1
|
Oh JS, Jo KJ, Kang MC, An BS, Kwon Y, Lim HW, Cho MH, Baik H, Yang CW. Measurement of dielectric function and bandgap of germanium telluride using monochromated electron energy-loss spectroscopy. Micron 2023; 172:103487. [PMID: 37285687 DOI: 10.1016/j.micron.2023.103487] [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: 03/27/2023] [Revised: 05/16/2023] [Accepted: 05/30/2023] [Indexed: 06/09/2023]
Abstract
Using a monochromator in transmission electron microscopy, a low-energy-loss spectrum can provide inter- and intra-band transition information for nanoscale devices with high energy and spatial resolutions. However, some losses, such as Cherenkov radiation, phonon scattering, and surface plasmon resonance superimposed at zero-loss peak, make it asymmetric. These pose limitations to the direct interpretation of optical properties, such as complex dielectric function and bandgap onset in the raw electron energy-loss spectra. This study demonstrates measuring the dielectric function of germanium telluride using an off-axis electron energy-loss spectroscopy method. The interband transition from the measured complex dielectric function agrees with the calculated band structure of germanium telluride. In addition, we compare the zero-loss subtraction models and propose a reliable routine for bandgap measurement from raw valence electron energy-loss spectra. Using the proposed method, the direct bandgap of germanium telluride thin film was measured from the low-energy-loss spectrum in transmission electron microscopy. The result is in good agreement with the bandgap energy measured using an optical method.
Collapse
Affiliation(s)
- Jin-Su Oh
- School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 16419, the Republic of Korea
| | - Kyu-Jin Jo
- School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 16419, the Republic of Korea
| | - Min-Chul Kang
- School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 16419, the Republic of Korea
| | - Byeong-Seon An
- School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 16419, the Republic of Korea
| | - Yena Kwon
- School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 16419, the Republic of Korea
| | - Hyeon-Wook Lim
- Department of Physics, Yonsei University, Seoul 03722, the Republic of Korea
| | - Mann-Ho Cho
- Department of Physics, Yonsei University, Seoul 03722, the Republic of Korea
| | - Hionsuck Baik
- Seoul Center, Korea Basic Science Institute (KBSI), Seoul 02841, the Republic of Korea
| | - Cheol-Woong Yang
- School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon 16419, the Republic of Korea.
| |
Collapse
|
2
|
Gordeeva A, Thersleff T, Hsu YJ, Liebske C, Ulmer P, Andersson O, Häussermann U. Electronic structure characterization of TiO2-II with the α-PbO2 structure by electron-energy-loss-spectroscopy and comparison with anatase, brookite, and rutile. J SOLID STATE CHEM 2023. [DOI: 10.1016/j.jssc.2023.123952] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/06/2023]
|
3
|
Konečná A, Iyikanat F, García de Abajo FJ. Entangling free electrons and optical excitations. SCIENCE ADVANCES 2022; 8:eabo7853. [PMID: 36427323 PMCID: PMC9699672 DOI: 10.1126/sciadv.abo7853] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Accepted: 10/07/2022] [Indexed: 05/30/2023]
Abstract
The inelastic interaction between flying particles and optical nanocavities gives rise to entangled states in which some excitations of the latter are paired with momentum changes in the former. Specifically, free-electron entanglement with nanocavity modes opens appealing opportunities associated with the strong interaction capabilities of the electrons. However, the achievable degree of entanglement is currently limited by the lack of control over the resulting state mixtures. Here, we propose a scheme to generate pure entanglement between designated optical-cavity excitations and separable free-electron states. We shape the electron wave function profile to select the accessible cavity modes and simultaneously associate them with targeted electron scattering directions. This concept is exemplified through theoretical calculations of free-electron entanglement with degenerate and nondegenerate plasmon modes in silver nanoparticles and atomic vibrations in an inorganic molecule. The generated entanglement can be further propagated through its electron component to extend quantum interactions beyond existing protocols.
Collapse
Affiliation(s)
- Andrea Konečná
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels, Barcelona 08860, Spain
- Central European Institute of Technology, Brno University of Technology, Brno 61200, Czech Republic
| | - Fadil Iyikanat
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels, Barcelona 08860, Spain
| | - F. Javier García de Abajo
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels, Barcelona 08860, Spain
- ICREA-Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spain
| |
Collapse
|
4
|
García de Abajo FJ, Dias EJC, Di Giulio V. Complete Excitation of Discrete Quantum Systems by Single Free Electrons. PHYSICAL REVIEW LETTERS 2022; 129:093401. [PMID: 36083663 DOI: 10.1103/physrevlett.129.093401] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2022] [Accepted: 07/26/2022] [Indexed: 06/15/2023]
Abstract
We reveal a wealth of nonlinear and recoil effects in the interaction between individual low-energy electrons (≲100 eV) and samples comprising a discrete number of states. Adopting a quantum theoretical description of combined free-electron and two-level systems, we find a maximum achievable excitation probability of 100%, which requires specific conditions relating to the coupling strength and the transition symmetry, as we illustrate through calculations for dipolar and quadrupolar modes. Strong recoil effects are observed when the kinetic energy of the probe lies close to the transition threshold, although the associated probability remains independent of the electron wave function even when fully accounting for nonlinear interactions with arbitrarily complex multilevel samples. Our work reveals the potential of free electrons to control localized excitations and delineates the boundaries of such control.
Collapse
Affiliation(s)
- F Javier García de Abajo
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain
- ICREA-Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spain
| | - Eduardo J C Dias
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain
| | - Valerio Di Giulio
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain
| |
Collapse
|
5
|
Yu R, Konečná A, de Abajo FJG. Inelastic Scattering of Electron Beams by Nonreciprocal Nanotructures. PHYSICAL REVIEW LETTERS 2021; 127:157404. [PMID: 34678034 DOI: 10.1103/physrevlett.127.157404] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Accepted: 09/09/2021] [Indexed: 06/13/2023]
Abstract
Probing optical excitations with high resolution is important for understanding their dynamics and controlling their interaction with other photonic elements. This can be done using state-of-the-art electron microscopes, which provide the means to sample optical excitations with combined meV-sub-nm energy-space resolution. For reciprocal photonic systems, electrons traveling in opposite directions produce identical signals, while this symmetry is broken in nonreciprocal structures. Here, we theoretically investigate this phenomenon by analyzing electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) for structures consisting of magnetically biased InAs as an instance of gyrotropic nonreciprocal material. We find that the spectral features associated with excitations of InAs films depend on the electron propagation direction in both EELS and CL, and can be tuned by varying the applied magnetic field within a relatively modest subtesla regime. The magnetic field modifies the optical field distribution of the sampled resonances, and this in turn produces a direction-dependent coupling to the electron. The present results pave the way to the use of electron microscope spectroscopies to explore the near-field characteristics of nonreciprocal systems with high spatial resolution.
Collapse
Affiliation(s)
- Renwen Yu
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain
| | - Andrea Konečná
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain
| | - F Javier García de Abajo
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain
- ICREA-Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spain
| |
Collapse
|
6
|
García
de Abajo FJ, Di Giulio V. Optical Excitations with Electron Beams: Challenges and Opportunities. ACS PHOTONICS 2021; 8:945-974. [PMID: 35356759 PMCID: PMC8939335 DOI: 10.1021/acsphotonics.0c01950] [Citation(s) in RCA: 42] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 02/17/2021] [Accepted: 02/19/2021] [Indexed: 05/20/2023]
Abstract
Free electron beams such as those employed in electron microscopes have evolved into powerful tools to investigate photonic nanostructures with an unrivaled combination of spatial and spectral precision through the analysis of electron energy losses and cathodoluminescence light emission. In combination with ultrafast optics, the emerging field of ultrafast electron microscopy utilizes synchronized femtosecond electron and light pulses that are aimed at the sampled structures, holding the promise to bring simultaneous sub-Å-sub-fs-sub-meV space-time-energy resolution to the study of material and optical-field dynamics. In addition, these advances enable the manipulation of the wave function of individual free electrons in unprecedented ways, opening sound prospects to probe and control quantum excitations at the nanoscale. Here, we provide an overview of photonics research based on free electrons, supplemented by original theoretical insights and discussion of several stimulating challenges and opportunities. In particular, we show that the excitation probability by a single electron is independent of its wave function, apart from a classical average over the transverse beam density profile, whereas the probability for two or more modulated electrons depends on their relative spatial arrangement, thus reflecting the quantum nature of their interactions. We derive first-principles analytical expressions that embody these results and have general validity for arbitrarily shaped electrons and any type of electron-sample interaction. We conclude with some perspectives on various exciting directions that include disruptive approaches to noninvasive spectroscopy and microscopy, the possibility of sampling the nonlinear optical response at the nanoscale, the manipulation of the density matrices associated with free electrons and optical sample modes, and appealing applications in optical modulation of electron beams, all of which could potentially revolutionize the use of free electrons in photonics.
Collapse
Affiliation(s)
- F. Javier García
de Abajo
- ICFO-Institut
de Ciencies Fotoniques, The Barcelona Institute
of Science and Technology, 08860 Castelldefels, Barcelona, Spain
- ICREA-Institució
Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spain
- E-mail:
| | - Valerio Di Giulio
- ICFO-Institut
de Ciencies Fotoniques, The Barcelona Institute
of Science and Technology, 08860 Castelldefels, Barcelona, Spain
| |
Collapse
|
7
|
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.
Collapse
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
| | | | | | | | | | | | | | | | | | | |
Collapse
|
8
|
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
| |
Collapse
|
9
|
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.
Collapse
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
| |
Collapse
|
10
|
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.
Collapse
|
11
|
Granerød CS, Aarseth BL, Nguyen PD, Bazioti C, Azarov A, Svensson BG, Vines L, Prytz Ø. Structural and optical properties of individual Zn 2GeO 4 particles embedded in ZnO. NANOTECHNOLOGY 2019; 30:225702. [PMID: 30743257 DOI: 10.1088/1361-6528/ab061c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Functionalizing transparent conducting oxides (TCOs) is an intriguing approach to expand the tunability and operation of optoelectronic devices. For example, forming nanoparticles that act as quantum wells or barriers in zinc oxide (ZnO), one of the main TCOs today, may expand its optical and electronic tunability. In this work, 800 keV Ge ions have been implanted at a dose of 1 × 1016 cm-2 into crystalline ZnO. After annealing at 1000 °C embedded disk-shaped particles with diameters up to 100 nm are formed. Scanning transmission electron microscopy shows that these are particles of the trigonal Zn2GeO4 phase. The particles are terminated by atomically sharp facets of the type {11 [Formula: see text] 0}, and the interface between the matrix and particles is decorated with misfit dislocations in order to accommodate the lattice mismatch between the two crystals. Electron energy loss spectroscopy has been employed to measure the band gap of individual nanoparticles, showing an onset of band-to-band transitions at 5.03 ± 0.02 eV. This work illustrates the advantages of using STEM characterization methods, where information of structure, growth, and properties can be directly obtained.
Collapse
|
12
|
Zhan W, Kosinskiy AY, Vines L, Johansen KM, Carvalho PA, Prytz Ø. ZnCr₂O₄ Inclusions in ZnO Matrix Investigated by Probe-Corrected STEM-EELS. MATERIALS (BASEL, SWITZERLAND) 2019; 12:ma12060888. [PMID: 30884841 PMCID: PMC6471317 DOI: 10.3390/ma12060888] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Revised: 03/12/2019] [Accepted: 03/13/2019] [Indexed: 06/09/2023]
Abstract
The ZnCr₂O₄/ZnO materials system has a wide range of potential applications, for example, as a photocatalytic material for waste-water treatment and gas sensing. In this study, probe-corrected high-resolution scanning transmission electron microscopy and geometric phase analysis were utilized to study the dislocation structure and strain distribution at the interface between zinc oxide (ZnO) and embedded zinc chromium oxide (ZnCr₂O₄) particles. Ball-milled and dry-pressed ZnO and chromium oxide (α-Cr₂O₃) powder formed ZnCr₂O₄ inclusions in ZnO with size ~400 nm, where the interface properties depended on the interface orientation. In particular, sharp interfaces were observed for ZnO [2113]/ZnCr₂O₄ [110] orientations, while ZnO [1210]/ZnCr₂O₄ [112] orientations revealed an interface over several atomic layers, with a high density of dislocations. Further, monochromated electron energy-loss spectroscopy was employed to map the optical band gap of ZnCr₂O₄ nanoparticles in the ZnO matrix and their interface, where the average band gap of ZnCr₂O4 nanoparticles was measured to be 3.84 ± 0.03 eV, in contrast to 3.22 ± 0.01 eV for the ZnO matrix.
Collapse
Affiliation(s)
- Wei Zhan
- Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, N-0316 Oslo, Norway.
| | - Andrey Yurievich Kosinskiy
- Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, N-0316 Oslo, Norway.
| | - Lasse Vines
- Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, N-0316 Oslo, Norway.
| | - Klaus Magnus Johansen
- Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, N-0316 Oslo, Norway.
| | | | - Øystein Prytz
- Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, N-0316 Oslo, Norway.
| |
Collapse
|
13
|
Wang S, Xu HD, Cai J, Wang YP, Tao HL, Cui Y, He M, Song B, Zhang ZH. Electronic structure of multiferroic BiFeO 3: Electron energy-loss spectroscopy and first-principles study. Micron 2019; 120:43-47. [PMID: 30763879 DOI: 10.1016/j.micron.2019.01.012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2019] [Revised: 01/30/2019] [Accepted: 01/30/2019] [Indexed: 10/27/2022]
Abstract
The electronic structure of BiFeO3 has been investigated by using electron energy loss spectrum and first-principle calculations. Assignments of the individual interband transitions have been accomplished by comparing the interband transition energy with the calculated PDOS. The DOS is mainly divided into two regions, the hybridized region of O 2p with Fe 3p in the valence band and that of O 2p hybridized with Bi 6p in the conduction band. From the simulation of high energy-loss near-edge structure, the core-hole effect is believed to be more significant. The feature groups for the experimental spectra of O K-edge and Fe L2,3-edge are consistent with simulation results.
Collapse
Affiliation(s)
- S Wang
- School of Materials Science and Engineering, Dalian Jiaotong University, Dalian, 116028, PR China
| | - H D Xu
- School of Materials Science and Engineering, Dalian Jiaotong University, Dalian, 116028, PR China
| | - J Cai
- School of Physics and Electronic Technology, Liaoning Normal University, Dalian, 116029, PR China
| | - Y P Wang
- School of Materials Science and Engineering, Dalian Jiaotong University, Dalian, 116028, PR China
| | - H L Tao
- School of Materials Science and Engineering, Dalian Jiaotong University, Dalian, 116028, PR China
| | - Y Cui
- School of Materials Science and Engineering, Dalian Jiaotong University, Dalian, 116028, PR China
| | - M He
- School of Materials Science and Engineering, Dalian Jiaotong University, Dalian, 116028, PR China
| | - B Song
- Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin, 150080, PR China
| | - Z H Zhang
- School of Materials Science and Engineering, Dalian Jiaotong University, Dalian, 116028, PR China.
| |
Collapse
|
14
|
Bologna N, Wirths S, Francaviglia L, Campanini M, Schmid H, Theofylaktopoulos V, Moselund KE, Fontcuberta I Morral A, Erni R, Riel H, Rossell MD. Dopant-Induced Modifications of Ga xIn (1- x)P Nanowire-Based p-n Junctions Monolithically Integrated on Si(111). ACS APPLIED MATERIALS & INTERFACES 2018; 10:32588-32596. [PMID: 30160109 DOI: 10.1021/acsami.8b10770] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Today, silicon is the most used material in photovoltaics, with the maximum conversion efficiency getting very close to the Shockley-Queisser limit for single-junction devices. Integrating silicon with higher band-gap ternary III-V absorbers is the path to increase the conversion efficiency. Here, we report on the first monolithic integration of Ga xIn(1- x)P vertical nanowires, and the associated p-n junctions, on silicon by the Au-free template-assisted selective epitaxy (TASE) method. We demonstrate that TASE allows for a high chemical homogeneity of ternary alloys through the nanowires. We then show the influence of doping on the chemical composition and crystal phase, the latter previously attributed to the role of the contact angle in the liquid phase in the vapor-liquid-solid technique. Finally, the emission of the p-n junction is investigated, revealing a shift in the energy of the intraband levels due to the incorporation of dopants. These results clarify some open questions on the effects of doping on ternary III-V nanowire growth and provide the path toward their integration on the silicon platform in order to apply them in next-generation photovoltaic and optoelectronic devices.
Collapse
Affiliation(s)
- Nicolas Bologna
- Electron Microscopy Center , Empa, Swiss Federal Laboratories for Materials Science and Technology , Dübendorf 8600 , Switzerland
- IBM Research-Zurich , Rüschlikon 8803 , Switzerland
| | | | | | - Marco Campanini
- Electron Microscopy Center , Empa, Swiss Federal Laboratories for Materials Science and Technology , Dübendorf 8600 , Switzerland
| | - Heinz Schmid
- IBM Research-Zurich , Rüschlikon 8803 , Switzerland
| | | | | | | | - Rolf Erni
- Electron Microscopy Center , Empa, Swiss Federal Laboratories for Materials Science and Technology , Dübendorf 8600 , Switzerland
| | - Heike Riel
- IBM Research-Zurich , Rüschlikon 8803 , Switzerland
| | - Marta D Rossell
- Electron Microscopy Center , Empa, Swiss Federal Laboratories for Materials Science and Technology , Dübendorf 8600 , Switzerland
- IBM Research-Zurich , Rüschlikon 8803 , Switzerland
| |
Collapse
|
15
|
Walther T. Comment on 'Nanoscale mapping of optical band gaps using monochromated electron energy loss spectroscopy'. NANOTECHNOLOGY 2018; 29:318001. [PMID: 29457780 DOI: 10.1088/1361-6528/aab07c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Affiliation(s)
- Thomas Walther
- Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield, United Kingdom
| |
Collapse
|
16
|
Exploring the capabilities of monochromated electron energy loss spectroscopy in the infrared regime. Sci Rep 2018; 8:5637. [PMID: 29618757 PMCID: PMC5884780 DOI: 10.1038/s41598-018-23805-5] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2018] [Accepted: 03/19/2018] [Indexed: 11/09/2022] Open
Abstract
Monochromated electron energy loss spectroscopy (EELS) is one of the leading techniques to study materials properties that correspond to low (<5 eV) energy losses (i.e. band-gaps, plasmons, and excitons) with nanoscale spatial resolution. Recently a new generation of monochromators have become available, opening regimes and unlocking excitations that were previously unobservable in the electron microscope. The capabilities of these new instruments are still being explored, and here we study the effect of monochromation on various aspects of EELS analysis in the infrared (<1 eV) regime. We investigate the effect of varying levels of monochromation on energy resolution, zero-loss peak (ZLP) tail reduction, ZLP tail shape, signal-to-noise-ratio, and spatial resolution. From these experiments, the new capabilities of monochromated EELS are shown to be highly promising for the future of localized spectroscopic analysis.
Collapse
|
17
|
Zhan W, Venkatachalapathy V, Aarholt T, Kuznetsov AY, Prytz Ø. Band gap maps beyond the delocalization limit: correlation between optical band gaps and plasmon energies at the nanoscale. Sci Rep 2018; 8:848. [PMID: 29339788 PMCID: PMC5770386 DOI: 10.1038/s41598-017-18949-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2017] [Accepted: 12/20/2017] [Indexed: 11/16/2022] Open
Abstract
Recent progresses in nanoscale semiconductor technology have heightened the need for measurements of band gaps with high spatial resolution. Band gap mapping can be performed through a combination of probe-corrected scanning transmission electron microscopy (STEM) and monochromated electron energy-loss spectroscopy (EELS), but are rare owing to the complexity of the experiments and the data analysis. Furthermore, although this method is far superior in terms of spatial resolution to any other techniques, it is still fundamentally resolution-limited due to inelastic delocalization of the EELS signal. In this work we have established a quantitative correlation between optical band gaps and plasmon energies using the Zn1−xCdxO/ZnO system as an example, thereby side-stepping the fundamental resolution limits of band gap measurements, and providing a simple and convenient approach to achieve band gap maps with unprecedented spatial resolution.
Collapse
Affiliation(s)
- Wei Zhan
- Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, P.O. Box 1048 Blindern, N-0316, Oslo, Norway
| | - Vishnukanthan Venkatachalapathy
- Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, P.O. Box 1048 Blindern, N-0316, Oslo, Norway
| | - Thomas Aarholt
- Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, P.O. Box 1048 Blindern, N-0316, Oslo, Norway
| | - Andrej Yu Kuznetsov
- Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, P.O. Box 1048 Blindern, N-0316, Oslo, Norway
| | - Øystein Prytz
- Department of Physics, Centre for Materials Science and Nanotechnology, University of Oslo, P.O. Box 1048 Blindern, N-0316, Oslo, Norway.
| |
Collapse
|
18
|
Granerød CS, Zhan W, Prytz Ø. Automated approaches for band gap mapping in STEM-EELS. Ultramicroscopy 2018; 184:39-45. [DOI: 10.1016/j.ultramic.2017.08.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Revised: 07/06/2017] [Accepted: 08/15/2017] [Indexed: 11/24/2022]
|
19
|
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.
Collapse
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
| |
Collapse
|
20
|
Azizi A, Wang Y, Lin Z, Wang K, Elias AL, Terrones M, Crespi VH, Alem N. Spontaneous Formation of Atomically Thin Stripes in Transition Metal Dichalcogenide Monolayers. NANO LETTERS 2016; 16:6982-6987. [PMID: 27673342 DOI: 10.1021/acs.nanolett.6b03075] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Whether an alloy is random or ordered can have profound effects on its properties. The close chemical similarity of W and Mo in the two-dimensional semiconductors MoS2 and WS2 has led to the expectation that WxMo1-xS2 is a random alloy. Here we report that triangular monolayer flakes of WxMo1-xS2 produced by sulfurization of MoO3/WO3 are not only nonrandom, but also anisotropic: W and Mo form atomically thin chains oriented parallel to the edges of the triangle, especially around x ∼ 0.5, as resolved by aberration-corrected transmission electron microscopy. First-principles calculations reveal that the binding energies of striped and random alloys are nearly identical but that phase segregation at the growth edge favors one metal over another depending on the local sulfur availability, independent of the composition deeper inside the monolayer. Thus, atomically thin striping is kinetically driven and controlled by fluctuations that couple the local chemical potentials of metals and chalcogenide. Considering the nearly identical electronic properties but very different atomic masses of Mo and W, the resulting striped alloy is electronically isotropic, but vibrationally anisotropic. Phonon anomalies associated with the stripe ordering are predicted, as is an anisotropic thermal conductivity. More generally, fluctuation-driven striping provides a mechanism to produce in-plane subnanometer superlattices within two-dimensional crystals, with broad implications for controlling the electronic, optical, and structural properties of these systems.
Collapse
Affiliation(s)
- Amin Azizi
- Department of Materials Science and Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Center for Two-Dimensional and Layered Materials, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Materials Research Institute, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Yuanxi Wang
- Center for Two-Dimensional and Layered Materials, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Materials Research Institute, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Department of Physics, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Zhong Lin
- Center for Two-Dimensional and Layered Materials, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Department of Physics, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Center for Atomically Thin Multifunctional Coatings (ATOMIC), The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Ke Wang
- Materials Research Institute, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Ana Laura Elias
- Center for Two-Dimensional and Layered Materials, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Department of Physics, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Center for Atomically Thin Multifunctional Coatings (ATOMIC), The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Mauricio Terrones
- Department of Materials Science and Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Center for Two-Dimensional and Layered Materials, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Materials Research Institute, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Department of Physics, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Department of Chemistry, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Center for Atomically Thin Multifunctional Coatings (ATOMIC), The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Vincent H Crespi
- Department of Materials Science and Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Center for Two-Dimensional and Layered Materials, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Materials Research Institute, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Department of Physics, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Department of Chemistry, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Nasim Alem
- Department of Materials Science and Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Center for Two-Dimensional and Layered Materials, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Materials Research Institute, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| |
Collapse
|
21
|
Suslu A, Wu K, Sahin H, Chen B, Yang S, Cai H, Aoki T, Horzum S, Kang J, Peeters FM, Tongay S. Unusual dimensionality effects and surface charge density in 2D Mg(OH)2. Sci Rep 2016; 6:20525. [PMID: 26846617 PMCID: PMC4742812 DOI: 10.1038/srep20525] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Accepted: 01/05/2016] [Indexed: 11/08/2022] Open
Abstract
We present two-dimensional Mg(OH)2 sheets and their vertical heterojunctions with CVD-MoS2 for the first time as flexible 2D insulators with anomalous lattice vibration and chemical and physical properties. New hydrothermal crystal growth technique enabled isolation of environmentally stable monolayer Mg(OH)2 sheets. Raman spectroscopy and vibrational calculations reveal that the lattice vibrations of Mg(OH)2 have fundamentally different signature peaks and dimensionality effects compared to other 2D material systems known to date. Sub-wavelength electron energy-loss spectroscopy measurements and theoretical calculations show that Mg(OH)2 is a 6 eV direct-gap insulator in 2D, and its optical band gap displays strong band renormalization effects from monolayer to bulk, marking the first experimental confirmation of confinement effects in 2D insulators. Interestingly, 2D-Mg(OH)2 sheets possess rather strong surface polarization (charge) effects which is in contrast to electrically neutral h-BN materials. Using 2D-Mg(OH)2 sheets together with CVD-MoS2 in the vertical stacking shows that a strong change transfer occurs from n-doped CVD-MoS2 sheets to Mg(OH)2, naturally depleting the semiconductor, pushing towards intrinsic doping limit and enhancing overall optical performance of 2D semiconductors. Results not only establish unusual confinement effects in 2D-Mg(OH)2, but also offer novel 2D-insulating material with unique physical, vibrational, and chemical properties for potential applications in flexible optoelectronics.
Collapse
Affiliation(s)
- Aslihan Suslu
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, 85287, USA
| | - Kedi Wu
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, 85287, USA
| | - Hasan Sahin
- Department of Physics, University of Antwerp, Campus Groenenborger, Groenenborgerlaan 171, 2020, Antwerp, Belgium
| | - Bin Chen
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, 85287, USA
| | - Sijie Yang
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, 85287, USA
| | - Hui Cai
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, 85287, USA
| | - Toshihiro Aoki
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, 85287, USA
- LeRoy Eyring Center for Solid State Science, Arizona State University, Tempe, AZ 85287, USA
| | - Seyda Horzum
- Department of Physics, University of Antwerp, Campus Groenenborger, Groenenborgerlaan 171, 2020, Antwerp, Belgium
| | - Jun Kang
- Department of Physics, University of Antwerp, Campus Groenenborger, Groenenborgerlaan 171, 2020, Antwerp, Belgium
| | - Francois M. Peeters
- Department of Physics, University of Antwerp, Campus Groenenborger, Groenenborgerlaan 171, 2020, Antwerp, Belgium
| | - Sefaattin Tongay
- School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, 85287, USA
| |
Collapse
|
22
|
MÁNUEL J, KOCH C, ÖZDÖL V, SIGLE W, VAN AKEN P, GARCÍA R, MORALES F. Inline electron holography and VEELS for the measurement of strain in ternary and quaternary (In,Al,Ga)N alloyed thin films and its effect on bandgap energy. J Microsc 2016; 261:27-35. [DOI: 10.1111/jmi.12312] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2015] [Accepted: 07/26/2015] [Indexed: 11/28/2022]
Affiliation(s)
- J.M. MÁNUEL
- IMEYMAT: Institute of Research on Electron Microscopy and Materials of the University of Cádiz; Cádiz Spain
| | - C.T. KOCH
- Department of Physics; Humboldt University; Berlin Germany
| | - V.B. ÖZDÖL
- National Center for Electron Microscopy; Lawrence Berkeley National Laboratory; Berkeley California U.S.A
| | - W. SIGLE
- Stuttgart Center for Electron Microscopy; Max Planck Institute for Solid State Research; Germany
| | - P.A. VAN AKEN
- Stuttgart Center for Electron Microscopy; Max Planck Institute for Solid State Research; Germany
| | - R. GARCÍA
- IMEYMAT: Institute of Research on Electron Microscopy and Materials of the University of Cádiz; Cádiz Spain
| | - F.M. MORALES
- IMEYMAT: Institute of Research on Electron Microscopy and Materials of the University of Cádiz; Cádiz Spain
| |
Collapse
|
23
|
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]
|
24
|
Dixit H, Beekman C, Schlepütz CM, Siemons W, Yang Y, Senabulya N, Clarke R, Chi M, Christen HM, Cooper VR. Understanding Strain-Induced Phase Transformations in BiFeO 3 Thin Films. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2015; 2:1500041. [PMID: 27980962 PMCID: PMC5115423 DOI: 10.1002/advs.201500041] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Revised: 04/30/2015] [Indexed: 05/12/2023]
Abstract
Experiments demonstrate that under large epitaxial strain a coexisting striped phase emerges in BiFeO3 thin films, which comprises a tetragonal-like (T') and an intermediate S' polymorph. It exhibits a relatively large piezoelectric response when switching between the coexisting phase and a uniform T' phase. This strain-induced phase transformation is investigated through a synergistic combination of first-principles theory and experiments. The results show that the S' phase is energetically very close to the T' phase, but is structurally similar to the bulk rhombohedral (R) phase. By fully characterizing the intermediate S' polymorph, it is demonstrated that the flat energy landscape resulting in the absence of an energy barrier between the T' and S' phases fosters the above-mentioned reversible phase transformation. This ability to readily transform between the S' and T' polymorphs, which have very different octahedral rotation patterns and c/a ratios, is crucial to the enhanced piezoelectricity in strained BiFeO3 films. Additionally, a blueshift in the band gap when moving from R to S' to T' is observed. These results emphasize the importance of strain engineering for tuning electromechanical responses or, creating unique energy harvesting photonic structures, in oxide thin film architectures.
Collapse
Affiliation(s)
- Hemant Dixit
- Materials Science and Technology Division Oak Ridge National Lab Oak Ridge TN 37831 USA
| | - Christianne Beekman
- Materials Science and Technology Division Oak Ridge National Lab Oak Ridge TN 37831 USA
| | | | - Wolter Siemons
- Materials Science and Technology Division Oak Ridge National Lab Oak Ridge TN 37831 USA
| | - Yongsoo Yang
- Department of Physics University of Michigan Ann Arbor MI 48109 USA
| | - Nancy Senabulya
- Department of Physics University of Michigan Ann Arbor MI 48109 USA
| | - Roy Clarke
- Department of Physics University of Michigan Ann Arbor MI 48109 USA
| | - Miaofang Chi
- Center for Nanophase Materials Sciences Oak Ridge National Lab Oak Ridge TN 37830 USA
| | - Hans M Christen
- Center for Nanophase Materials Sciences Oak Ridge National Lab Oak Ridge TN 37830 USA
| | - Valentino R Cooper
- Materials Science and Technology Division Oak Ridge National Lab Oak Ridge TN 37831 USA
| |
Collapse
|
25
|
Ke X, Bittencourt C, Van Tendeloo G. Possibilities and limitations of advanced transmission electron microscopy for carbon-based nanomaterials. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2015; 6:1541-57. [PMID: 26425406 PMCID: PMC4578338 DOI: 10.3762/bjnano.6.158] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2015] [Accepted: 06/25/2015] [Indexed: 05/28/2023]
Abstract
A major revolution for electron microscopy in the past decade is the introduction of aberration correction, which enables one to increase both the spatial resolution and the energy resolution to the optical limit. Aberration correction has contributed significantly to the imaging at low operating voltages. This is crucial for carbon-based nanomaterials which are sensitive to electron irradiation. The research of carbon nanomaterials and nanohybrids, in particular the fundamental understanding of defects and interfaces, can now be carried out in unprecedented detail by aberration-corrected transmission electron microscopy (AC-TEM). This review discusses new possibilities and limits of AC-TEM at low voltage, including the structural imaging at atomic resolution, in three dimensions and spectroscopic investigation of chemistry and bonding. In situ TEM of carbon-based nanomaterials is discussed and illustrated through recent reports with particular emphasis on the underlying physics of interactions between electrons and carbon atoms.
Collapse
Affiliation(s)
- Xiaoxing Ke
- EMAT, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
- Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing 100124, China
| | - Carla Bittencourt
- Chemistry of Interaction Plasma Surface (ChiPS), University of Mons, Place du Parc 20, 7000 Mons, Belgium
| | | |
Collapse
|
26
|
Logar M, Xu S, Acharya S, Prinz FB. Variation of energy density of states in quantum dot arrays due to interparticle electronic coupling. NANO LETTERS 2015; 15:1855-1860. [PMID: 25670055 DOI: 10.1021/nl5046507] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Subnanometer-resolved local electron energy structure was measured in PbS quantum dot superlattice arrays using valence electron energy loss spectroscopy with scanning transmission electron microscopy. We found smaller values of the lowest available transition energies and an increased density of electronic states in the space between quantum dots with shorter interparticle spacing, indicating extension of carrier wave functions as a result of interparticle electronic coupling. A quantum simulation verified both trends and illustrated the wave function extension effect.
Collapse
Affiliation(s)
- Manca Logar
- Department of Mechanical Engineering and ‡Department of Material Science and Engineering, Stanford University , Stanford, California 94305, United States
| | | | | | | |
Collapse
|
27
|
Park GS, Park SY, Heo S, Kwon O, Cho K, Han KY, Kang SJ, Yoon A, Kim M. Origin of leakage paths driven by electric fields in Al-doped TiO2 films. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2014; 26:8225-8230. [PMID: 25366700 DOI: 10.1002/adma.201403647] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2014] [Revised: 09/26/2014] [Indexed: 06/04/2023]
Abstract
The growth of leakage current paths in Al-doped TiO2 (ATO) films is observed by in situ TEM under negative bias stress. Through systematic HAADF-STEM, STEM-EDS, and STEM-EELS studies, it is confirmed that the electric field-induced growth of the Ru-doped TiO2 phase is the main reason for the ATO film's negative leakage.
Collapse
Affiliation(s)
- Gyeong-Su Park
- Samsung Advanced Institute of Technology, San 14-1, Nongseo-Ri, Kiheung-Eub, Yongin-Si, Kyeonggi-Do, 446-712, South Korea
| | | | | | | | | | | | | | | | | |
Collapse
|
28
|
WALTHER T. Electron microscopy of quantum dots. J Microsc 2014; 257:171-8. [PMID: 25406030 DOI: 10.1111/jmi.12196] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2014] [Accepted: 10/16/2014] [Indexed: 11/30/2022]
Affiliation(s)
- T. WALTHER
- Department of Electronic & Electrical Engineering; University of Sheffield; Sheffield S1 3JD U.K
| |
Collapse
|
29
|
Keller D, Buecheler S, Reinhard P, Pianezzi F, Pohl D, Surrey A, Rellinghaus B, Erni R, Tiwari AN. Local band gap measurements by VEELS of thin film solar cells. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2014; 20:1246-1253. [PMID: 24690441 DOI: 10.1017/s1431927614000543] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
This work presents a systematic study that evaluates the feasibility and reliability of local band gap measurements of Cu(In,Ga)Se2 thin films by valence electron energy-loss spectroscopy (VEELS). The compositional gradients across the Cu(In,Ga)Se2 layer cause variations in the band gap energy, which are experimentally determined using a monochromated scanning transmission electron microscope (STEM). The results reveal the expected band gap variation across the Cu(In,Ga)Se2 layer and therefore confirm the feasibility of local band gap measurements of Cu(In,Ga)Se2 by VEELS. The precision and accuracy of the results are discussed based on the analysis of individual error sources, which leads to the conclusion that the precision of our measurements is most limited by the acquisition reproducibility, if the signal-to-noise ratio of the spectrum is high enough. Furthermore, we simulate the impact of radiation losses on the measured band gap value and propose a thickness-dependent correction. In future work, localized band gap variations will be measured on a more localized length scale to investigate, e.g., the influence of chemical inhomogeneities and dopant accumulations at grain boundaries.
Collapse
Affiliation(s)
- Debora Keller
- 1Empa-Swiss Federal Laboratories for Materials Science and Technology,Laboratory for Thin Films and Photovoltaics,Ueberlandstrasse 129,CH-8600 Duebendorf,Switzerland
| | - Stephan Buecheler
- 1Empa-Swiss Federal Laboratories for Materials Science and Technology,Laboratory for Thin Films and Photovoltaics,Ueberlandstrasse 129,CH-8600 Duebendorf,Switzerland
| | - Patrick Reinhard
- 1Empa-Swiss Federal Laboratories for Materials Science and Technology,Laboratory for Thin Films and Photovoltaics,Ueberlandstrasse 129,CH-8600 Duebendorf,Switzerland
| | - Fabian Pianezzi
- 1Empa-Swiss Federal Laboratories for Materials Science and Technology,Laboratory for Thin Films and Photovoltaics,Ueberlandstrasse 129,CH-8600 Duebendorf,Switzerland
| | - Darius Pohl
- 3Institute for Metallic Materials,IFW Dresden,P.O. Box 270116,D-01171 Dresden,Germany
| | - Alexander Surrey
- 3Institute for Metallic Materials,IFW Dresden,P.O. Box 270116,D-01171 Dresden,Germany
| | - Bernd Rellinghaus
- 3Institute for Metallic Materials,IFW Dresden,P.O. Box 270116,D-01171 Dresden,Germany
| | - Rolf Erni
- 2Empa-Swiss Federal Laboratories for Materials Science and Technology,Electron Microscopy Center,Ueberlandstrasse 129,CH-8600 Duebendorf,Switzerland
| | - Ayodhya N Tiwari
- 1Empa-Swiss Federal Laboratories for Materials Science and Technology,Laboratory for Thin Films and Photovoltaics,Ueberlandstrasse 129,CH-8600 Duebendorf,Switzerland
| |
Collapse
|
30
|
Zhang Y, Utke I, Michler J, Ilari G, Rossell MD, Erni R. Growth and characterization of CNT-TiO2 heterostructures. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2014; 5:946-55. [PMID: 25161830 PMCID: PMC4142836 DOI: 10.3762/bjnano.5.108] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2014] [Accepted: 06/12/2014] [Indexed: 05/28/2023]
Abstract
A thriving field in nanotechnology is to develop synergetic functions of nanomaterials by taking full advantages of unique properties of each component. In this context, combining TiO2 nanocrystals and carbon nanotubes (CNTs) offers enhanced photosensitivity and improved photocatalytic efficiency, which is key to achieving sustainable energy and preventing environmental pollution. Hence, it has aroused a tremendous research interest. This report surveys recent research on the topic of synthesis and characterization of the CNT-TiO2 interface. In particular, atomic layer deposition (ALD) offers a good control of the size, crystallinity and morphology of TiO2 on CNTs. Analytical transmission electron microscopy (TEM) techniques such as electron energy loss spectroscopy (EELS) in scanning transmission mode provides structural, chemical and electronic information with an unprecedented spatial resolution and increasingly superior energy resolution, and hence is a necessary tool to characterize the CNT-TiO2 interface, as well as other technologically relevant CNT-metal/metal oxide material systems.
Collapse
Affiliation(s)
- Yucheng Zhang
- Electron Microscopy Center, EMPA, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
| | - Ivo Utke
- Laboratory of Mechanics of Materials and Nanostructure, EMPA, Swiss Federal Laboratories for Materials Science and Technology, Feuerwerkstrasse 39, CH-3602 Thun, Switzerland
| | - Johann Michler
- Laboratory of Mechanics of Materials and Nanostructure, EMPA, Swiss Federal Laboratories for Materials Science and Technology, Feuerwerkstrasse 39, CH-3602 Thun, Switzerland
| | - Gabriele Ilari
- Electron Microscopy Center, EMPA, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
| | - Marta D Rossell
- Electron Microscopy Center, EMPA, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
| | - Rolf Erni
- Electron Microscopy Center, EMPA, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland
| |
Collapse
|
31
|
Dennenwaldt T, Ciston J, Dahmen U, Ching WY, Pucher FJ, Schnick W, Scheu C. High-resolution spectroscopy of bonding in a novel BeP2N4 compound. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2014; 20:664-670. [PMID: 24698285 DOI: 10.1017/s1431927614000713] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The recently discovered compound BeP2N4 that crystallizes in the phenakite-type structure has potential application as a high strength optoelectronic material. Therefore, it is important to analyze experimentally the electronic structure, which was done in the present work by monochromated electron energy-loss spectroscopy. The detection of Be is challenging due to its low atomic number and easy removal under electron bombardment. We were able to determine the bonding behavior and coordination of the individual atomic species including Be. This is evident from a good agreement between experimental electron energy-loss near-edge structures of the Be-K-, P-L2,3-, and N-K-edges and density functional theory calculations.
Collapse
Affiliation(s)
- Teresa Dennenwaldt
- 1Department of Chemistry and Center for NanoScience,Ludwig-Maximilians-Universität München,Butenandtstr. 5-13,81377 Munich,Germany
| | - Jim Ciston
- 2Lawrence Berkeley National Laboratory,National Center for Electron Microscopy,Berkeley,CA 94720,USA
| | - Ulrich Dahmen
- 2Lawrence Berkeley National Laboratory,National Center for Electron Microscopy,Berkeley,CA 94720,USA
| | - Wai-Yim Ching
- 3Department of Physics and Astronomy,University of Missouri-Kansas City,Kansas City,MO 64110,USA
| | - Florian J Pucher
- 1Department of Chemistry and Center for NanoScience,Ludwig-Maximilians-Universität München,Butenandtstr. 5-13,81377 Munich,Germany
| | - Wolfgang Schnick
- 1Department of Chemistry and Center for NanoScience,Ludwig-Maximilians-Universität München,Butenandtstr. 5-13,81377 Munich,Germany
| | - Christina Scheu
- 1Department of Chemistry and Center for NanoScience,Ludwig-Maximilians-Universität München,Butenandtstr. 5-13,81377 Munich,Germany
| |
Collapse
|
32
|
Kiewidt L, Karamehmedović M, Matyssek C, Hergert W, Mädler L, Wriedt T. Numerical simulation of Electron Energy Loss Spectroscopy using a Generalized Multipole Technique. Ultramicroscopy 2013; 133:101-8. [DOI: 10.1016/j.ultramic.2013.07.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Revised: 06/11/2013] [Accepted: 07/02/2013] [Indexed: 10/26/2022]
|
33
|
Keast V. An introduction to the calculation of valence EELS: Quantum mechanical methods for bulk solids. Micron 2013; 44:93-100. [DOI: 10.1016/j.micron.2012.08.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Accepted: 08/02/2012] [Indexed: 11/30/2022]
|
34
|
Zhou W, Oxley MP, Lupini AR, Krivanek OL, Pennycook SJ, Idrobo JC. Single atom microscopy. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2012; 18:1342-1354. [PMID: 23146658 DOI: 10.1017/s1431927612013335] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We show that aberration-corrected scanning transmission electron microscopy operating at low accelerating voltages is able to analyze, simultaneously and with single atom resolution and sensitivity, the local atomic configuration, chemical identities, and optical response at point defect sites in monolayer graphene. Sequential fast-scan annular dark-field (ADF) imaging provides direct visualization of point defect diffusion within the graphene lattice, with all atoms clearly resolved and identified via quantitative image analysis. Summing multiple ADF frames of stationary defects produce images with minimized statistical noise and reduced distortions of atomic positions. Electron energy-loss spectrum imaging of single atoms allows the delocalization of inelastic scattering to be quantified, and full quantum mechanical calculations are able to describe the delocalization effect with good accuracy. These capabilities open new opportunities to probe the defect structure, defect dynamics, and local optical properties in 2D materials with single atom sensitivity.
Collapse
Affiliation(s)
- Wu Zhou
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
| | | | | | | | | | | |
Collapse
|
35
|
Eljarrat A, Estradé S, Gačević Z, Fernández-Garrido S, Calleja E, Magén C, Peiró F. Optoelectronic properties of InAlN/GaN distributed bragg reflector heterostructure examined by valence electron energy loss spectroscopy. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2012; 18:1143-1154. [PMID: 23058502 DOI: 10.1017/s1431927612001328] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
High-resolution monochromated electron energy loss spectroscopy (EELS) at subnanometric spatial resolution and <200 meV energy resolution has been used to assess the valence band properties of a distributed Bragg reflector multilayer heterostructure composed of InAlN lattice matched to GaN. This work thoroughly presents the collection of methods and computational tools put together for this task. Among these are zero-loss-peak subtraction and nonlinear fitting tools, and theoretical modeling of the electron scattering distribution. EELS analysis allows retrieval of a great amount of information: indium concentration in the InAlN layers is monitored through the local plasmon energy position and calculated using a bowing parameter version of Vegard Law. Also a dielectric characterization of the InAlN and GaN layers has been performed through Kramers-Kronig analysis of the Valence-EELS data, allowing band gap energy to be measured and an insight on the polytypism of the GaN layers.
Collapse
Affiliation(s)
- A Eljarrat
- Laboratory of Electron NanoScopies, LENS-MIND-IN2UB, Dept. Electrónica, Universitat de Barcelona, Marti i Franqués 1, Barcelona, Spain.
| | | | | | | | | | | | | |
Collapse
|
36
|
Aguiar JA, Reed BW, Ramasse QM, Erni R, Browning ND. Quantifying the low-energy limit and spectral resolution in valence electron energy loss spectroscopy. Ultramicroscopy 2012; 124:130-8. [PMID: 23154033 DOI: 10.1016/j.ultramic.2012.08.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Revised: 08/15/2012] [Accepted: 08/18/2012] [Indexed: 11/30/2022]
Abstract
While the development of monochromators for scanning transmission electron microscopes (STEM) has improved our ability to resolve spectral features in the 0-5 eV energy range of the electron energy loss spectrum, the overall benefits relative to unfiltered microscopes have been difficult to quantify. Simple curve fitting and reciprocal space models that extrapolate the expected behavior of the zero-loss peak are not enough to fully exploit the optimal spectral limit and can hinder the ease of interpreting the resulting spectra due to processing-induced artifacts. To address this issue, here we present a quantitative comparison of two processing methods for performing ZLP removal and for defining the low-energy spectral limit applied to three microscopes with different intrinsic emission and energy resolutions. Applying the processing techniques to spectroscopic data obtained from each instrument leads in each case to a marked improvement in the spectroscopic limit, regardless of the technique implemented or the microscope setup. The example application chosen to benchmark these processing techniques is the energy limit obtained from a silicon wedge sample as a function of thickness. Based on these results, we conclude on the possibility to resolve statistically significant spectral features to within a hundred meV of the native instrumental energy spread, opening up the future prospect of tracking phonon peaks as new and improved hardware becomes available.
Collapse
Affiliation(s)
- Jeffery A Aguiar
- Department of Chemical Engineering and Materials Science, University of California Davis, One Shields Ave, Davis, CA 95618, USA.
| | | | | | | | | |
Collapse
|
37
|
Zhou W, Pennycook SJ, Idrobo JC. Probing the electronic structure and optical response of a graphene quantum disk supported on monolayer graphene. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2012; 24:314213. [PMID: 22820876 DOI: 10.1088/0953-8984/24/31/314213] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
In this paper, we show that a graphene quantum disk (GQD) can be generated on monolayer graphene via structural modification using the electron beam. The electronic structure and local optical responses of the GQD, supported on monolayer graphene, were probed with electron energy-loss spectrum imaging on an aberration-corrected scanning transmission electron microscope. We observe that for small GQD, ~1.3 nm in diameter, the electronic structure and optical response are governed by the dominating edge states, and are distinctly different from either monolayer graphene or double-layer graphene. Highly localized plasmon modes are generated at the GQD due to the confinement from the edge of the GQD in all directions. The highly localized optical response from GQDs could find use in designing nanoscale optoelectronic and plasmonic devices based on monolayer graphene.
Collapse
Affiliation(s)
- Wu Zhou
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
| | | | | |
Collapse
|
38
|
Zhou W, Pennycook SJ, Idrobo JC. Localization of inelastic electron scattering in the low-loss energy regime. Ultramicroscopy 2011; 119:51-6. [PMID: 22206602 DOI: 10.1016/j.ultramic.2011.11.013] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2011] [Revised: 10/25/2011] [Accepted: 11/14/2011] [Indexed: 10/15/2022]
Abstract
The spatial resolution and contrast level in electron energy-loss spectroscopy (EELS) imaging depend on the delocalization of the inelastic electron scattering cross sections. Theoretical calculations within the dipole approximation provide the lower limit for the delocalization of low loss signals, and suggest that atomic resolution EELS imaging in the low loss energy regime (<50 eV) should be possible. Here, we directly measure the localization of the inelastic electron scattering at different energy loss in the low loss regime using a clean open edge of monolayer graphene. Our results demonstrate that the delocalization depends both on the energy loss and the specific electron excitation mode contributing to the energy loss. While the plasmons are delocalized over 1.2 nm, sub-nm enhancement is observed at the edge for the low-loss signal at 11 eV, indicating the possible formation of a one-dimensional plasmon (or inter-band transition) at the edge of monolayer graphene. Our results also suggest that if the initial states or final states are atomically localized, atomic resolution EELS imaging could be obtained even in the low loss region of the spectra.
Collapse
Affiliation(s)
- Wu Zhou
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
| | | | | |
Collapse
|
39
|
Browning ND, Campbell GH, Evans JE, LaGrange TB, Reed BW. Electron Microscopy and Spectroscopy on the Ultrafast Timescale. Chemphyschem 2010; 11:781-2. [DOI: 10.1002/cphc.200900937] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
|
40
|
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]
|
41
|
Park J, Heo S, Chung JG, Kim H, Lee H, Kim K, Park GS. Bandgap measurement of thin dielectric films using monochromated STEM-EELS. Ultramicroscopy 2009; 109:1183-8. [DOI: 10.1016/j.ultramic.2009.04.005] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2008] [Revised: 04/06/2009] [Accepted: 04/28/2009] [Indexed: 10/20/2022]
|
42
|
Potapov PL, Engelmann HJ, Zschech E, Stöger-Pollach M. Measuring the dielectric constant of materials from valence EELS. Micron 2008; 40:262-8. [PMID: 18755592 DOI: 10.1016/j.micron.2008.07.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2008] [Revised: 07/17/2008] [Accepted: 07/17/2008] [Indexed: 10/21/2022]
Abstract
Valence EELS combined with STEM provides an approach to determine the dielectric constant of materials in the optical range of frequencies. The paper describes the experimental procedure and discusses the critical aspects of valence electron energy-loss spectroscopy (VEELS) treatment. In particular, the relativistic losses might affect strongly the results, and therefore they have to be subtracted from the spectra prior the analysis. The normalization of the energy-loss function is performed assuming an uniform thickness of the investigated area, which is reasonably fulfilled for carefully prepared FIB samples. This procedure requires the presence of at least one reference material with known dielectric properties to determine the absolute thickness. Examples of measuring the dielectric constant for several materials and structures are presented.
Collapse
Affiliation(s)
- P L Potapov
- AMD Saxony Fab36 LLC & Co. KG, Wilschdorfer Landstr. 101, D-01109 Dresden, Germany.
| | | | | | | |
Collapse
|
43
|
Nanomaterial electronic structure investigation by valence electron energy loss spectroscopy—An example of doped ZnO nanowires. Micron 2008; 39:703-8. [DOI: 10.1016/j.micron.2007.10.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
44
|
Prospects for analyzing the electronic properties in nanoscale systems by VEELS. Ultramicroscopy 2008; 108:270-6. [DOI: 10.1016/j.ultramic.2007.07.008] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2007] [Accepted: 07/05/2007] [Indexed: 11/22/2022]
|
45
|
Erni R, Browning ND. The impact of surface and retardation losses on valence electron energy-loss spectroscopy. Ultramicroscopy 2008; 108:84-99. [PMID: 17481821 DOI: 10.1016/j.ultramic.2007.03.005] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2006] [Revised: 03/08/2007] [Accepted: 03/20/2007] [Indexed: 11/30/2022]
Abstract
The inelastic scattering of fast electrons transmitting thin foils of silicon (Si), silicon nitride (Si(3)N(4)), gallium arsenide (GaAs), gallium nitride (GaN) and cadmium selenide (CdSe) was analyzed using dielectric theory. In particular, the impact of surface and bulk retardation losses on valence electron energy-loss spectroscopy (VEELS) was studied as a function of the foil thickness. It is shown that for the materials analyzed, surface and retardation losses can cause a systematic, thickness-dependent modulation of the dielectric volume losses, which can hamper the determination of the bulk dielectric data as well as the identification of band-gap and interband transition energies by VEELS. For Si and GaAs, where the dielectric function is strongly peaked with high absolute values, retardation losses lead to additional intensity maxima in the spectrum. For thin films of these materials (below approximately 100 nm), the additional intensity maxima are related to retardation effects due to the finite size of the sample leading to the excitation of guided light modes. For thicker films, exceeding about 200 nm, the intensity maxima are caused by bulk retardation losses, i.e., Cerenkov losses. Although thickness-dependent modulations were observed for Si(3)N(4), GaN and CdSe, the form of the dielectric functions and their lower maxima, means that for TEM samples < 100 nm thick, the band-gap energies of these materials can be accurately identified by VEELS. Guidelines are given that allow for forecasting the impact of surface and retardation losses on VEELS.
Collapse
Affiliation(s)
- Rolf Erni
- EMAT, University of Antwerp, Groenenborgerlaan 171, B 2020 Antwerp, Belgium.
| | | |
Collapse
|
46
|
Stöger-Pollach M, Schattschneider P. The influence of relativistic energy losses on bandgap determination using valence EELS. Ultramicroscopy 2007; 107:1178-85. [PMID: 17399902 DOI: 10.1016/j.ultramic.2007.01.015] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2006] [Revised: 01/17/2007] [Accepted: 01/31/2007] [Indexed: 11/21/2022]
Abstract
Since monochromated transmission electron microscopes have become available, the determination of bandgaps and optical properties using electron energy loss spectrometry (EELS) has again attracted interest. The underlying idea is very simple: below the bandgap energy no transitions can contribute to the valence EELS signal. However, the bandgap cannot be directly read out from the recorded data. Therefore the optical properties cannot be determined correctly from the low loss using the Kramers-Kronig relations. We will discuss under which conditions relativistic effects may be suppressed. It is demonstrated that scanning TEM (STEM) geometry is not applicable for most bandgap measurements.
Collapse
Affiliation(s)
- M Stöger-Pollach
- University Service Center for Transmission Electron Microscopy, Technische Universität Wien, A-1040 Wien, Austria.
| | | |
Collapse
|
47
|
Schamm S, Bonafos C, Coffin H, Cherkashin N, Carrada M, Ben Assayag G, Claverie A, Tencé M, Colliex C. Imaging Si nanoparticles embedded in SiO(2) layers by (S)TEM-EELS. Ultramicroscopy 2007; 108:346-57. [PMID: 17616256 DOI: 10.1016/j.ultramic.2007.05.008] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2006] [Revised: 05/10/2007] [Accepted: 05/25/2007] [Indexed: 11/21/2022]
Abstract
Fabrication of systems in which Si nanoparticles are embedded in a thin silica layer is today mature for non-volatile memory and opto-electronics applications. The control of the different parameters (position, size and density) of the nanoparticles population is a key point to optimize the properties of such systems. A review of dedicated transmission electron microscopy (TEM) methods, which can be used to measure these parameters, is presented with an emphasis on those relying on electron energy-loss spectroscopy (EELS). Defocused bright-field imaging can be used in order to determine topographic information of a whole assembly of nanoparticles, but it is not efficient for looking at individual nanoparticles. High-resolution electron imaging or dark-field imaging can be of help in the case of crystalline particles but they always provide underestimated values of the nanocrystals population. EELS imaging in the low-energy-loss domain around the Si plasmon peak, which gives rise to strong signals, is the only way to visualize all Si nanoparticles within a silica film and to perform reliable size and density measurements. Two complementary types of experiments are investigated and discussed more extensively: direct imaging with a transmission electron microscope equipped with an imaging filter (EFTEM) and indirect imaging from spectrum-imaging data acquired with a scanning transmission electron microscope equipped with a spectrometer (STEM-PEELS). The direct image (EFTEM) and indirect set of spectra (STEM-PEELS) are processed in order to deliver images where the contribution of the silica matrix is minimized. The contrast of the resulting images can be enhanced with adapted numerical filters for further morphometric analysis. The two methods give equivalent results, with an easier access for EFTEM and the possibility of a more detailed study of the EELS signatures in the case of STEM-PEELS. Irradiation damage in such systems is also discussed.
Collapse
Affiliation(s)
- S Schamm
- nMat Group, CEMES-CNRS, 31055 Toulouse, France.
| | | | | | | | | | | | | | | | | |
Collapse
|
48
|
Erni R, Browning ND. Quantification of the size-dependent energy gap of individual CdSe quantum dots by valence electron energy-loss spectroscopy. Ultramicroscopy 2007; 107:267-73. [PMID: 16996213 DOI: 10.1016/j.ultramic.2006.08.002] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2006] [Revised: 07/27/2006] [Accepted: 08/09/2006] [Indexed: 11/28/2022]
Abstract
Valence electron energy-loss spectroscopy (VEELS) performed in a monochromated scanning transmission electron microscope was used to measure the energy gaps of individual quantum dots (QDs). The gap energies of a series of CdSe QDs measured by VEELS reveal the expected quantum confinement effect; the gap energy increases with decreasing particle size. However, the values derived from these first VEELS measurements of single QDs are larger than the values commonly measured by optical spectroscopy. As standard optical methods lack the spatial resolution to probe individual nanoparticles, the particle-size distribution influences the optical response. It is suggested that the impact of the particle-size distribution accounts for the discrepancy between the energy-gap values derived from VEELS of single QDs and from optical methods of ensembles of QDs.
Collapse
Affiliation(s)
- Rolf Erni
- Department of Chemical Engineering and Materials Science, University of California Davis, One Shields Ave., Davis, CA 95616, USA.
| | | |
Collapse
|
49
|
Walther T, Stegmann H. Preliminary results from the first monochromated and aberration corrected 200-kV field-emission scanning transmission electron microscope. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2006; 12:498-505. [PMID: 19830942 DOI: 10.1017/s1431927606060697] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Experimental results from the first monochromated and aberration-corrected scanning transmission electron microscope operated at 200 kV are described. The formation of an electron probe with a diameter of less than 0.2 nm at an energy width significantly under 0.3 eV and its planned application to the chemical analysis of nanometer-scale structures in materials science are described. Both energy and spatial resolution will benefit from this: The monochromator improves the energy resolution for studies of energy loss near edge structures. The Cs corrector allows formation of either a smaller probe for a given beam current or yields, at fixed probe size, an enhanced beam current density using a larger condenser aperture. We also point out another advantage of the combination of both components: Increasing the convergence angle by using larger condenser apertures in an aberration-corrected instrument will enlarge the undesirable chromatic focus spread. This in turn influences spatial resolution. The effect of polychromatic probe tails is proportional to the product of convergence angle, chromatic aberration constant, and energy spread. It can thus be compensated for in our new instrument by decreasing the energy width by the same factor as the beam convergence is increased to form a more intense probe. An alternative in future developments might be hardware correction of the chromatic aberration, which could eliminate the chromatic probe spread completely.
Collapse
Affiliation(s)
- Thomas Walther
- Center of Advanced European Studies and Research (caesar), Electron Microscopy Group, Ludwig-Erhard-Allee 2, D-53175 Bonn, Germany.
| | | |
Collapse
|
50
|
Mhawi AA, Fernandes AB, Ottensmeyer FP. Low-energy-loss electron microscopy of doxorubicin in human breast cancer MCF-7 cells: localization by color. J Struct Biol 2006; 158:80-92. [PMID: 17174106 DOI: 10.1016/j.jsb.2006.10.024] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2006] [Revised: 10/16/2006] [Accepted: 10/22/2006] [Indexed: 10/23/2022]
Abstract
The distribution of the anti-cancer drug doxorubicin (DOX) in human breast cancer MCF-7 cells was imaged directly by low-energy-loss electron microscopy (EM) without specific antibodies or heavy metal stains, using only the electron-induced molecular orbital excitation of the drug. Cells treated with DOX were examined live by confocal fluorescence microscopy and as very thin sections in an electron microscope equipped with an electron energy filter having an energy resolution of 1 eV. The distribution of DOX obtained by EM from pairs of images at energy losses of 3+/-1 eV and 10+/-1 eV agreed with fluorescence microscope observations, but provided much more detail, easily distinguishing localization between nuclear membrane and perimembrane compartments and between vacuolated nucleoli and perinucleolar chromatin. Treatment times up to 1h and DOX concentrations up to 30 microM indicated a progression of DOX ingress from higher concentrations in the nuclear membrane to labeling of the nucleolus. Subsequently DOX moved into perinucleolar chromatin and concentrated in perimembrane chromatin aggregations. Quantification of the DOX signal indicated a decay half-life of 320 e/A2 under electron irradiation, whereas each image at 3000 x required 10 e/A2. The results point to a new field of high resolution microanalysis: color electron microscopy.
Collapse
Affiliation(s)
- A Amir Mhawi
- Ontario Cancer Institute and Department of Medical Biophysics, University of Toronto, 610 University Avenue, Toronto, Ont., Canada M5G 2M9
| | | | | |
Collapse
|