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Masia F, Langbein W, Fischer S, Krisponeit JO, Falta J. Low-energy electron microscopy intensity-voltage data - Factorization, sparse sampling and classification. J Microsc 2023; 289:91-106. [PMID: 36288376 PMCID: PMC10108219 DOI: 10.1111/jmi.13155] [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: 02/09/2022] [Revised: 09/15/2022] [Accepted: 10/17/2022] [Indexed: 01/14/2023]
Abstract
Low-energy electron microscopy (LEEM) taken as intensity-voltage (I-V) curves provides hyperspectral images of surfaces, which can be used to identify the surface type, but are difficult to analyse. Here, we demonstrate the use of an algorithm for factorizing the data into spectra and concentrations of characteristic components (FSC3 ) for identifying distinct physical surface phases. Importantly, FSC3 is an unsupervised and fast algorithm. As example data we use experiments on the growth of praseodymium oxide or ruthenium oxide on ruthenium single crystal substrates, both featuring a complex distribution of coexisting surface components, varying in both chemical composition and crystallographic structure. With the factorization result a sparse sampling method is demonstrated, reducing the measurement time by 1-2 orders of magnitude, relevant for dynamic surface studies. The FSC3 concentrations are providing the features for a support vector machine-based supervised classification of the surface types. Here, specific surface regions which have been identified structurally, via their diffraction pattern, as well as chemically by complementary spectro-microscopic techniques, are used as training sets. A reliable classification is demonstrated on both example LEEM I-V data sets.
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Affiliation(s)
- Francesco Masia
- School of Biosciences, Cardiff University, Cardiff, UK.,School of Physics and Astronomy, Cardiff University, Cardiff, UK
| | | | - Simon Fischer
- Institute of Solid State Physics, University of Bremen, Bremen, Germany
| | - Jon-Olaf Krisponeit
- Institute of Solid State Physics, University of Bremen, Bremen, Germany.,MAPEX Center for Materials and Processes, University of Bremen, Bremen, Germany
| | - Jens Falta
- Institute of Solid State Physics, University of Bremen, Bremen, Germany.,MAPEX Center for Materials and Processes, University of Bremen, Bremen, Germany
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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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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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Krisponeit JO, Damaschke B, Moshnyaga V, Samwer K. Layer-by-Layer Resistive Switching: Multistate Functionality due to Electric-Field-Induced Healing of Dead Layers. Phys Rev Lett 2019; 122:136801. [PMID: 31012616 DOI: 10.1103/physrevlett.122.136801] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Indexed: 06/09/2023]
Abstract
Materials exhibiting reversible resistive switching in electrical fields are highly demanded for functional elements in oxide electronics. In particular, multilevel switching effects allow for advanced applications like neuromorphic circuits. Here, we report a structurally driven switching mechanism involving the so-called "dead" layers of perovskite manganite surfaces. Forming a tunnel barrier whose thickness can be changed in monolayer steps by electrical fields, the switching effect exhibits well-defined and robust resistive states.
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Affiliation(s)
- Jon-Olaf Krisponeit
- Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
- MAPEX Center for Materials and Processes, University of Bremen, 28359 Bremen, Germany
| | - Bernd Damaschke
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
| | - Vasily Moshnyaga
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
| | - Konrad Samwer
- I. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany
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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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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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