1
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Stöger-Pollach M, Bukvišova K, Zenz K, Stöger L, Scales Z. Important aspects of investigating optical excitations in semiconductors using a scanning transmission electron microscope. J Microsc 2024; 293:138-145. [PMID: 37924264 DOI: 10.1111/jmi.13242] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2023] [Revised: 10/23/2023] [Accepted: 10/31/2023] [Indexed: 11/06/2023]
Abstract
Since semiconductor structures are becoming smaller and smaller, the examination methods must also take this development into account. Optical methods have long reached their limits here, but small dimensions are also a challenge for electron beam techniques, especially when it comes to determining optical properties. In this paper, electron microscopic methods of investigating optical properties are discussed. Special attention is given to the physical limits and how to deal with them. We will cover electron energy loss spectrometry as well as cathodoluminescence spectrometry. We pay special attention to inelastic delocalisation, radiation damage, the Čerenkov effect, interference effects of optical excitations and higher diffraction orders on a grating analyser for the cathodoluminescence signal.
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Affiliation(s)
- Michael Stöger-Pollach
- University Service Center for TEM, TU Wien, Vienna, Austria
- Institute for Solid State Physics, TU Wien, Vienna, Austria
| | | | - Keanu Zenz
- Institute for Solid State Physics, TU Wien, Vienna, Austria
| | - Leo Stöger
- Institute for Solid State Physics, TU Wien, Vienna, Austria
- Atominstitut der TU Wien, Vienna, Austria
| | - Ze Scales
- University Service Center for TEM, TU Wien, Vienna, Austria
- KAI Kompetenzzentrum Automobil- und Insdustrieelektronik GmbH, Villach, Austria
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2
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Stöger-Pollach M, Zenz K, Ursin F, Schilberg J, Stöger L. A correction for higher-order refraction in cathodoluminescence spectrometry. Ultramicroscopy 2023; 251:113770. [PMID: 37267709 DOI: 10.1016/j.ultramic.2023.113770] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2022] [Revised: 05/12/2023] [Accepted: 05/26/2023] [Indexed: 06/04/2023]
Abstract
Cathodoluminescence (CL) is a developing analytical method in electron microscopy, because of its excellent energy resolution. Usually a Czerny-Turner type spectrometer is employed, having a blazed grating as analyzer. Unlike a prism analyzer, where the dispersion depends on the refractive index of the prism itself leading to a non-linear spectral distribution, the grating has the advantage that the spectral distribution depends linearly on the wavelength. As a draw-back, higher-order refraction alters the measured optical spectrum at larger wavelengths. In general, blazed gratings are used in order to minimize this effect in a certain spectral range. Nevertheless, the higher-order intensities can be still significant. In the present study we present a method for correcting the acquired optical spectra with respect to higher order diffraction intensities and apply it to CaO and GaN CL-spectra.
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Affiliation(s)
- Michael Stöger-Pollach
- University Service Center for Transmission Electron Microscopy (USTEM), Technische Universität Wien, Wiedner Hauptstraße 8-10, 1040 Wien, Austria; Institute of Solid State Physics, Technische Universität Wien, Wiedner Hauptstraße 8-10, 1040 Wien, Austria.
| | - Keanu Zenz
- Institute of Solid State Physics, Technische Universität Wien, Wiedner Hauptstraße 8-10, 1040 Wien, Austria
| | - Felix Ursin
- Institute of Solid State Physics, Technische Universität Wien, Wiedner Hauptstraße 8-10, 1040 Wien, Austria
| | - Johannes Schilberg
- Institute of Solid State Physics, Technische Universität Wien, Wiedner Hauptstraße 8-10, 1040 Wien, Austria
| | - Leo Stöger
- Institute of Solid State Physics, Technische Universität Wien, Wiedner Hauptstraße 8-10, 1040 Wien, Austria
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3
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Rao F, An Y, Huang X, Zhu L, Gong S, Shi X, Lu J, Gao J, Huang Y, Wang Q, Liu P, Zhu G. “X-Scheme” Charge Separation Induced by Asymmetrical Localized Electronic Band Structures at the Ceria Oxide Facet Junction. ACS Catal 2023. [DOI: 10.1021/acscatal.2c04954] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- Fei Rao
- School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710119, P. R. China
| | - Yurong An
- School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710119, P. R. China
| | - Xiaoyang Huang
- Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Main Building, Cardiff CF10 3AT, U.K
| | - Lujun Zhu
- School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710119, P. R. China
| | - Siwen Gong
- School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710119, P. R. China
| | - Xianjin Shi
- State Key Lab of Loess and Quaternary Geology (SKLLQG), Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, P. R. China
| | - Jiangbo Lu
- School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710119, P. R. China
| | - Jianzhi Gao
- School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710119, P. R. China
| | - Yu Huang
- State Key Lab of Loess and Quaternary Geology (SKLLQG), Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, P. R. China
| | - Qizhao Wang
- School Water and Environment, Key Lab Subsurface Hydrol Ecol Effects Arid Reg, Minist Educ, Chang’an University, Xi’an 710054, P. R. China
| | - Peng Liu
- School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710119, P. R. China
| | - Gangqiang Zhu
- School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710119, P. R. China
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4
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Cañas J, Reyes DF, Zakhtser A, Dussarrat C, Teramoto T, Gutiérrez M, Gheeraert E. High-Quality SiO2/O-Terminated Diamond Interface: Band-Gap, Band-Offset and Interfacial Chemistry. NANOMATERIALS (BASEL, SWITZERLAND) 2022; 12:4125. [PMID: 36500747 PMCID: PMC9739220 DOI: 10.3390/nano12234125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 11/10/2022] [Accepted: 11/16/2022] [Indexed: 06/17/2023]
Abstract
Silicon oxide atomic layer deposition synthesis development over the last few years has open the route to its use as a dielectric within diamond electronics. Its great band-gap makes it a promising material for the fabrication of diamond-metal-oxide field effects transistor gates. Having a sufficiently high barrier both for holes and electrons is mandatory to work in accumulation and inversion regimes without leakage currents, and no other oxide can fulfil this requisite due to the wide diamond band-gap. In this work, the heterojunction of atomic-layer-deposited silicon oxide and (100)-oriented p-type oxygen-terminated diamond is studied using scanning transmission electron microscopy in its energy loss spectroscopy mode and X-ray photoelectron spectroscopy. The amorphous phase of silicon oxide was successfully synthesized with a homogeneous band-gap of 9.4 eV. The interface between the oxide and diamond consisted mainly of single- and double-carbon-oxygen bonds with a low density of interface states and a straddling band setting with a 2.0 eV valence band-offset and 1.9 eV conduction band-offset.
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Affiliation(s)
- Jesús Cañas
- Dpto. Ciencia de los Materiales, Universidad de Cadiz, 11510 Puerto Real, Spain
- Université Grenoble Alpes, CNRS, Grenoble INP, Institut Neel, 38000 Grenoble, France
| | - Daniel F. Reyes
- Dpto. Ciencia de los Materiales, Universidad de Cadiz, 11510 Puerto Real, Spain
- Instituto de Ciencia de Materiales de Sevilla (CSIC-Univ. Sevilla), Avda. Americo Vespucio 49, 41092 Sevilla, Spain
| | - Alter Zakhtser
- Université Grenoble Alpes, CNRS, LTM, 38000 Grenoble, France
| | - Christian Dussarrat
- Air Liquide Laboratories, Yokosuka 239-0847, Japan
- Japanese-French Laboratory for Semiconductor Physics and Technology J-F AST, CNRS, Université Grenoble Alpes, Grenoble INP, University of Tsukuba, Ibaraki 305-8577, Japan
| | - Takashi Teramoto
- Air Liquide Laboratories, Yokosuka 239-0847, Japan
- Japanese-French Laboratory for Semiconductor Physics and Technology J-F AST, CNRS, Université Grenoble Alpes, Grenoble INP, University of Tsukuba, Ibaraki 305-8577, Japan
| | - Marina Gutiérrez
- Dpto. Ciencia de los Materiales, Universidad de Cadiz, 11510 Puerto Real, Spain
| | - Etienne Gheeraert
- Université Grenoble Alpes, CNRS, Grenoble INP, Institut Neel, 38000 Grenoble, France
- Japanese-French Laboratory for Semiconductor Physics and Technology J-F AST, CNRS, Université Grenoble Alpes, Grenoble INP, University of Tsukuba, Ibaraki 305-8577, Japan
- University of Tsukuba, Tsukuba 305-8573, Japan
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5
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Yang H, Konečná A, Xu X, Cheong SW, Batson PE, García de Abajo FJ, Garfunkel E. Simultaneous Imaging of Dopants and Free Charge Carriers by Monochromated EELS. ACS NANO 2022; 16:18795-18805. [PMID: 36317944 DOI: 10.1021/acsnano.2c07540] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Doping inhomogeneities in solids are not uncommon, but their microscopic observation and understanding are limited due to the lack of bulk-sensitive experimental techniques with high enough spatial and spectral resolution. Here, we demonstrate nanoscale imaging of both dopants and free charge carriers in La-doped BaSnO3 (BLSO) using high-resolution electron energy-loss spectroscopy (EELS). By analyzing high- and low-energy excitations in EELS, we reveal chemical and electronic inhomogeneities within a single BLSO nanocrystal. The inhomogeneous doping leads to distinctive localized infrared surface plasmons, including a previously unobserved plasmon mode that is highly confined between high- and low-doping regions. We further quantify the carrier density, effective mass, and dopant activation percentage by EELS and transport measurements on the bulk single crystals of BLSO. These results not only represent a practical approach for studying heterogeneities in solids and understanding structure-property relationships at the nanoscale, but also demonstrate the possibility of infrared plasmon tuning by leveraging nanoscale doping texture.
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Affiliation(s)
- Hongbin Yang
- Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey08854, United States
| | - Andrea Konečná
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860Castelldefels, Barcelona, Spain
- Central European Institute of Technology, Brno University of Technology, 61200Brno, Czech Republic
| | - Xianghan Xu
- Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey08854, United States
| | - Sang-Wook Cheong
- Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey08854, United States
| | - Philip E Batson
- Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey08854, United States
| | - F Javier García de Abajo
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860Castelldefels, Barcelona, Spain
- ICREA-Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010Barcelona, Spain
| | - Eric Garfunkel
- Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey08854, United States
- Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey08854, United States
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6
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Yan X, Jin Q, Jiang Y, Yao T, Li X, Tao A, Gao C, Chen C, Ma X, Ye H. Direct Determination of Band Gap of Defects in a Wide Band Gap Semiconductor. ACS APPLIED MATERIALS & INTERFACES 2022; 14:36875-36881. [PMID: 35926161 DOI: 10.1021/acsami.2c10143] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Crystal defects play an important role in the degradation and failure of semiconductor materials and devices. Direct determination of band gap of defects is a critical step for clarifying how the defects affect the physical properties of semiconductors. Here, high-quality aluminum nitride (AlN) thin films were grown epitaxially on single-crystal Al2O3 substrates via pulsed laser deposition. The atomic structure and band gap of three types of inversion domain boundaries (IDBs) in AlN were determined using aberration-corrected transmission electron microscopy and atomic-resolution valence electron energy-loss spectroscopy. It was found that the band gap of all of the IDBs reduces evidently compared to that of the bulk AlN. The maximum band gap reduction of the IDBs is 1.0 eV. First-principles calculations revealed that the band gap reduction of the IDBs is mainly due to the rise of pz orbital at the valence band maximum, which originates from the elongated Al-N bonds along the [0001] direction at the IDBs. The successful band gap determination of defects paves an avenue for quantitatively evaluating the effect of defects on the performance of semiconductor materials and devices.
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Affiliation(s)
- Xuexi Yan
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, School of Material Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
- Jihua Lab, Foshan 528251, China
| | - Qianqian Jin
- School of Microelectronics and Materials Engineering, Guangxi University of Science and Technology, Liuzhou 545006, China
| | - Yixiao Jiang
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, School of Material Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
- Jihua Lab, Foshan 528251, China
| | - Tingting Yao
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, School of Material Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
- Jihua Lab, Foshan 528251, China
| | - Xiang Li
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, School of Material Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
- Jihua Lab, Foshan 528251, China
| | - Ang Tao
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, School of Material Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
- Jihua Lab, Foshan 528251, China
| | - Chunyang Gao
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, School of Material Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
- Jihua Lab, Foshan 528251, China
| | - Chunlin Chen
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, School of Material Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
- Jihua Lab, Foshan 528251, China
| | - Xiuliang Ma
- Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, School of Material Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
- State Key Lab of Advanced Processing and Recycling on Non-Ferrous Metals, Lanzhou University of Technology, Lanzhou 730050, China
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7
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Zamani RR, Hage FS, Eljarrat A, Namazi L, Ramasse QM, Dick KA. Unraveling electronic band structure of narrow-bandgap p-n nanojunctions in heterostructured nanowires. Phys Chem Chem Phys 2021; 23:25019-25023. [PMID: 34730587 DOI: 10.1039/d1cp03275e] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The electronic band structure of complex nanostructured semiconductors has a considerable effect on the final electronic and optical properties of the material and, ultimately, on the functionality of the devices incorporating them. Valence electron energy-loss spectroscopy (VEELS) in the transmission electron microscope (TEM) provides the possibility of measuring this property of semiconductors with high spatial resolution. However, it still represents a challenge for narrow-bandgap semiconductors, since an electron beam with low energy spread is required. Here we demonstrate that by means of monochromated VEELS we can study the electronic band structure of narrow-gap materials GaSb and InAs in the form of heterostructured nanowires, with bandgap values down to 0.5 eV, especially important for newly developed structures with unknown bandgaps. Using complex heterostructured InAs-GaSb nanowires, we determine a bandgap value of 0.54 eV for wurtzite InAs. Moreover, we directly compare the bandgaps of wurtzite and zinc blende polytypes of GaSb in a single nanostructure, measured here as 0.84 and 0.75 eV, respectively. This allows us to solve an existing controversy in the band alignment between these structures arising from theoretical predictions. The findings demonstrate the potential of monochromated VEELS to provide a better understanding of the band alignment at the heterointerfaces of narrow-bandgap complex nanostructured materials with high spatial resolution. This is especially important for semiconductor device applications where even the slightest variations of the electronic band structure at the nanoscale can play a crucial role in their functionality.
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Affiliation(s)
- Reza R Zamani
- Solid State Physics, Lund University, Box 118, Lund 22100, Sweden. .,Department of Physics, Chalmers University of Technology, Gothenburg 41296, Sweden
| | - Fredrik S Hage
- SuperSTEM Laboratory, SciTech Daresbury Campus, Daresbury WA4 4AD, UK.,Department of Materials, University of Oxford, Oxford OX1 3PH, UK.,Department of Physics/Centre for Materials Science and Nanotechnology, University of Oslo, Oslo 0318, Norway
| | - Alberto Eljarrat
- Institute of Physics, Humboldt University of Berlin, Berlin 12489, Germany
| | - Luna Namazi
- Solid State Physics, Lund University, Box 118, Lund 22100, Sweden.
| | - Quentin M Ramasse
- SuperSTEM Laboratory, SciTech Daresbury Campus, Daresbury WA4 4AD, UK.,School of Chemical and Process Engineering and School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
| | - Kimberly A Dick
- Solid State Physics, Lund University, Box 118, Lund 22100, Sweden. .,Centre for Analysis and Synthesis, Lund University, Box 124, Lund 22100, Sweden
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8
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Sharona H, Bhat U. Nature of optical excitations and bandgap of Re xMo 1-xS 2alloy at nanoscale probed from high resolution low loss electron energy loss spectroscopy. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2021; 33:455901. [PMID: 34380118 DOI: 10.1088/1361-648x/ac1caf] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/11/2021] [Accepted: 08/11/2021] [Indexed: 06/13/2023]
Abstract
The two-dimensional (2D) transitional metal dichalcogenides (TMDS) have become an intensive research topic recently. The alloys of these TMDs have offered continuous tunability of the bandstructure and carrier concentration, providing a new opportunity for various device applications. Here the rich variations in optical excitations in RexMo1-xS2alloy at the nanoscale region are shown. The alloy bandgap and charge response are probed by low-loss high-resolution transmission electron energy loss spectroscopy (HR-EELS). Concurrent density functional theory calculations revealed many electronic structures from n-type semiconductors to metallic and p-type semiconducting nature with band bowing effect. The alloying-induced Peierls distortion leads to a change in crystal symmetry and decreased interlayer coupling. These alloys undergo indirect to direct bandgap transition with the function of Re concentration. These unique correlated structural and electronic properties of these 2D alloys can be potentially applicable for various electronic and optoelectronic devices.
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Affiliation(s)
- H Sharona
- International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064, India
| | - U Bhat
- International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560064, India
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9
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Stöger-Pollach M, Pichler CF, Dan T, Zickler GA, Bukvišová K, Eibl O, Brandstätter F. Coherent light emission in cathodoluminescence when using GaAs in a scanning (transmission) electron microscope. Ultramicroscopy 2021; 224:113260. [PMID: 33774193 DOI: 10.1016/j.ultramic.2021.113260] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Revised: 12/18/2020] [Accepted: 03/09/2021] [Indexed: 11/28/2022]
Abstract
For most materials science oriented applications incoherent cathodoluminescence (CL) is of main interest, for which the recombination of electron-hole pairs yields the emission of light. However, the incoherent signal is superimposed by coherently excited photons, similar to the situation for X-rays in Energy-Dispersive X-ray spectra (EDX). In EDX two very different processes superimpose in each spectrum: Bremsstrahlung and characteristic X-ray radiation. Both processes yield X-rays, however, their origin is substantially different. Therefore, in the present CL study we focus on the coherent emission of light, in particular Čerenkov radiation. We use a 200μm thick GaAs sample, not electron transparent and therefore not acting as a light guide, and investigate the radiation emitted from the top surface of the sample generated by back-scattered electrons on their way out of the specimen. The CL spectra revealed a pronounced peak corresponding to the expected interband transition. This peak was at 892 nm at room temperature and shifted to 845 nm at 80 K. The coherent light emission significantly modifies the shape of CL spectra at elevated beam energies. For the first time, by the systematic variation of current and energy of primary electrons we could distinguish the coherent and incoherent light superimposed in CL spectra. These findings are essential for the correct interpretation of CL spectra in STEM. The Čerenkov intensity as well as the total intensity in a spectrum scales linearly with the beam current. Additionally, we investigate the influence of asymmetric mirrors on the spectral shapes, collecting roughly only half of the whole solid angle. Different emission behaviour of different physical causes thus lead to changes in the overall spectral shape.
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Affiliation(s)
- Michael Stöger-Pollach
- University Service Centre for Transmission Electron Microscopy (USTEM), Technische Universität Wien, Wiedner Hauptstraße 8-10, 1040 Wien, Austria; Institute for Solid State Physics, Technische Universität Wien, Wiedner Hauptstraße 8-10, 1040 Wien, Austria.
| | - Cornelia F Pichler
- Institute for Solid State Physics, Technische Universität Wien, Wiedner Hauptstraße 8-10, 1040 Wien, Austria
| | - Topa Dan
- Naturhistorisches Museum Wien, Burgring 7, 1010 Wien, Austria
| | - Gregor A Zickler
- Department for Chemistry and Physics of Materials, Paris Lodron Universität Salzburg, Jakob-Haringer Str. 2A, 5020 Salzburg, Austria
| | - Kristýna Bukvišová
- Central European Institute of Technology (CEITEC), Brno University of Technology, Purkyňova 123, Brno 612 00, Czech Republic
| | - Oliver Eibl
- University Service Centre for Transmission Electron Microscopy (USTEM), Technische Universität Wien, Wiedner Hauptstraße 8-10, 1040 Wien, Austria; Institute for Solid State Physics, Technische Universität Wien, Wiedner Hauptstraße 8-10, 1040 Wien, Austria
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10
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Brescia R, Toso S, Ramasse Q, Manna L, Shamsi J, Downing C, Calzolari A, Bertoni G. Bandgap determination from individual orthorhombic thin cesium lead bromide nanosheets by electron energy-loss spectroscopy. NANOSCALE HORIZONS 2020; 5:1610-1617. [PMID: 33140817 DOI: 10.1039/d0nh00477d] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Inorganic lead halide perovskites are promising candidates for optoelectronic applications, due to their high photoluminescence quantum yield and narrow emission line widths. Particularly attractive is the possibility to vary the bandgap as a function of the halide composition and the size or shape of the crystals at the nanoscale. Here we present an aberration-corrected scanning transmission electron microscopy (STEM) and monochromated electron energy-loss spectroscopy (EELS) study of extended nanosheets of CsPbBr3. We demonstrate their orthorhombic crystal structure and their lateral termination with Cs-Br planes. The bandgaps are measured from individual nanosheets, avoiding the effect of the size distribution which is present in standard optical spectroscopy techniques. We find an increase of the bandgap starting at thicknesses below 10 nm, confirming the less marked effect of 1D confinement in nanosheets compared to the 3D confinement observed in quantum dots, as predicted by density functional theory calculations and optical spectroscopy data from ensemble measurements.
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Affiliation(s)
- Rosaria Brescia
- Electron Microscopy Facility, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Stefano Toso
- Nanochemistry Department, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy and International Doctoral Program in Science, Università Cattolica del Sacro Cuore, 25121 Brescia, Italy
| | - Quentin Ramasse
- SuperSTEM, SciTech Daresbury Science and Innovation Campus, Keckwick Lane, Daresbury WA4 4AD, UK. and School of Chemical and Process Engineering & School of Physics, University of Leeds, Leeds LS29JT, UK
| | - Liberato Manna
- Nanochemistry Department, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Javad Shamsi
- Nanochemistry Department, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
| | - Clive Downing
- The Advanced Microscopy Laboratory, CRANN, Trinity College Dublin (TCD), Dublin, Ireland
| | - Arrigo Calzolari
- CNR - Istituto Nanoscienze, Via Campi 213/A, 41125 Modena, Italy.
| | - Giovanni Bertoni
- CNR - Istituto Nanoscienze, Via Campi 213/A, 41125 Modena, Italy. and IMEM - CNR, Istituto dei Materiali per l'Elettronica e il Magnetismo, Parco Area delle Scienze 37/A, 43124 Parma, Italy
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11
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Lyu F, Sun Y, Yang Q, Tang B, Li M, Li Z, Sun M, Gao P, Ye LH, Chen Q. Thickness-dependent band gap of α-In 2Se 3: from electron energy loss spectroscopy to density functional theory calculations. NANOTECHNOLOGY 2020; 31:315711. [PMID: 32294630 DOI: 10.1088/1361-6528/ab8998] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
α-In2Se3 has attracted increasing attention in recent years due to its excellent electrical and optical properties. Especially, attention has been paid to its peculiar ferroelectric and piezoelectric properties which most other two-dimensional (2D) materials do not possess. This paper presents the first measurement of the thickness-dependent band gaps of few-layer α-In2Se3 by electron energy loss spectroscopy (EELS). The band gap increases with decreasing film thickness which varies from 1.44 eV in a 48 nm thick area to 1.64 eV in an 8 nm thick area of the samples. Further, by combining the improved exchange-correlation potential and proper screening of the internal electric field in an advanced 2D electronic structure technique, we have been able to obtain the structural dependence of the band gap within density functional theory up to hundreds of atoms. This is also the first calculation of a similar type for 2D ferroelectric materials. Both experiment and theory suggest that the variation of the band gap of α-In2Se3 fits well with the quantum confinement model for 2D materials.
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Affiliation(s)
- Fengjiao Lyu
- Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing 100871, People's Republic of China
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12
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Stöger-Pollach M, Löffler S, Maurer N, Bukvišová K. Using Cˇerenkov radiation for measuring the refractive index in thick samples by interferometric cathodoluminescence. Ultramicroscopy 2020; 214:113011. [DOI: 10.1016/j.ultramic.2020.113011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2020] [Revised: 04/24/2020] [Accepted: 04/25/2020] [Indexed: 10/24/2022]
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13
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Affiliation(s)
- Dongdong Xiao
- Beijing National Laboratory for Condensed Matter PhysicsInstitute of PhysicsChinese Academy of Sciences Beijing 100190 China
| | - Lin Gu
- Beijing National Laboratory for Condensed Matter PhysicsInstitute of PhysicsChinese Academy of Sciences Beijing 100190 China
- School of physical sciencesUniversity of Chinese Academy of Sciences Beijing 100049 China
- Songshan Lake Materials Laboratory Dongguan Guangdong 523808 China
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14
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Das PP, Guzzinati G, Coll C, Gomez Perez A, Nicolopoulos S, Estrade S, Peiro F, Verbeeck J, Zompra AA, Galanis AS. Reliable Characterization of Organic & Pharmaceutical Compounds with High Resolution Monochromated EEL Spectroscopy. Polymers (Basel) 2020; 12:polym12071434. [PMID: 32605004 PMCID: PMC7408036 DOI: 10.3390/polym12071434] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 06/22/2020] [Accepted: 06/23/2020] [Indexed: 11/16/2022] Open
Abstract
Organic and biological compounds (especially those related to the pharmaceutical industry) have always been of great interest for researchers due to their importance for the development of new drugs to diagnose, cure, treat or prevent disease. As many new API (active pharmaceutical ingredients) and their polymorphs are in nanocrystalline or in amorphous form blended with amorphous polymeric matrix (known as amorphous solid dispersion—ASD), their structural identification and characterization at nm scale with conventional X-Ray/Raman/IR techniques becomes difficult. During any API synthesis/production or in the formulated drug product, impurities must be identified and characterized. Electron energy loss spectroscopy (EELS) at high energy resolution by transmission electron microscope (TEM) is expected to be a promising technique to screen and identify the different (organic) compounds used in a typical pharmaceutical or biological system and to detect any impurities present, if any, during the synthesis or formulation process. In this work, we propose the use of monochromated TEM-EELS, to analyze selected peptides and organic compounds and their polymorphs. In order to validate EELS for fingerprinting (in low loss/optical region) and by further correlation with advanced DFT, simulations were utilized.
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Affiliation(s)
- Partha Pratim Das
- NanoMegas SPRL, Boulevard Edmond Machtens 79, B1080 Brussels, Belgium; (A.G.P.); (A.S.G.)
- Electron Crystallography Solutions SL, Calle Orense 8, 28020 Madrid, Spain
- Correspondence: (P.P.D.); (S.N.)
| | - Giulio Guzzinati
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium; (G.G.); (J.V.)
| | - Catalina Coll
- LENS-MIND, Department of Electronics and Biomedical Engineering, Universitat de Barcelona, 08028 Barcelona, Spain; (C.C.); (S.E.); (F.P.)
- Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, 08028 Barcelona, Spain
| | - Alejandro Gomez Perez
- NanoMegas SPRL, Boulevard Edmond Machtens 79, B1080 Brussels, Belgium; (A.G.P.); (A.S.G.)
| | - Stavros Nicolopoulos
- NanoMegas SPRL, Boulevard Edmond Machtens 79, B1080 Brussels, Belgium; (A.G.P.); (A.S.G.)
- Correspondence: (P.P.D.); (S.N.)
| | - Sonia Estrade
- LENS-MIND, Department of Electronics and Biomedical Engineering, Universitat de Barcelona, 08028 Barcelona, Spain; (C.C.); (S.E.); (F.P.)
- Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, 08028 Barcelona, Spain
| | - Francesca Peiro
- LENS-MIND, Department of Electronics and Biomedical Engineering, Universitat de Barcelona, 08028 Barcelona, Spain; (C.C.); (S.E.); (F.P.)
- Institute of Nanoscience and Nanotechnology (IN2UB), Universitat de Barcelona, 08028 Barcelona, Spain
| | - Johan Verbeeck
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium; (G.G.); (J.V.)
| | | | - Athanassios S. Galanis
- NanoMegas SPRL, Boulevard Edmond Machtens 79, B1080 Brussels, Belgium; (A.G.P.); (A.S.G.)
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15
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Wei J, Ogawa T, Feng B, Yokoi T, Ishikawa R, Kuwabara A, Matsunaga K, Shibata N, Ikuhara Y. Direct Measurement of Electronic Band Structures at Oxide Grain Boundaries. NANO LETTERS 2020; 20:2530-2536. [PMID: 32134272 DOI: 10.1021/acs.nanolett.9b05298] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Grain boundaries (GBs) modulate the macroscopic properties in polycrystalline materials because they have different atomic and electronic structures from the bulk. Despite the progress on the understanding of GB atomic structures, knowledge of the localized electronic band structures is still lacking. Here, we experimentally characterized the atomic structures and the band gaps of four typical GBs in α-Al2O3 by scanning transmission electron microscopy and valence electron energy-loss spectroscopy (EELS). It was found that the band gaps of the GBs are narrowed by 0.5-2.1 eV compared with that of 8.8 eV in the bulk. By combing core-loss EELS with first-principles calculations, we elucidated that the band gap reductions directly correlate with the decrease of the coordination numbers of Al and O ions at the GBs. These results provide in-depth understanding between the local atomic and electronic band structures for GBs and demonstrate a novel electronic-structure analysis for crystalline defects.
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Affiliation(s)
- Jiake Wei
- Institute of Engineering Innovation, The University of Tokyo, Tokyo 113-8656, Japan
| | - Takafumi Ogawa
- Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587, Japan
| | - Bin Feng
- Institute of Engineering Innovation, The University of Tokyo, Tokyo 113-8656, Japan
| | - Tatsuya Yokoi
- Department of Materials Physics, Nagoya University, Nagoya 464-8601, Japan
| | - Ryo Ishikawa
- Institute of Engineering Innovation, The University of Tokyo, Tokyo 113-8656, Japan
- Japan Science and Technology Agency, PRESTO, Kawaguchi, Saitama 332-0012, Japan
| | - Akihide Kuwabara
- Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587, Japan
| | - Katsuyuki Matsunaga
- Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587, Japan
- Department of Materials Physics, Nagoya University, Nagoya 464-8601, Japan
| | - Naoya Shibata
- Institute of Engineering Innovation, The University of Tokyo, Tokyo 113-8656, Japan
- Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587, Japan
| | - Yuichi Ikuhara
- Institute of Engineering Innovation, The University of Tokyo, Tokyo 113-8656, Japan
- Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587, Japan
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16
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Eljarrat A, Koch CT. Design and application of a relativistic Kramers-Kronig analysis algorithm. Ultramicroscopy 2019; 206:112825. [PMID: 31400584 DOI: 10.1016/j.ultramic.2019.112825] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2019] [Revised: 07/15/2019] [Accepted: 07/26/2019] [Indexed: 10/26/2022]
Abstract
Low-loss electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope probes the valence electron density and relevant optoelectronic properties such as band gap energies and other band structure transitions. The measured spectra can be formulated in a dielectric theory framework, comparable to optical spectroscopies and ab-initio simulations. Moreover, Kramers-Kronig analysis (KKA), an inverse algorithm based on the same name relations, can be employed for the retrieval of the complex dielectric function. However, spurious contributions traditionally not considered in this framework typically impact low-loss EELS modifying the spectral shapes and precluding the correct measurement and retrieval of the dielectric information. A relativistic KKA algorithm is able to account for the bulk and surface radiative-loss contributions to low-loss EELS, revealing the correct dielectric properties. Using a synthetic low-loss EELS model, we propose some modifications on the naive implementation of this algorithm that broadens its range of application. The robustness of the algorithm is improved by regularization, applying previous knowledge about the shape and smoothness of the correction term. Additionally, our efficient numerical integration methodology allows processing hyperspectral datasets in a reasonable amount of time. Harnessing these abilities, we show how simultaneous relativistic KKA processing of several spectra can share information to produce an improved result.
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Affiliation(s)
- Alberto Eljarrat
- Department of Physics, Humboldt University of Berlin, Newtonstraße 15, Berlin 12489, Germany.
| | - Christoph T Koch
- Department of Physics, Humboldt University of Berlin, Newtonstraße 15, Berlin 12489, Germany
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17
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Charging ain't all bad: Complex physics in DyScO 3. Ultramicroscopy 2019; 203:119-124. [PMID: 30554733 DOI: 10.1016/j.ultramic.2018.12.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2018] [Accepted: 12/05/2018] [Indexed: 11/20/2022]
Abstract
Although charging is ubiquitous in electron microscopy, its effects are typically avoided or ignored. However, avoiding charging is not possible in some materials, e.g. lanthanide scandates with well-ordered surfaces positively charge immensely under electron beam illumination because of their electronic structure, and ignoring charging can leave new science undiscovered. In this work, a combination of rapidly acquired electron energy loss spectra and cross-correlation were used to understand and overcome charging effects in DyScO3. A 5.4 eV band gap was extracted from the charging-corrected loss spectrum, in good agreement with previously reported band gaps, and a 3.8 eV in-gap peak was attributed to surface states via comparison with density functional theory calculations. Additionally, ultraviolet photoelectron spectroscopy measurements indicated that under some conditions well-annealed DyScO3 surfaces charge negatively causing upward band bending associated with occupied surface states in the gap. As was previously found in the case of positive charging under electron beam illumination with in-situ flexoelectric bending observations, the magnitude of negative charging under ultraviolet illumination is Zener tunneling limited in well-annealed DyScO3.
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18
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Zamani RR, Arbiol J. Understanding semiconductor nanostructures via advanced electron microscopy and spectroscopy. NANOTECHNOLOGY 2019; 30:262001. [PMID: 30812017 DOI: 10.1088/1361-6528/ab0b0a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Transmission electron microscopy (TEM) offers an ample range of complementary techniques which are able to provide essential information about the physical, chemical and structural properties of materials at the atomic scale, and hence makes a vast impact on our understanding of materials science, especially in the field of semiconductor one-dimensional (1D) nanostructures. Recent advancements in TEM instrumentation, in particular aberration correction and monochromation, have enabled pioneering experiments in complex nanostructure material systems. This review aims to address these understandings through the applications of the methodology for semiconductor nanostructures. It points out various electron microscopy techniques, in particular scanning TEM (STEM) imaging and spectroscopy techniques, with their already-employed or potential applications on 1D nanostructured semiconductors. We keep the main focus of the paper on the electronic and optoelectronic properties of such semiconductors, and avoid expanding it further. In the first part of the review, we give a brief introduction to each of the STEM-based techniques, without detailed elaboration, and mention the recent technological and conceptual developments which lead to novel characterization methodologies. For further reading, we refer the audience to a handful of papers in the literature. In the second part, we highlight the recent examples of application of the STEM methodology on the 1D nanostructure semiconductor materials, especially III-V, II-V, and group IV bare and heterostructure systems. The aim is to address the research questions on various physical properties and introduce solutions by choosing the appropriate technique that can answer the questions. Potential applications will also be discussed, the ones that have already been used for bulk and 2D materials, and have shown great potential and promise for 1D nanostructure semiconductors.
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Affiliation(s)
- Reza R Zamani
- Department of Physics, Chalmers University of Technology, Gothenburg, SE-41296, Sweden. Interdisciplinary Centre for Electron Microscopy (CIME), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne 1015, Switzerland
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19
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Measurement of Diffusion and Segregation in Semiconductor Quantum Dots and Quantum Wells by Transmission Electron Microscopy: A Guide. NANOMATERIALS 2019; 9:nano9060872. [PMID: 31181748 PMCID: PMC6630582 DOI: 10.3390/nano9060872] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Revised: 06/03/2019] [Accepted: 06/04/2019] [Indexed: 11/16/2022]
Abstract
Strategies are discussed to distinguish interdiffusion and segregation and to measure key parameters such as diffusivities and segregation lengths in semiconductor quantum dots and quantum wells by electron microscopy methods. Spectroscopic methods are usually necessary when the materials systems are complex while imaging methods may suffice for binary or simple ternary compounds where atomic intermixing is restricted to one type of sub-lattice. The emphasis on methodology should assist microscopists in evaluating and quantifying signals from electron micrographs and related spectroscopic data. Examples presented include CdS/ZnS core/shell particles and SiGe, InGaAs and InGaN quantum wells.
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20
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Meng Q, Xu G, Xin H, Stach EA, Zhu Y, Su D. Quantification of Charge Transfer at the Interfaces of Oxide Thin Films. J Phys Chem A 2019; 123:4632-4637. [PMID: 31050895 DOI: 10.1021/acs.jpca.9b02802] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The interfacial electronic distribution in transition-metal oxide thin films is crucial to their interfacial physical or chemical behaviors. Core-loss electron energy-loss spectroscopy (EELS) may potentially give valuable information of local electronic density of state at high spatial resolution. Here, we studied the electronic properties at the interface of Pb(Zr0.2Ti0.8)O3 (PZT)/4.8 nm La0.8Sr0.2MnO3 (LSMO)/SrTiO3 (STO) using valance-EELS with a scanning transmission electron microscope. Modeled with dielectric function theory, the charge transfer in the vicinity of the interfaces of PZT/LSMO and LSMO/STO was determined from the shifts of plasma peaks of valence EELS (VEELS), agreeing with theoretical prediction. Our work demonstrates that the VEELS method enables a high-efficient quantification of the charge transfer at interfaces, shedding light on the charge-transfer issues at heterogenous interfaces in physical and chemical devices.
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21
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Fundamentals of cathodoluminescence in a STEM: The impact of sample geometry and electron beam energy on light emission of semiconductors. Ultramicroscopy 2019; 200:111-124. [DOI: 10.1016/j.ultramic.2019.03.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Revised: 03/01/2019] [Accepted: 03/03/2019] [Indexed: 11/23/2022]
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22
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Brodusch N, Demers H, Gellé A, Moores A, Gauvin R. Electron energy-loss spectroscopy (EELS) with a cold-field emission scanning electron microscope at low accelerating voltage in transmission mode. Ultramicroscopy 2018; 203:21-36. [PMID: 30595397 DOI: 10.1016/j.ultramic.2018.12.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Revised: 12/18/2018] [Accepted: 12/23/2018] [Indexed: 11/29/2022]
Abstract
A commercial electron energy-loss spectrometer (EELS) attached to a high-resolution cold-field emission scanning electron microscope in transmission mode (STEM) is evaluated and its potential for characterizing materials science thin specimens at low accelerating voltage is reviewed. Despite the increased beam radiation damage at SEM voltages on sensitive compounds, we describe some potential applications which benefit from lowering the primary electrons voltage on less-sensitive specimens. We report bandgap measurements on several dielectrics which were facilitated by the lack of Cherenkov radiation losses at 30 kV. The possibility of volume plasmon imaging to probe local composition changes in complex materials was demonstrated using energy-filtered STEM, either via spectrum imaging or elemental mapping using the "three-windows" method. As plasmonic materials are increasing used for energy, electronics or biomedical applications, the ability of reliably evaluate their properties at low accelerating voltage in a SEM is very appealing and is demonstrated. The energy resolution of the spectrometer, taken as the full width at half maximum of the zero-loss peak, was routinely measured at around 0.55 eV and it is demonstrated that t/λ ratios up to 1.5 allowed practical EEL spectroscopy at 30 kV.
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Affiliation(s)
- Nicolas Brodusch
- Department of Mining and Materials Engineering, McGill University, Montréal, Québec H3A 0C5, Canada.
| | - Hendrix Demers
- Department of Mining and Materials Engineering, McGill University, Montréal, Québec H3A 0C5, Canada
| | - Alexandra Gellé
- Department of Chemistry, McGill University, Montréal, Québec H3A 0C5, Canada
| | - Audrey Moores
- Department of Chemistry, McGill University, Montréal, Québec H3A 0C5, Canada
| | - Raynald Gauvin
- Department of Mining and Materials Engineering, McGill University, Montréal, Québec H3A 0C5, Canada.
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23
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Meng Q, Wu L, Xin HL, Zhu Y. Retrieving the energy-loss function from valence electron energy-loss spectrum: Separation of bulk-, surface-losses and Cherenkov radiation. Ultramicroscopy 2018; 194:175-181. [PMID: 30149218 DOI: 10.1016/j.ultramic.2018.08.014] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Revised: 08/09/2018] [Accepted: 08/19/2018] [Indexed: 11/16/2022]
Abstract
With recent rapid advancement in electron microscopy instrumentation, in particular, bright electron sources and monochromators, valence electron energy-loss spectroscopy (VEELS) has become attractive for retrieving band structures, optical properties, dielectric functions and phonon information of materials. However, Cherenkov radiation and surface-loss contribution significantly alter fine structures of VEELS, even in simple semiconductors and insulators. This leads to the problem that dielectric function or bandgap structure of these materials cannot be determined correctly if these effects are not removed. In this work we present a solution to this dilemma. We demonstrate that energy-loss function and real part of inverse complex dielectric function can be retrieved from raw data of VEELS. Based on the calculated example of Si, the limitation of our approach is discussed. We believe that our approach represents an improvement over previous procedures and has a broad prospect for applications.
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Affiliation(s)
- Qingping Meng
- Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton NY 11973, USA.
| | - Lijun Wu
- Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton NY 11973, USA
| | - Huolin L Xin
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton NY 11973, USA
| | - Yimei Zhu
- Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton NY 11973, USA.
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24
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Guzzinati G, Altantzis T, Batuk M, De Backer A, Lumbeeck G, Samaee V, Batuk D, Idrissi H, Hadermann J, Van Aert S, Schryvers D, Verbeeck J, Bals S. Recent Advances in Transmission Electron Microscopy for Materials Science at the EMAT Lab of the University of Antwerp. MATERIALS (BASEL, SWITZERLAND) 2018; 11:E1304. [PMID: 30060556 PMCID: PMC6117696 DOI: 10.3390/ma11081304] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/29/2018] [Revised: 07/25/2018] [Accepted: 07/26/2018] [Indexed: 01/13/2023]
Abstract
The rapid progress in materials science that enables the design of materials down to the nanoscale also demands characterization techniques able to analyze the materials down to the same scale, such as transmission electron microscopy. As Belgium's foremost electron microscopy group, among the largest in the world, EMAT is continuously contributing to the development of TEM techniques, such as high-resolution imaging, diffraction, electron tomography, and spectroscopies, with an emphasis on quantification and reproducibility, as well as employing TEM methodology at the highest level to solve real-world materials science problems. The lab's recent contributions are presented here together with specific case studies in order to highlight the usefulness of TEM to the advancement of materials science.
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Affiliation(s)
- Giulio Guzzinati
- EMAT, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.
| | - Thomas Altantzis
- EMAT, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.
| | - Maria Batuk
- EMAT, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.
| | - Annick De Backer
- EMAT, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.
| | - Gunnar Lumbeeck
- EMAT, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.
| | - Vahid Samaee
- EMAT, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.
| | - Dmitry Batuk
- EMAT, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.
| | - Hosni Idrissi
- EMAT, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.
- Institute of Mechanics, Materials and Civil Engineering, Université catholique de Louvain, Louvain-la-Neuve 1348, Belgium.
| | - Joke Hadermann
- EMAT, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.
| | - Sandra Van Aert
- EMAT, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.
| | | | - Johan Verbeeck
- EMAT, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.
| | - Sara Bals
- EMAT, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.
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25
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Crozier PA. Vibrational and valence aloof beam EELS: A potential tool for nondestructive characterization of nanoparticle surfaces. Ultramicroscopy 2017; 180:104-114. [DOI: 10.1016/j.ultramic.2017.03.011] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2016] [Revised: 03/10/2017] [Accepted: 03/11/2017] [Indexed: 11/25/2022]
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26
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Vatanparast M, Egoavil R, Reenaas TW, Verbeeck J, Holmestad R, Vullum PE. Bandgap measurement of high refractive index materials by off-axis EELS. Ultramicroscopy 2017; 182:92-98. [PMID: 28666140 DOI: 10.1016/j.ultramic.2017.06.019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Revised: 06/18/2017] [Accepted: 06/19/2017] [Indexed: 10/19/2022]
Abstract
In the present work Cs aberration corrected and monochromated scanning transmission electron microscopy electron energy loss spectroscopy (STEM-EELS) has been used to explore experimental set-ups that allow bandgaps of high refractive index materials to be determined. Semi-convergence and -collection angles in the µrad range were combined with off-axis or dark field EELS to avoid relativistic losses and guided light modes in the low loss range to contribute to the acquired EEL spectra. Off-axis EELS further supressed the zero loss peak and the tail of the zero loss peak. The bandgap of several GaAs-based materials were successfully determined by simple regression analyses of the background subtracted EEL spectra. The presented set-up does not require that the acceleration voltage is set to below the Čerenkov limit and can be applied over the entire acceleration voltage range of modern TEMs and for a wide range of specimen thicknesses.
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Affiliation(s)
- Maryam Vatanparast
- Department of Physics, NTNU (Norwegian University of Science and Technology), 7491 Trondheim, Norway.
| | - Ricardo Egoavil
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Turid W Reenaas
- Department of Physics, NTNU (Norwegian University of Science and Technology), 7491 Trondheim, Norway
| | - Johan Verbeeck
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Randi Holmestad
- Department of Physics, NTNU (Norwegian University of Science and Technology), 7491 Trondheim, Norway
| | - Per Erik Vullum
- Department of Physics, NTNU (Norwegian University of Science and Technology), 7491 Trondheim, Norway; SINTEF Materials and Chemistry, 7065 Trondheim, Norway
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27
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Wallisch W, Stöger-Pollach M, Navickas E. Consequences of the CMR effect on EELS in TEM. Ultramicroscopy 2017; 179:84-89. [PMID: 28448829 DOI: 10.1016/j.ultramic.2017.04.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Revised: 04/11/2017] [Accepted: 04/14/2017] [Indexed: 11/25/2022]
Abstract
Double perovskite oxides have gained in importance and exhibit negative magnetoresistance, which is known as colossal magnetoresistance (CMR) effect. Using a La2CoMnO6 (LCM) thin film layer, we proved that the physical consequences of the CMR effect do also influence the electron energy loss spectrometry (EELS) signal. We observed a change of the band gap at low energy losses and were able to study the magnetisation with chemical sensitivity by employing energy loss magnetic chiral dichroism (EMCD) below the Curie temperature TC, where the CMR effect becomes significant.
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Affiliation(s)
- Wolfgang Wallisch
- University Service Centre for Transmission Electron Microscopy, Technische Universitát Wien, Wiedner Hauptstraße 8-10, A-1040 Wien, Austria.
| | - Michael Stöger-Pollach
- University Service Centre for Transmission Electron Microscopy, Technische Universitát Wien, Wiedner Hauptstraße 8-10, A-1040 Wien, Austria
| | - Edvinas Navickas
- Institute of Chemical Technologies and Analytics, Technische Universität Wien, Getreidemarkt 9, A-1040 Wien, Austria
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28
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Jeem M, Zhang L, Ishioka J, Shibayama T, Iwasaki T, Kato T, Watanabe S. Tuning Optoelectrical Properties of ZnO Nanorods with Excitonic Defects via Submerged Illumination. NANO LETTERS 2017; 17:2088-2093. [PMID: 28157326 DOI: 10.1021/acs.nanolett.7b00324] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
When applied in optoelectronic devices, a ZnO semiconductor dominantly absorbs or emits ultraviolet light because of its direct electron transition through a wide energy bandgap. On the contrary, crystal defects and nanostructure morphology are the chief key factors for indirect, interband transitions of ZnO optoelectronic devices in the visible light range. By ultraviolet illumination in ultrapure water, we demonstrate here a conceptually unique approach to tune the shape of ZnO nanorods from tapered to capped-end via apical surface morphology control. We show that oxygen vacancy point defects activated by excitonic effects near the tip-edge of a nanorod serve as an optoelectrical hotspot for the light-driven formation and tunability of the optoelectrical properties. A double increase of electron energy absorption on near band edge energy of ZnO was observed near the tip-edge of the tapered nanorod. The optoelectrical hotspot explanation rivals that of conventional electrostatics, impurity control, and alkaline pH control-associated mechanisms. Thus, it highlights a new perspective to understanding light-driven nanorod formation in pure neutral water.
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Affiliation(s)
| | | | | | | | - Tomio Iwasaki
- Research & Development Group, Hitachi, Ltd. , 7-1-1 Omika, Hitachi, Ibaraki 3191292, Japan
| | - Takahiko Kato
- Research & Development Group, Hitachi, Ltd. , 7-1-1 Omika, Hitachi, Ibaraki 3191292, Japan
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Stöger-Pollach M, Kachtík L, Miesenberger B, Retzl P. Transition radiation in EELS and cathodoluminescence. Ultramicroscopy 2017; 173:31-35. [DOI: 10.1016/j.ultramic.2016.11.020] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Revised: 11/16/2016] [Accepted: 11/20/2016] [Indexed: 11/16/2022]
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31
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Wei BQ, Yan N, Gao JX, Li DD, Shang ZG, He K. Absolute thickness measurement of pyrolytic graphite spheroids by STEM-EELS. Micron 2016; 91:41-48. [PMID: 27721207 DOI: 10.1016/j.micron.2016.10.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Revised: 10/02/2016] [Accepted: 10/02/2016] [Indexed: 10/20/2022]
Abstract
This paper studies the absolute thickness measurement of pyrolytic graphite spheroids (GSs) by using STEM-EELS mode with log-ratio method and Kramers-Kroning (K-K) method, taking the measured thickness from TEM image as reference that is the diameter of GSs ranging from 60 to 250nm. The effect of collection semi-angle (β) on thickness measurement has been investigated. It is found that in general the thickness obtained by K-K analysis with surface effect corrected shows the best accuracy, followed by K-K sum rule and then log-ratio method for the three different collection semi-angles of 12.4, 17.3 and 21.1mrad applied. Of these angles, the smallest one gives an overestimated result and the largest one gives an underestimated result, whereas between the two, the angle of 17.3mrad that is about 2x convergence semi-angle (9.0mrad) is identified as more appropriate for K-K analysis. The surface-scattering correction, inelastic mean free path of GS and effect of refractive index n on thickness measurement for different β angles are also investigated. Moreover, the optical property deduced from the data collected at the center of graphite spheroid, which is related to its microstructure, is characterized by K-K analysis.
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Affiliation(s)
- B Q Wei
- School of Materials Science and Engineering, Central South University, Changsha 410083, China
| | - N Yan
- Advanced Research Centre, Central South University, Changsha 410083, China
| | - J X Gao
- School of Materials Science and Engineering, Central South University, Changsha 410083, China
| | - D D Li
- School of Materials Science and Engineering, Central South University, Changsha 410083, China
| | - Z G Shang
- Advanced Research Centre, Central South University, Changsha 410083, China
| | - K He
- School of Materials Science and Engineering, Central South University, Changsha 410083, China; Advanced Research Centre, Central South University, Changsha 410083, China.
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Bowman W, March K, Hernandez C, Crozier P. Measuring bandgap states in individual non-stoichiometric oxide nanoparticles using monochromated STEM EELS: The Praseodymium–ceria case. Ultramicroscopy 2016; 167:5-10. [DOI: 10.1016/j.ultramic.2016.04.009] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Revised: 04/21/2016] [Accepted: 04/26/2016] [Indexed: 11/25/2022]
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Sakaguchi N, Tanda L, Kunisada Y. Measurement of the dielectric function of α-Al2O3 by transmission electron microscopy - Electron energy-loss spectroscopy without Cerenkov radiation effects. Ultramicroscopy 2016; 169:37-43. [PMID: 27448199 DOI: 10.1016/j.ultramic.2016.07.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Revised: 06/30/2016] [Accepted: 07/03/2016] [Indexed: 11/24/2022]
Abstract
The dielectric function of α-Al2O3 was measured by electron energy-loss spectroscopy (EELS) coupled with the difference method. The influence of Cerenkov radiation was significant in measurements using a 200kV transmission electron microscope (TEM) and the correct dielectric function could not be obtained using the conventional EELS procedure. However, a good agreement between the optical data and EELS for the dielectric functions was obtained via a 60kV TEM. Combining EELS and the difference method, however, provided an accurate measurement of the dielectric function for α-Al2O3 even at an accelerating voltage of 200kV. The combination of EELS and the difference method in the nano-beam diffraction mode could derive an accurate dielectric function with superior spatial resolution regardless of the occurrence of Cerenkov radiation.
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Affiliation(s)
- Norihito Sakaguchi
- Laboratory of Integrated Function Materials, Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.
| | - Luka Tanda
- Laboratory of Integrated Function Materials, Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
| | - Yuji Kunisada
- Laboratory of Integrated Function Materials, Center for Advanced Research of Energy and Materials, Faculty of Engineering, Hokkaido University, Kita-13, Nishi-8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
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Sakaguchi N, Tanda L, Kunisada Y. Improving the measurement of dielectric function by TEM-EELS: avoiding the retardation effect. Microscopy (Oxf) 2016; 65:415-421. [DOI: 10.1093/jmicro/dfw023] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Accepted: 05/30/2016] [Indexed: 11/12/2022] Open
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Mendis BG, Howkins A, Stowe D, Major JD, Durose K. The role of transition radiation in cathodoluminescence imaging and spectroscopy of thin-foils. Ultramicroscopy 2016; 167:31-42. [PMID: 27163963 DOI: 10.1016/j.ultramic.2016.05.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2015] [Revised: 03/10/2016] [Accepted: 05/02/2016] [Indexed: 11/15/2022]
Abstract
There is renewed interest in cathodoluminescence (CL) in the transmission electron microscope, since it can be combined with low energy loss spectroscopy measurements and can also be used to probe defects, such as grain boundaries and dislocations, at high spatial resolution. Transition radiation (TR), which is emitted when the incident electron crosses the vacuum-specimen interface, is however an important artefact that has received very little attention. The importance of TR is demonstrated on a wedge shaped CdTe specimen of varying thickness. For small specimen thicknesses (<250nm) grain boundaries are not visible in the panchromatic CL image. Grain boundary contrast is produced by electron-hole recombination within the foil, and a large fraction of that light is lost to multiple-beam interference, so that thicker specimens are required before the grain boundary signal is above the TR background. This is undesirable for high spatial resolution. Furthermore, the CL spectrum contains additional features due to TR which are not part of the 'bulk' specimen. Strategies to minimise the effects of TR are also discussed.
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Affiliation(s)
- B G Mendis
- Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
| | - A Howkins
- Experimental Techniques Centre, Brunel University, Uxbridge UB8 3PH, UK
| | - D Stowe
- Gatan UK, 25 Nuffield Way, Abingdon, Oxfordshire OX14 1RL, UK
| | - J D Major
- Stephenson Institute for Renewable Energy, University of Liverpool, Liverpool L69 7ZF, UK
| | - K Durose
- Stephenson Institute for Renewable Energy, University of Liverpool, Liverpool L69 7ZF, UK
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36
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On the validity of the Čerenkov limit as a criterion for precise band gap measurements by VEELS. Ultramicroscopy 2016; 160:80-83. [DOI: 10.1016/j.ultramic.2015.10.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Revised: 10/05/2015] [Accepted: 10/06/2015] [Indexed: 11/21/2022]
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37
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The Čerenkov limit of Si, GaAs and GaP in electron energy loss spectrometry. Ultramicroscopy 2015; 157:73-8. [DOI: 10.1016/j.ultramic.2015.06.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Revised: 05/29/2015] [Accepted: 06/04/2015] [Indexed: 11/21/2022]
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38
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A short note on how to convert a conventional analytical TEM into an analytical Low Voltage TEM. Ultramicroscopy 2014; 145:94-7. [DOI: 10.1016/j.ultramic.2014.01.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2013] [Revised: 11/29/2013] [Accepted: 01/10/2014] [Indexed: 11/19/2022]
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39
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Low voltage EELS—How low? Ultramicroscopy 2014; 145:98-104. [DOI: 10.1016/j.ultramic.2013.07.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Revised: 06/26/2013] [Accepted: 07/01/2013] [Indexed: 11/23/2022]
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40
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Egerton R, Mcleod R, Malac M. Validity of the dipole approximation in TEM-EELS studies. Microsc Res Tech 2014; 77:773-8. [DOI: 10.1002/jemt.22398] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2014] [Accepted: 06/17/2014] [Indexed: 11/10/2022]
Affiliation(s)
- R.F. Egerton
- Physics Department; University of Alberta; Edmonton Canada T6G 2E1
| | - R.A. Mcleod
- Physics Department; University of Alberta; Edmonton Canada T6G 2E1
- National Institute for Nanotechnology; Edmonton Canada T6G 2M9
| | - M. Malac
- Physics Department; University of Alberta; Edmonton Canada T6G 2E1
- National Institute for Nanotechnology; Edmonton Canada T6G 2M9
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41
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Zhu J, Crozier PA, Ercius P, Anderson JR. Derivation of optical properties of carbonaceous aerosols by monochromated electron energy-loss spectroscopy. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2014; 20:748-759. [PMID: 24735494 DOI: 10.1017/s143192761400049x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Monochromated electron energy-loss spectroscopy (EELS) is employed to determine the optical properties of carbonaceous aerosols from the infrared to the ultraviolet region of the spectrum. It is essential to determine their optical properties to understand their accurate contribution to radiative forcing for climate change. The influence of surface and interface plasmon effects on the accuracy of dielectric data determined from EELS is discussed. Our measurements show that the standard thin film formulation of Kramers-Kronig analysis can be employed to make accurate determination of the dielectric function for carbonaceous particles down to about 40 nm in size. The complex refractive indices of graphitic and amorphous carbon spherules found in the atmosphere were determined over the wavelength range 200-1,200 nm. The graphitic carbon was strongly absorbing black carbon, whereas the amorphous carbon shows a more weakly absorbing brown carbon profile. The EELS approach provides an important tool for exploring the variation in optical properties of atmospheric carbon.
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Affiliation(s)
- Jiangtao Zhu
- 1School for Engineering of Matter,Transport and Energy,Arizona State University,Tempe,AZ 85287,USA
| | - Peter A Crozier
- 1School for Engineering of Matter,Transport and Energy,Arizona State University,Tempe,AZ 85287,USA
| | - Peter Ercius
- 2Lawrence Berkeley National Laboratory,National Center for Electron Microscopy,Berkeley,CA 94720,USA
| | - James R Anderson
- 1School for Engineering of Matter,Transport and Energy,Arizona State University,Tempe,AZ 85287,USA
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Yurtsever A, Couillard M, Hyun JK, Muller DA. Thickness measurements using photonic modes in monochromated electron energy-loss spectroscopy. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2014; 20:723-730. [PMID: 24612729 DOI: 10.1017/s1431927614000245] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Characteristic energies of photonic modes are a sensitive function of a nanostructures' geometrical parameters. In the case of translationally invariant planar waveguides, the eigen-energies reside in the infrared to ultraviolet parts of the optical spectrum and they sensitively depend on the thickness of the waveguide. Using swift electrons and the inherent Cherenkov radiation in dielectrics, the energies of such photonic states can be effectively probed via monochromated electron energy-loss spectroscopy (EELS). Here, by exploiting the strong photonic signals in EELS with 200 keV electrons, we correlate the energies of waveguide peaks in the 0.5-3.5 eV range with planar thicknesses of the samples. This procedure enables us to measure the thicknesses of cross-sectional transmission electron microscopy samples over a 1-500 nm range and with best-case accuracies below ± 2%. The measurements are absolute with the only requirement being the optical dielectric function of the material. Furthermore, we provide empirical formulation for rapid and direct thickness estimations for a 50-500 nm range. We demonstrate the methodology for two semiconducting materials, silicon and gallium arsenide, and discuss how it can be applied to other dielectrics that produce strong optical fingerprints in EELS. The asymptotic form of the loss function for two-dimensional materials is also discussed.
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Affiliation(s)
- Aycan Yurtsever
- 1School of Applied and Engineering Physics,Cornell University,Ithaca,NY 14850,USA
| | - Martin Couillard
- 1School of Applied and Engineering Physics,Cornell University,Ithaca,NY 14850,USA
| | - Jerome K Hyun
- 1School of Applied and Engineering Physics,Cornell University,Ithaca,NY 14850,USA
| | - David A Muller
- 1School of Applied and Engineering Physics,Cornell University,Ithaca,NY 14850,USA
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Jung HJ, Dasgupta NP, Van Stockum PB, Koh AL, Sinclair R, Prinz FB. Spatial variation of available electronic excitations within individual quantum dots. NANO LETTERS 2013; 13:716-721. [PMID: 23276278 DOI: 10.1021/nl304400c] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Quantum dots (QDs) allow for manipulation of the position and energy levels of electrons at sub-10 nm length scales through control of material chemistry, size, and shape. It is known from optical studies that the bandgap of semiconductor QDs increases as their size decreases due to the narrowing of the quantum confinement potential. The mechanism of quantum confinement also indicates that the localized properties within individual QDs should depend on their shape in addition to their size, but direct observations of this effect have proven challenging due to the limited spatial resolution of measurement techniques at this scale and the ability to remove contributions from the surroundings. Here we present experimental evidence of spatial variations in the lowest available electron transition energy within a series of single electrically isolated QDs due to a dome-shaped geometry, measured using electron energy-loss spectroscopy in a (scanning) transmission electron microscope [(S)TEM-EELS]. We observe a consistent increase in the energy onset of electronic excitations from the lateral center of the dot toward the edges, which we attribute purely to shape. This trend is in qualitative agreement with a simple quantum simulation of the local density of states in a dome-shaped QD.
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Affiliation(s)
- Hee Joon Jung
- Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA
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44
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Kadkhodazadeh S. High resolution STEM of quantum dots and quantum wires. Micron 2013; 44:75-92. [DOI: 10.1016/j.micron.2012.10.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Revised: 10/07/2012] [Accepted: 10/08/2012] [Indexed: 11/29/2022]
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45
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Prospects for electron microscopy characterisation of solar cells: opportunities and challenges. Ultramicroscopy 2012; 119:82-96. [PMID: 22209471 DOI: 10.1016/j.ultramic.2011.09.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2011] [Accepted: 09/08/2011] [Indexed: 11/22/2022]
Abstract
Several electron microscopy techniques available for characterising thin-film solar cells are described, including recent advances in instrumentation, such as aberration-correction, monochromators, time-resolved cathodoluminescence and focused ion-beam microscopy. Two generic problems in thin-film solar cell characterisation, namely electrical activity of grain boundaries and 3D morphology of excitionic solar cells, are also discussed from the standpoint of electron microscopy. The opportunities as well as challenges facing application of these techniques to thin-film and excitonic solar cells are highlighted.
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Kaiser U, Biskupek J, Meyer JC, Leschner J, Lechner L, Rose H, Stöger-Pollach M, Khlobystov AN, Hartel P, Müller H, Haider M, Eyhusen S, Benner G. Transmission electron microscopy at 20 kV for imaging and spectroscopy. Ultramicroscopy 2011; 111:1239-46. [PMID: 21801697 DOI: 10.1016/j.ultramic.2011.03.012] [Citation(s) in RCA: 139] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2010] [Revised: 03/10/2011] [Accepted: 03/16/2011] [Indexed: 10/18/2022]
Abstract
The electron optical performance of a transmission electron microscope (TEM) is characterized for direct spatial imaging and spectroscopy using electrons with energies as low as 20 keV. The highly stable instrument is equipped with an electrostatic monochromator and a C(S)-corrector. At 20 kV it shows high image contrast even for single-layer graphene with a lattice transfer of 213 pm (tilted illumination). For 4 nm thick Si, the 200 reflections (271.5 pm) were directly transferred (axial illumination). We show at 20 kV that radiation-sensitive fullerenes (C(60)) within a carbon nanotube container withstand an about two orders of magnitude higher electron dose than at 80 kV. In spectroscopy mode, the monochromated low-energy electron beam enables the acquisition of EELS spectra up to very high energy losses with exceptionally low background noise. Using Si and Ge, we show that 20 kV TEM allows the determination of dielectric properties and narrow band gaps, which were not accessible by TEM so far. These very first results demonstrate that low kV TEM is an exciting new tool for determination of structural and electronic properties of different types of nano-materials.
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Affiliation(s)
- U Kaiser
- Central Facility of Electron Microscopy, Group of Electron Microscopy of Materials Science, Ulm University, Albert-Einstein-Allee 11, 89081 Ulm, Germany.
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47
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Wu CT, Chu MW, Chen LC, Chen KH, Chen CW, Chen CH. Spectroscopic characterizations of individual single-crystalline GaN nanowires in visible/ultra-violet regime. Micron 2010; 41:827-32. [DOI: 10.1016/j.micron.2010.05.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2010] [Revised: 05/04/2010] [Accepted: 05/04/2010] [Indexed: 11/16/2022]
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48
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Low voltage TEM: influences on electron energy loss spectrometry experiments. Micron 2010; 41:577-84. [PMID: 20471277 DOI: 10.1016/j.micron.2010.04.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Revised: 04/02/2010] [Accepted: 04/18/2010] [Indexed: 11/20/2022]
Abstract
We discuss the advantages and disadvantages of electron energy loss spectrometry (EELS) a transmission electron microscope (TEM) at different high tensions. Instrumental effects such as energy resolution, spatial resolution, and point spread function of the detecting system, as well as physical effects like inelastic (Coloumb) delocalization and Cerenkov losses are dealt with. It is found that the actually available equipment is suitable for performing low voltage experiments. The energy resolution of a thermo-ionic emitter can be tremendously improved at lower energies, and the detector also has advantageous behaviour.
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49
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Probing non-dipole allowed excitations in highly correlated materials with nanoscale resolution. Ultramicroscopy 2009; 109:1333-7. [DOI: 10.1016/j.ultramic.2009.06.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2009] [Revised: 06/04/2009] [Accepted: 06/10/2009] [Indexed: 11/17/2022]
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50
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Gu L, Sigle W, Koch CT, Nelayah J, Srot V, van Aken PA. Mapping of valence energy losses via energy-filtered annular dark-field scanning transmission electron microscopy. Ultramicroscopy 2009; 109:1164-70. [DOI: 10.1016/j.ultramic.2009.05.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2008] [Revised: 02/06/2009] [Accepted: 05/01/2009] [Indexed: 11/27/2022]
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