and Fe and copper phthalocyanine (C32H16N8Cu) on the Al2O3/Ni3Al(111) surface. Comparison of Ag, Au, Sn, and Pb growth on the Mo(110) surface has shown a number of similarities between these adsorption systems, except that surface alloy formation has only been observed in the case of Sn and Au. In the Pb/Mo(110) and Pb/Ni3Al(111) adsorption systems selective formation of uniform Pb island heights during metal thin film growth has been observed and interpreted in terms of quantum size effects. Furthermore, our studies showed that Al2O3 on Ni3Al(111) exhibits a large superstructure in which the unit cell has a commensurate relation with the substrate lattice. In addition, copper phthalocyanine chemisorbed weakly onto an ultra-thin Al2O3 film on Ni3Al(111) and showed a poor template effect of the Al2O3/Ni3Al(111) system. In the case of iron cluster growth on Al2O3/Ni3Al(111) the nucleation sites were independent of deposition temperature, yet the cluster shape showed a dependence. In this system, Fe clusters formed a regular hexagonal lattice on the Al2O3/Ni3Al(111).
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40
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Chen HYT, Pacchioni G. Properties of two-dimensional insulators: a DFT study of Co adsorption on NaCl and MgO ultrathin films. Phys Chem Chem Phys 2014; 16:21838-45. [PMID: 25199958 DOI: 10.1039/c4cp03470h] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The interaction of TM atoms like Co with two-dimensional NaCl/Au(111) and MgO/Ag(001) ultrathin films is completely different.
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Affiliation(s)
- Hsin-Yi Tiffany Chen
- Dipartimento di Scienza dei Materiali
- Università di Milano- Bicocca
- 20125 Milano, Italy
| | - Gianfranco Pacchioni
- Dipartimento di Scienza dei Materiali
- Università di Milano- Bicocca
- 20125 Milano, Italy
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41
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Noguera C, Goniakowski J. Structural phase diagrams of supported oxide nanowires from extended Frenkel-Kontorova models of diatomic chains. J Chem Phys 2013; 139:084703. [DOI: 10.1063/1.4818542] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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42
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Rahe P, Kittelmann M, Neff JL, Nimmrich M, Reichling M, Maass P, Kühnle A. Tuning molecular self-assembly on bulk insulator surfaces by anchoring of the organic building blocks. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2013; 25:3948-3956. [PMID: 23907708 DOI: 10.1002/adma.201300604] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Revised: 03/25/2013] [Indexed: 06/02/2023]
Abstract
Molecular self-assembly constitutes a versatile strategy for creating functional structures on surfaces. Tuning the subtle balance between intermolecular and molecule-surface interactions allows structure formation to be tailored at the single-molecule level. While metal surfaces usually exhibit interaction strengths in an energy range that favors molecular self-assembly, dielectric surfaces having low surface energies often lack sufficient interactions with adsorbed molecules. As a consequence, application-relevant, bulk insulating materials pose significant challenges when considering them as supporting substrates for molecular self-assembly. Here, the current status of molecular self-assembly on surfaces of wide-bandgap dielectric crystals, investigated under ultrahigh vacuum conditions at room temperature, is reviewed. To address the major issues currently limiting the applicability of molecular self-assembly principles in the case of dielectric surfaces, a systematic discussion of general strategies is provided for anchoring organic molecules to bulk insulating materials.
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Affiliation(s)
- Philipp Rahe
- Department of Physics and Astronomy, 115 South 1400 East, The University of Utah, Salt Lake City, UT 84112-0830, USA.
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43
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Jaouen T, Tricot S, Delhaye G, Lépine B, Sébilleau D, Jézéquel G, Schieffer P. Layer-resolved study of Mg atom incorporation at the MgO/Ag(001) buried interface. PHYSICAL REVIEW LETTERS 2013; 111:027601. [PMID: 23889444 DOI: 10.1103/physrevlett.111.027601] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Indexed: 06/02/2023]
Abstract
By combining x-ray excited Auger electron diffraction experiments and multiple scattering calculations we reveal a layer-resolved shift for the Mg KL23L23 Auger transition in MgO ultrathin films (4-6 Å) on Ag(001). This resolution is exploited to demonstrate the possibility of controlling Mg atom incorporation at the MgO/Ag(001) interface by exposing the MgO films to a Mg flux. A substantial reduction of the MgO/Ag(001) work function is observed during the exposition phase and reflects both band-offset variations at the interface and band bending effects in the oxide film.
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Affiliation(s)
- T Jaouen
- Département de Physique and Fribourg Center for Nanomaterials, Université de Fribourg, CH-1700 Fribourg, Switzerland.
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44
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Ling S, Watkins MB, Shluger AL. Effects of atomic scale roughness at metal/insulator interfaces on metal work function. Phys Chem Chem Phys 2013; 15:19615-24. [DOI: 10.1039/c3cp53590h] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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45
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Surnev S, Fortunelli A, Netzer FP. Structure-property relationship and chemical aspects of oxide-metal hybrid nanostructures. Chem Rev 2012; 113:4314-72. [PMID: 23237602 DOI: 10.1021/cr300307n] [Citation(s) in RCA: 141] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Affiliation(s)
- Svetlozar Surnev
- Surface and Interface Physics, Institute of Physics, Karl-Franzens University, Graz A-8010 Graz, Austria
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46
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Pacchioni G, Freund H. Electron Transfer at Oxide Surfaces. The MgO Paradigm: from Defects to Ultrathin Films. Chem Rev 2012; 113:4035-72. [DOI: 10.1021/cr3002017] [Citation(s) in RCA: 241] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Gianfranco Pacchioni
- Dipartimento di Scienza dei
Materiali, Università di Milano-Bicocca, Via R. Cozzi, 53−20125,
Milano, Italy
| | - Hajo Freund
- Fritz-Haber-Insitut
der MPG,
Department of Chemical Physics, Faradayweg 4-6, 14195 Berlin, Germany
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47
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Müller-Sajak D, Islam S, Pfnür H, Hofmann KR. Temperature stability of ultra-thin mixed BaSr-oxide layers and their transformation. NANOTECHNOLOGY 2012; 23:305202. [PMID: 22750846 DOI: 10.1088/0957-4484/23/30/305202] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
In the context of investigations of physical, chemical and electrical properties of ultra-thin layers of epitaxial and monocrystalline Sr(0.3)Ba(0.7)O on Si(100), we also investigated their thermal stability with x-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), and low energy electron diffraction (LEED). At temperatures above 400 °C, transformation into silicate layers sets in. The stoichiometry after complete transformation was determined to be close to (Ba(0.8)Sr(0.2))(2)SiO(4) except for layers of only a few monolayers, where the silicate is not stoichiometric. There are strong indications that this silicate is stable until it desorbs at temperatures above 750 °C. Crystallinity, as seen with LEED, is lost during this transformation. Although transformation into silicate is coupled with metal desorption and compactification of the layers, they seem to remain closed. In addition, traces of Ba silicide at the Si interface were detected after layer desorption. This silicide cannot be desorbed thermally. The silicate layer has a bandgap of 5.9 ± 0.2 eV already for 3 ML thickness. Upon exposure to air, carbon and oxygen containing species, but no hydroxide, are formed irreversibly.
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Affiliation(s)
- D Müller-Sajak
- Institut für Festkörperphysik, Leibniz Universität Hannover, Appelstrasse 2, D-30167 Hannover, Germany
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Pacchioni G. Two-Dimensional Oxides: Multifunctional Materials for Advanced Technologies. Chemistry 2012; 18:10144-58. [DOI: 10.1002/chem.201201117] [Citation(s) in RCA: 77] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Gao F, Goodman DW. Model Catalysts: Simulating the Complexities of Heterogeneous Catalysts. Annu Rev Phys Chem 2012; 63:265-86. [DOI: 10.1146/annurev-physchem-032511-143722] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Feng Gao
- Chemical and Materials Science Division, Pacific Northwest National Laboratory, Richland, Washington 99352;
| | - D. Wayne Goodman
- Department of Chemistry, Texas A&M University, College Station, Texas 77842-3012
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Vaida ME, Bernhardt TM. Surface-aligned femtochemistry: Photoinduced reaction dynamics of CH3I and CH3Br on MgO(100). Faraday Discuss 2012; 157:437-49; discussion 475-500. [DOI: 10.1039/c2fd20104f] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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