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Werkovits A, Hollweger SB, Niederreiter M, Risse T, Cartus JJ, Sterrer M, Matera S, Hofmann OT. Kinetic Trapping of Charge-Transfer Molecules at Metal Interfaces. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2024; 128:3082-3089. [PMID: 38414835 PMCID: PMC10895664 DOI: 10.1021/acs.jpcc.3c08262] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 01/23/2024] [Accepted: 01/24/2024] [Indexed: 02/29/2024]
Abstract
Despite the common expectation that conjugated organic molecules on metals adsorb in a flat-lying layer, several recent studies have found coverage-dependent transitions to upright-standing phases, which exhibit notably different physical properties. In this work, we argue that from an energetic perspective, thermodynamically stable upright-standing phases may be more common than hitherto thought. However, for kinetic reasons, this phase may often not be observed experimentally. Using first-principles kinetic Monte Carlo simulations, we find that the structure with lower molecular density is (almost) always formed first, reminiscent of Ostwald's rule of stages. The phase transitions to the upright-standing phase are likely to be kinetically hindered under the conditions typically used in surface science. The simulation results are experimentally confirmed for the adsorption of tetracyanoethylene on Cu(111) using infrared and X-ray photoemission spectroscopy. Investigating both the role of the growth conditions and the energetics of the interface, we find that the time for the phase transition is determined mostly by the deposition rate and, thus, is mostly independent of the nature of the molecule.
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Affiliation(s)
- Anna Werkovits
- Institute
of Solid State Physics, Graz University of Technology, Petersgasse 16/II, 8010 Graz, Austria
| | - Simon B. Hollweger
- Institute
of Solid State Physics, Graz University of Technology, Petersgasse 16/II, 8010 Graz, Austria
| | - Max Niederreiter
- Institute
of Physics, University of Graz, Universitätsplatz 5, 8010 Graz, Austria
| | - Thomas Risse
- Institut
für Chemie und Biochemie, Freie Universität Berlin, Arminallee 22, 14195 Berlin, Germany
| | - Johannes J. Cartus
- Institute
of Solid State Physics, Graz University of Technology, Petersgasse 16/II, 8010 Graz, Austria
| | - Martin Sterrer
- Institute
of Physics, University of Graz, Universitätsplatz 5, 8010 Graz, Austria
| | - Sebastian Matera
- Theory
Department, Fritz Haber Institute of the
MPG, Faradayweg 4-6, 14195 Berlin-Dahlem, Germany
| | - Oliver T. Hofmann
- Institute
of Solid State Physics, Graz University of Technology, Petersgasse 16/II, 8010 Graz, Austria
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Niederreiter M, Cartus J, Werkovits A, Hofmann OT, Risse T, Sterrer M. Interplay of Adsorption Geometry and Work Function Evolution at the TCNE/Cu(111) Interface. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2023; 127:24266-24273. [PMID: 38148848 PMCID: PMC10749461 DOI: 10.1021/acs.jpcc.3c06422] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Revised: 11/21/2023] [Accepted: 11/22/2023] [Indexed: 12/28/2023]
Abstract
The adsorption of organic electron acceptors on metal surfaces is a powerful way to change the effective work function of the substrate through the formation of charge-transfer-induced dipoles. The work function of the interfaces is hence controlled by the redistribution of charges upon adsorption of the organic layer, which depends not only on the electron affinity of the organic material but also on the adsorption geometry. As shown in this work, the latter dependence controls the work function also in the case of adsorbate layers exhibiting a mixture of various adsorption geometries. Based on a combined experimental (core-level and infrared spectroscopy) and theoretical (density functional theory) study for tetracyanoethylene (TCNE) on Cu(111), we find that TCNE adsorbs in at least three different orientations, depending on TCNE coverage. At low coverage, flat lying TCNE dominates, as it possesses the highest adsorption energy. At a higher coverage, additionally, two different standing orientations are found. This is accompanied by a large increase in the work function of almost 3 eV at full monolayer coverage. Our results suggest that the large increase in work function is mainly due to the surface dipole of the free CN groups of the standing molecules and less dependent on the charge-transfer dipole of the differently oriented and charged molecules. This, in turn, opens new opportunities to control the work function of interfaces, e.g., by synthetic modification of the adsorbates, which may allow one to alter the adsorption geometries of the molecules as well as their contributions to the interface dipoles and, hence, the work function.
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Affiliation(s)
- Max Niederreiter
- Institute
of Physics, University of Graz, NAWI Graz, Universitätsplatz
5, 8010 Graz, Austria
| | - Johannes Cartus
- Institute
of Solid State Physics, Graz University
of Technology, NAWI Graz, Petersgasse, 16/II, 8010 Graz, Austria
| | - Anna Werkovits
- Institute
of Solid State Physics, Graz University
of Technology, NAWI Graz, Petersgasse, 16/II, 8010 Graz, Austria
| | - Oliver T. Hofmann
- Institute
of Solid State Physics, Graz University
of Technology, NAWI Graz, Petersgasse, 16/II, 8010 Graz, Austria
| | - Thomas Risse
- Institute
of Chemistry and Biochemistry, Freie Universität
Berlin, Arminallee 22, 14195 Berlin, Germany
| | - Martin Sterrer
- Institute
of Physics, University of Graz, NAWI Graz, Universitätsplatz
5, 8010 Graz, Austria
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Hofmann OT, Zojer E, Hörmann L, Jeindl A, Maurer RJ. First-principles calculations of hybrid inorganic-organic interfaces: from state-of-the-art to best practice. Phys Chem Chem Phys 2021; 23:8132-8180. [PMID: 33875987 PMCID: PMC8237233 DOI: 10.1039/d0cp06605b] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Accepted: 03/05/2021] [Indexed: 12/18/2022]
Abstract
The computational characterization of inorganic-organic hybrid interfaces is arguably one of the technically most challenging applications of density functional theory. Due to the fundamentally different electronic properties of the inorganic and the organic components of a hybrid interface, the proper choice of the electronic structure method, of the algorithms to solve these methods, and of the parameters that enter these algorithms is highly non-trivial. In fact, computational choices that work well for one of the components often perform poorly for the other. As a consequence, default settings for one materials class are typically inadequate for the hybrid system, which makes calculations employing such settings inefficient and sometimes even prone to erroneous results. To address this issue, we discuss how to choose appropriate atomistic representations for the system under investigation, we highlight the role of the exchange-correlation functional and the van der Waals correction employed in the calculation and we provide tips and tricks how to efficiently converge the self-consistent field cycle and to obtain accurate geometries. We particularly focus on potentially unexpected pitfalls and the errors they incur. As a summary, we provide a list of best practice rules for interface simulations that should especially serve as a useful starting point for less experienced users and newcomers to the field.
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Affiliation(s)
- Oliver T Hofmann
- Institute of Solid State Physics, Graz University of Technology, NAWI Graz, Petersgasse 16/II, 8010 Graz, Austria.
| | - Egbert Zojer
- Institute of Solid State Physics, Graz University of Technology, NAWI Graz, Petersgasse 16/II, 8010 Graz, Austria.
| | - Lukas Hörmann
- Institute of Solid State Physics, Graz University of Technology, NAWI Graz, Petersgasse 16/II, 8010 Graz, Austria.
| | - Andreas Jeindl
- Institute of Solid State Physics, Graz University of Technology, NAWI Graz, Petersgasse 16/II, 8010 Graz, Austria.
| | - Reinhard J Maurer
- Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK
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