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Kodalle T, Byranvand MM, Goudreau M, Das C, Roy R, Kot M, Briesenick S, Zohdi M, Rai M, Tamura N, Flege JI, Hempel W, Sutter-Fella CM, Saliba M. An Integrated Deposition and Passivation Strategy for Controlled Crystallization of 2D/3D Halide Perovskite Films. Adv Mater 2024:e2309154. [PMID: 38415385 DOI: 10.1002/adma.202309154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Revised: 02/05/2024] [Indexed: 02/29/2024]
Abstract
This work introduces a simplified deposition procedure for multidimensional (2D/3D) perovskite thin films, integrating a phenethylammonium chloride (PEACl)-treatment into the antisolvent step when forming the 3D perovskite. This simultaneous deposition and passivation strategy reduces the number of synthesis steps while simultaneously stabilizing the halide perovskite film and improving the photovoltaic performance of resulting solar cell devices to 20.8%. Using a combination of multimodal in situ and additional ex situ characterizations, it is demonstrated that the introduction of PEACl during the perovskite film formation slows down the crystal growth process, which leads to a larger average grain size and narrower grain size distribution, thus reducing carrier recombination at grain boundaries and improving the device's performance and stability. The data suggests that during annealing of the wet film, the PEACl diffuses to the surface of the film, forming hydrophobic (quasi-)2D structures that protect the bulk of the perovskite film from humidity-induced degradation.
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Affiliation(s)
- Tim Kodalle
- Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California, 94720, USA
- Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California, 94720, USA
| | - Mahdi Malekshahi Byranvand
- Institute for Photovoltaics, University of Stuttgart, Pfaffenwaldring 47, 70569, Stuttgart, Germany
- Helmholtz Young Investigator Group FRONTRUNNER IEK5-Photovoltaik, Forschungszentrum Jülich, 52425, Jülich, Germany
| | - Meredith Goudreau
- Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California, 94720, USA
| | - Chittaranjan Das
- Institute for Photovoltaics, University of Stuttgart, Pfaffenwaldring 47, 70569, Stuttgart, Germany
- Helmholtz Young Investigator Group FRONTRUNNER IEK5-Photovoltaik, Forschungszentrum Jülich, 52425, Jülich, Germany
| | - Rajarshi Roy
- Institute for Photovoltaics, University of Stuttgart, Pfaffenwaldring 47, 70569, Stuttgart, Germany
| | - Małgorzata Kot
- Chair of Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, 03046, Cottbus, Germany
| | - Simon Briesenick
- Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California, 94720, USA
- Department of Physics, Ernest Rutherford Physics Building, McGill University, 3600 Rue University, Montrèal, QC H3A 2T8, Canada
| | - Mohammadreza Zohdi
- Institute for Photovoltaics, University of Stuttgart, Pfaffenwaldring 47, 70569, Stuttgart, Germany
| | - Monika Rai
- Institute for Photovoltaics, University of Stuttgart, Pfaffenwaldring 47, 70569, Stuttgart, Germany
| | - Nobumichi Tamura
- Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California, 94720, USA
| | - Jan Ingo Flege
- Chair of Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, 03046, Cottbus, Germany
| | - Wolfram Hempel
- Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW), 70563, Stuttgart, Germany
| | - Carolin M Sutter-Fella
- Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California, 94720, USA
| | - Michael Saliba
- Institute for Photovoltaics, University of Stuttgart, Pfaffenwaldring 47, 70569, Stuttgart, Germany
- Helmholtz Young Investigator Group FRONTRUNNER IEK5-Photovoltaik, Forschungszentrum Jülich, 52425, Jülich, Germany
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Das C, Roy R, Kedia M, Kot M, Zuo W, Félix R, Sobol T, Flege JI, Saliba M. Unraveling the Role of Perovskite in Buried Interface Passivation. ACS Appl Mater Interfaces 2023; 15:56500-56510. [PMID: 37991727 DOI: 10.1021/acsami.3c13085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2023]
Abstract
Interfaces in perovskite solar cells play a crucial role in their overall performance, and therefore, detailed fundamental studies are needed for a better understanding. In the case of the classical n-i-p architecture, TiO2 is one of the most used electron-selective layers and can induce chemical reactions that influence the performance of the overall device stack. The interfacial properties at the TiO2/perovskite interface are often neglected, owing to the difficulty in accessing this interface. Here, we use X-rays of variable energies to study the interface of (compact and mesoporous) TiO2/perovskite in such a n-i-p architecture. The X-ray photoelectron spectroscopy and X-ray absorption spectroscopy methods show that the defect states present in the TiO2 layer are passivated by a chemical interaction of the perovskite precursor solution during the formation of the perovskite layer and form an organic layer at the interface. Such passivation of intrinsic defects in TiO2 removes charge recombination centers and shifts the bands upward. Therefore, interface defect passivation by oxidation of Ti3+ states, the organic cation layer, and an upward band bending at the TiO2/perovskite interface explain the origin of an improved electron extraction and hole-blocking nature of TiO2 in the n-i-p perovskite solar cells.
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Affiliation(s)
- Chittaranjan Das
- Institute for Photovoltaics (ipv), University of Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart, Germany
- Helmholtz Young Investigator Group, IEK5-Photovoltaik, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Rajarshi Roy
- Institute for Photovoltaics (ipv), University of Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart, Germany
| | - Mayank Kedia
- Institute for Photovoltaics (ipv), University of Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart, Germany
- Helmholtz Young Investigator Group, IEK5-Photovoltaik, Forschungszentrum Jülich, 52425 Jülich, Germany
| | - Małgorzata Kot
- Chair of Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Straße 1, 03046 Cottbus, Germany
| | - Weiwei Zuo
- Institute for Photovoltaics (ipv), University of Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart, Germany
| | - Roberto Félix
- Department Interface Design, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), Hahn-Meitner-Platz 1, 14109 Berlin, Germany
| | - Tomasz Sobol
- SOLARIS National Synchrotron Radiation Centre, Jagiellonian University, 31-007 Krakow, Poland
| | - Jan Ingo Flege
- Chair of Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Straße 1, 03046 Cottbus, Germany
| | - Michael Saliba
- Institute for Photovoltaics (ipv), University of Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart, Germany
- Helmholtz Young Investigator Group, IEK5-Photovoltaik, Forschungszentrum Jülich, 52425 Jülich, Germany
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Zuo W, Byranvand MM, Kodalle T, Zohdi M, Lim J, Carlsen B, Magorian Friedlmeier T, Kot M, Das C, Flege JI, Zong W, Abate A, Sutter-Fella CM, Li M, Saliba M. Coordination Chemistry as a Universal Strategy for a Controlled Perovskite Crystallization. Adv Mater 2023; 35:e2302889. [PMID: 37312254 DOI: 10.1002/adma.202302889] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2023] [Revised: 05/26/2023] [Indexed: 06/15/2023]
Abstract
The most efficient and stable perovskite solar cells (PSCs) are made from a complex mixture of precursors. Typically, to then form a thin film, an extreme oversaturation of the perovskite precursor is initiated to trigger nucleation sites, e.g., by vacuum, an airstream, or a so-called antisolvent. Unfortunately, most oversaturation triggers do not expel the lingering (and highly coordinating) dimethyl sulfoxide (DMSO), which is used as a precursor solvent, from the thin films; this detrimentally affects long-term stability. In this work, (the green) dimethyl sulfide (DMS) is introduced as a novel nucleation trigger for perovskite films combining, uniquely, high coordination and high vapor pressure. This gives DMS a universal scope: DMS replaces other solvents by coordinating more strongly and removes itself once the film formation is finished. To demonstrate this novel coordination chemistry approach, MAPbI3 PSCs are processed, typically dissolved in hard-to-remove (and green) DMSO achieving 21.6% efficiency, among the highest reported efficiencies for this system. To confirm the universality of the strategy, DMS is tested for FAPbI3 as another composition, which shows higher efficiency of 23.5% compared to 20.9% for a device fabricated with chlorobenzene. This work provides a universal strategy to control perovskite crystallization using coordination chemistry, heralding the revival of perovskite compositions with pure DMSO.
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Affiliation(s)
- Weiwei Zuo
- Institute for Photovoltaics (ipv), University of Stuttgart, Pfaffenwaldring 47, 70569, Stuttgart, Germany
| | - Mahdi Malekshahi Byranvand
- Institute for Photovoltaics (ipv), University of Stuttgart, Pfaffenwaldring 47, 70569, Stuttgart, Germany
- Helmholtz Young Investigator Group FRONTRUNNER, IEK5-Photovoltaik, Forschungszentrum Jülich, 52425, Jülich, Germany
| | - Tim Kodalle
- Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, 94720, USA
| | - Mohammadreza Zohdi
- Institute for Photovoltaics (ipv), University of Stuttgart, Pfaffenwaldring 47, 70569, Stuttgart, Germany
| | - Jaekeun Lim
- Institute for Photovoltaics (ipv), University of Stuttgart, Pfaffenwaldring 47, 70569, Stuttgart, Germany
| | - Brian Carlsen
- Laboratory of Photomolecular Science, École Polytechnique Fédérale de Lausanne, 1015, Lausanne, Switzerland
| | - Theresa Magorian Friedlmeier
- Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW), Meitnerstrasse 1, 70563, Stuttgart, Germany
| | - Małgorzata Kot
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Strasse 1, 03046, Cottbus, Germany
| | - Chittaranjan Das
- Institute for Photovoltaics (ipv), University of Stuttgart, Pfaffenwaldring 47, 70569, Stuttgart, Germany
- Helmholtz Young Investigator Group FRONTRUNNER, IEK5-Photovoltaik, Forschungszentrum Jülich, 52425, Jülich, Germany
| | - Jan Ingo Flege
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Strasse 1, 03046, Cottbus, Germany
| | - Wansheng Zong
- Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany
| | - Antonio Abate
- Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109, Berlin, Germany
- Department of Chemical, Materials and Production Engineering, University of Naples Federico II, pzz.le Vincenzo Tecchio 80, Naples, 80125, Italy
| | - Carolin M Sutter-Fella
- Molecular Foundry, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, 94720, USA
| | - Meng Li
- Key Lab for Special Functional Materials of Ministry of Education, National & Local Joint Engineering Research Center for High-efficiency Display and Lighting Technology, School of Materials Science and Engineering, Collaborative Innovation Center of Nano Functional Materials and Applications, Henan University, Kaifeng, 475004, China
| | - Michael Saliba
- Institute for Photovoltaics (ipv), University of Stuttgart, Pfaffenwaldring 47, 70569, Stuttgart, Germany
- Helmholtz Young Investigator Group FRONTRUNNER, IEK5-Photovoltaik, Forschungszentrum Jülich, 52425, Jülich, Germany
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Mazur M, Kapuścik P, Weichbrodt W, Domaradzki J, Mazur P, Kot M, Flege JI. WO 3 Thin-Film Optical Gas Sensors Based on Gasochromic Effect towards Low Hydrogen Concentrations. Materials (Basel) 2023; 16:ma16103831. [PMID: 37241458 DOI: 10.3390/ma16103831] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Revised: 05/15/2023] [Accepted: 05/16/2023] [Indexed: 05/28/2023]
Abstract
Hydrogen gas sensors have recently attracted increased interest due to the explosive nature of H2 and its strategic importance in the sustainable global energy system. In this paper, the tungsten oxide thin films deposited by innovative gas impulse magnetron sputtering have been investigated in terms of their response to H2. It was found that the most favourable annealing temperature in terms of sensor response value, as well as response and recovery times, was achieved at 673 K. This annealing process caused a change in the WO3 cross-section morphology from a featureless and homogenous form to a rather columnar one, but still maintaining the same surface homogeneity. In addition to that, the full-phase transition from an amorphous to nanocrystalline form occurred with a crystallite size of 23 nm. It was found that the sensor response to only 25 ppm of H2 was equal to 6.3, which is one of the best results presented in the literature so far of WO3 optical gas sensors based on a gasochromic effect. Moreover, the results of the gasochromic effect were correlated with the changes in the extinction coefficient and the concentration of the free charge carriers, which is also a novel approach to the understanding of the gasochromic phenomenon.
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Affiliation(s)
- Michał Mazur
- Faculty of Electronics, Photonics and Microsystems, Wroclaw University of Science and Technology, Janiszewskiego 11/17, 50-372 Wroclaw, Poland
| | - Paulina Kapuścik
- Faculty of Electronics, Photonics and Microsystems, Wroclaw University of Science and Technology, Janiszewskiego 11/17, 50-372 Wroclaw, Poland
| | - Wiktoria Weichbrodt
- Faculty of Electronics, Photonics and Microsystems, Wroclaw University of Science and Technology, Janiszewskiego 11/17, 50-372 Wroclaw, Poland
| | - Jarosław Domaradzki
- Faculty of Electronics, Photonics and Microsystems, Wroclaw University of Science and Technology, Janiszewskiego 11/17, 50-372 Wroclaw, Poland
| | - Piotr Mazur
- Institute of Experimental Physics, University of Wroclaw, Max Born 9, 50-204 Wroclaw, Poland
| | - Małgorzata Kot
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Strasse 1, D-03046 Cottbus, Germany
| | - Jan Ingo Flege
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Strasse 1, D-03046 Cottbus, Germany
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Pożarowska E, Pleines L, Ewert M, Prieto MJ, Tănase LC, Caldas LDS, Tiwari A, Schmidt T, Falta J, Krasovskii E, Morales C, Flege JI. Preparation and stability of the hexagonal phase of samarium oxide on Ru(0001). Ultramicroscopy 2023; 250:113755. [PMID: 37216832 DOI: 10.1016/j.ultramic.2023.113755] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2023] [Revised: 04/15/2023] [Accepted: 05/08/2023] [Indexed: 05/24/2023]
Abstract
We have used low-energy electron microscopy (LEEM), micro-illumination low-energy electron diffraction (µLEED) supported by ab initio calculations, and X-ray absorption spectroscopy (XAS) to investigate in-situ and in real-time the structural properties of Sm2O3 deposits grown on Ru(0001), a rare-earth metal oxide model catalyst. Our results show that samarium oxide grows in a hexagonal A-Sm2O3 phase on Ru(0001), exhibiting a (0001) oriented-top facet and (113) side facets. Upon annealing, a structural transition from the hexagonal to cubic phase occurs, in which the Sm cations exhibit the +3 oxidation state. The unexpected initial growth in the A-Sm2O3 hexagonal phase and its gradual transition to a mixture with cubic C-Sm2O3 showcases the complexity of the system and the critical role of the substrate in the stabilization of the hexagonal phase, which was previously reported only at high pressures and temperatures for bulk samaria. Besides, these results highlight the potential interactions that Sm could have with other catalytic compounds with respect to the here gathered insights on the preparation conditions and the specific compounds with which it interacts.
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Affiliation(s)
- Emilia Pożarowska
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, 03046 Cottbus, Germany
| | - Linus Pleines
- Institute of Solid State Physics, University of Bremen, 28359 Bremen, Germany
| | - Moritz Ewert
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, 03046 Cottbus, Germany
| | - Mauricio J Prieto
- Department of Interface Science, Fritz-Haber Institute, 14195 Berlin, Germany
| | - Liviu C Tănase
- Department of Interface Science, Fritz-Haber Institute, 14195 Berlin, Germany
| | | | - Aarti Tiwari
- Department of Interface Science, Fritz-Haber Institute, 14195 Berlin, Germany
| | - Thomas Schmidt
- Department of Interface Science, Fritz-Haber Institute, 14195 Berlin, Germany
| | - Jens Falta
- Institute of Solid State Physics, University of Bremen, 28359 Bremen, Germany
| | - Eugene Krasovskii
- Departamento de Polímeros y Materiales Avanzados: Física, Química y Tecnología, Universidad del Pais Vasco UPV/EHU, 20080 San Sebastián/Donostia, Spain; IKERBASQUE, Basque Foundation for Science, E-48013 Bilbao, Spain; Donostia International Physics Center (DIPC), E-20018 San Sebastián, Spain
| | - Carlos Morales
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, 03046 Cottbus, Germany
| | - Jan Ingo Flege
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, 03046 Cottbus, Germany.
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Buß L, Braud N, Ewert M, Jugovac M, Menteş TO, Locatelli A, Falta J, Flege JI. Unraveling van der Waals epitaxy: A real-time in-situ study of MoSe2 growth on graphene/Ru(0001). Ultramicroscopy 2023; 250:113749. [PMID: 37186986 DOI: 10.1016/j.ultramic.2023.113749] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2023] [Revised: 03/31/2023] [Accepted: 05/04/2023] [Indexed: 05/17/2023]
Abstract
In the present work we investigate the growth of monolayer MoSe2 on selenium-intercalated graphene on Ru(0001), a model layered heterostructure combining a transition metal dichalcogenide with graphene, using low energy electron microscopy and micro-diffraction. Real-time observation of MoSe2 on graphene growth reveals the island nucleation dynamics at the nanoscale. Upon annealing, larger islands are formed by sliding and attachment of multiple nanometer-sized MoSe2 flakes. Local micro-spot angle-resolved photoemission spectroscopy reveals the electronic structure of the heterostructure, indicating that no charge transfer occurs within adjacent layers. The observed behavior is attributed to intercalation of Se at the graphene/Ru(0001) interface. The unperturbed nature of the proposed heterostructure therefore renders it as a model system for investigations of graphene supported TMD nanostructures.
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Affiliation(s)
- Lars Buß
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Straße 1, Cottbus 03046, Germany.
| | - Nicolas Braud
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, Bremen 28359, Germany
| | - Moritz Ewert
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Straße 1, Cottbus 03046, Germany
| | - Matteo Jugovac
- Elettra-Sincrotrone Trieste S.C.p.A, S.S. 14km 163.5 in AREA Science Park, Trieste, Italy
| | - Tevfik Onur Menteş
- Elettra-Sincrotrone Trieste S.C.p.A, S.S. 14km 163.5 in AREA Science Park, Trieste, Italy
| | - Andrea Locatelli
- Elettra-Sincrotrone Trieste S.C.p.A, S.S. 14km 163.5 in AREA Science Park, Trieste, Italy
| | - Jens Falta
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, Bremen 28359, Germany; MAPEX Center for Materials and Processes, P.O. Box 303 440, 28334, Bremen, Germany
| | - Jan Ingo Flege
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Straße 1, Cottbus 03046, Germany
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Mańkowska E, Mazur M, Domaradzki J, Mazur P, Kot M, Flege JI. Hydrogen Gas Sensing Properties of Mixed Copper-Titanium Oxide Thin Films. Sensors (Basel) 2023; 23:3822. [PMID: 37112164 PMCID: PMC10144612 DOI: 10.3390/s23083822] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/06/2023] [Revised: 03/31/2023] [Accepted: 04/07/2023] [Indexed: 06/19/2023]
Abstract
Hydrogen is an efficient source of clean and environmentally friendly energy. However, because it is explosive at concentrations higher than 4%, safety issues are a great concern. As its applications are extended, the need for the production of reliable monitoring systems is urgent. In this work, mixed copper-titanium oxide ((CuTi)Ox) thin films with various copper concentrations (0-100 at.%), deposited by magnetron sputtering and annealed at 473 K, were investigated as a prospective hydrogen gas sensing material. Scanning electron microscopy was applied to determine the morphology of the thin films. Their structure and chemical composition were investigated by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The prepared films were nanocrystalline mixtures of metallic copper, cuprous oxide, and titanium anatase in the bulk, whereas at the surface only cupric oxide was found. In comparison to the literature, the (CuTi)Ox thin films already showed a sensor response to hydrogen at a relatively low operating temperature of 473 K without using any extra catalyst. The best sensor response and sensitivity to hydrogen gas were found in the mixed copper-titanium oxides containing similar atomic concentrations of both metals, i.e., 41/59 and 56/44 of Cu/Ti. Most probably, this effect is related to their similar morphology and to the simultaneous presence of Cu and Cu2O crystals in these mixed oxide films. In particular, the studies of surface oxidation state revealed that it was the same for all annealed films and consisted only of CuO. However, in view of their crystalline structure, they consisted of Cu and Cu2O nanocrystals in the thin film volume.
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Affiliation(s)
- Ewa Mańkowska
- Faculty of Electronic, Photonics and Microsystems, Wrocław University of Science and Technology, Janiszewskiego 11/17, 50-372 Wrocław, Poland
| | - Michał Mazur
- Faculty of Electronic, Photonics and Microsystems, Wrocław University of Science and Technology, Janiszewskiego 11/17, 50-372 Wrocław, Poland
| | - Jarosław Domaradzki
- Faculty of Electronic, Photonics and Microsystems, Wrocław University of Science and Technology, Janiszewskiego 11/17, 50-372 Wrocław, Poland
| | - Piotr Mazur
- Institute of Experimental Physics, University of Wrocław, Max Born 9, 50-204 Wrocław, Poland
| | - Małgorzata Kot
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Strasse 1, 03046 Cottbus, Germany
| | - Jan Ingo Flege
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Zuse-Strasse 1, 03046 Cottbus, Germany
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Baki A, Abdeldayem M, Morales C, Flege JI, Klimm D, Bierwagen O, Schwarzkopf J. Potential of La-Doped SrTiO 3 Thin Films Grown by Metal-Organic Vapor Phase Epitaxy for Thermoelectric Applications. Cryst Growth Des 2023; 23:2522-2530. [PMID: 37065440 PMCID: PMC10101556 DOI: 10.1021/acs.cgd.2c01438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2022] [Revised: 02/27/2023] [Indexed: 06/19/2023]
Abstract
La-doped SrTiO3 thin films with high structural quality were homoepitaxially grown by the metal-organic vapor phase epitaxy (MOVPE) technique. Thermogravimetric characterization of the metal-organic precursors determines suitable flash evaporator temperatures for transferring the liquid source materials in the gas phase of the reactor chamber. An adjustment of the charge carrier concentration in the films, which is necessary for optimizing the thermoelectric power factor, was performed by introducing a defined amount of the metal-organic compound La(tmhd)3 and tetraglyme to the liquid precursor solution. X-ray diffraction and atomic force microscopy verified the occurrence of the pure perovskite phase exhibiting a high structural quality for all La concentrations. The electrical conductivity of the films obtained from Hall-effect measurements increases linearly with the La concentration in the gas phase, which is attributed to the incorporation of La3+ ions on the Sr2+ perovskite sites by substitution inferred from photoemission spectroscopy. The resulting structural defects were discussed concerning the formation of occasional Ruddlesden-Popper-like defects. The thermoelectric properties determined by Seebeck measurements demonstrate the high potential of SrTiO3 thin films grown by MOVPE for thermoelectric applications.
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Affiliation(s)
- Aykut Baki
- Leibniz-Institut
für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany
| | - Mohamed Abdeldayem
- Leibniz-Institut
für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany
| | - Carlos Morales
- Brandenburgische
Technische Universität Cottbus-Senftenberg, FG Angewandte Physik
und Halbleiterspektroskopie, Konrad-Zuse-Straße 1, 03046 Cottbus, Germany
| | - Jan Ingo Flege
- Brandenburgische
Technische Universität Cottbus-Senftenberg, FG Angewandte Physik
und Halbleiterspektroskopie, Konrad-Zuse-Straße 1, 03046 Cottbus, Germany
| | - Detlef Klimm
- Leibniz-Institut
für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany
| | - Oliver Bierwagen
- Paul-Drude-Institut
für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany
| | - Jutta Schwarzkopf
- Leibniz-Institut
für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany
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9
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de Lourdes Gonzalez-Juarez M, Morales C, Flege JI, Flores E, Martin-Gonzalez M, Nandhakumar I, Bradshaw D. Tunable Carrier Type of a Semiconducting 2D Metal-Organic Framework Cu 3(HHTP) 2. ACS Appl Mater Interfaces 2022; 14:12404-12411. [PMID: 35230804 PMCID: PMC9096791 DOI: 10.1021/acsami.2c00089] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Accepted: 02/17/2022] [Indexed: 05/25/2023]
Abstract
In this work, a switch from n-type to p-type conductivity in electrodeposited Cu3(2,3,6,7,10,11-hexahydroxytriphenylene)2 [Cu3(HHTP2)] has been observed, which is most likely due to oxygen molecular doping. The synthesis of electrically conductive 2D metal-organic frameworks (MOFs) has been achieved through the introduction of highly conjugated organic linkers coordinated to their constituent metal-ion centers. However, the porous structure and unsaturated metal sites in MOFs make them susceptible to ambient adsorbates, which can affect their charge transport properties. This phenomenon has been experimentally investigated by GIXRD, Hall effect and Seebeck measurements, and X-ray photoelectron spectroscopy.
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Affiliation(s)
| | - Carlos Morales
- Applied
Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus−Senftenberg, Konrad-Zuse-Strasse 1, D-03046 Cottbus, Germany
| | - Jan Ingo Flege
- Applied
Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus−Senftenberg, Konrad-Zuse-Strasse 1, D-03046 Cottbus, Germany
| | - Eduardo Flores
- Instituto
de Micro y Nanotecnología (IMN-CNM-CSIC), C/ Isaac Newton 8, PTM, E-28760 Tres Cantos, Spain
- Centro
de Nanociencias y Nanotecnología (CNyN), Universidad Nacional Autónoma de México (UNAM), Ensenada, Baja California C.P. 22860, Mexico
| | - Marisol Martin-Gonzalez
- Instituto
de Micro y Nanotecnología (IMN-CNM-CSIC), C/ Isaac Newton 8, PTM, E-28760 Tres Cantos, Spain
| | - Iris Nandhakumar
- School
of Chemistry, University of Southampton, Southampton SO17 1BJ, U.K.
| | - Darren Bradshaw
- School
of Chemistry, University of Southampton, Southampton SO17 1BJ, U.K.
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10
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Janowitz C, Mahmoodinezhad A, Kot M, Morales C, Naumann F, Plate P, Zoellner MH, Bärwolf F, Stolarek D, Wenger C, Henkel K, Flege JI. Toward controlling the Al 2O 3/ZnO interface properties by in situ ALD preparation. Dalton Trans 2022; 51:9291-9301. [DOI: 10.1039/d1dt04008a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The electronic band alignment of an alumina/zinc oxide thin-film heterostructure solely grown by atomic layer deposition has been determined by XPS/UPS depth profiling, correlating the electronic properties with the interface chemical composition.
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Affiliation(s)
- Christoph Janowitz
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus–Senftenberg, K.-Zuse-Str. 1, 03046 Cottbus, Germany
| | - Ali Mahmoodinezhad
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus–Senftenberg, K.-Zuse-Str. 1, 03046 Cottbus, Germany
| | - Małgorzata Kot
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus–Senftenberg, K.-Zuse-Str. 1, 03046 Cottbus, Germany
| | - Carlos Morales
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus–Senftenberg, K.-Zuse-Str. 1, 03046 Cottbus, Germany
| | - Franziska Naumann
- SENTECH Instruments GmbH, Schwarzschildstraße 2, 12489 Berlin, Germany
| | - Paul Plate
- SENTECH Instruments GmbH, Schwarzschildstraße 2, 12489 Berlin, Germany
| | - Marvin Hartwig Zoellner
- IHP – Leibniz-Institut für innovative Mikroelektronik, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany
| | - Florian Bärwolf
- IHP – Leibniz-Institut für innovative Mikroelektronik, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany
| | - David Stolarek
- IHP – Leibniz-Institut für innovative Mikroelektronik, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany
| | - Christian Wenger
- IHP – Leibniz-Institut für innovative Mikroelektronik, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany
| | - Karsten Henkel
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus–Senftenberg, K.-Zuse-Str. 1, 03046 Cottbus, Germany
| | - Jan Ingo Flege
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus–Senftenberg, K.-Zuse-Str. 1, 03046 Cottbus, Germany
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11
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Krisponeit JO, Fischer S, Esser S, Moshnyaga V, Schmidt T, Piper LFJ, Flege JI, Falta J. The morphology of VO 2/TiO 2(001): terraces, facets, and cracks. Sci Rep 2020; 10:22374. [PMID: 33361795 PMCID: PMC7758337 DOI: 10.1038/s41598-020-78584-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [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: 08/14/2020] [Accepted: 11/20/2020] [Indexed: 12/03/2022] Open
Abstract
Vanadium dioxide (VO2) features a pronounced, thermally-driven metal-to-insulator transition at 340 K. Employing epitaxial stress on rutile \documentclass[12pt]{minimal}
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\begin{document}$$\text{TiO}_{2}(001)$$\end{document}TiO2(001) substrates, the transition can be tuned to occur close to room temperature. Striving for applications in oxide-electronic devices, the lateral homogeneity of such samples must be considered as an important prerequisite for efforts towards miniaturization. Moreover, the preparation of smooth surfaces is crucial for vertically stacked devices and, hence, the design of functional interfaces. Here, the surface morphology of \documentclass[12pt]{minimal}
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\begin{document}$$\text{VO}_2/\text{TiO}_2(001)$$\end{document}VO2/TiO2(001) films was analyzed by low-energy electron microscopy and diffraction as well as scanning probe microscopy. The formation of large terraces could be achieved under temperature-induced annealing, but also the occurrence of facets was observed and characterized. Further, we report on quasi-periodic arrangements of crack defects which evolve due to thermal stress under cooling. While these might impair some applicational endeavours, they may also present crystallographically well-oriented nano-templates of bulk-like properties for advanced approaches.
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Affiliation(s)
- Jon-Olaf Krisponeit
- Institute of Solid State Physics, University of Bremen, 28359, Bremen, Germany. .,MAPEX Center for Materials and Processes, University of Bremen, 28359, Bremen, Germany.
| | - Simon Fischer
- Institute of Solid State Physics, University of Bremen, 28359, Bremen, Germany
| | - Sven Esser
- Experimentalphysik VI, Universität Augsburg, 86159, Augsburg, Germany.,I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077, Göttingen, Germany
| | - Vasily Moshnyaga
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077, Göttingen, Germany
| | - Thomas Schmidt
- Institute of Solid State Physics, University of Bremen, 28359, Bremen, Germany.,MAPEX Center for Materials and Processes, University of Bremen, 28359, Bremen, Germany
| | | | - Jan Ingo Flege
- Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, 03046, Cottbus, Germany
| | - Jens Falta
- Institute of Solid State Physics, University of Bremen, 28359, Bremen, Germany.,MAPEX Center for Materials and Processes, University of Bremen, 28359, Bremen, Germany
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12
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von Boehn B, Penschke C, Li X, Paier J, Sauer J, Krisponeit JO, Flege JI, Falta J, Marchetto H, Franz T, Lilienkamp G, Imbihl R. Reaction dynamics of metal/oxide catalysts: Methanol oxidation at vanadium oxide films on Rh(1 1 1) from UHV to 10−2 mbar. J Catal 2020. [DOI: 10.1016/j.jcat.2020.03.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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13
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Luches P, Gasperi G, Sauerbrey M, Valeri S, Falta J, Flege JI. Dynamics of the Interaction Between Ceria and Platinum During Redox Processes. Front Chem 2019; 7:57. [PMID: 30800651 PMCID: PMC6375856 DOI: 10.3389/fchem.2019.00057] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2018] [Accepted: 01/21/2019] [Indexed: 11/13/2022] Open
Abstract
The work is focused on understanding the dynamics of the processes which occur at the interface between ceria and platinum during redox processes, by investigating an inverse catalytic model system made of ceria epitaxial islands and ultrathin films supported on Pt(111). The evolution of the morphology, structure and electronic properties is analyzed in real-time during reduction and oxidation, using low-energy electron microscopy and spatially resolved low-energy electron diffraction. The reduction is induced using different methods, namely thermal treatments in ultra-high vacuum and in H2 as well as deposition of Ce on the oxide surface, while re-oxidation is obtained by exposure to oxygen at elevated temperature. The use of two different epitaxial systems, continuous films and nanostructures, allows determining the influence of platinum proximity on the stabilization of the specific phases observed. The factors that limit the reversibility of the observed modifications with the different oxidation treatments are also discussed. The obtained results highlight important aspects of the cerium oxide/Pt interaction that are relevant for a complete understanding of the behavior of Pt/CeO2 catalysts.
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Affiliation(s)
- Paola Luches
- Istituto Nanoscienze, Consiglio Nazionale delle Ricerche, Modena, Italy
| | - Gabriele Gasperi
- Istituto Nanoscienze, Consiglio Nazionale delle Ricerche, Modena, Italy.,Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Università degli Studi di Modena e Reggio Emilia, Modena, Italy
| | - Marc Sauerbrey
- Institute of Solid State Physics, University of Bremen, Bremen, Germany.,MAPEX Center for Materials and Processes, University of Bremen, Bremen, Germany
| | - Sergio Valeri
- Istituto Nanoscienze, Consiglio Nazionale delle Ricerche, Modena, Italy.,Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Università degli Studi di Modena e Reggio Emilia, Modena, Italy
| | - Jens Falta
- Institute of Solid State Physics, University of Bremen, Bremen, Germany.,MAPEX Center for Materials and Processes, University of Bremen, Bremen, Germany
| | - Jan Ingo Flege
- Institute of Solid State Physics, University of Bremen, Bremen, Germany.,MAPEX Center for Materials and Processes, University of Bremen, Bremen, Germany.,Applied Physics and Semiconductor Spectroscopy, Brandenburg University of Technology Cottbus-Senftenberg, Cottbus, Germany
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14
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Flege JI, Höcker J, Sadowski JT, Senanayake SD, Falta J. Nucleation, morphology, and structure of sub‐nm thin ceria islands on Rh(111). SURF INTERFACE ANAL 2018. [DOI: 10.1002/sia.6567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Jan Ingo Flege
- Institute of Solid State Physics University of Bremen Otto‐Hahn‐Allee 1 28359 Bremen Germany
- Applied Physics and Semiconductor Spectroscopy Brandenburg University of Technology Cottbus‐Senftenberg Konrad‐Zuse‐Str. 1 03046 Cottbus Germany
| | - Jan Höcker
- Institute of Solid State Physics University of Bremen Otto‐Hahn‐Allee 1 28359 Bremen Germany
| | - Jerzy T. Sadowski
- Center for Functional Nanomaterials, Brookhaven National Laboratory Upton NY 11973 USA
| | | | - Jens Falta
- Institute of Solid State Physics University of Bremen Otto‐Hahn‐Allee 1 28359 Bremen Germany
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15
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Schaefer A, Hagman B, Höcker J, Hejral U, Flege JI, Gustafson J. Thermal reduction of ceria nanostructures on rhodium(111) and re-oxidation by CO 2. Phys Chem Chem Phys 2018; 20:19447-19457. [PMID: 29998237 DOI: 10.1039/c8cp01505h] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The thermal reduction of cerium oxide nanostructures deposited on a rhodium(111) single crystal surface and the re-oxidation of the structures by exposure to CO2 were investigated. Two samples are compared: a rhodium surface covered to ≈60% by one to two O-Ce-O trilayer high islands and a surface covered to ≈65% by islands of four O-Ce-O trilayer thickness. Two main results stand out: (1) the thin islands reduce at a lower temperature (870-890 K) and very close to Ce2O3, while the thicker islands need higher temperature for reduction and only reduce to about CeO1.63 at a maximum temperature of 920 K. (2) Ceria is re-oxidized by CO2. The rhodium surface promotes the re-oxidation by splitting the CO2 and thus providing atomic oxygen. The process shows a clear temperature dependence. The maximum oxidation state of the oxide reached by re-oxidation with CO2 differs for the two samples, showing that the thinner structures require a higher temperature for re-oxidation with CO2. Adsorbed carbon species, potentially blocking reactive sites, desorb from both samples at the same temperature and cannot be the sole origin for the observed differences. Instead, an intrinsic property of the differently sized CeOx islands must be at the origin of the observed temperature dependence of the re-oxidation by CO2.
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Affiliation(s)
- Andreas Schaefer
- Department of Chemistry and Chemical Engineering - Competence Centre for Catalysis, Chalmers University of Technology, Gothenburg, 412 96, Sweden.
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16
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Höcker J, Krisponeit JO, Cambeis J, Zakharov A, Niu Y, Wei G, Colombi Ciacchi L, Falta J, Schaefer A, Flege JI. Growth and structure of ultrathin praseodymium oxide layers on ruthenium(0001). Phys Chem Chem Phys 2018; 19:3480-3485. [PMID: 27827476 DOI: 10.1039/c6cp06853g] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The growth, morphology, structure, and stoichiometry of ultrathin praseodymium oxide layers on Ru(0001) were studied using low-energy electron microscopy and diffraction, photoemission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. At a growth temperature of 760 °C, the oxide is shown to form hexagonally close-packed (A-type) Pr2O3(0001) islands that are up to 3 nm high. Depending on the local substrate step density, the islands either adopt a triangular shape on sufficiently large terraces or acquire a trapezoidal shape with the long base aligned along the substrate steps.
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Affiliation(s)
- Jan Höcker
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, D-28359 Bremen, Germany.
| | - Jon-Olaf Krisponeit
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, D-28359 Bremen, Germany. and MAPEX Institute for Materials and Processes, University of Bremen, D-28359 Bremen, Germany
| | - Julian Cambeis
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, D-28359 Bremen, Germany.
| | | | - Yuran Niu
- MAX IV Laboratory, Box 118, 221 00 Lund, Sweden
| | - Gang Wei
- Bremen Center for Computational Materials Science, Am Fallturm 1, D-28359 Bremen, Germany
| | - Lucio Colombi Ciacchi
- MAPEX Institute for Materials and Processes, University of Bremen, D-28359 Bremen, Germany and Bremen Center for Computational Materials Science, Am Fallturm 1, D-28359 Bremen, Germany
| | - Jens Falta
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, D-28359 Bremen, Germany. and MAPEX Institute for Materials and Processes, University of Bremen, D-28359 Bremen, Germany
| | - Andreas Schaefer
- Division of Synchrotron Radiation Research, Lund University, 221 00 Lund, Sweden
| | - Jan Ingo Flege
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, D-28359 Bremen, Germany. and MAPEX Institute for Materials and Processes, University of Bremen, D-28359 Bremen, Germany
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17
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Höcker J, Krisponeit JO, Schmidt T, Falta J, Flege JI. The cubic-to-hexagonal phase transition of cerium oxide particles: dynamics and structure. Nanoscale 2017; 9:9352-9358. [PMID: 28534898 DOI: 10.1039/c6nr09760j] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [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
Cerium oxide is often applied in today's catalysts due to its remarkable oxygen storage capacity. The changes in stoichiometry during reaction are linked to structural modifications, which in turn affect its catalytic activity. We present a real-time in situ study of the structural transformations of cerium oxide particles on ruthenium(0001) at high temperatures of 700 °C in ultra-high vacuum. Our results demonstrate that the reduction from CeO2 to cubic Ce2O3 proceeds via ordered intermediary phases. The final reduction step from cubic to hexagonal Ce2O3 is accompanied by a lattice expansion, the formation of two new surface terminations, a partial dissolution of the cerium oxide particles, and a massive mass transport of cerium from the particles to the substrate. The conclusions allow for new insights into the structure, stability, and dynamics of cerium oxide nanoparticles in strongly reducing environments.
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Affiliation(s)
- Jan Höcker
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, D-28359 Bremen, Germany.
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18
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Flege JI, Krisponeit JO, Höcker J, Hoppe M, Niu Y, Zakharov A, Schaefer A, Falta J, Krasovskii EE. Nanoscale analysis of the oxidation state and surface termination of praseodymium oxide ultrathin films on ruthenium(0001). Ultramicroscopy 2017; 183:61-66. [PMID: 28526269 DOI: 10.1016/j.ultramic.2017.05.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2016] [Revised: 04/18/2017] [Accepted: 05/09/2017] [Indexed: 10/19/2022]
Abstract
The complex structure and morphology of ultrathin praseodymia films deposited on a ruthenium(0001) single crystal substrate by reactive molecular beam epitaxy is analyzed by intensity-voltage low-energy electron microscopy in combination with theoretical calculations within an ab initio scattering theory. A rich coexistence of various nanoscale crystalline surface structures is identified for the as-grown samples, notably comprising two distinct oxygen-terminated hexagonal Pr2O3(0001) surface phases as well as a cubic Pr2O3(111) and a fluorite PrO2(111) surface component. Furthermore, scattering theory reveals a striking similarity between the electron reflectivity spectra of praseodymia and ceria due to very efficient screening of the nuclear charge by the extra 4f electron in the former case.
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Affiliation(s)
- J I Flege
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany; MAPEX Center for Materials and Processes, University of Bremen, 28359 Bremen, Germany.
| | - J-O Krisponeit
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany; MAPEX Center for Materials and Processes, University of Bremen, 28359 Bremen, Germany
| | - J Höcker
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany
| | - M Hoppe
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany
| | - Y Niu
- MAX IV Laboratory, Box 118, 221 00 Lund, Sweden
| | - A Zakharov
- MAX IV Laboratory, Box 118, 221 00 Lund, Sweden
| | - A Schaefer
- Division of Synchrotron Radiation Research, Lund University, 221 00 Lund, Sweden
| | - J Falta
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany; MAPEX Center for Materials and Processes, University of Bremen, 28359 Bremen, Germany
| | - E E Krasovskii
- Departamento de Física de Materiales, Universidad del Pais Vasco UPV/EHU, 20080 San Sebastián/Donostia, Basque Country, Spain; Donostia International Physics Center (DIPC), 20018 San Sebastián/Donostia, Basque Country, Spain; IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Spain
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19
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Ahrens C, Flege JI, Jaye C, Fischer DA, Schmidt T, Falta J. Isotropic thin PTCDA films on GaN(0 0 0 1). J Phys Condens Matter 2016; 28:475003. [PMID: 27667820 DOI: 10.1088/0953-8984/28/47/475003] [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: 06/06/2023]
Abstract
The growth of 3, 4, 9, 10-perylene tetracarboxylic dianhydride (PTCDA) on the Ga-polar GaN(0 0 0 1) surface has been studied by x-ray photoelectron spectroscopy (XPS), spot profile analysis low-energy electron diffraction (SPA-LEED), near edge x-ray absorption fine structure (NEXAFS), and scanning tunneling microscopy (STM). The stoichiometric ratios derived from XPS indicate that the molecules remain intact upon adsorption on the surface. Furthermore, no chemical shifts can be observed in the C 1s and O 1s core levels with progressing deposition of PTCDA, suggesting none or only weak interactions between the molecules and the substrate. NEXAFS data indicate the PTCDA molecules being oriented with their molecular plane parallel to the surface. High-resolution STM shows PTCDA islands of irregular shape on the sub-micron scale, and together with corresponding SPA-LEED data reveals a lateral ordering of the molecules that is compatible with the presence of (1 0 2) oriented PTCDA nano-crystals. SPA-LEED moreover clearly shows the presence of homogeneously distributed rotational domains of two-dimensionally isotropic PTCDA.
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Affiliation(s)
- Ch Ahrens
- Institute of Solid State Physics, University Bremen, PO Box 330440, Bremen 28334, Germany
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20
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Ewert M, Schmidt T, Flege JI, Heidmann I, Grzela T, Klesse WM, Foerster M, Aballe L, Schroeder T, Falta J. Morphology and chemical composition of cobalt germanide islands on Ge(001). Nanotechnology 2016; 27:325705. [PMID: 27348504 DOI: 10.1088/0957-4484/27/32/325705] [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: 06/06/2023]
Abstract
The reactive growth of cobalt germanide on Ge(001) was investigated by means of in situ x-ray absorption spectroscopy photoemission electron microscopy (XAS-PEEM), micro-illumination low-energy electron diffraction (μ-LEED), and ex situ atomic force microscopy (AFM). At a Co deposition temperature of 670 °C, a rich morphology with different island shapes and dimensions is observed, and a correlation between island morphology and stoichiometry is found. By combining XAS-PEEM and μ-LEED, we were able to identify a large part of the islands to consist of CoGe2, with many of them having an unusual epitaxial relationship: CoGe2 [Formula: see text] [Formula: see text] Ge [Formula: see text]. Side facets with (112) and (113) orientation have been found for such islands. However, two additional phases were observed, most likely Co5Ge7 and CoGe. Comparing growth on Ge(001) single crystals and on Ge(001)/Si(001) epilayer substrates, the occurrence of these intermediate phases seems to be promoted by defects or residual strain.
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Affiliation(s)
- M Ewert
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany
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21
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Flege JI, Höcker J, Kaemena B, Menteş TO, Sala A, Locatelli A, Gangopadhyay S, Sadowski JT, Senanayake SD, Falta J. Growth and characterization of epitaxially stabilized ceria(001) nanostructures on Ru(0001). Nanoscale 2016; 8:10849-10856. [PMID: 27165117 DOI: 10.1039/c6nr02393b] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We have studied (001) surface terminated cerium oxide nanoparticles grown on a ruthenium substrate using physical vapor deposition. Their morphology, shape, crystal structure, and chemical state are determined by low-energy electron microscopy and micro-diffraction, scanning probe microscopy, and synchrotron-based X-ray absorption spectroscopy. Square islands are identified as CeO2 nanocrystals exhibiting a (001) oriented top facet of varying size; they have a height of about 7 to 10 nm and a side length between about 50 and 500 nm, and are terminated with a p(2 × 2) surface reconstruction. Micro-illumination electron diffraction reveals the existence of a coincidence lattice at the interface to the ruthenium substrate. The orientation of the side facets of the rod-like particles is identified as (111); the square particles are most likely of cuboidal shape, exhibiting (100) oriented side facets. The square and needle-like islands are predominantly found at step bunches and may be grown exclusively at temperatures exceeding 1000 °C.
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Affiliation(s)
- Jan Ingo Flege
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany. and MAPEX Center for Materials and Processes, University of Bremen, 28359 Bremen, Germany
| | - Jan Höcker
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany.
| | - Björn Kaemena
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany.
| | - T Onur Menteş
- Elettra-Sincrotrone Trieste S.C.p.A., S.S. 14 - km 163, 5 in AREA Science Park, 34149 Trieste, Italy
| | - Alessandro Sala
- Elettra-Sincrotrone Trieste S.C.p.A., S.S. 14 - km 163, 5 in AREA Science Park, 34149 Trieste, Italy
| | - Andrea Locatelli
- Elettra-Sincrotrone Trieste S.C.p.A., S.S. 14 - km 163, 5 in AREA Science Park, 34149 Trieste, Italy
| | | | - Jerzy T Sadowski
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Sanjaya D Senanayake
- Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Jens Falta
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany. and MAPEX Center for Materials and Processes, University of Bremen, 28359 Bremen, Germany
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22
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Flege JI, Lachnitt J, Mazur D, Sutter P, Falta J. Role of RuO2(100) in surface oxidation and CO oxidation catalysis on Ru(0001). Phys Chem Chem Phys 2016; 18:213-9. [DOI: 10.1039/c5cp05807d] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Oxidation of Ru(0001) induces the simultaneous formation of RuO2(100) and RuO2(110) and a structure-sensitive oxygen spillover during CO oxidation.
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Affiliation(s)
- Jan Ingo Flege
- Institute of Solid State Physics
- University of Bremen
- 28359 Bremen
- Germany
| | - Jan Lachnitt
- Faculty of Mathematics and Physics
- Department of Surface and Plasma Science
- Charles University in Prague
- 18000 Prague 8
- Czech Republic
| | - Daniel Mazur
- Faculty of Mathematics and Physics
- Department of Surface and Plasma Science
- Charles University in Prague
- 18000 Prague 8
- Czech Republic
| | - Peter Sutter
- Center for Functional Nanomaterials
- Brookhaven National Laboratory
- Upton
- USA
| | - Jens Falta
- Institute of Solid State Physics
- University of Bremen
- 28359 Bremen
- Germany
- MAPEX Center for Materials and Processes
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23
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Flege JI, Herd B, Goritzka J, Over H, Krasovskii EE, Falta J. Nanoscale Origin of Mesoscale Roughening: Real-Time Tracking and Identification of Three Distinct Ruthenium Oxide Phases in Ruthenium Oxidation. ACS Nano 2015; 9:8468-8473. [PMID: 26171635 DOI: 10.1021/acsnano.5b03393] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The structural modification of the Ru(0001) surface is followed in real-time using low-energy electron microscopy at elevated temperatures during exposure to molecular oxygen. We observe the nucleation and growth of three different RuO2 facets, which are unambiguously identified by single-domain microspot low-energy electron diffraction (μLEED) analysis from regions of 250 nm in diameter. Structural identification is then pushed to the true nanoscale by employing very-low-energy electron reflectivity spectra R(E) from regions down to 10 nm for structural fingerprinting of complex reactions such as the oxidation of metal surfaces. Calculations of R(E) with an ab initio scattering theory confirm the growth of (110), (100), and (101) orientations of RuO2 and explain the shape of the R(E) spectra in terms of the conducting band structure. This methodology is ideally suited to identify the structure of supported ultrathin films and dynamic transformations at multicomponent interfaces down to few nanometer lateral resolution at elevated temperature and in reactive environments.
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Affiliation(s)
- Jan Ingo Flege
- Institute of Solid State Physics, University of Bremen , Otto-Hahn-Allee 1, 28359 Bremen, Germany
| | - Benjamin Herd
- Department of Physical Chemistry, Justus-Liebig-University , Heinrich-Buff-Ring 58, 35392 Gießen, Germany
| | - Jan Goritzka
- Department of Physical Chemistry, Justus-Liebig-University , Heinrich-Buff-Ring 58, 35392 Gießen, Germany
| | - Herbert Over
- Department of Physical Chemistry, Justus-Liebig-University , Heinrich-Buff-Ring 58, 35392 Gießen, Germany
| | - Eugene E Krasovskii
- Departamento de Física de Materiales, Universidad del Pais Vasco UPV/EHU , 20080 San Sebastián/Donostia, Basque Country, Spain
- Donostia International Physics Center (DIPC) , 20018 San Sebastián/Donostia, Basque Country, Spain
- IKERBASQUE, Basque Foundation for Science , 48011 Bilbao, Spain
| | - Jens Falta
- Institute of Solid State Physics, University of Bremen , Otto-Hahn-Allee 1, 28359 Bremen, Germany
- MAPEX Center for Materials and Processes, University of Bremen , 28359 Bremen, Germany
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24
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Abstract
Electron scattering by oxygen monolayers on the Ru(0 0 0 1) surface is studied both experimentally and theoretically. Sharp transmission resonances at low energies are revealed and established to originate from critical points of a special kind in the complex band structure of the substrate. Electron reflection from the clean and oxidized Ru(0 0 0 1) is measured for kinetic energies up to 40 eV at normal incidence for oxygen coverages of 1/4, 1/2, 3/4, and one monolayer. The reflection spectra R(E) are analyzed using a Bloch-waves based ab initio scattering theory. In addition to the substrate-induced resonances the reconstructed (2 × 1) and (2 × 2) surfaces show surface resonances due to pre-emergent secondary diffraction beams. The R(E) spectra are shown to give unambiguous evidence of the hcp stacking of the oxygen layer.
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Affiliation(s)
- E E Krasovskii
- Departamento de Física de Materiales, Universidad del Pais Vasco UPV/EHU, 20080 San Sebastián/Donostia, Spain. Donostia International Physics Center (DIPC), 20018 San Sebastián/Donostia, Spain. IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Spain
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25
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Watcharinyanon S, I. Johansson L, Xia C, Ingo Flege J, Meyer A, Falta J, Virojanadara C. Ytterbium Intercalation of Epitaxial Graphene Grown on Si-Face SiC. ACTA ACUST UNITED AC 2013. [DOI: 10.4236/graphene.2013.22010] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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26
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Speckmann M, Schmidt T, Flege JI, Sadowski JT, Sutter P, Falta J. Temperature dependent low energy electron microscopy study of Ge island growth on bare and Ga terminated Si(112). J Phys Condens Matter 2009; 21:314020. [PMID: 21828581 DOI: 10.1088/0953-8984/21/31/314020] [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: 05/31/2023]
Abstract
The pre-adsorption of Ga on Si(112) leads to a drastic change of the morphology of subsequently grown Ge islands. In contrast to the case for Ge growth on bare Si(112), even nanowire growth can be achieved on Ga terminated Si(112). Employing low energy electron microscopy and low energy electron diffraction, the initial phase of Ge nucleation and Ge island growth was systematically analysed for growth temperatures between 420 and 610 °C, both on clean and on Ga terminated Si(112). In both cases the island density exhibits an Arrhenius-like behaviour, from which diffusion barrier heights of about 1.3 and 1.0 eV can be estimated for growth with and without Ga pre-adsorption, respectively. The Ge island shape on the bare Si(112) surface is found to be nearly circular over the whole temperature range, whereas the shapes of the Ge islands on the Ga terminated Si(112) become highly anisotropic for higher temperatures. Ge nanowires with sizes of up to 2 µm along the [Formula: see text] direction are observed.
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Affiliation(s)
- M Speckmann
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany
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27
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Flege JI, Sutter P. Nanoscale analysis of Ru(0001) oxidation using low-energy and photoemission electron microscopy. J Phys Condens Matter 2009; 21:314018. [PMID: 21828579 DOI: 10.1088/0953-8984/21/31/314018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
CO oxidation over oxygen-rich Ru(0001) surfaces is one of the most studied catalytic oxidation reactions in surface science and of widespread interest as a model system for the redox chemistry of transition metal model catalysts. Here, we present an extensive low-energy electron microscopy (LEEM) and photoemission electron microscopy study of the oxidation of Ru(0001), which constitutes a crucial step in understanding the overall surface reaction. After characterizing the different surface nanoscale morphologies observed depending on the oxidation temperature, three distinct oxygen-rich phases are identified by dark-field microscopy and local valence-band spectroscopy. Furthermore, in situ LEEM allows us to follow the growth of single rutile oxide nuclei in real time and determine the relevant activation barriers that induce quasi-one-dimensional growth of oxide nanorods, whose growth rate is limited by O incorporation.
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28
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Sutter P, Bennett PA, Flege JI, Sutter E. Steering liquid Pt-Si nanodroplets on Si(100) by interactions with surface steps. Phys Rev Lett 2007; 99:125504. [PMID: 17930517 DOI: 10.1103/physrevlett.99.125504] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2007] [Indexed: 05/25/2023]
Abstract
Liquid eutectic Pt-Si droplets, migrating across a Si(100) surface due to an applied temperature gradient, interact measurably with surface steps. An analysis of the interaction yields a critical size of hundreds of nanometers below which droplets are constrained to move parallel to monolayer steps. Bunches of closely spaced steps are capable of guiding larger, micron-sized droplets. This steering by steps or step bunches may be used for the controlled manipulation of liquid droplets on patterned surfaces, and affects fundamental surface processes such as coarsening.
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Affiliation(s)
- P Sutter
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA.
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29
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Schmidt T, Flege JI, Gangopadhyay S, Clausen T, Locatelli A, Heun S, Falta J. Alignment of Ge nanoislands on Si(111) by Ga-induced substrate self-patterning. Phys Rev Lett 2007; 98:066104. [PMID: 17358960 DOI: 10.1103/physrevlett.98.066104] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2006] [Indexed: 05/14/2023]
Abstract
A novel mechanism is described which enables the selective formation of three-dimensional Ge islands. Submonolayer adsorption of Ga on Si(111) at high temperature leads to a self-organized two-dimensional pattern formation by separation of the 7 x 7 substrate and Ga/Si(111)-(square root[3] x square root[3])-R30 degrees domains. The latter evolve at step edges and domain boundaries of the initial substrate reconstruction. Subsequent Ge deposition results in the growth of 3D islands which are aligned at the boundaries between bare and Ga-covered domains. This result is explained in terms of preferential nucleation conditions due to a modulation of the surface chemical potential.
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Affiliation(s)
- Th Schmidt
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany
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30
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Schmidt T, Kröger R, Flege JI, Clausen T, Falta J, Janzen A, Zahl P, Kury P, Kammler M, Horn-von Hoegen M. Less strain energy despite fewer misfit dislocations: the impact of ordering. Phys Rev Lett 2006; 96:066101. [PMID: 16606012 DOI: 10.1103/physrevlett.96.066101] [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] [Received: 08/10/2005] [Indexed: 05/08/2023]
Abstract
The average strain state of Ge films grown on Si(111) by surfactant mediated epitaxy has been compared to the ordering of the interfacial misfit dislocation network. Surprisingly, a smaller degree of average lattice relaxation was found in films grown at higher temperature. On the other hand, these films exhibit a better ordered dislocation network. This effect energetically compensates the higher strain at higher growth temperature, leading to the conclusion that, apart from the formation of misfit dislocations, their ordering represents an important channel for lattice-strain energy relaxation.
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Affiliation(s)
- Th Schmidt
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany.
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