1
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Weymouth AJ, Roche E, Giessibl FJ. From a free electron gas to confined states: A mixed island of PTCDA and copper phthalocyanine on Ag(111). BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2022; 13:1572-1577. [PMID: 36628110 PMCID: PMC9795859 DOI: 10.3762/bjnano.13.131] [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: 04/25/2022] [Accepted: 11/30/2022] [Indexed: 06/17/2023]
Abstract
When perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) is deposited on the Ag(111) surface at submonolayer coverage, it forms islands under which the native Shockley state of the Ag(111) surface can no longer be found. Previous work has shown that this state shifts upwards to form a new interface state starting at 0.6 V above the Fermi level, having properties of a two-dimensional electron gas (2DEG). We investigated mixed islands of PTCDA and copper phthalocyanine (CuPc) to study the change in the electronic state with the addition of an electron donor. We no longer observe a 2DEG state and instead identify states at 0.46 and 0.79 V. While one state appears in dI/dV images as an array of one-dimensional quantum wells, our analysis shows that this state does not act as a free electron gas and that the features are instead localized above individual PTCDA molecules.
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Affiliation(s)
- Alfred J Weymouth
- Institute of Experimental and Applied Physics, Department of Physics, University of Regensburg, 93053 Regensburg, Germany
| | - Emily Roche
- Institute of Experimental and Applied Physics, Department of Physics, University of Regensburg, 93053 Regensburg, Germany
| | - Franz J Giessibl
- Institute of Experimental and Applied Physics, Department of Physics, University of Regensburg, 93053 Regensburg, Germany
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2
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de Oteyza DG, Frederiksen T. Carbon-based nanostructures as a versatile platform for tunable π-magnetism. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 34:443001. [PMID: 35977474 DOI: 10.1088/1361-648x/ac8a7f] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Accepted: 08/17/2022] [Indexed: 06/15/2023]
Abstract
Emergence ofπ-magnetism in open-shell nanographenes has been theoretically predicted decades ago but their experimental characterization was elusive due to the strong chemical reactivity that makes their synthesis and stabilization difficult. In recent years, on-surface synthesis under vacuum conditions has provided unprecedented opportunities for atomically precise engineering of nanographenes, which in combination with scanning probe techniques have led to a substantial progress in our capabilities to realize localized electron spin states and to control electron spin interactions at the atomic scale. Here we review the essential concepts and the remarkable advances in the last few years, and outline the versatility of carbon-basedπ-magnetic materials as an interesting platform for applications in spintronics and quantum technologies.
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Affiliation(s)
- Dimas G de Oteyza
- Nanomaterials and Nanotechnology Research Center (CINN), CSIC-UNIOVI-PA, E-33940 El Entrego, Spain
- Donostia International Physics Center (DIPC)-UPV/EHU, E-20018 San Sebastián, Spain
| | - Thomas Frederiksen
- Donostia International Physics Center (DIPC)-UPV/EHU, E-20018 San Sebastián, Spain
- Ikerbasque, Basque Foundation for Science, E-48013 Bilbao, Spain
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3
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Boné T, Windischbacher A, Sättele MS, Greulich K, Egger L, Jauk T, Lackner F, Bettinger HF, Peisert H, Chassé T, Ramsey MG, Sterrer M, Koller G, Puschnig P. Demonstrating the Impact of the Adsorbate Orientation on the Charge Transfer at Organic-Metal Interfaces. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2021; 125:9129-9137. [PMID: 34055126 PMCID: PMC8154845 DOI: 10.1021/acs.jpcc.1c01306] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Revised: 04/15/2021] [Indexed: 06/12/2023]
Abstract
Charge-transfer processes at molecule-metal interfaces play a key role in tuning the charge injection properties in organic-based devices and thus, ultimately, the device performance. Here, the metal's work function and the adsorbate's electron affinity are the key factors that govern the electron transfer at the organic/metal interface. In our combined experimental and theoretical work, we demonstrate that the adsorbate's orientation may also be decisive for the charge transfer. By thermal cycloreversion of diheptacene isomers, we manage to produce highly oriented monolayers of the rodlike, electron-acceptor molecule heptacene on a Cu(110) surface with molecules oriented either along or perpendicular to the close-packed metal rows. This is confirmed by scanning tunneling microscopy (STM) images as well as by angle-resolved ultraviolet photoemission spectroscopy (ARUPS). By utilizing photoemission tomography momentum maps, we show that the lowest unoccupied molecular orbital (LUMO) is fully occupied and also, the LUMO + 1 gets significantly filled when heptacene is oriented along the Cu rows. Conversely, for perpendicularly aligned heptacene, the molecular energy levels are shifted significantly toward the Fermi energy, preventing charge transfer to the LUMO + 1. These findings are fully confirmed by our density functional calculations and demonstrate the possibility to tune the charge transfer and level alignment at organic-metal interfaces through the adjustable molecular alignment.
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Affiliation(s)
| | | | - Marie S. Sättele
- Institute
of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
- Institute
of Organic Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Katharina Greulich
- Institute
of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Larissa Egger
- Institute
of Physics, University of Graz, 8010 Graz, Austria
| | - Thomas Jauk
- Institute
of Experimental Physics, Graz University of Technology, 8010 Graz, Austria
| | - Florian Lackner
- Institute
of Experimental Physics, Graz University of Technology, 8010 Graz, Austria
| | - Holger F. Bettinger
- Institute
of Organic Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Heiko Peisert
- Institute
of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | - Thomas Chassé
- Institute
of Physical and Theoretical Chemistry, University of Tübingen, 72076 Tübingen, Germany
| | | | - Martin Sterrer
- Institute
of Physics, University of Graz, 8010 Graz, Austria
| | - Georg Koller
- Institute
of Physics, University of Graz, 8010 Graz, Austria
| | - Peter Puschnig
- Institute
of Physics, University of Graz, 8010 Graz, Austria
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4
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Wang Q, Yang J, Franco-Cañellas A, Bürker C, Niederhausen J, Dombrowski P, Widdascheck F, Breuer T, Witte G, Gerlach A, Duhm S, Schreiber F. Pentacene/perfluoropentacene bilayers on Au(111) and Cu(111): impact of organic-metal coupling strength on molecular structure formation. NANOSCALE ADVANCES 2021; 3:2598-2606. [PMID: 36134152 PMCID: PMC9419101 DOI: 10.1039/d1na00040c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2021] [Accepted: 03/08/2021] [Indexed: 05/12/2023]
Abstract
As crucial element in organic opto-electronic devices, heterostructures are of pivotal importance. In this context, a comprehensive study of the properties on a simplified model system of a donor-acceptor (D-A) bilayer structure is presented, using ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED) and normal-incidence X-ray standing wave (NIXSW) measurements. Pentacene (PEN) as donor and perfluoropentacene (PFP) as acceptor material are chosen to produce bilayer structures on Au(111) and Cu(111) by sequential monolayer deposition of the two materials. By comparing the adsorption behavior of PEN/PFP bilayers on such weakly and strongly interacting substrates, it is found that: (i) the adsorption distance of the first layer (PEN or PFP) indicates physisorption on Au(111), (ii) the characteristics of the bilayer structure on Au(111) are (almost) independent of the deposition sequence, and hence, (iii) in both cases a mixed bilayer is formed on the Au substrate. This is in striking contrast to PFP/PEN bilayers on Cu(111), where strong chemisorption pins PEN molecules to the metal surface and no intermixing is induced by subsequent PFP deposition. The results illustrate the strong tendency of PEN and PFP molecules to mix, which has important implications for the fabrication of PEN/PFP heterojunctions.
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Affiliation(s)
- Qi Wang
- Institut für Angewandte Physik, Universität Tübingen 72076 Tübingen Germany
- Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices and Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University Suzhou 215123 People's Republic of China
| | - Jiacheng Yang
- Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices and Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University Suzhou 215123 People's Republic of China
| | | | - Christoph Bürker
- Institut für Angewandte Physik, Universität Tübingen 72076 Tübingen Germany
| | - Jens Niederhausen
- Helmholtz Zentrum Berlin für Materialien und Energie GmbH 14109 Berlin Germany
| | - Pierre Dombrowski
- Fachbereich Physik, Philipps-Universität Marburg 35032 Marburg Germany
| | - Felix Widdascheck
- Fachbereich Physik, Philipps-Universität Marburg 35032 Marburg Germany
| | - Tobias Breuer
- Fachbereich Physik, Philipps-Universität Marburg 35032 Marburg Germany
| | - Gregor Witte
- Fachbereich Physik, Philipps-Universität Marburg 35032 Marburg Germany
| | - Alexander Gerlach
- Institut für Angewandte Physik, Universität Tübingen 72076 Tübingen Germany
| | - Steffen Duhm
- Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices and Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University Suzhou 215123 People's Republic of China
| | - Frank Schreiber
- Institut für Angewandte Physik, Universität Tübingen 72076 Tübingen Germany
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5
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Weymouth AJ, Riegel E, Simmet B, Gretz O, Giessibl FJ. Lateral Force Microscopy Reveals the Energy Barrier of a Molecular Switch. ACS NANO 2021; 15:3264-3271. [PMID: 33523628 DOI: 10.1021/acsnano.0c09965] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Copper phthalocyanine (CuPc) is a small molecule often used in organic light emitting diodes where it is deposited on a conducting electrode. Previous scanning tunneling microscopy (STM) studies of CuPc on Cu(111) have shown that inelastic tunneling events can cause CuPc to switch between a ground state and two symmetrically equivalent metastable states in which the molecule is rotated. We investigated CuPc on Cu(111) and Ag(111) with STM and lateral force microscopy (LFM). Even without inelastic events, the presence of the tip can induce rotations and upon closer approach, causes the rotated states to be favored. Combining STM measurements at various temperatures and LFM measurements, we show that the long-range attraction of the tip changes the potential energy landscape of this molecular switch. We can also determine the geometry of the rotated and ground states. We compare our observations of CuPc on Cu(111) to CuPc on Ag(111). On Ag(111), CuPc appears flat and does not rotate. Stronger bonding typically involves shorter bond lengths, larger shifts of energy levels, and structural stability. Although the binding of CuPc to Cu(111) is stronger than that on Ag(111), the nonplanar geometry of CuPc on Cu(111) is accompanied by two metastable states which are not present on the Ag(111) surface.
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Affiliation(s)
| | | | | | - Oliver Gretz
- University of Regensburg, Regensburg 93053, Germany
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6
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Sättele M, Windischbacher A, Egger L, Haags A, Hurdax P, Kirschner H, Gottwald A, Richter M, Bocquet F, Soubatch S, Tautz FS, Bettinger HF, Peisert H, Chassé T, Ramsey MG, Puschnig P, Koller G. Going beyond Pentacene: Photoemission Tomography of a Heptacene Monolayer on Ag(110). THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2021; 125:2918-2925. [PMID: 33603943 PMCID: PMC7883341 DOI: 10.1021/acs.jpcc.0c09062] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/06/2020] [Revised: 01/15/2021] [Indexed: 06/12/2023]
Abstract
Longer acenes such as heptacene are promising candidates for optoelectronic applications but are unstable in their bulk structure as they tend to dimerize. This makes the growth of well-defined monolayers and films problematic. In this article, we report the successful preparation of a highly oriented monolayer of heptacene on Ag(110) by thermal cycloreversion of diheptacenes. In a combined effort of angle-resolved photoemission spectroscopy and density functional theory (DFT) calculations, we characterize the electronic and structural properties of the molecule on the surface in detail. Our investigations allow us to unambiguously confirm the successful fabrication of a highly oriented complete monolayer of heptacene and to describe its electronic structure. By comparing experimental momentum maps of photoemission from frontier orbitals of heptacene and pentacene, we shed light on differences between these two acenes regarding their molecular orientation and energy-level alignment on the metal surfaces.
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Affiliation(s)
- Marie
S. Sättele
- Institute
of Physical and Theoretical Chemistry, University
of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
- Institute
of Organic Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Andreas Windischbacher
- 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
| | - Anja Haags
- Peter
Grünberg Institut (PGI-3), Forschungszentrum
Jülich, 52425 Jülich, Germany
- Jülich
Aachen Research Alliance (JARA), Fundamentals
of Future Information Technology, 52425 Jülich, Germany
- Experimental
Physics IV A, RWTH Aachen University, 52074 Aachen, Germany
| | - Philipp Hurdax
- Institute
of Physics, University of Graz, NAWI Graz, Universitätsplatz
5, 8010 Graz, Austria
| | - Hans Kirschner
- Physikalisch-Technische
Bundesanstalt, Abbestr.
2-12, 10587 Berlin, Germany
| | - Alexander Gottwald
- Physikalisch-Technische
Bundesanstalt, Abbestr.
2-12, 10587 Berlin, Germany
| | - Mathias Richter
- Physikalisch-Technische
Bundesanstalt, Abbestr.
2-12, 10587 Berlin, Germany
| | - François
C. Bocquet
- Peter
Grünberg Institut (PGI-3), Forschungszentrum
Jülich, 52425 Jülich, Germany
- Jülich
Aachen Research Alliance (JARA), Fundamentals
of Future Information Technology, 52425 Jülich, Germany
| | - Serguei Soubatch
- Peter
Grünberg Institut (PGI-3), Forschungszentrum
Jülich, 52425 Jülich, Germany
- Jülich
Aachen Research Alliance (JARA), Fundamentals
of Future Information Technology, 52425 Jülich, Germany
| | - F. Stefan Tautz
- Peter
Grünberg Institut (PGI-3), Forschungszentrum
Jülich, 52425 Jülich, Germany
- Jülich
Aachen Research Alliance (JARA), Fundamentals
of Future Information Technology, 52425 Jülich, Germany
- Experimental
Physics IV A, RWTH Aachen University, 52074 Aachen, Germany
| | - Holger F. Bettinger
- Institute
of Organic Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Heiko Peisert
- Institute
of Physical and Theoretical Chemistry, University
of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Thomas Chassé
- Institute
of Physical and Theoretical Chemistry, University
of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany
| | - Michael G. Ramsey
- Institute
of Physics, University of Graz, NAWI Graz, Universitätsplatz
5, 8010 Graz, Austria
| | - Peter Puschnig
- 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
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7
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Franco-Cañellas A, Duhm S, Gerlach A, Schreiber F. Binding and electronic level alignment of π-conjugated systems on metals. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2020; 83:066501. [PMID: 32101802 DOI: 10.1088/1361-6633/ab7a42] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
We review the binding and energy level alignment of π-conjugated systems on metals, a field which during the last two decades has seen tremendous progress both in terms of experimental characterization as well as in the depth of theoretical understanding. Precise measurements of vertical adsorption distances and the electronic structure together with ab initio calculations have shown that most of the molecular systems have to be considered as intermediate cases between weak physisorption and strong chemisorption. In this regime, the subtle interplay of different effects such as covalent bonding, charge transfer, electrostatic and van der Waals interactions yields a complex situation with different adsorption mechanisms. In order to establish a better understanding of the binding and the electronic level alignment of π-conjugated molecules on metals, we provide an up-to-date overview of the literature, explain the fundamental concepts as well as the experimental techniques and discuss typical case studies. Thereby, we relate the geometric with the electronic structure in a consistent picture and cover the entire range from weak to strong coupling.
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Affiliation(s)
- Antoni Franco-Cañellas
- Institut für Angewandte Physik, Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
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8
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Tan A, Zhang PP. Interfacial charge transfer enhancement via formation of binary molecular assemblies on electronically corrugated boron nitride. Phys Chem Chem Phys 2019; 21:26146-26153. [PMID: 31750465 DOI: 10.1039/c9cp04853g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Using scanning tunneling microscopy/spectroscopy (STM/STS) in conjunction with finite element simulation, we investigate the interfacial behaviors in single-component zinc phthalocyanine (ZnPc) and hexadecafluorinated zinc phthalocyanine (F16ZnPc) molecular overlayers as well as their 1 : 1 mixed-phase superstructures on h-BN/Cu(111). We show that the formation of the binary molecular superstructure drastically increases the charge transfer between F16ZnPc molecules and the substrate, which is attributed to the greater electrostatic stability of the binary assembly compared to that of the pure phase. This study highlights the significant complication in the design of donor-acceptor molecular thin films as the presence of the substrate, even a weakly interacting one, such as h-BN/metal, can still perturb the intermolecular charge transfer and thereby the physical behaviors of the hybrid system via interfacial processes.
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Affiliation(s)
- A Tan
- Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-2320, USA.
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9
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Combined orbital tomography study of multi-configurational molecular adsorbate systems. Nat Commun 2019; 10:5255. [PMID: 31748503 PMCID: PMC6868194 DOI: 10.1038/s41467-019-13254-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Accepted: 10/31/2019] [Indexed: 11/16/2022] Open
Abstract
Molecular reactivity is determined by the energy levels and spatial extent of the frontier orbitals. Orbital tomography based on angle-resolved photoelectron spectroscopy is an elegant method to study the electronic structure of organic adsorbates, however, it is conventionally restricted to systems with one single rotational domain. In this work, we extend orbital tomography to systems with multiple rotational domains. We characterise the hydrogen evolution catalyst Co-pyrphyrin on an Ag(110) substrate and compare it with the empty pyrphyrin ligand. In combination with low-energy electron diffraction and DFT simulations, we fully determine adsorption geometry and both energetics and spatial distributions of the valence electronic states. We find two states close to the Fermi level in Co-pyrphyrin with Co \documentclass[12pt]{minimal}
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\begin{document}$$3d$$\end{document}3d character that are not present in the empty ligand. In addition, we identify several energetically nearly equivalent adsorption geometries that are important for the understanding of the electronic structure. The ability to disentangle and fully elucidate multi-configurational systems renders orbital tomography much more useful to study realistic catalytic systems. The shape and energy of frontier orbitals determine the reactivity of molecular systems. Combining orbital tomography based on photoelectron spectroscopy with electron diffraction and DFT, the authors investigate a complex multi-configurational adsorbate system revealing adsorptions geometries and hierarchy and geometry of molecular orbitals.
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10
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Yang X, Egger L, Fuchsberger J, Unzog M, Lüftner D, Hajek F, Hurdax P, Jugovac M, Zamborlini G, Feyer V, Koller G, Puschnig P, Tautz FS, Ramsey MG, Soubatch S. Coexisting Charge States in a Unary Organic Monolayer Film on a Metal. J Phys Chem Lett 2019; 10:6438-6445. [PMID: 31573816 DOI: 10.1021/acs.jpclett.9b02231] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The electronic and geometric structures of tetracene films on Ag(110) and Cu(110) have been studied with photoemission tomography and compared to that of pentacene. Despite similar energy level alignment of the two oligoacenes on these surfaces revealed by conventional ultraviolet photoelectron spectroscopy, the momentum-space resolved photoemission tomography reveals a significant difference in both structural and electronic properties of tetracene and pentacene films. Particularly, the saturated monolayer of tetracene on Ag(110) is found to consist of two molecular species that, despite having the same orientation, are electronically very different-while one molecule remains neutral, another is charged because of electron donation from the substrate.
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Affiliation(s)
- Xiaosheng Yang
- Peter Grünberg Institut (PGI-3) , Forschungszentrum Jülich , 52425 Jülich , Germany
- Jülich Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology , 52425 Jülich , Germany
- Experimental Physics IV A , RWTH Aachen University , 52074 Aachen , Germany
| | - Larissa Egger
- Institute of Physics , University of Graz , NAWI Graz, 8010 Graz , Austria
| | - Jana Fuchsberger
- Institute of Physics , University of Graz , NAWI Graz, 8010 Graz , Austria
| | - Martin Unzog
- Institute of Physics , University of Graz , NAWI Graz, 8010 Graz , Austria
| | - Daniel Lüftner
- Institute of Physics , University of Graz , NAWI Graz, 8010 Graz , Austria
| | - Felix Hajek
- Institute of Physics , University of Graz , NAWI Graz, 8010 Graz , Austria
| | - Philipp Hurdax
- Institute of Physics , University of Graz , NAWI Graz, 8010 Graz , Austria
| | - Matteo Jugovac
- Peter Grünberg Institut (PGI-6) , Forschungszentrum Jülich , 52425 Jülich , Germany
| | - Giovanni Zamborlini
- Peter Grünberg Institut (PGI-6) , Forschungszentrum Jülich , 52425 Jülich , Germany
| | - Vitaliy Feyer
- Peter Grünberg Institut (PGI-6) , Forschungszentrum Jülich , 52425 Jülich , Germany
| | - Georg Koller
- Institute of Physics , University of Graz , NAWI Graz, 8010 Graz , Austria
| | - Peter Puschnig
- Institute of Physics , University of Graz , NAWI Graz, 8010 Graz , Austria
| | - F Stefan Tautz
- Peter Grünberg Institut (PGI-3) , Forschungszentrum Jülich , 52425 Jülich , Germany
- Jülich Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology , 52425 Jülich , Germany
- Experimental Physics IV A , RWTH Aachen University , 52074 Aachen , Germany
| | - Michael G Ramsey
- Institute of Physics , University of Graz , NAWI Graz, 8010 Graz , Austria
| | - Serguei Soubatch
- Peter Grünberg Institut (PGI-3) , Forschungszentrum Jülich , 52425 Jülich , Germany
- Jülich Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology , 52425 Jülich , Germany
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11
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Xuan F, Chen Y, Quek SY. Quasiparticle Levels at Large Interface Systems from Many-Body Perturbation Theory: The XAF-GW Method. J Chem Theory Comput 2019; 15:3824-3835. [PMID: 31084031 DOI: 10.1021/acs.jctc.9b00229] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
We present a fully ab initio approach based on many-body perturbation theory in the GW approximation to compute the quasiparticle levels of large interface systems without significant covalent interactions between the different components of the interface (meaning that the different components can be separated without the creation of dangling bonds). The only assumption in our approach is that the polarizability matrix (chi) of the interface can be given by the sum of the polarizability matrices of individual components of the interface. We show analytically, using a two-state hybridized model, that this assumption is valid even in the presence of interface hybridization to form bonding and antibonding states up to first order in the overlap matrix elements involved in the hybridization. We validate our approach by showing that the band structure obtained in our method is almost identical to that obtained using a regular GW calculation for bilayer black phosphorus, where interlayer hybridization is significant. Significant savings in computational time and memory are obtained by computing chi only for the smallest subunit cell of each component and expanding (unfolding) the chi matrix to that in the unit cell of the interface. To treat interface hybridization, the full wave functions of the interface are used in computing the self-energy. We thus call the method XAF-GW (X, eXpand-chi; A, Add-chi; F, Full wave functions). Compared to GW-embedding type approaches in the literature, the XAF-GW approach is not limited to specific screening environments or to nonhybridized interface systems. XAF-GW can also be applied to systems with different dimensionalities, as well as to Moire superlattices such as in twisted bilayers. We illustrate the generality and usefulness of our approach by applying it to self-assembled PTCDA monolayers on Au(111) and Ag(111) and PTCDA monolayers on graphite-supported monolayer WSe2. In all cases, the predicted HOMO and LUMO levels agree well with experimental measurements.
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Affiliation(s)
- Fengyuan Xuan
- Centre for Advanced 2D Materials , National University of Singapore , Block S14, Level 6, 6 Science Drive 2 , Singapore 117546 , Singapore
| | - Yifeng Chen
- Centre for Advanced 2D Materials , National University of Singapore , Block S14, Level 6, 6 Science Drive 2 , Singapore 117546 , Singapore
| | - Su Ying Quek
- Centre for Advanced 2D Materials , National University of Singapore , Block S14, Level 6, 6 Science Drive 2 , Singapore 117546 , Singapore.,Department of Physics , National University of Singapore , 2 Science Drive 3 , Singapore 117542 , Singapore
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12
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Harbers R, Heepenstrick T, Perepichka DF, Sokolowski M. Pure and mixed ordered monolayers of tetracyano-2,6-naphthoquinodimethane and hexathiapentacene on the Ag(100) surface. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2019; 10:1188-1199. [PMID: 31293856 PMCID: PMC6604726 DOI: 10.3762/bjnano.10.118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/13/2018] [Accepted: 05/16/2019] [Indexed: 06/09/2023]
Abstract
We report on mixed ordered monolayers of the electron acceptor-type molecule tetracyano-2,6-naphthoquinodimethane (TNAP) and the electron donor-type molecule hexathiapentacene (HTPEN). This investigation was motivated by the general question which type of mixed stoichiometric structures are formed on a surface by molecules that are otherwise typically used for the synthesis of bulk charge-transfer materials. The layers were obtained by vacuum deposition on the Ag(100) surface and analyzed by low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). The formation of the mixed structure occurs spontaneously. An important motif for the structure formation is given by hydrogen bonds between the TNAP molecules. Both molecules, TNAP and HTPEN also form well-ordered monolayers on the Ag(100) surface on their own. In all structures, the molecules are adsorbed in a planar orientation on the surface. We discuss the influence of intermolecular charge transfer on the ordering in the mixed structure.
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Affiliation(s)
- Robert Harbers
- Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstraße 12, 53115 Bonn, Germany
| | - Timo Heepenstrick
- Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstraße 12, 53115 Bonn, Germany
| | - Dmitrii F Perepichka
- Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, H3A 0B8, Quebec, Canada
| | - Moritz Sokolowski
- Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstraße 12, 53115 Bonn, Germany
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13
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Chen MT, Hofmann OT, Gerlach A, Bröker B, Bürker C, Niederhausen J, Hosokai T, Zegenhagen J, Vollmer A, Rieger R, Müllen K, Schreiber F, Salzmann I, Koch N, Zojer E, Duhm S. Energy-level alignment at strongly coupled organic-metal interfaces. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:194002. [PMID: 30673641 DOI: 10.1088/1361-648x/ab0171] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Energy-level alignment at organic-metal interfaces plays a crucial role for the performance of organic electronic devices. However, reliable models to predict energetics at strongly coupled interfaces are still lacking. We elucidate contact formation of 1,2,5,6,9,10-coronenehexone (COHON) to the (1 1 1)-surfaces of coinage metals by means of ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, the x-ray standing wave technique, and density functional theory calculations. While for low COHON thicknesses, the work-functions of the systems vary considerably, for thicker organic films Fermi-level pinning leads to identical work functions of 5.2 eV for all COHON-covered metals irrespective of the pristine substrate work function and the interfacial interaction strength.
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Affiliation(s)
- Meng-Ting Chen
- Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices and Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren-Ai Road, Suzhou 215123, People's Republic of China
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14
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Stadtmüller B, Grad L, Seidel J, Haag F, Haag N, Cinchetti M, Aeschlimann M. Modification of Pb quantum well states by the adsorption of organic molecules. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:134005. [PMID: 30625428 DOI: 10.1088/1361-648x/aafcf5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The successful implementation of nanoscale materials in next generation optoelectronic devices crucially depends on our ability to functionalize and design low dimensional materials according to the desired field of application. Recently, organic adsorbates have revealed an enormous potential to alter the occupied surface band structure of tunable materials by the formation of tailored molecule-surface bonds. Here, we extend this concept of adsorption-induced surface band structure engineering to the unoccupied part of the surface band structure. This is achieved by our comprehensive investigation of the unoccupied band structure of a lead (Pb) monolayer film on the Ag(1 1 1) surface prior and after the adsorption of one monolayer of the aromatic molecule 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA). Using two-photon momentum microscopy, we show that the unoccupied states of the Pb/Ag(1 1 1) bilayer system are dominated by a parabolic quantum well state (QWS) in the center of the surface Brillouin zone with Pb p[Formula: see text] orbital character and a side band with almost linear dispersion showing Pb p[Formula: see text] orbital character. After the adsorption of PTCDA, the Pb side band remains completely unaffected while the signal of the Pb QWS is fully suppressed. This adsorption induced change in the unoccupied Pb band structure coincides with an interfacial charge transfer from the Pb layer into the PTCDA molecule. We propose that this charge transfer and the correspondingly vertical (partially chemical) interaction across the PTCDA/Pb interface suppresses the existence of the QWS in the Pb layer. Our results hence unveil a new possibility to orbital selectively tune and control the entire surface band structure of low dimensional systems by the adsorption of organic molecules.
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Affiliation(s)
- Benjamin Stadtmüller
- Department of Physics and OPTIMAS Research Center, TU Kaiserslautern, Erwin-Schrödinger-Strasse 46, 67663 Kaiserslautern, Germany. Graduate School of Excellence Materials Science in Mainz, Erwin-Schrödinger-Strasse 46, 67663 Kaiserslautern, Germany
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15
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Thussing S, Fernández L, Jakob P. Thermal stability and interlayer exchange processes in heterolayers of TiOPc and PTCDA on Ag(1 1 1). JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:134002. [PMID: 30625431 DOI: 10.1088/1361-648x/aafcf8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Organic-organic interfaces, in particular donor-acceptor type heterointerfaces, represent central elements of organic electronic devices. Understanding and controlling their physical properties is key to improve and modify their performance. For this purpose we have investigated the structural properties and thermal evolution of molecular heterointerface model systems. Specifically, various stacked titanyl-phthalocyanine (TiOPc)-3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) heterolayers grown on Ag(1 1 1) have been examined using Fourier transform infrared absorption spectroscopy and spot-profile analysis low-energy electron diffraction. An accurate description of the thermal evolution and prevalence of the various phases of TiOPc and PTCDA is derived from the spectral signatures of the two molecular species explored in previous studies. Exceptionally high thermal stability is found for stacked heterolayers comprising TiOPc double layers with characteristic up-down arrangement of its axial Ti-O unit and single layers of PTCDA. Thereby, interlayer exchange is negligible in a wide temperature range ([Formula: see text] K). This is ascribed to attractive intermolecular interaction (dipole-dipole interaction, hydrogen bonding) among the TiOPc molecules oriented face-to-face within the TiOPc bilayer sheet. Stacked layers of comprising single layers of TiOPc and of PTCDA turn out to be thermally much less stable and more heterogeneous. In the course of their thermal evolution, a number of processes such as interlayer exchange, TiOPc double-layer formation and dewetting are encountered.
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Affiliation(s)
- S Thussing
- Fachbereich Physik und Wissenschaftliches Zentrum für Materialwissenschaften der Philipps-Universität Marburg, Renthof 5, 35032 Marburg, Germany
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16
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Felter J, Wolters J, Bocquet FC, Tautz FS, Kumpf C. Momentum microscopy on the micrometer scale: photoemission micro-tomography applied to single molecular domains. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:114003. [PMID: 30616228 DOI: 10.1088/1361-648x/aafc45] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Photoemission tomography (PT) is a newly developed method for analyzing angular resolved photoemission data. In combination with momentum microscopy it allows for a comprehensive investigation of the electronic structure of (in particular) metal-organic interfaces as they occur in organic electronic devices. The most interesting aspect in this context is the band alignment, the control of which is indispensable for designing devices. Since PT is based on characteristic photoemission patterns that are used as fingerprints, the method works well as long as these patterns are uniquely representing the specific molecular orbital they are originating from. But this limiting factor is often not fulfilled for systems exhibiting many differently oriented molecules, as they may occur on highly symmetric substrate surfaces. Here we show that this limitation can be lifted by recording the photoemission data in a momentum microscope and limiting the probed surface area to only a few micrometers squared, since this corresponds to a typical domain size for many systems. We demonstrate this by recording data from a single domain of the archetypal adsorbate system 1,4,5,8-naphthalenetetracarboxylic dianhydride on Cu(0 0 1). This proof of principle experiment paves the way for establishing the photoemission [Formula: see text]-tomography method as an ideal tool for investigating the electronic structure of metal-organic interfaces with so far unraveled clarity and unambiguity.
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Affiliation(s)
- Janina Felter
- Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany. Jülich Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology, 52425 Jülich, Germany
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17
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Buimaga-Iarinca L, Morari C. The effect of translation on the binding energy for transition-metal porphyrines adsorbed on Ag(111) surface. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2019; 10:706-717. [PMID: 30931212 PMCID: PMC6423576 DOI: 10.3762/bjnano.10.70] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Accepted: 02/22/2019] [Indexed: 06/09/2023]
Abstract
The characteristics of interaction between six transition-metal porphyrines and the Ag(111) surface are detailed here as resulted from DFT calculations. Van der Waals interactions as well as the strong correlation in 3d orbitals of transition metals were taken into account in all calculations, including the structural relaxation. For each system we investigate four relative positions of the metallic atom on top the surface. We show that the interaction between the transition metal and silver is the result of a combination between the dispersion interaction, charge transfer and weak chemical interaction. The detailed analysis of the physical properties, such as dipolar and magnetic moments and the molecule-surface charge transfer, analyzed for different geometric configurations allows us to propose qualitative models, relevant for the understanding of the self-assembly processes and related phenomena.
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Affiliation(s)
- Luiza Buimaga-Iarinca
- National Institute for Research and Development of Isotopic and Molecular Technologies,67-103 Donat, 400293 Cluj-Napoca, Romania
| | - Cristian Morari
- National Institute for Research and Development of Isotopic and Molecular Technologies,67-103 Donat, 400293 Cluj-Napoca, Romania
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18
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Duncan DA, Casado Aguilar P, Paszkiewicz M, Diller K, Bondino F, Magnano E, Klappenberger F, Píš I, Rubio A, Barth JV, Pérez Paz A, Allegretti F. Local adsorption structure and bonding of porphine on Cu(111) before and after self-metalation. J Chem Phys 2019; 150:094702. [PMID: 30849887 DOI: 10.1063/1.5084027] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have experimentally determined the lateral registry and geometric structure of free-base porphine (2H-P) and copper-metalated porphine (Cu-P) adsorbed on Cu(111), by means of energy-scanned photoelectron diffraction (PhD), and compared the experimental results to density functional theory (DFT) calculations that included van der Waals corrections within the Tkatchenko-Scheffler approach. Both 2H-P and Cu-P adsorb with their center above a surface bridge site. Consistency is obtained between the experimental and DFT-predicted structural models, with a characteristic change in the corrugation of the four N atoms of the molecule's macrocycle following metalation. Interestingly, comparison with previously published data for cobalt porphine adsorbed on the same surface evidences a distinct increase in the average height of the N atoms above the surface through the series 2H-P, Cu-P, and cobalt porphine. Such an increase strikingly anti-correlates the DFT-predicted adsorption strength, with 2H-P having the smallest adsorption height despite the weakest calculated adsorption energy. In addition, our findings suggest that for these macrocyclic compounds, substrate-to-molecule charge transfer and adsorption strength may not be univocally correlated.
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Affiliation(s)
- D A Duncan
- Physics Department E20, Technical University of Munich, 85748 Garching, Germany
| | - P Casado Aguilar
- Physics Department E20, Technical University of Munich, 85748 Garching, Germany
| | - M Paszkiewicz
- Physics Department E20, Technical University of Munich, 85748 Garching, Germany
| | - K Diller
- Physics Department E20, Technical University of Munich, 85748 Garching, Germany
| | - F Bondino
- IOM-CNR, Laboratorio TASC, S.S. 14-km 163.5, 34149 Basovizza, Trieste, Italy
| | - E Magnano
- IOM-CNR, Laboratorio TASC, S.S. 14-km 163.5, 34149 Basovizza, Trieste, Italy
| | - F Klappenberger
- Physics Department E20, Technical University of Munich, 85748 Garching, Germany
| | - I Píš
- IOM-CNR, Laboratorio TASC, S.S. 14-km 163.5, 34149 Basovizza, Trieste, Italy
| | - A Rubio
- Nano-Bio Spectroscopy Group and ETSF, Universidad del País Vasco, 20018 San Sebastián, Spain
| | - J V Barth
- Physics Department E20, Technical University of Munich, 85748 Garching, Germany
| | - A Pérez Paz
- Nano-Bio Spectroscopy Group and ETSF, Universidad del País Vasco, 20018 San Sebastián, Spain
| | - F Allegretti
- Physics Department E20, Technical University of Munich, 85748 Garching, Germany
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19
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Schwarz M, Duncan DA, Garnica M, Ducke J, Deimel PS, Thakur PK, Lee TL, Allegretti F, Auwärter W. Quantitative determination of a model organic/insulator/metal interface structure. NANOSCALE 2018; 10:21971-21977. [PMID: 30444513 PMCID: PMC6289171 DOI: 10.1039/c8nr06387g] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Accepted: 09/28/2018] [Indexed: 05/22/2023]
Abstract
By combining X-ray photoelectron spectroscopy, X-ray standing waves and scanning tunneling microscopy, we investigate the geometric and electronic structure of a prototypical organic/insulator/metal interface, namely cobalt porphine on monolayer hexagonal boron nitride (h-BN) on Cu(111). Specifically, we determine the adsorption height of the organic molecule and show that the original planar molecular conformation is preserved in contrast to the adsorption on Cu(111). In addition, we highlight the electronic decoupling provided by the h-BN spacer layer and find that the h-BN-metal separation is not significantly modified by the molecular adsorption. Finally, we find indication of a temperature dependence of the adsorption height, which might be a signature of strongly-anisotropic thermal vibrations of the weakly bonded molecules.
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Affiliation(s)
- Martin Schwarz
- Physics Department
, Technical University of Munich
,
85748 Garching
, Germany
.
;
| | - David A. Duncan
- Diamond Light Source
, Harwell Science and Innovation Campus
,
Didcot OX11 0DE
, UK
| | - Manuela Garnica
- Physics Department
, Technical University of Munich
,
85748 Garching
, Germany
.
;
| | - Jacob Ducke
- Physics Department
, Technical University of Munich
,
85748 Garching
, Germany
.
;
| | - Peter S. Deimel
- Physics Department
, Technical University of Munich
,
85748 Garching
, Germany
.
;
| | - Pardeep K. Thakur
- Diamond Light Source
, Harwell Science and Innovation Campus
,
Didcot OX11 0DE
, UK
| | - Tien-Lin Lee
- Diamond Light Source
, Harwell Science and Innovation Campus
,
Didcot OX11 0DE
, UK
| | - Francesco Allegretti
- Physics Department
, Technical University of Munich
,
85748 Garching
, Germany
.
;
| | - Willi Auwärter
- Physics Department
, Technical University of Munich
,
85748 Garching
, Germany
.
;
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20
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Zhang YC, Lee DY. Intercalating Single-Atom Metal Centers into an Organic Monolayer with a Full-Sample Coverage. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:13387-13394. [PMID: 30346778 DOI: 10.1021/acs.langmuir.8b02968] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Thiolate self-assembled monolayers (SAMs) have been widely used as a straightforward method to functionalize the surface of a common substrate with selective organic functional groups. Here we describe a process that further introduces isolated metal centers into an organic SAM using solutions of metallic porphyrin so that different organic groups and metal single-atoms can be simultaneously exposed on top of the surface. The entire process employs only common laboratory equipment and mild-temperature (<100 °C) incubation to create a full-sample (>cm2) SAM coverage. Each step in this process is closely monitored and discussed using nm-scale scanning tunneling microscopy (STM) images. This work can be straightforwardly adopted by research groups interested in such a diversely customizable surface but without access to a vacuum-based deposition technology. The porphyrin molecules are shown to intercalate among closely packed thiolate SAM domains, and STM characterization shows that the entire mixed monolayer is stable in an ambient condition. This process also does not involve any tip-assisted desorption or lithography procedure and can thus be applied toward substrates of other shapes beyond a flat surface.
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Affiliation(s)
- Yi C Zhang
- Department of Chemistry and Materials Science & Engineering Program , Washington State University , Pullman , Washington 99164 , United States
| | - David Y Lee
- Department of Chemistry and Materials Science & Engineering Program , Washington State University , Pullman , Washington 99164 , United States
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21
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Steiner C, Yang Z, Gliemann BD, Meinhardt U, Gurrath M, Ammon M, Meyer B, Kivala M, Maier S. Binary supramolecular networks of bridged triphenylamines with different substituents and identical scaffolds. Chem Commun (Camb) 2018; 54:11554-11557. [PMID: 30272078 DOI: 10.1039/c8cc04410d] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Based on scanning tunneling microscopy experiments combined with density functional theory, we report the formation and the electronic structure of porous binary supramolecular networks on Au(111). The two triphenylamine derivatives with identical scaffolds intermix due to a maximization of the overall number of H-bonds instead of an optimization of the H-bond strength in the bonding motif. The HOMO-LUMO gap is defined by both molecules, which is typical for electron donor-acceptor networks.
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Affiliation(s)
- Christian Steiner
- Department of Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erwin-Rommel-Straße 1, D-91058 Erlangen, Germany.
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22
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Baby A, Gruenewald M, Zwick C, Otto F, Forker R, van Straaten G, Franke M, Stadtmüller B, Kumpf C, Brivio GP, Fratesi G, Fritz T, Zojer E. Fully Atomistic Understanding of the Electronic and Optical Properties of a Prototypical Doped Charge-Transfer Interface. ACS NANO 2017; 11:10495-10508. [PMID: 28902494 PMCID: PMC5656979 DOI: 10.1021/acsnano.7b05828] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
The current study generates profound atomistic insights into doping-induced changes of the optical and electronic properties of the prototypical PTCDA/Ag(111) interface. For doping K atoms are used, as KxPTCDA/Ag(111) has the distinct advantage of forming well-defined stoichiometric phases. To arrive at a conclusive, unambiguous, and fully atomistic understanding of the interface properties, we combine state-of-the-art density-functional theory calculations with optical differential reflectance data, photoelectron spectra, and X-ray standing wave measurements. In combination with the full structural characterization of the KxPTCDA/Ag(111) interface by low-energy electron diffraction and scanning tunneling microscopy experiments (ACS Nano 2016, 10, 2365-2374), the present comprehensive study provides access to a fully characterized reference system for a well-defined metal-organic interface in the presence of dopant atoms, which can serve as an ideal benchmark for future research and applications. The combination of the employed complementary techniques allows us to understand the peculiarities of the optical spectra of K2PTCDA/Ag(111) and their counterintuitive similarity to those of neutral PTCDA layers. They also clearly describe the transition from a metallic character of the (pristine) adsorbed PTCDA layer on Ag(111) to a semiconducting state upon doping, which is the opposite of the effect (degenerate) doping usually has on semiconducting materials. All experimental and theoretical efforts also unanimously reveal a reduced electronic coupling between the adsorbate and the substrate, which goes hand in hand with an increasing adsorption distance of the PTCDA molecules caused by a bending of their carboxylic oxygens away from the substrate and toward the potassium atoms.
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Affiliation(s)
- Anu Baby
- Institute
of Solid State Physics, NAWI Graz, Graz
University of Technology, Petersgasse 16, 8010 Graz, Austria
- Department
of Materials Science, University of Milano-Bicocca, Via R. Cozzi 55, 20125 Milano, Italy
| | - Marco Gruenewald
- Institute
of Solid State Physics, Friedrich Schiller
University Jena, Helmholtzweg
5, 07743 Jena, Germany
| | - Christian Zwick
- Institute
of Solid State Physics, Friedrich Schiller
University Jena, Helmholtzweg
5, 07743 Jena, Germany
| | - Felix Otto
- Institute
of Solid State Physics, Friedrich Schiller
University Jena, Helmholtzweg
5, 07743 Jena, Germany
| | - Roman Forker
- Institute
of Solid State Physics, Friedrich Schiller
University Jena, Helmholtzweg
5, 07743 Jena, Germany
| | - Gerben van Straaten
- Peter
Grünberg Institut (PGI-3), Forschungszentrum
Jülich, 52425 Jülich, Germany
- Jülich
Aachen Research Alliance (JARA)−Fundamentals of Future Information
Technology, 52425 Jülich, Germany
| | - Markus Franke
- Peter
Grünberg Institut (PGI-3), Forschungszentrum
Jülich, 52425 Jülich, Germany
- Jülich
Aachen Research Alliance (JARA)−Fundamentals of Future Information
Technology, 52425 Jülich, Germany
| | - Benjamin Stadtmüller
- Department
of Physics and Research Center OPTIMAS, University of Kaiserslautern, 67663 Kaiserslautern, Germany
- Graduate
School of Excellence Materials Science in Mainz, Erwin-Schrödinger-Straβe 46, 67663 Kaiserslautern, Germany
| | - Christian Kumpf
- Peter
Grünberg Institut (PGI-3), Forschungszentrum
Jülich, 52425 Jülich, Germany
- Jülich
Aachen Research Alliance (JARA)−Fundamentals of Future Information
Technology, 52425 Jülich, Germany
| | - Gian Paolo Brivio
- Department
of Materials Science, University of Milano-Bicocca, Via R. Cozzi 55, 20125 Milano, Italy
| | - Guido Fratesi
- Department
of Materials Science, University of Milano-Bicocca, Via R. Cozzi 55, 20125 Milano, Italy
- Dipartimento
di Fisica, Università degli Studi
di Milano, Via Celoria
16, 20133 Milano, Italy
- E-mail:
| | - Torsten Fritz
- Institute
of Solid State Physics, Friedrich Schiller
University Jena, Helmholtzweg
5, 07743 Jena, Germany
- E-mail:
| | - Egbert Zojer
- Institute
of Solid State Physics, NAWI Graz, Graz
University of Technology, Petersgasse 16, 8010 Graz, Austria
- E-mail:
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23
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Multi-orbital charge transfer at highly oriented organic/metal interfaces. Nat Commun 2017; 8:335. [PMID: 28839127 PMCID: PMC5570996 DOI: 10.1038/s41467-017-00402-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 06/22/2017] [Indexed: 11/09/2022] Open
Abstract
The molecule-substrate interaction plays a key role in charge injection organic-based devices. Charge transfer at molecule-metal interfaces strongly affects the overall physical and magnetic properties of the system, and ultimately the device performance. Here, we report theoretical and experimental evidence of a pronounced charge transfer involving nickel tetraphenyl porphyrin molecules adsorbed on Cu(100). The exceptional charge transfer leads to filling of the higher unoccupied orbitals up to LUMO+3. As a consequence of this strong interaction with the substrate, the porphyrin's macrocycle sits very close to the surface, forcing the phenyl ligands to bend upwards. Due to this adsorption configuration, scanning tunneling microscopy cannot reliably probe the states related to the macrocycle. We demonstrate that photoemission tomography can instead access the Ni-TPP macrocycle electronic states and determine the reordering and filling of the LUMOs upon adsorption, thereby confirming the remarkable charge transfer predicted by density functional theory calculations.Charge transfer at molecule-metal interfaces affects the overall physical and magnetic properties of organic-based devices, and ultimately their performance. Here, the authors report evidence of a pronounced charge transfer involving nickel tetraphenyl porphyrin molecules adsorbed on copper.
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24
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Henneke C, Felter J, Schwarz D, Stefan Tautz F, Kumpf C. Controlling the growth of multiple ordered heteromolecular phases by utilizing intermolecular repulsion. NATURE MATERIALS 2017; 16:628-633. [PMID: 28272503 DOI: 10.1038/nmat4858] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Accepted: 01/16/2017] [Indexed: 06/06/2023]
Abstract
Metal/organic interfaces and their structural, electronic, spintronic and thermodynamic properties have been investigated intensively, aiming to improve and develop future electronic devices. In this context, heteromolecular phases add new design opportunities simply by combining different molecules. However, controlling the desired phases in such complex systems is a challenging task. Here, we report an effective way of steering the growth of a bimolecular system composed of adsorbate species with opposite intermolecular interactions-repulsive and attractive, respectively. The repulsive species forms a two-dimensional lattice gas, the density of which controls which crystalline phases are stable. Critical gas phase densities determine the constant-area phase diagram that describes our experimental observations, including eutectic regions with three coexisting phases. We anticipate the general validity of this type of phase diagram for binary systems containing two-dimensional gas phases, and also show that the density of the gas phase allows engineering of the interface structure.
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Affiliation(s)
- Caroline Henneke
- Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
- Jülich Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology, 52425 Jülich, Germany
| | - Janina Felter
- Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
- Jülich Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology, 52425 Jülich, Germany
| | - Daniel Schwarz
- Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
- Jülich Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology, 52425 Jülich, Germany
| | - F Stefan Tautz
- Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
- Jülich Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology, 52425 Jülich, Germany
| | - Christian Kumpf
- Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
- Jülich Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology, 52425 Jülich, Germany
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25
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Teichert C. Heteromolecular phases: Opposite interaction matters. NATURE MATERIALS 2017; 16:604-606. [PMID: 28419080 DOI: 10.1038/nmat4873] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Affiliation(s)
- Christian Teichert
- Institute of Physics of the Montanuniversitaet Leoben, Leoben 8700, Austria
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26
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Liu ZF, Egger DA, Refaely-Abramson S, Kronik L, Neaton JB. Energy level alignment at molecule-metal interfaces from an optimally tuned range-separated hybrid functional. J Chem Phys 2017. [DOI: 10.1063/1.4975321] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Zhen-Fei Liu
- Molecular Foundry and Materials Sciences Division,
Lawrence Berkeley National Laboratory, Berkeley, California
94720, USA
- Department of Physics, University of California, Berkeley, California 94720, USA
| | - David A. Egger
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel
| | - Sivan Refaely-Abramson
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel
| | - Leeor Kronik
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel
| | - Jeffrey B. Neaton
- Molecular Foundry and Materials Sciences Division,
Lawrence Berkeley National Laboratory, Berkeley, California
94720, USA
- Department of Physics, University of California, Berkeley, California 94720, USA
- Kavli Energy Nanosciences Institute at Berkeley, Berkeley, California 94720, USA
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27
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Bouju X, Mattioli C, Franc G, Pujol A, Gourdon A. Bicomponent Supramolecular Architectures at the Vacuum–Solid Interface. Chem Rev 2017; 117:1407-1444. [DOI: 10.1021/acs.chemrev.6b00389] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- Xavier Bouju
- CEMES-CNRS, 29 Rue J. Marvig, 31055 Toulouse, France
| | | | - Grégory Franc
- CEMES-CNRS, 29 Rue J. Marvig, 31055 Toulouse, France
| | - Adeline Pujol
- Université de Toulouse, UPS, CNRS, CEMES, 118 route de Narbonne, 31062 Toulouse, France
| | - André Gourdon
- CEMES-CNRS, 29 Rue J. Marvig, 31055 Toulouse, France
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28
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Zhao YL, Wang W, Qi F, Li JF, Kuang G, Zhang RQ, Lin N, Van Hove MA. Donor/Acceptor Properties of Aromatic Molecules in Complex Metal-Molecule Interfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:451-458. [PMID: 28030772 DOI: 10.1021/acs.langmuir.6b02649] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We present a comparative study, combining density functional theory with scanning tunneling microscopy/spectroscopy, of two aromatic molecules bonded with a variable number of Cu adatom(s) on a Cu(111) surface. The two molecules, 1,3,5-tris(pyridyl)benzene (TPyB) and 1,3,5-tris(4-radical-phenyl)benzene (TPB), possess the same aromatic backbone but bond weakly versus strongly to Cu with different terminal groups, respectively. We find that TPyB and TPB exhibit, respectively, small versus large charge transfers between the surface and the molecule; this contrast results in opposite shifts in the calculated density of states distributions and thus explains the opposite STS peak shifts observed in our experiments. The two molecules exhibit weak donor versus strong acceptor characters. This work provides a fundamental understanding, on a single-molecule level, of the principle that selecting specific functional groups can effectively and intentionally modify the molecular electronic properties in a wider class of molecule-metal interfaces.
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Affiliation(s)
- Yan-Ling Zhao
- Institute of Computational and Theoretical Studies & Department of Physics, Hong Kong Baptist University , Hong Kong, China
| | - Weihua Wang
- Department of Physics, The Hong Kong University of Science and Technology , Hong Kong, China
| | - Fei Qi
- Institute of Computational and Theoretical Studies & Department of Physics, Hong Kong Baptist University , Hong Kong, China
| | - Jian-Fu Li
- Department of Physics and Materials Science, City University of Hong Kong , Hong Kong, China
| | - Guowen Kuang
- Department of Physics, The Hong Kong University of Science and Technology , Hong Kong, China
| | - Rui-Qin Zhang
- Department of Physics and Materials Science, City University of Hong Kong , Hong Kong, China
| | - Nian Lin
- Department of Physics, The Hong Kong University of Science and Technology , Hong Kong, China
| | - Michel A Van Hove
- Institute of Computational and Theoretical Studies & Department of Physics, Hong Kong Baptist University , Hong Kong, China
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29
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Energy Level Shifts at the Silica/Ru(0001) Heterojunction Driven by Surface and Interface Dipoles. Top Catal 2016. [DOI: 10.1007/s11244-016-0704-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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30
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Wruss E, Hofmann O, Egger DA, Verwüster E, Gerlach A, Schreiber F, Zojer E. Adsorption Behavior of Nonplanar Phthalocyanines: Competition of Different Adsorption Conformations. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2016; 120:6869-6875. [PMID: 27066160 PMCID: PMC4819946 DOI: 10.1021/acs.jpcc.6b00312] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Revised: 02/21/2016] [Indexed: 05/09/2023]
Abstract
Using density functional theory augmented with state-of-the-art van der Waals corrections, we studied the geometric and electronic properties of nonplanar chlorogallium-phthalocyanine GaClPc molecules adsorbed on Cu(111). Comparing these results with published experimental data for adsorption heights, we found indications for breaking of the metal-halogen bond when the molecule is heated during or after the deposition process. Interestingly, the work-function change induced by this dissociated geometry is the same as that computed for an intact adsorbate layer in the "Cl-down" configuration, with both agreeing well with the experimental photoemission data. This is unexpected, as the chemical natures of the adsorbates and the adsorption distances are markedly different in the two cases. The observation is explained as a consequence of Fermi-level pinning due to fractional charge transfer at the interface. Our results show that rationalizing the adsorption configurations on the basis of electronic interface properties alone can be ambiguous and that additional insight from dispersion-corrected DFT simulations is desirable.
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Affiliation(s)
- Elisabeth Wruss
- Institute
of Solid State Physics, NAWI Graz, Graz
University of Technology, 8010 Graz, Austria
| | - Oliver
T. Hofmann
- Institute
of Solid State Physics, NAWI Graz, Graz
University of Technology, 8010 Graz, Austria
| | - David A. Egger
- Institute
of Solid State Physics, NAWI Graz, Graz
University of Technology, 8010 Graz, Austria
| | - Elisabeth Verwüster
- Institute
of Solid State Physics, NAWI Graz, Graz
University of Technology, 8010 Graz, Austria
| | - Alexander Gerlach
- Institut
für Angewandte Physik, Universität
Tübingen, 72076 Tübingen, Germany
| | - Frank Schreiber
- Institut
für Angewandte Physik, Universität
Tübingen, 72076 Tübingen, Germany
| | - Egbert Zojer
- Institute
of Solid State Physics, NAWI Graz, Graz
University of Technology, 8010 Graz, Austria
- E-mail:
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31
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Goiri E, Borghetti P, El-Sayed A, Ortega JE, de Oteyza DG. Multi-Component Organic Layers on Metal Substrates. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2016; 28:1340-1368. [PMID: 26662076 DOI: 10.1002/adma.201503570] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2015] [Revised: 08/31/2015] [Indexed: 05/28/2023]
Abstract
Increasingly high hopes are being placed on organic semiconductors for a variety of applications. Progress along these lines, however, requires the design and growth of increasingly complex systems with well-defined structural and electronic properties. These issues have been studied and reviewed extensively in single-component layers, but the focus is gradually shifting towards more complex and functional multi-component assemblies such as donor-acceptor networks. These blends show different properties from those of the corresponding single-component layers, and the understanding on how these properties depend on the different supramolecular environment of multi-component assemblies is crucial for the advancement of organic devices. Here, our understanding of two-dimensional multi-component layers on solid substrates is reviewed. Regarding the structure, the driving forces behind the self-assembly of these systems are described. Regarding the electronic properties, recent insights into how these are affected as the molecule's supramolecular environment changes are explained. Key information for the design and controlled growth of complex, functional multicomponent structures by self-assembly is summarized.
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Affiliation(s)
- Elizabeth Goiri
- Donostia International Physics Center, E-20018, Paseo Manuel Lardizabal 4, Donostia-San Sebastián, Spain
- Centro de Fisica de Materiales CSIC/UPV-EHU-Materials Physics Center, E-20018, Donostia-San Sebastián, Spain
| | - Patrizia Borghetti
- Donostia International Physics Center, E-20018, Paseo Manuel Lardizabal 4, Donostia-San Sebastián, Spain
- Centro de Fisica de Materiales CSIC/UPV-EHU-Materials Physics Center, E-20018, Donostia-San Sebastián, Spain
- Institut des NanoSciences de Paris, CNRS, UMR 7588, 4 Place Jussieu, Paris, 75005, France
| | - Afaf El-Sayed
- Centro de Fisica de Materiales CSIC/UPV-EHU-Materials Physics Center, E-20018, Donostia-San Sebastián, Spain
- Physics Dept., Faculty of Science, Al-Azhar University, 11754, Cairo, Egypt
| | - J Enrique Ortega
- Donostia International Physics Center, E-20018, Paseo Manuel Lardizabal 4, Donostia-San Sebastián, Spain
- Centro de Fisica de Materiales CSIC/UPV-EHU-Materials Physics Center, E-20018, Donostia-San Sebastián, Spain
- Universidad del Pais Vasco, Dpto. de Física Aplicada I, E-20018, Donostia-San Sebastián, Spain
| | - Dimas G de Oteyza
- Donostia International Physics Center, E-20018, Paseo Manuel Lardizabal 4, Donostia-San Sebastián, Spain
- Centro de Fisica de Materiales CSIC/UPV-EHU-Materials Physics Center, E-20018, Donostia-San Sebastián, Spain
- Ikerbasque, Basque Foundation for Science, E-48011, Bilbao, Spain
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32
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Edlbauer H, Zojer E, Hofmann OT. Postadsorption Work Function Tuning via Hydrogen Pressure Control. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2015; 119:27162-27172. [PMID: 26692915 PMCID: PMC4671103 DOI: 10.1021/acs.jpcc.5b08827] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Revised: 11/06/2015] [Indexed: 05/24/2023]
Abstract
The work function of metal substrates can be easily tuned, for instance, by adsorbing layers of molecular electron donors and acceptors. In this work, we discuss the possibility of changing the donor/acceptor mixing ratio reversibly after adsorption by choosing a donor/acceptor pair that is coupled via a redox reaction and that is in equilibrium with a surrounding gas phase. We discuss such a situation for the example of tetrafluoro-1,4-benzenediol (TFBD)/tetrafluoro-1,4-benzoquinone (TFBQ), adsorbed on Cu(111) and Ag(111) surfaces. We use density functional theory and ab initio thermodynamics to show that arbitrary TFBD/TFBQ mixing ratios can be set using hydrogen pressures attainable in low to ultrahigh vacuum. Adjusting the mixing ratio allows modifying the work function over a range of about 1 eV. Finally, we contrast single-species submonolayers with mixed layers to discuss why the resulting inhomogeneities in the electrostatic energy above the surface have different impacts on the interfacial level alignment and the work function.
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33
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Zhao Y, Wu Q, Chen Q, Wang J. Molecular self-assembly on two-dimensional atomic crystals: insights from molecular dynamics simulations. J Phys Chem Lett 2015; 6:4518-4524. [PMID: 26523464 DOI: 10.1021/acs.jpclett.5b02147] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
van der Waals (vdW) epitaxy of ultrathin organic films on two-dimensional (2D) atomic crystals has become a sovereign area because of their unique advantages in organic electronic devices. However, the dynamic mechanism of the self-assembly remains elusive. Here, we visualize the nanoscale self-assembly of organic molecules on graphene and boron nitride monolayer from a disordered state to a 2D lattice via molecular dynamics simulation for the first time. It is revealed that the assembly toward 2D ordered structures is essentially the minimization of the molecule-molecule interaction, that is, the vdW interaction in nonpolar systems and the vdW and Coulomb interactions in polar systems that are the decisive factors for the formation of the 2D ordering. The role of the substrate is mainly governing the array orientation of the adsorbates. The mechanisms unveiled here are generally applicable to a broad class of organic thin films via vdW epitaxy.
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Affiliation(s)
- Yinghe Zhao
- Department of Physics, Southeast University , Nanjing 211189, China
| | - Qisheng Wu
- Department of Physics, Southeast University , Nanjing 211189, China
| | - Qian Chen
- Department of Physics, Southeast University , Nanjing 211189, China
| | - Jinlan Wang
- Department of Physics, Southeast University , Nanjing 211189, China
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34
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Cochrane KA, Schiffrin A, Roussy TS, Capsoni M, Burke SA. Pronounced polarization-induced energy level shifts at boundaries of organic semiconductor nanostructures. Nat Commun 2015; 6:8312. [PMID: 26440933 PMCID: PMC4600718 DOI: 10.1038/ncomms9312] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Accepted: 08/11/2015] [Indexed: 11/09/2022] Open
Abstract
Organic semiconductor devices rely on the movement of charge at and near interfaces, making an understanding of energy level alignment at these boundaries an essential element of optimizing materials for electronic and optoelectronic applications. Here we employ low temperature scanning tunneling microscopy and spectroscopy to investigate a model system: two-dimensional nanostructures of the prototypical organic semiconductor, PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride) adsorbed on NaCl (2 ML)/Ag(111). Pixel-by-pixel scanning tunneling spectroscopy allows mapping of occupied and unoccupied electronic states across these nanoislands with sub-molecular spatial resolution, revealing strong electronic differences between molecules at the edges and those in the centre, with energy level shifts of up to 400 meV. We attribute this to the change in electrostatic environment at the boundaries of clusters, namely via polarization of neighbouring molecules. The observation of these strong shifts illustrates a crucial issue: interfacial energy level alignment can differ substantially from the bulk electronic structure in organic materials. Interfaces are essential in organic semiconductor devices, yet the detailed connection between interface geometry and energy level alignment are not fully understood. Here, Cochrane et al. quantify energy level shifts with sub-molecular resolution within a nanoscale model organic semiconductor system.
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Affiliation(s)
- K A Cochrane
- Department of Chemistry, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1
| | - A Schiffrin
- Department of Physics and Astronomy, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1.,Quantum Matter Institute, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z4
| | - T S Roussy
- Department of Physics and Astronomy, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1
| | - M Capsoni
- Department of Physics and Astronomy, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1
| | - S A Burke
- Department of Chemistry, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1.,Department of Physics and Astronomy, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z1.,Quantum Matter Institute, University of British Columbia, Vancouver British Columbia, Canada V6T 1Z4
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35
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Exploring three-dimensional orbital imaging with energy-dependent photoemission tomography. Nat Commun 2015; 6:8287. [PMID: 26437297 PMCID: PMC4600719 DOI: 10.1038/ncomms9287] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2015] [Accepted: 08/06/2015] [Indexed: 11/08/2022] Open
Abstract
Recently, it has been shown that experimental data from angle-resolved photoemission spectroscopy on oriented molecular films can be utilized to retrieve real-space images of molecular orbitals in two dimensions. Here, we extend this orbital tomography technique by performing photoemission initial state scans as a function of photon energy on the example of the brickwall monolayer of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) on Ag(110). The overall dependence of the photocurrent on the photon energy can be well accounted for by assuming a plane wave for the final state. However, the experimental data, both for the highest occupied and the lowest unoccupied molecular orbital of PTCDA, exhibits an additional modulation attributed to final state scattering effects. Nevertheless, as these effects beyond a plane wave final state are comparably small, we are able, with extrapolations beyond the attainable photon energy range, to reconstruct three-dimensional images for both orbitals in agreement with calculations for the adsorbed molecule. Experimental data from angle-resolved photoemission spectroscopy can be utilized on molecular films to retrieve real-space images of molecular orbitals in two dimensions. Here, by scanning initial states as a function of photon energy, the authors can reconstruct three-dimensional orbital images.
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36
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Offenbacher H, Lüftner D, Ules T, Reinisch EM, Koller G, Puschnig P, Ramsey MG. Orbital tomography: Molecular band maps, momentum maps and the imaging of real space orbitals of adsorbed molecules. JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 2015; 204:92-101. [PMID: 26752804 PMCID: PMC4691939 DOI: 10.1016/j.elspec.2015.04.023] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The frontier orbitals of molecules are the prime determinants of their chemical, optical and electronic properties. Arguably, the most direct method of addressing the (filled) frontier orbitals is ultra-violet photoemission spectroscopy (UPS). Although UPS is a mature technique from the early 1970s on, the angular distribution of the photoemitted electrons was thought to be too complex to be analysed quantitatively. Recently angle resolved UPS (ARUPS) work on conjugated molecules both, in ordered thick films and chemisorbed monolayers, has shown that the angular (momentum) distribution of the photocurrent from orbital emissions can be simply understood. The approach, based on the assumption of a plane wave final state is becoming known as orbital tomography. Here we will demonstrate, with selected examples of pentacene (5A) and sexiphenyl (6P), the potential of orbital tomography. First it will be shown how the full angular distribution of the photocurrent (momentum map) from a specific orbital is related to the real space orbital by a Fourier transform. Examples of the reconstruction of 5A orbitals will be given and the procedure for recovering the lost phase information will be outlined. We then move to examples of sexiphenyl where we interrogate the original band maps of thick sexiphenyl in the light of our understanding of orbital tomography that has developed since then. With comparison to theoretical simulations of the molecular band maps, the molecular conformation and orientation will be concluded. New results for the sexiphenyl monolayer on Al(1 1 0) will then be presented. From the band maps it will be concluded that the molecule is planarised and adopts a tilted geometry. Finally the momentum maps down to HOMO-11 will be analysed and real space orbitals reconstructed.
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Affiliation(s)
| | | | | | | | - Georg Koller
- Institute of Physics, University of Graz, Universitätsplatz 5, 8010 Graz, Austria
| | | | - Michael G. Ramsey
- Institute of Physics, University of Graz, Universitätsplatz 5, 8010 Graz, Austria
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37
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Egger DA, Liu ZF, Neaton JB, Kronik L. Reliable energy level alignment at physisorbed molecule-metal interfaces from density functional theory. NANO LETTERS 2015; 15:2448-55. [PMID: 25741626 PMCID: PMC4392703 DOI: 10.1021/nl504863r] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Revised: 03/04/2015] [Indexed: 05/17/2023]
Abstract
A key quantity for molecule-metal interfaces is the energy level alignment of molecular electronic states with the metallic Fermi level. We develop and apply an efficient theoretical method, based on density functional theory (DFT) that can yield quantitatively accurate energy level alignment information for physisorbed metal-molecule interfaces. The method builds on the "DFT+Σ" approach, grounded in many-body perturbation theory, which introduces an approximate electron self-energy that corrects the level alignment obtained from conventional DFT for missing exchange and correlation effects associated with the gas-phase molecule and substrate polarization. Here, we extend the DFT+Σ approach in two important ways: first, we employ optimally tuned range-separated hybrid functionals to compute the gas-phase term, rather than rely on GW or total energy differences as in prior work; second, we use a nonclassical DFT-determined image-charge plane of the metallic surface to compute the substrate polarization term, rather than the classical DFT-derived image plane used previously. We validate this new approach by a detailed comparison with experimental and theoretical reference data for several prototypical molecule-metal interfaces, where excellent agreement with experiment is achieved: benzene on graphite (0001), and 1,4-benzenediamine, Cu-phthalocyanine, and 3,4,9,10-perylene-tetracarboxylic-dianhydride on Au(111). In particular, we show that the method correctly captures level alignment trends across chemical systems and that it retains its accuracy even for molecules for which conventional DFT suffers from severe self-interaction errors.
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Affiliation(s)
- David A. Egger
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel
| | - Zhen-Fei Liu
- Molecular Foundry and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - Jeffrey B. Neaton
- Molecular Foundry and Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
- Department
of Physics, University of California, Berkeley, California 94720, United States
- Kavli Energy Nanosciences Institute at Berkeley, Berkeley, California 94720, United States
| | - Leeor Kronik
- Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel
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38
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Scheele M, Brütting W, Schreiber F. Coupled organic–inorganic nanostructures (COIN). Phys Chem Chem Phys 2015; 17:97-111. [DOI: 10.1039/c4cp03094j] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Materials to devices: coupled organic–inorganic nanostructures provide versatile perspectives for quantum dot-based optoelectronic devices.
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Affiliation(s)
- M Scheele
- Institute of Physical and Theoretical Chemistry, University of Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany.
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39
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Borghetti P, El-Sayed A, Goiri E, Rogero C, Lobo-Checa J, Floreano L, Ortega JE, de Oteyza DG. Spectroscopic fingerprints of work-function-controlled phthalocyanine charging on metal surfaces. ACS NANO 2014; 8:12786-95. [PMID: 25426520 DOI: 10.1021/nn5060333] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
The electronic character of a π-conjugated molecular overlayer on a metal surface can change from semiconducting to metallic, depending on how molecular orbitals arrange with respect to the electrode's Fermi level. Molecular level alignment is thus a key property that strongly influences the performance of organic-based devices. In this work, we report how the electronic level alignment of copper phthalocyanines on metal surfaces can be tailored by controlling the substrate work function. We even show the way to finely tune it for one fixed phthalocyanine-metal combination without the need to intercalate substrate-functionalizing buffer layers. Instead, the work function is trimmed by appropriate design of the phthalocyanine's supramolecular environment, such that charge transfer into empty molecular levels can be triggered across the metal-organic interface. These intriguing observations are the outcome of a powerful combination of surface-sensitive electron spectroscopies, which further reveal a number of characteristic spectroscopic fingerprints of a lifted LUMO degeneracy associated with the partial phthalocyanine charging.
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Affiliation(s)
- Patrizia Borghetti
- Donostia International Physics Center, Paseo Manuel Lardizabal 4, San Sebastián, Spain
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40
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Willenbockel M, Lüftner D, Stadtmüller B, Koller G, Kumpf C, Soubatch S, Puschnig P, Ramsey MG, Tautz FS. The interplay between interface structure, energy level alignment and chemical bonding strength at organic-metal interfaces. Phys Chem Chem Phys 2014; 17:1530-48. [PMID: 25475998 DOI: 10.1039/c4cp04595e] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
What do energy level alignments at metal-organic interfaces reveal about the metal-molecule bonding strength? Is it permissible to take vertical adsorption heights as indicators of bonding strengths? In this paper we analyse 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) on the three canonical low index Ag surfaces to provide exemplary answers to these questions. Specifically, we employ angular resolved photoemission spectroscopy for a systematic study of the energy level alignments of the two uppermost frontier states in ordered monolayer phases of PTCDA. Data are analysed using the orbital tomography approach. This allows the unambiguous identification of the orbital character of these states, and also the discrimination between inequivalent species. Combining this experimental information with DFT calculations and the generic Newns-Anderson chemisorption model, we analyse the alignments of highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) with respect to the vacuum levels of bare and molecule-covered surfaces. This reveals clear differences between the two frontier states. In particular, on all surfaces the LUMO is subject to considerable bond stabilization through the interaction between the molecular π-electron system and the metal, as a consequence of which it also becomes occupied. Moreover, we observe a larger bond stabilization for the more open surfaces. Most importantly, our analysis shows that both the orbital binding energies of the LUMO and the overall adsorption heights of the molecule are linked to the strength of the chemical interaction between the molecular π-electron system and the metal, in the sense that stronger bonding leads to shorter adsorption heights and larger orbital binding energies.
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Affiliation(s)
- M Willenbockel
- Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
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Duden T, Thust A, Kumpf C, Tautz FS. Focal-series reconstruction in low-energy electron microscopy. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2014; 20:968-973. [PMID: 24717211 DOI: 10.1017/s1431927614000403] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In low-energy electron microscopy (LEEM) we commonly encounter images which, beside amplitude contrast, also show signatures of phase contrast. The images are usually interpreted by following the evolution of the contrast during the experiment, and assigning gray levels to morphological changes. Through reconstruction of the exit wave, two aspects of LEEM can be addressed: (1) the resolution can be improved by exploiting the full information limit of the microscope and (2) electron phase shifts which contribute to the image contrast can be extracted. In this article, linear exit wave reconstruction from a through-focal series of LEEM images is demonstrated. As a model system we utilize a heteromolecular monolayer consisting of the organic molecules 3,4,9,10-perylene tetracarboxylic dianhydride and Cu-II-Phthalocyanine, adsorbed on a Ag(111) surface.
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Affiliation(s)
- Thomas Duden
- 1Peter Grünberg Institut (PGI-3),Forschungszentrum Jülich,52425 Jülich,Germany
| | - Andreas Thust
- 2Ernst Ruska-Centrum (ER-C) and Peter Grünberg Institut (PGI-5),Forschungszentrum Jülich,52425 Jülich,Germany
| | - Christian Kumpf
- 1Peter Grünberg Institut (PGI-3),Forschungszentrum Jülich,52425 Jülich,Germany
| | - F Stefan Tautz
- 1Peter Grünberg Institut (PGI-3),Forschungszentrum Jülich,52425 Jülich,Germany
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