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Machado Ferreira de Araujo F, Duarte-Ruiz D, Saßnick HD, Gentzmann MC, Huthwelker T, Cocchi C. Electronic Structure and Core Spectroscopy of Scandium Fluoride Polymorphs. Inorg Chem 2023; 62:4238-4247. [PMID: 36858964 PMCID: PMC10015455 DOI: 10.1021/acs.inorgchem.2c04357] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/03/2023]
Abstract
Microscopic knowledge of the structural, energetic, and electronic properties of scandium fluoride is still incomplete despite the relevance of this material as an intermediate for the manufacturing of Al-Sc alloys. In a work based on first-principles calculations and X-ray spectroscopy, we assess the stability and electronic structure of six computationally predicted ScF3 polymorphs, two of which correspond to experimentally resolved single-crystal phases. In the theoretical analysis based on density functional theory (DFT), we identify similarities among the polymorphs based on their formation energies, charge-density distribution, and electronic properties (band gaps and density of states). We find striking analogies between the results obtained for the low- and high-temperature phases of the material, indirectly confirming that the transition occurring between them mainly consists of a rigid rotation of the lattice. With this knowledge, we examine the X-ray absorption spectra from the Sc and F K-edge contrasting first-principles results obtained from the solution of the Bethe-Salpeter equation on top of all-electron DFT with high-energy-resolution fluorescence detection measurements. Analysis of the computational results sheds light on the electronic origin of the absorption maxima and provides information on the prominent excitonic effects that characterize all spectra. A comparison with measurements confirms that the sample is mainly composed of the high- and low-temperature polymorphs of ScF3. However, some fine details in the experimental results suggest that the probed powder sample may contain defects and/or residual traces of metastable polymorphs.
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Affiliation(s)
| | - Daniel Duarte-Ruiz
- Institute of Physics, Carl-von-Ossietzky Universität Oldenburg, 26129 Oldenburg, Germany
| | | | - Marie C Gentzmann
- Bundesanstalt für Materialforschung und-prüfung, Unter den Eichen 87, 12205 Berlin, Germany
| | - Thomas Huthwelker
- Swiss Light Source (SLS), Paul Scherrer Institut (PSI), 5232 Villigen, Switzerland
| | - Caterina Cocchi
- Institute of Physics, Carl-von-Ossietzky Universität Oldenburg, 26129 Oldenburg, Germany.,Physics Department and IRIS Adlershof, Humboldt-Universität zu Berlin, 12489 Berlin, Germany
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Soft X-ray characterization of halide perovskite film by scanning transmission X-ray microscopy. Sci Rep 2022; 12:4520. [PMID: 35296696 PMCID: PMC8927596 DOI: 10.1038/s41598-022-08256-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2021] [Accepted: 02/25/2022] [Indexed: 11/10/2022] Open
Abstract
Organic–inorganic metal halide perovskites (MHPs) have recently been receiving a lot of attention due to their newfound application in optoelectronic devices, including perovskite solar cells (PSCs) which have reached power conversion efficiencies as high as 25.5%. However, the fundamental mechanisms in PSCs, including the correlation of degradation with the excellent optoelectrical properties of the perovskite absorbers, are poorly understood. In this paper, we have explored synchrotron-based soft X-ray characterization as an effective technique for the compositional analysis of MHP thin films. Most synchrotron-based studies used for investigating MHPs so far are based on hard X-rays (5–10 keV) which include various absorption edges (Pb L-edge, I L-edge, Br K-edge, etc.) but are not suited for the analysis of the organic component in these materials. In order to be sensitive to a maximum number of elements, we have employed soft X-ray-based scanning transmission X-ray microscopy (STXM) as a spectro-microscopy technique for the characterization of MHPs. We examined its sensitivity to iodine and organic components, aging, or oxidation by-products in MHPs to make sure that our suggested method is suitable for studying MHPs. Furthermore, methylammonium triiodide with different deposition ratios of PbI2 and CH3NH3I (MAI), and different thicknesses, were characterized for chemical inhomogeneity at the nanoscale by STXM. Through these measurements, we demonstrate that STXM is very sensitive to chemical composition and homogeneity in MHPs. Thus, we highlight the utility of STXM for an in-depth analysis of physical and chemical phenomena in PSCs.
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Ab Initio Quantum-Mechanical Predictions of Semiconducting Photocathode Materials. MICROMACHINES 2021; 12:mi12091002. [PMID: 34577646 PMCID: PMC8471183 DOI: 10.3390/mi12091002] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Revised: 08/17/2021] [Accepted: 08/20/2021] [Indexed: 11/16/2022]
Abstract
Ab initio Quantum-Mechanical methods are well-established tools for material characterization and discovery in many technological areas. Recently, state-of-the-art approaches based on density-functional theory and many-body perturbation theory were successfully applied to semiconducting alkali antimonides and tellurides, which are currently employed as photocathodes in particle accelerator facilities. The results of these studies have unveiled the potential of ab initio methods to complement experimental and technical efforts for the development of new, more efficient materials for vacuum electron sources. Concomitantly, these findings have revealed the need for theory to go beyond the status quo in order to face the challenges of modeling such complex systems and their properties in operando conditions. In this review, we summarize recent progress in the application of ab initio many-body methods to investigate photocathode materials, analyzing the merits and the limitations of the standard approaches with respect to the confronted scientific questions. In particular, we emphasize the necessary trade-off between computational accuracy and feasibility that is intrinsic to these studies, and propose possible routes to optimize it. We finally discuss novel schemes for computationally-aided material discovery that are suitable for the development of ultra-bright electron sources toward the incoming era of artificial intelligence.
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Amador R, Saßnick HD, Cocchi C. Electronic structure and optical properties of Na 2KSb and NaK 2Sb from first-principles many-body theory. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:365502. [PMID: 34167098 DOI: 10.1088/1361-648x/ac0e70] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Accepted: 06/24/2021] [Indexed: 06/13/2023]
Abstract
In the search for novel materials for vacuum electron sources, multi-alkali antimonides and in particular sodium-potassium-antimonides have been recently regarded as especially promising due to their favorable electronic and optical properties. In the framework of density-functional theory and many-body perturbation theory, we investigate the electronic structure and the dielectric response of two representative members of this family, namely Na2KSb and NaK2Sb. We find that both materials have a direct gap, which is on the order of 1.5 eV in Na2KSb and 1.0 eV in NaK2Sb. In either system, valence and conduction bands are dominated by Sb states withp- ands-character, respectively. The imaginary part of the dielectric function, computed upon explicit inclusion of electron-hole interactions to characterize the optical response of the materials, exhibits maxima starting from the near-infrared region, extending up to the visible and the ultraviolet band. With our analysis, we clarify that the lowest-energy excitations are non-excitonic in nature and that their binding energy is on the order of 100 meV. Our results confirm the potential of Na2KSb and NaK2Sb as photoemissive materials for vacuum electron sources, photomultipliers, and imaging devices.
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Affiliation(s)
- Raymond Amador
- Humboldt-Universität zu Berlin, Physics Department and IRIS Adlershof, 12489 Berlin, Germany
- Helmholtz-Zentrum Berlin, 12489, Berlin, Germany
| | | | - Caterina Cocchi
- Humboldt-Universität zu Berlin, Physics Department and IRIS Adlershof, 12489 Berlin, Germany
- Carl von Ossietzky Universität Oldenburg, Institute of Physics, 26129 Oldenburg, Germany
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Wilks RG, Erbing A, Sadoughi G, Starr DE, Handick E, Meyer F, Benkert A, Iannuzzi M, Hauschild D, Yang W, Blum M, Weinhardt L, Heske C, Snaith HJ, Odelius M, Bär M. Dynamic Effects and Hydrogen Bonding in Mixed-Halide Perovskite Solar Cell Absorbers. J Phys Chem Lett 2021; 12:3885-3890. [PMID: 33856793 DOI: 10.1021/acs.jpclett.1c00745] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The organic component (methylammonium) of CH3NH3PbI3-xClx-based perovskites shows electronic hybridization with the inorganic framework via H-bonding between N and I sites. Femtosecond dynamics induced by core excitation are shown to strongly influence the measured X-ray emission spectra and the resonant inelastic soft X-ray scattering of the organic components. The N K core excitation leads to a greatly increased N-H bond length that modifies and strengthens the interaction with the inorganic framework compared to that in the ground state. The study indicates that excited-state dynamics must be accounted for in spectroscopic studies of this perovskite solar cell material, and the organic-inorganic hybridization interaction suggests new avenues for probing the electronic structure of this class of materials. It is incidentally shown that beam damage to the methylamine component can be avoided by moving the sample under the soft X-ray beam to minimize exposure and that this procedure is necessary to prevent the creation of experimental artifacts.
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Affiliation(s)
- Regan G Wilks
- Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), 14109 Berlin, Germany
| | - Axel Erbing
- Department of Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
| | - Golnaz Sadoughi
- Department of Physics, University of Oxford, Clarendon Laboratory, Oxford OX1 3PJ, U.K
| | - David E Starr
- Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), 14109 Berlin, Germany
| | - Evelyn Handick
- Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), 14109 Berlin, Germany
| | - Frank Meyer
- Experimental Physics 7, University of Würzburg, 97074 Würzburg, Germany
| | - Andreas Benkert
- Experimental Physics 7, University of Würzburg, 97074 Würzburg, Germany
- Institute for Photon Science and Synchrotron Radiation (IPS), Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany
| | - Marcella Iannuzzi
- Physical Chemistry Institute, University of Zürich, 8057 Zürich, Switzerland
| | - Dirk Hauschild
- Institute for Photon Science and Synchrotron Radiation (IPS), Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany
- Institute for Chemical Technology and Polymer Chemistry (ITCP), Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
- Department of Chemistry and Biochemistry, University of Nevada, Las Vegas, Las Vegas, Nevada 89154, United States
| | - Wanli Yang
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720-8229, United States
| | - Monika Blum
- Department of Chemistry and Biochemistry, University of Nevada, Las Vegas, Las Vegas, Nevada 89154, United States
- Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720-8229, United States
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720-8176, United States
| | - Lothar Weinhardt
- Institute for Photon Science and Synchrotron Radiation (IPS), Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany
- Institute for Chemical Technology and Polymer Chemistry (ITCP), Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
- Department of Chemistry and Biochemistry, University of Nevada, Las Vegas, Las Vegas, Nevada 89154, United States
| | - Clemens Heske
- Institute for Photon Science and Synchrotron Radiation (IPS), Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen, Germany
- Institute for Chemical Technology and Polymer Chemistry (ITCP), Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe, Germany
- Department of Chemistry and Biochemistry, University of Nevada, Las Vegas, Las Vegas, Nevada 89154, United States
| | - Henry J Snaith
- Department of Physics, University of Oxford, Clarendon Laboratory, Oxford OX1 3PJ, U.K
| | - Michael Odelius
- Department of Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
| | - Marcus Bär
- Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH (HZB), 14109 Berlin, Germany
- Helmholtz-Institute Erlangen-Nürnberg for Renewable Energy (HI ERN), 90429 Nürnberg, Germany
- Department of Chemistry and Pharmacy, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 91058 Erlangen, Germany
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Cocchi C, Mistry S, Schmeißer M, Kühn J, Kamps T. First-principles many-body study of the electronic and optical properties of CsK 2Sb, a semiconducting material for ultra-bright electron sources. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2019; 31:014002. [PMID: 30500782 DOI: 10.1088/1361-648x/aaedee] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We present a comprehensive first-principles investigation of the electronic and optical properties of CsK2Sb, a semiconducting material for ultra-bright electron sources for particle accelerators. Our study, based on density-functional theory and many-body perturbation theory, provides all the ingredients to model the emission of this material as a photocathode, including band gap, band dispersion, and optical absorption. An accurate description of these properties beyond the mean-field picture is relevant to take into account many-body effects. We discuss our results in the context of state-of-the-art electron sources for particle accelerators to set the stage towards improved modeling of quantum efficiency, intrinsic emittance, and other relevant quantities determining the macroscopic characteristics of photocathodes for ultra-bright beams.
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Affiliation(s)
- Caterina Cocchi
- Physics Department, Humboldt-Universität zu Berlin, Berlin, Germany. IRIS Adlershof, Humboldt-Universität zu Berlin, Berlin, Germany
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Vorwerk C, Hartmann C, Cocchi C, Sadoughi G, Habisreutinger SN, Félix R, Wilks RG, Snaith HJ, Bär M, Draxl C. Correction to "Exciton-Dominated Core-Level Absorption Spectra of Hybrid Organic-Inorganic Lead Halide Perovskites". J Phys Chem Lett 2018; 9:3193. [PMID: 29856635 DOI: 10.1021/acs.jpclett.8b01552] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
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