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Vempati S, Deinert JC, Gierster L, Bogner L, Richter C, Mutz N, Blumstengel S, Zykov A, Kowarik S, Garmshausen Y, Hildebrandt J, Hecht S, Stähler J. Uncovering the (un-)occupied electronic structure of a buried hybrid interface. J Phys Condens Matter 2019; 31:094001. [PMID: 30562727 DOI: 10.1088/1361-648x/aaf98a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The energy level alignment at organic/inorganic (o/i) semiconductor interfaces is crucial for any light-emitting or -harvesting functionality. Essential is the access to both occupied and unoccupied electronic states directly at the interface, which is often deeply buried underneath thick organic films and challenging to characterize. We use several complementary experimental techniques to determine the electronic structure of p -quinquephenyl pyridine (5P-Py) adsorbed on ZnO(1 0 -1 0). The parent anchoring group, pyridine, significantly lowers the work function by up to 2.9 eV and causes an occupied in-gap state (IGS) directly below the Fermi level E F. Adsorption of upright-standing 5P-Py also leads to a strong work function reduction of up to 2.1 eV and to a similar IGS. The latter is then used as an initial state for the transient population of three normally unoccupied molecular levels through optical excitation and, due to its localization right at the o/i interface, provides interfacial sensitivity, even for thick 5P-Py films. We observe two final states above the vacuum level and one bound state at around 2 eV above E F, which we attribute to the 5P-Py LUMO. By the separate study of anchoring group and organic dye combined with the exploitation of the occupied IGS for selective interfacial photoexcitation, this work provides a new pathway for characterizing the electronic structure at buried o/i interfaces.
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Affiliation(s)
- S Vempati
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Abt. Physikalische Chemie, Faradayweg 4-6, 14195 Berlin, Germany
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2
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Kowarik S, Bogula L, Boitano S, Carlà F, Pithan H, Schäfer P, Wilming H, Zykov A, Pithan L. A novel 3D printed radial collimator for x-ray diffraction. Rev Sci Instrum 2019; 90:035102. [PMID: 30927801 DOI: 10.1063/1.5063520] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Accepted: 02/01/2019] [Indexed: 06/09/2023]
Abstract
We demonstrate the use of a 3D printed radial collimator in X-ray powder diffraction and surface sensitive grazing incidence X-ray diffraction. We find a significant improvement in the overall signal to background ratio of up to 100 and a suppression of more than a factor 3 · 105 for undesirable Bragg reflections generated by the X-ray "transparent" windows of the sample environment. The background reduction and the removal of the high intensity signals from the windows, which limit the detector's dynamic range, enable significantly higher sensitivity in experiments within sample environments such as vacuum chambers and gas- or liquid-cells. Details of the additively manufactured steel collimator geometry, alignment strategies using X-ray fluorescence, and data analysis are also briefly discussed. The flexibility and affordability of 3D prints enable designs optimized for specific detectors and sample environments, without compromising the degrees of freedom of the diffractometer.
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Affiliation(s)
- S Kowarik
- Bundesanstalt für Materialforschung und -Prüfung, Unter den Eichen 44-46, 12203 Berlin, Germany
| | - L Bogula
- Institut für Physik, Humboldt Universität zu Berlin, 12489 Berlin, Germany
| | - S Boitano
- ESRF-The European Synchrotron, 71, Avenue des Martyrs, CS 40220, 38043 Grenoble Cedex 9, France
| | - F Carlà
- ESRF-The European Synchrotron, 71, Avenue des Martyrs, CS 40220, 38043 Grenoble Cedex 9, France
| | - H Pithan
- Petrinum Brilon, Zur Jakobuslinde 2, 59929 Brilon, Germany
| | - P Schäfer
- Institut für Physik, Humboldt Universität zu Berlin, 12489 Berlin, Germany
| | - H Wilming
- Institute for Theoretical Physics, ETH Zürich, Wolfgang-Pauli-Str. 27, 8093 Zürich, Switzerland
| | - A Zykov
- Institut für Physik, Humboldt Universität zu Berlin, 12489 Berlin, Germany
| | - L Pithan
- ESRF-The European Synchrotron, 71, Avenue des Martyrs, CS 40220, 38043 Grenoble Cedex 9, France
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Weber C, Pithan L, Zykov A, Bommel S, Carla F, Felici R, Knie C, Bléger D, Kowarik S. Multiple timescales in the photoswitching kinetics of crystalline thin films of azobenzene-trimers. J Phys Condens Matter 2017; 29:434001. [PMID: 28809755 DOI: 10.1088/1361-648x/aa8654] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Functional materials that exhibit photoinduced structural phase transitions are highly interesting for applications in optomechanics and mechanochemistry. It is, however, still not fully understood how photochemical reactions, which are often accompanied by molecular motion, proceed in confined and crystalline environments. Here we show that thin films of azobenzene trimers exhibit high structural order and determine the crystallographic unit cell. We demonstrate that thin film can be switched partially reversibly between a crystalline and an amorphous phase. The time constant of the photoinduced amorphisation as measured with real-time x-ray diffraction ([Formula: see text]220 s) lies between the two time constants (120 s and 2870 s) of the ensemble photoisomerisation processes that are measured via optical spectroscopy. Our observation of a photoinduced shrinking of the crystalline domains indicates a cascading process, in which photoisomerisation starts at the surface of the thin film and propagates deeper into the crystalline layer by introducing disorder and generating free volume. This finding is important for the rapidly evolving research field of photoresponsive thin films and smart crystalline materials in general.
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Affiliation(s)
- C Weber
- Department of Physics, Humboldt-Universität zu Berlin, Berlin, Germany
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Bommel S, Kleppmann N, Weber C, Spranger H, Schäfer P, Novak J, Roth S, Schreiber F, Klapp S, Kowarik S. Unravelling the multilayer growth of the fullerene C60 in real time. Nat Commun 2014; 5:5388. [PMID: 25369851 PMCID: PMC4272254 DOI: 10.1038/ncomms6388] [Citation(s) in RCA: 72] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2014] [Accepted: 09/26/2014] [Indexed: 11/18/2022] Open
Abstract
Molecular semiconductors are increasingly used in devices, but understanding of elementary nanoscopic processes in molecular film growth is in its infancy. Here we use real-time in situ specular and diffuse X-ray scattering in combination with kinetic Monte Carlo simulations to study C60 nucleation and multilayer growth. We determine a self-consistent set of energy parameters describing both intra- and interlayer diffusion processes in C60 growth. This approach yields an effective Ehrlich-Schwoebel barrier of EES=110 meV, diffusion barrier of ED=540 meV and binding energy of EB=130 meV. Analysing the particle-resolved dynamics, we find that the lateral diffusion is similar to colloids, but characterized by an atom-like Schwoebel barrier. Our results contribute to a fundamental understanding of molecular growth processes in a system, which forms an important intermediate case between atoms and colloids.
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Affiliation(s)
- S. Bommel
- Institut für Physik, Humboldt-Universität zu
Berlin, Newtonstrasse 15, 12489
Berlin, Germany
- Deutsches Elektronen-Synchrotron (DESY), Notkestrasse
85, 22607
Hamburg, Germany
| | - N. Kleppmann
- Institut für Theoretische Physik, Technische Universität
Berlin, Hardenbergstrasse 36, 10623
Berlin, Germany
| | - C. Weber
- Institut für Physik, Humboldt-Universität zu
Berlin, Newtonstrasse 15, 12489
Berlin, Germany
| | - H. Spranger
- Institut für Physik, Humboldt-Universität zu
Berlin, Newtonstrasse 15, 12489
Berlin, Germany
| | - P. Schäfer
- Institut für Physik, Humboldt-Universität zu
Berlin, Newtonstrasse 15, 12489
Berlin, Germany
| | - J. Novak
- Institut für Angewandte Physik, Universität
Tübingen, Auf der Morgenstelle 10, 72076
Tübingen, Germany
| | - S.V. Roth
- Deutsches Elektronen-Synchrotron (DESY), Notkestrasse
85, 22607
Hamburg, Germany
| | - F. Schreiber
- Institut für Angewandte Physik, Universität
Tübingen, Auf der Morgenstelle 10, 72076
Tübingen, Germany
| | - S.H.L. Klapp
- Institut für Theoretische Physik, Technische Universität
Berlin, Hardenbergstrasse 36, 10623
Berlin, Germany
| | - S. Kowarik
- Institut für Physik, Humboldt-Universität zu
Berlin, Newtonstrasse 15, 12489
Berlin, Germany
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Sparenberg M, Zykov A, Beyer P, Pithan L, Weber C, Garmshausen Y, Carlà F, Hecht S, Blumstengel S, Henneberger F, Kowarik S. Controlling the growth mode of para-sexiphenyl (6P) on ZnO by partial fluorination. Phys Chem Chem Phys 2014; 16:26084-93. [DOI: 10.1039/c4cp04048a] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Partial fluorination of para-sexiphenyl significantly alters the growth process on ZnO(101̄0) avoiding the phase coexistence of unsubstituted para-sexiphenyl and leading to smooth layer-by-layer growth.
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Affiliation(s)
- M. Sparenberg
- Humboldt Universität zu Berlin
- Department of Physics
- Berlin, Germany
| | - A. Zykov
- Humboldt Universität zu Berlin
- Department of Physics
- Berlin, Germany
| | - P. Beyer
- Humboldt Universität zu Berlin
- Department of Physics
- Berlin, Germany
| | - L. Pithan
- Humboldt Universität zu Berlin
- Department of Physics
- Berlin, Germany
| | - C. Weber
- Humboldt Universität zu Berlin
- Department of Physics
- Berlin, Germany
| | - Y. Garmshausen
- Humboldt-Universität zu Berlin
- Department of Chemistry & IRIS Adlershof
- Berlin, Germany
| | - F. Carlà
- ESRF
- Experiment Division
- Grenoble, France
| | - S. Hecht
- Humboldt-Universität zu Berlin
- Department of Chemistry & IRIS Adlershof
- Berlin, Germany
| | - S. Blumstengel
- Humboldt Universität zu Berlin
- Department of Physics
- Berlin, Germany
| | - F. Henneberger
- Humboldt Universität zu Berlin
- Department of Physics
- Berlin, Germany
| | - S. Kowarik
- Humboldt Universität zu Berlin
- Department of Physics
- Berlin, Germany
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Weber C, Frank C, Bommel S, Rukat T, Leitenberger W, Schäfer P, Schreiber F, Kowarik S. Chain-length dependent growth dynamics of n-alkanes on silica investigated by energy-dispersive x-ray reflectivity in situ and in real-time. J Chem Phys 2012; 136:204709. [DOI: 10.1063/1.4719530] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
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Amassian A, Desai TV, Kowarik S, Hong S, Woll AR, Malliaras GG, Schreiber F, Engstrom JR. Coverage dependent adsorption dynamics in hyperthermal organic thin film growth. J Chem Phys 2009; 130:124701. [PMID: 19334866 PMCID: PMC2736575 DOI: 10.1063/1.3088835] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2008] [Accepted: 01/29/2009] [Indexed: 01/13/2023] Open
Abstract
We have examined the dynamics of adsorption of diindenoperylene (DIP) on SiO(2) and SiO(2) modified with an interfacial organic layer using in situ real time synchrotron x-ray scattering, focusing on the effects of coverage. On both surfaces we observe a substantial increase in the probability of adsorption with increasing coverage, which is most dramatic at the highest incident kinetic energies. On the initially uncovered surfaces, we observe a smooth decrease in the probability of adsorption with increasing incident kinetic energy, indicative of trapping-mediated adsorption. Once both surfaces are covered by DIP, the effects of incident kinetic energy are greatly reduced, and trapping is very efficient over the range of kinetic energies examined. Possible reasons for efficient trapping at high coverage and at high incident kinetic energy include more efficient momentum transfer due to mass matching, and possibly direct molecular insertion. Comparison to results on another small-molecule, pentacene, suggests that this behavior should be common to hyperthermal growth of a variety of other small-molecule thin films.
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Affiliation(s)
- A Amassian
- Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA
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Kowarik S, Gerlach A, Sellner S, Schreiber F, Cavalcanti L, Konovalov O. Real-time observation of structural and orientational transitions during growth of organic thin films. Phys Rev Lett 2006; 96:125504. [PMID: 16605925 DOI: 10.1103/physrevlett.96.125504] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2005] [Indexed: 05/08/2023]
Abstract
We study kinetically controlled orientational and structural transitions of molecular thin films during growth in situ and in real time, using diindenoperylene (DIP) as an example. By time-resolved surface-sensitive x-ray scattering (out of plane and in plane), we follow the organic molecular beam deposition of DIP on silicon oxide, on stepped sapphire, and on rubrene as an organic model surface. We identify transitions for the few-monolayer (ML) regime, as well as for thick (several 10's of ML) films. We show that the differences in the interaction of DIP with the substrate change the thickness as well as temperature range of the transitions, which include (transient) strain, subtle changes of the orientation, as well as complete reorientation. These effects should be considered rather general features of the growth of organics, which, with its orientational degrees of freedom, is qualitatively different from growth of inorganics.
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Affiliation(s)
- S Kowarik
- Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, United Kingdom
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Kowarik S, Gerlach A, Sellner S, Schreiber F, Pflaum J, Cavalcanti L, Konovalov O. Anomalous roughness evolution of rubrene thin films observed in real time during growth. Phys Chem Chem Phys 2006; 8:1834-6. [PMID: 16633669 DOI: 10.1039/b517866e] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We study the growth and structure of thin films of the organic semiconductor rubrene during organic molecular beam deposition (OMBD) on silicon oxide in situ and in real time using X-ray scattering. Using in situ grazing incidence diffraction (GID) we find a small degree of local order but an otherwise largely disordered structure, consistent with out of plane scans. Monitoring the surface morphology in real time during growth, we find relatively smooth films (surface roughness sigma below approximately 15 A for thicknesses up to at least 600 A) and a significant delay before the onset of roughening. This anomalous roughening in the beginning and crossover to normal roughening later during growth may be related to conformational changes of rubrene in the early stages of growth.
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Affiliation(s)
- S Kowarik
- Physical and Theoretical Chemistry, Oxford University, South Parks Road, Oxford OX1 3QZ, UK
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