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da Silva Alvim R, Borges I, Alves RMB, Capaz RB, Leitão AA. CO adsorption on MgO thin-films: formation and interaction of surface charged defects. Phys Chem Chem Phys 2023; 25:28982-28997. [PMID: 37859503 DOI: 10.1039/d3cp03320a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2023]
Abstract
Two-dimensional (2D) materials formed by thin-films of metal oxides that grow on metal supports are commonly used in heterogeneous catalysis and multilayer electronic devices. Despite extensive research on these systems, the effects of charged defects at supported oxides on surface processes are still not clear. In this work, we perform spin-polarized density-functional theory (DFT) calculations to investigate formation and interaction of charged magnesium and oxygen vacancies, and Al dopants on MgO(001)/Ag(001) surface. The results show a sizable interface compressive effect that decreases the metal work function as electrons are added on the MgO surface with a magnesium vacancy. This surface displays a larger formation energy in a water environment (O-rich condition) even with additional Al-doping. Under these conditions, we found that a polar molecule such as CO is more strongly adsorbed on the low-coordination oxygen sites due to a larger contribution of the channeled electronic transport with the silver interface regardless of the surface charge. Therefore, these findings elucidate how surface intrinsic vacancies can influence or contribute to charge transfer, which allows one to explore more specific reactions at different surface topologies for more efficient catalysts for CO2 conversion.
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Affiliation(s)
- Raphael da Silva Alvim
- Departamento de Engenharia Química, Escola Politécnica, Universidade de São Paulo (USP), São Paulo, SP, 05508-900, Brazil.
- Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Juiz de Fora (UFJF), Juiz de Fora, MG, 36036-330, Brazil
| | - Itamar Borges
- Departamento de Química, Instituto Militar de Engenharia (IME), Rio de Janeiro, RJ, 22290-270, Brazil
| | - Rita Maria Brito Alves
- Departamento de Engenharia Química, Escola Politécnica, Universidade de São Paulo (USP), São Paulo, SP, 05508-900, Brazil.
| | - Rodrigo B Capaz
- Instituto de Física, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, 21941-972, Brazil
- Brazilian Nanotechnology National Laboratory (LNNano), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, SP, 13083-100, Brazil
| | - Alexandre Amaral Leitão
- Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Juiz de Fora (UFJF), Juiz de Fora, MG, 36036-330, Brazil
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Hurdax P, Hollerer M, Egger L, Koller G, Yang X, Haags A, Soubatch S, Tautz FS, Richter M, Gottwald A, Puschnig P, Sterrer M, Ramsey MG. Controlling the electronic and physical coupling on dielectric thin films. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2020; 11:1492-1503. [PMID: 33083197 PMCID: PMC7537406 DOI: 10.3762/bjnano.11.132] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Accepted: 08/25/2020] [Indexed: 06/11/2023]
Abstract
Ultrathin dielectric/insulating films on metals are often used as decoupling layers to allow for the study of the electronic properties of adsorbed molecules without electronic interference from the underlying metal substrate. However, the presence of such decoupling layers may effectively change the electron donating properties of the substrate, for example, by lowering its work function and thus enhancing the charging of the molecular adsorbate layer through electron tunneling. Here, an experimental study of the charging of para-sexiphenyl (6P) on ultrathin MgO(100) films supported on Ag(100) is reported. By deliberately changing the work function of the MgO(100)/Ag(100) system, it is shown that the charge transfer (electronic coupling) into the 6P molecules can be controlled, and 6P monolayers with uncharged molecules (Schottky-Mott regime) and charged and uncharged molecules (Fermi level pinning regime) can be obtained. Furthermore, it was found that charge transfer and temperature strongly influence the orientation, conformation, and wetting behavior (physical coupling) of the 6P layers on the MgO(100) thin films.
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Affiliation(s)
- Philipp Hurdax
- Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010 Graz, Austria
| | - Michael Hollerer
- Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010 Graz, Austria
| | - Larissa Egger
- Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010 Graz, Austria
| | - Georg Koller
- Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010 Graz, Austria
| | - Xiaosheng Yang
- Peter Grünberg Institute (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
- Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology, 52425 Jülich, Germany
- Experimentalphysik IV A, RWTH Aachen University, 52074 Aachen, Germany
| | - Anja Haags
- Peter Grünberg Institute (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
- Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology, 52425 Jülich, Germany
- Experimentalphysik IV A, RWTH Aachen University, 52074 Aachen, Germany
| | - Serguei Soubatch
- Peter Grünberg Institute (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
- Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology, 52425 Jülich, Germany
| | - Frank Stefan Tautz
- Peter Grünberg Institute (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
- Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology, 52425 Jülich, Germany
- Experimentalphysik IV A, RWTH Aachen University, 52074 Aachen, Germany
| | - Mathias Richter
- Physikalisch-Technische Bundesanstalt (PTB), 10587 Berlin, Germany
| | | | - Peter Puschnig
- Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010 Graz, Austria
| | - Martin Sterrer
- Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010 Graz, Austria
| | - Michael G Ramsey
- Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010 Graz, Austria
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Lewandowski M, Pabisiak T, Michalak N, Miłosz Z, Babačić V, Wang Y, Hermanowicz M, Palotás K, Jurga S, Kiejna A. On the Structure of Ultrathin FeO Films on Ag(111). NANOMATERIALS (BASEL, SWITZERLAND) 2018; 8:E828. [PMID: 30322159 PMCID: PMC6215274 DOI: 10.3390/nano8100828] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Revised: 10/08/2018] [Accepted: 10/09/2018] [Indexed: 11/16/2022]
Abstract
Ultrathin transition metal oxide films exhibit unique physical and chemical properties not observed for the corresponding bulk oxides. These properties, originating mainly from the limited thickness and the interaction with the support, make those films similar to other supported 2D materials with bulk counterparts, such as transition metal dichalcogenides. Ultrathin iron oxide (FeO) films, for example, were shown to exhibit unique electronic, catalytic and magnetic properties that depend on the type of the used support. Ag(111) has always been considered a promising substrate for FeO growth, as it has the same surface symmetry, only ~5% lattice mismatch, is considered to be weakly-interacting and relatively resistant to oxidation. The reports on the growth and structure of ultrathin FeO films on Ag(111) are scarce and often contradictory to each other. We attempted to shed more light on this system by growing the films using different preparation procedures and studying their structure using scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). We observed the formation of a previously unreported Moiré superstructure with 45 Å periodicity, as well as other reconstructed and reconstruction-free surface species. The experimental results obtained by us and other groups indicate that the structure of FeO films on this particular support critically depends on the films' preparation conditions. We also performed density functional theory (DFT) calculations on the structure and properties of a conceptual reconstruction-free FeO film on Ag(111). The results indicate that such a film, if successfully grown, should exhibit tunable thickness-dependent properties, being substrate-influenced in the monolayer regime and free-standing-FeO-like when in the bilayer form.
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Affiliation(s)
- Mikołaj Lewandowski
- NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland.
| | - Tomasz Pabisiak
- Institute of Experimental Physics, University of Wrocław, Pl. M. Borna 9, 50-204 Wrocław, Poland.
| | - Natalia Michalak
- Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań, Poland.
| | - Zygmunt Miłosz
- NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland.
| | - Višnja Babačić
- NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland.
| | - Ying Wang
- NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland.
| | - Michał Hermanowicz
- Institute of Physics, Poznan University of Technology, Piotrowo 3, 60-965 Poznań, Poland.
| | - Krisztián Palotás
- MTA-SZTE Reaction Kinetics and Surface Chemistry Research Group, University of Szeged, 6720 Szeged, Hungary.
| | - Stefan Jurga
- NanoBioMedical Centre, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland.
| | - Adam Kiejna
- Institute of Experimental Physics, University of Wrocław, Pl. M. Borna 9, 50-204 Wrocław, Poland.
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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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Larciprete R, Lacovig P, Orlando F, Dalmiglio M, Omiciuolo L, Baraldi A, Lizzit S. Chemical gating of epitaxial graphene through ultrathin oxide layers. NANOSCALE 2015; 7:12650-12658. [PMID: 26148485 DOI: 10.1039/c5nr02936h] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We achieved a controllable chemical gating of epitaxial graphene grown on metal substrates by exploiting the electrostatic polarization of ultrathin SiO2 layers synthesized below it. Intercalated oxygen diffusing through the SiO2 layer modifies the metal-oxide work function and hole dopes graphene. The graphene/oxide/metal heterostructure behaves as a gated plane capacitor with the in situ grown SiO2 layer acting as a homogeneous dielectric spacer, whose high capacity allows the Fermi level of graphene to be shifted by a few hundreds of meV when the oxygen coverage at the metal substrate is of the order of 0.5 monolayers. The hole doping can be finely tuned by controlling the amount of interfacial oxygen, as well as by adjusting the thickness of the oxide layer. After complete thermal desorption of oxygen the intrinsic doping of SiO2 supported graphene is evaluated in the absence of contaminants and adventitious adsorbates. The demonstration that the charge state of graphene can be changed by chemically modifying the buried oxide/metal interface hints at the possibility of tuning the level and sign of doping by the use of other intercalants capable of diffusing through the ultrathin porous dielectric and reach the interface with the metal.
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Affiliation(s)
- Rosanna Larciprete
- CNR-Institute for Complex Systems, Via Fosso del Cavaliere 100, 00133 Roma, Italy.
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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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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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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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