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Dreher M, Witte G. Selective saturation of step-edges as a tool to control the growth of molecular fibres. Phys Chem Chem Phys 2021; 23:8023-8029. [PMID: 33533346 DOI: 10.1039/d0cp06725c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The concept of bottom-up self-organisation has become a promising alternative for structuring molecular materials, which are hardly accessible by conventional top-down approaches such as lithography due to their limited chemical robustness. While these materials often tend to form three-dimensional, crystalline islands or fibres upon film growth, the size and orientation of such fibres are mainly governed by appropriate preparation conditions as well as microscopic interactions at the interface with the supporting surface. Substrate surface defects such as vacancies or step-edges, which cannot be completely ruled out on real surfaces on the mesoscopic scale, can act as preferred nucleation sites for molecules that leads to parasitic film growth competing with their intrinsic alignment prevailing on an ideal surface. In the present study, we demonstrate for the case of para-quaterphenyl (p-4P) that the presence of azimuthally disordered, fibres on Ag(111) surfaces can be understood as a superposition of step-mediated nucleation and the intrinsic epitaxial fibre growth on ideal surfaces. We validate the concept by purposely exposing the silver substrates briefly to oxygen or even ambient air to passivate the more reactive step-sites, which hampers subsequently grown molecular films to nucleate at these step-edges. This yields a truly epitaxial alignment as well as an enlargement of the fibres present on the whole sample.
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Affiliation(s)
- Maximilian Dreher
- Molekulare Festkörperphysik, Philipps-University Marburg, D-35032 Marburg, Germany.
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Casalegno M, Moret M, Resel R, Raos G. Surface Reconstructions in Organic Crystals: Simulations of the Effect of Temperature and Defectivity on Bulk and (001) Surfaces of 2,2':6',2″-Ternaphthalene. CRYSTAL GROWTH & DESIGN 2016; 16:412-422. [PMID: 26834509 PMCID: PMC4720359 DOI: 10.1021/acs.cgd.5b01405] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Revised: 11/17/2015] [Indexed: 06/05/2023]
Abstract
2,2':6',2″-Ternaphthalene (NNN) is a novel, blue-emitting material, suitable for preparation of organic light-emitting diodes. Its crystal structure has been solved recently, but its thermal behavior and surface properties have not yet been explored, partly due to the difficulty in obtaining high quality crystals. In the present study we use classical molecular dynamics to investigate the thermal behavior of bulk and (001) surfaces of NNN. Our bulk simulations indicate the occurrence of a phase transition at about 600 K. The transition is facilitated by the presence of a free (001) surface, since a reconstruction leading to a very similar structure occurs around 550 K in our surface models. This holds for both ideal and defective surface models, containing a small number of vacancies (one or two missing molecules in the outermost layer). In all cases, the process is triggered by thermal motion and involves the reorientation of the molecules with respect to the (001) plane. Both the bulk and surface phases share the monoclinic space group P21/a with a herringbone disposition of molecules. These findings and their implications for the use of NNN in organic electronics are discussed.
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Affiliation(s)
- Mosè Casalegno
- Dipartimento di Chimica, Materiali e Ingegneria Chimica "G. Natta", Politecnico di Milano , Via L. Mancinelli 7, 20131 Milano, Italy
| | - Massimo Moret
- Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca , Via R. Cozzi 55, 20125 Milano, Italy
| | - Roland Resel
- Institut für Festkörperphysik, Technische Universität Graz , 60101 Graz, Austria
| | - Guido Raos
- Dipartimento di Chimica, Materiali e Ingegneria Chimica "G. Natta", Politecnico di Milano , Via L. Mancinelli 7, 20131 Milano, Italy
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Röthel C, Radziown M, Resel R, Zimmer A, Simbrunner C, Werzer O. Complex Behavior of Caffeine Crystallites on Muscovite Mica Surfaces. CRYSTAL GROWTH & DESIGN 2015; 15:4563-4570. [PMID: 26366127 PMCID: PMC4561387 DOI: 10.1021/acs.cgd.5b00833] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Revised: 07/30/2015] [Indexed: 05/11/2023]
Abstract
Defined fabrication of organic thin films is highly desired in technological, as well as pharmaceutical, applications since morphology and crystal structure are directly linked to physical, electrical, and optical properties. Within this work, the directed growth of caffeine deposited by hot wall epitaxy (HWE) on muscovite mica is studied. Optical and atomic force microscopy measurements reveal the presence of caffeine needles exhibiting a preferable alignment in the azimuthal directions with respect to the orientation of the defined mica surface. Specular X-ray diffraction and X-ray diffraction pole figure measurements give evidence that the β-polymorphic form of caffeine forms on the mica surface. All results consent that caffeine molecules have an edge-on conformation i.e. minimizing their interaction area with the surface. Furthermore, the azimuthal alignment of the long caffeine needle axis takes place along the [11̅0], [100], and [110] real space directions of mica; needles are observed every 60° azimuthally. While mica has a complex surface structure with mirror planes and lowered oxygen rows, the slightly disturbed 3-fold symmetry dictates the crystal alignment. This is different to previous findings for solution cast caffeine growth on mica. For HWE the needles align solely along the mica main directions whereby solution cast needles show an additional needle splitting due to a different alignment of caffeine with respect to the surface.
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Affiliation(s)
- Christian Röthel
- Institute
of Pharmaceutical Sciences, Department of Pharmaceutical Technology, Karl-Franzens Universität Graz, Universitätsplatz 1, 8010 Graz, Austria
- Institute
of Solid State Physics, Graz University
of Technology, Petersgasse
16, 8010 Graz, Austria
- E-mail:
| | - Michal Radziown
- Institute
of Semiconductor and Solid State Physics, Johannes Kepler Universität Linz, Altenbergerstraße 69, 4040 Linz, Austria
| | - Roland Resel
- Institute
of Solid State Physics, Graz University
of Technology, Petersgasse
16, 8010 Graz, Austria
| | - Andreas Zimmer
- Institute
of Pharmaceutical Sciences, Department of Pharmaceutical Technology, Karl-Franzens Universität Graz, Universitätsplatz 1, 8010 Graz, Austria
| | - Clemens Simbrunner
- Institute
of Semiconductor and Solid State Physics, Johannes Kepler Universität Linz, Altenbergerstraße 69, 4040 Linz, Austria
- Institute
of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany
| | - Oliver Werzer
- Institute
of Pharmaceutical Sciences, Department of Pharmaceutical Technology, Karl-Franzens Universität Graz, Universitätsplatz 1, 8010 Graz, Austria
- E-mail:
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Tavares L, Cadelano M, Quochi F, Simbrunner C, Schwabegger G, Saba M, Mura A, Bongiovanni G, Filho DADS, da Cunha W, Rubahn HG, Kjelstrup-Hansen J. Efficient Exciton Diffusion and Resonance-Energy Transfer in Multilayered Organic Epitaxial Nanofibers. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2015; 119:15689-15697. [PMID: 26191119 PMCID: PMC4500454 DOI: 10.1021/acs.jpcc.5b02405] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/12/2015] [Revised: 06/10/2015] [Indexed: 06/04/2023]
Abstract
Multilayered epitaxial nanofibers are exemplary model systems for the study of exciton dynamics and lasing in organic materials because of their well-defined morphology, high luminescence efficiencies, and color tunability. We use temperature-dependent continuous wave and picosecond photoluminescence (PL) spectroscopy to quantify exciton diffusion and resonance-energy transfer (RET) processes in multilayered nanofibers consisting of alternating layers of para-hexaphenyl (p6P) and α-sexithiophene (6T) serving as exciton donor and acceptor material, respectively. The high probability for RET processes is confirmed by quantum chemical calculations. The activation energy for exciton diffusion in p6P is determined to be as low as 19 meV, proving p6P epitaxial layers also as a very suitable donor material system. The small activation energy for exciton diffusion of the p6P donor material, the inferred high p6P-to-6T resonance-energy-transfer efficiency, and the observed weak PL temperature dependence of the 6T acceptor material together result in an exceptionally high optical emission performance of this all-organic material system, thus making it well suited, for example, for organic light-emitting devices.
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Affiliation(s)
- Luciana Tavares
- NanoSYD,
Mads Clausen Institute, University of Southern
Denmark, Alsion 2, DK-6400 Sønderborg, Denmark
| | - Michele Cadelano
- Department
of Physics, University of Cagliari, Complesso Universitario di Monserrato, I-09042 Monserrato, Cagliari, Italy
| | - Francesco Quochi
- Department
of Physics, University of Cagliari, Complesso Universitario di Monserrato, I-09042 Monserrato, Cagliari, Italy
| | - Clemens Simbrunner
- Institute
of Semiconductor and Solid State Physics, Johannes Kepler University Linz, A-4040 Linz, Austria
- Institute
of Solid State Physics, University of Bremen, D-28359 Bremen, Germany
| | - Günther Schwabegger
- Institute
of Semiconductor and Solid State Physics, Johannes Kepler University Linz, A-4040 Linz, Austria
| | - Michele Saba
- Department
of Physics, University of Cagliari, Complesso Universitario di Monserrato, I-09042 Monserrato, Cagliari, Italy
| | - Andrea Mura
- Department
of Physics, University of Cagliari, Complesso Universitario di Monserrato, I-09042 Monserrato, Cagliari, Italy
| | - Giovanni Bongiovanni
- Department
of Physics, University of Cagliari, Complesso Universitario di Monserrato, I-09042 Monserrato, Cagliari, Italy
| | | | | | - Horst-Günter Rubahn
- NanoSYD,
Mads Clausen Institute, University of Southern
Denmark, Alsion 2, DK-6400 Sønderborg, Denmark
| | - Jakob Kjelstrup-Hansen
- NanoSYD,
Mads Clausen Institute, University of Southern
Denmark, Alsion 2, DK-6400 Sønderborg, Denmark
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