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Nekita S, Yanagimoto S, Sannomiya T, Akiba K, Takiguchi M, Sumikura H, Takagi I, Nakamura KG, Yip S, Meng Y, Ho JC, Okuyama T, Murayama M, Saito H. Diffusion-Dominated Luminescence Dynamics of CsPbBr 3 Studied Using Cathodoluminescence and Microphotoluminescence Spectroscopy. NANO LETTERS 2024; 24:3971-3977. [PMID: 38501652 DOI: 10.1021/acs.nanolett.4c00483] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/20/2024]
Abstract
Time-resolved or time-correlation measurements using cathodoluminescence (CL) reveal the electronic and optical properties of semiconductors, such as their carrier lifetimes, at the nanoscale. However, halide perovskites, which are promising optoelectronic materials, exhibit significantly different decay dynamics in their CL and photoluminescence (PL). We conducted time-correlation CL measurements of CsPbBr3 using Hanbury Brown-Twiss interferometry and compared them with time-resolved PL. The measured CL decay time was on the order of subnanoseconds and was faster than PL decay at an excited carrier density of 2.1 × 1018 cm-3. Our experiment and analytical model revealed the CL dynamics induced by individual electron incidences, which are characterized by highly localized carrier generation followed by a rapid decrease in carrier density due to diffusion. This carrier diffusion can play a dominant role in the CL decay time for undoped semiconductors, in general, when the diffusion dynamics are faster than the carrier recombination.
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Affiliation(s)
- Sho Nekita
- Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasugakoen, Kasuga, Fukuoka 816-8580, Japan
| | - Sotatsu Yanagimoto
- Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama 226-8503, Japan
| | - Takumi Sannomiya
- Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama 226-8503, Japan
| | - Keiichirou Akiba
- Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama 226-8503, Japan
- Takasaki Institute for Advanced Quantum Science, National Institutes for Quantum Science and Technology (QST), 1233 Watanuki, Takasaki, Gunma 370-1292, Japan
| | - Masato Takiguchi
- Nanophotonics Center, NTT Corp., 3-1, Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan
- NTT Basic Research Laboratories, NTT Corp., 3-1, Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan
| | - Hisashi Sumikura
- Nanophotonics Center, NTT Corp., 3-1, Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan
- NTT Basic Research Laboratories, NTT Corp., 3-1, Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan
| | - Itsuki Takagi
- Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama 226-8503, Japan
| | - Kazutaka G Nakamura
- Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama 226-8503, Japan
- Laboratory for Materials and Structures, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama 226-8503, Japan
| | - SenPo Yip
- Institute for Materials Chemistry and Engineering, Kyushu University, 6-1 Kasugakoen, Kasuga, Fukuoka 816-8580, Japan
| | - You Meng
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon 999077, Hong Kong SAR
| | - Johnny C Ho
- Institute for Materials Chemistry and Engineering, Kyushu University, 6-1 Kasugakoen, Kasuga, Fukuoka 816-8580, Japan
- Department of Materials Science and Engineering, City University of Hong Kong, Kowloon 999077, Hong Kong SAR
- State Key Laboratory of Terahertz and Millimeter Waves, City University of Hong Kong, Kowloon 999077, Hong Kong SAR
| | - Tetsuya Okuyama
- National Institute of Technology, Kurume College, 1-1-1 Komorino, Kurume, Fukuoka 830-8555, Japan
| | - Mitsuhiro Murayama
- Institute for Materials Chemistry and Engineering, Kyushu University, 6-1 Kasugakoen, Kasuga, Fukuoka 816-8580, Japan
- Department of Materials Science and Engineering, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Hikaru Saito
- Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama 226-8503, Japan
- Institute for Materials Chemistry and Engineering, Kyushu University, 6-1 Kasugakoen, Kasuga, Fukuoka 816-8580, Japan
- Pan-Omics Data-Driven Research Innovation Center, Kyushu University, Fukuoka 816-8580, Japan
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Tian Y, Yang D, Ma Y, Li Z, Li J, Deng Z, Tian H, Yang H, Sun S, Li J. Spatiotemporal Visualization of Photogenerated Carriers on an Avalanche Photodiode Surface Using Ultrafast Scanning Electron Microscopy. NANOMATERIALS (BASEL, SWITZERLAND) 2024; 14:310. [PMID: 38334581 PMCID: PMC10857202 DOI: 10.3390/nano14030310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2023] [Revised: 01/25/2024] [Accepted: 01/30/2024] [Indexed: 02/10/2024]
Abstract
The spatiotemporal evolution of photogenerated charge carriers on surfaces and at interfaces of photoactive materials is an important issue for understanding fundamental physical processes in optoelectronic devices and advanced materials. Conventional optical probe-based microscopes that provide indirect information about the dynamic behavior of photogenerated carriers are inherently limited by their poor spatial resolution and large penetration depth. Herein, we develop an ultrafast scanning electron microscope (USEM) with a planar emitter. The photoelectrons per pulse in this USEM can be two orders of magnitude higher than that of a tip emitter, allowing the capture of high-resolution spatiotemporal images. We used the contrast change of the USEM to examine the dynamic nature of surface carriers in an InGaAs/InP avalanche photodiode (APD) after femtosecond laser excitation. It was observed that the photogenerated carriers showed notable longitudinal drift, lateral diffusion, and carrier recombination associated with the presence of photovoltaic potential at the surface. This work demonstrates an in situ multiphysics USEM platform with the capability to stroboscopically record carrier dynamics in space and time.
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Affiliation(s)
- Yuan Tian
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Dong Yang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yu Ma
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Zhongwen Li
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
| | - Jun Li
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
| | - Zhen Deng
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
| | - Huanfang Tian
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
| | - Huaixin Yang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Shuaishuai Sun
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
- Songshan Lake Materials Laboratory, Dongguan 523808, China
| | - Jianqi Li
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; (Y.T.); (D.Y.); (Y.M.); (Z.L.); (J.L.); (Z.D.); (H.T.); (H.Y.); (S.S.)
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
- Songshan Lake Materials Laboratory, Dongguan 523808, China
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3
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Dang Z, Chen Y, Fang Z. Cathodoluminescence Nanoscopy: State of the Art and Beyond. ACS NANO 2023; 17:24431-24448. [PMID: 38054434 DOI: 10.1021/acsnano.3c07593] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/07/2023]
Abstract
Cathodoluminescence (CL) nanoscopy is proven to be a powerful tool to explore nanoscale optical properties, whereby free electron beams achieve a spatial resolution far beyond the diffraction limit of light. With developed methods for the control of electron beams and the collection of light, the dimension of information that CL can access has been expanded to include polarization, momentum, and time, holding promise to provide invaluable insights into the study of materials and optical near-field dynamics. With a focus on the burgeoning field of CL nanoscopy, this perspective outlines the recent advancements and applications of this technique, as illustrated by the salient experimental works. In addition, as an outlook for future research, several appealing directions that may bring about developments and discoveries are highlighted.
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Affiliation(s)
- Zhibo Dang
- School of Physics, State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Collaborative Innovation Center of Quantum Matter, and Nano-optoelectronics Frontier Center of Ministry of Education, Peking University, Beijing 100871, People's Republic of China
| | - Yuxiang Chen
- School of Physics, State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Collaborative Innovation Center of Quantum Matter, and Nano-optoelectronics Frontier Center of Ministry of Education, Peking University, Beijing 100871, People's Republic of China
| | - Zheyu Fang
- School of Physics, State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Collaborative Innovation Center of Quantum Matter, and Nano-optoelectronics Frontier Center of Ministry of Education, Peking University, Beijing 100871, People's Republic of China
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4
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Moradifar P, Liu Y, Shi J, Siukola Thurston ML, Utzat H, van Driel TB, Lindenberg AM, Dionne JA. Accelerating Quantum Materials Development with Advances in Transmission Electron Microscopy. Chem Rev 2023. [PMID: 37979189 DOI: 10.1021/acs.chemrev.2c00917] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2023]
Abstract
Quantum materials are driving a technology revolution in sensing, communication, and computing, while simultaneously testing many core theories of the past century. Materials such as topological insulators, complex oxides, superconductors, quantum dots, color center-hosting semiconductors, and other types of strongly correlated materials can exhibit exotic properties such as edge conductivity, multiferroicity, magnetoresistance, superconductivity, single photon emission, and optical-spin locking. These emergent properties arise and depend strongly on the material's detailed atomic-scale structure, including atomic defects, dopants, and lattice stacking. In this review, we describe how progress in the field of electron microscopy (EM), including in situ and in operando EM, can accelerate advances in quantum materials and quantum excitations. We begin by describing fundamental EM principles and operation modes. We then discuss various EM methods such as (i) EM spectroscopies, including electron energy loss spectroscopy (EELS), cathodoluminescence (CL), and electron energy gain spectroscopy (EEGS); (ii) four-dimensional scanning transmission electron microscopy (4D-STEM); (iii) dynamic and ultrafast EM (UEM); (iv) complementary ultrafast spectroscopies (UED, XFEL); and (v) atomic electron tomography (AET). We describe how these methods could inform structure-function relations in quantum materials down to the picometer scale and femtosecond time resolution, and how they enable precision positioning of atomic defects and high-resolution manipulation of quantum materials. For each method, we also describe existing limitations to solve open quantum mechanical questions, and how they might be addressed to accelerate progress. Among numerous notable results, our review highlights how EM is enabling identification of the 3D structure of quantum defects; measuring reversible and metastable dynamics of quantum excitations; mapping exciton states and single photon emission; measuring nanoscale thermal transport and coupled excitation dynamics; and measuring the internal electric field and charge density distribution of quantum heterointerfaces- all at the quantum materials' intrinsic atomic and near atomic-length scale. We conclude by describing open challenges for the future, including achieving stable sample holders for ultralow temperature (below 10K) atomic-scale spatial resolution, stable spectrometers that enable meV energy resolution, and high-resolution, dynamic mapping of magnetic and spin fields. With atomic manipulation and ultrafast characterization enabled by EM, quantum materials will be poised to integrate into many of the sustainable and energy-efficient technologies needed for the 21st century.
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Affiliation(s)
- Parivash Moradifar
- Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
| | - Yin Liu
- Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
- Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States
| | - Jiaojian Shi
- Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
- SLAC National Accelerator Laboratory, 2575 Sand Hill Road MS69, Menlo Park, California 94025, United States
| | | | - Hendrik Utzat
- Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
- Department of Chemistry, University of California Berkeley, Berkeley, California 94720, United States
| | - Tim B van Driel
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States
| | - Aaron M Lindenberg
- Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
- SLAC National Accelerator Laboratory, 2575 Sand Hill Road MS69, Menlo Park, California 94025, United States
| | - Jennifer A Dionne
- Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States
- Department of Radiology, Stanford University, Stanford, California 94305, United States
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5
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Loeto K, Kusch G, Ghosh S, Kappers MJ, Oliver RA. Quantitative analysis of carbon impurity concentrations in GaN epilayers by cathodoluminescence. Micron 2023; 172:103489. [PMID: 37385074 DOI: 10.1016/j.micron.2023.103489] [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: 02/14/2023] [Revised: 05/30/2023] [Accepted: 05/30/2023] [Indexed: 07/01/2023]
Abstract
In this work, a technique for quantifying carbon doping concentrations in GaN:C/AlGaN buffer structures using cathodoluminescence (CL) is presented. The method stems from the knowledge that the blue and yellow luminescence intensity in CL spectra of GaN varies with the carbon doping concentration. By calculating the blue and yellow luminescence peak intensities normalised to the peak GaN near-band-edge intensity for GaN layers of known carbon concentrations, calibration curves that show the change in normalised blue and yellow luminescence intensity with carbon concentration in the 1016 - 1019 cm-3 range were derived at both room temperature and 10 K. The utility of such calibration curves was then examined by testing against an unknown sample containing multiple carbon-doped GaN layers. The results obtained from CL using the normalised blue luminescence calibration curves are in close agreement with those from secondary-ion mass spectroscopy (SIMS). However,the method fails when applying calibration curves obtained from the normalised yellow luminescence likely due to the influence of native VGa defects acting in this luminescence region. Although this work shows that indeed CL can be used as a quantitative tool to measure carbon doping concentrations in GaN:C, it is noted that the intrinsic broadening effects innate to CL can make it difficult to differentiate between the intensity variations in thin ( < 500 nm) multilayered GaN:C structures such as the ones studied in this work.
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Affiliation(s)
- K Loeto
- Department of Materials Science and Metallurgy, University of Cambridge, CB3 0FS Cambridge, United Kingdom.
| | - G Kusch
- Department of Materials Science and Metallurgy, University of Cambridge, CB3 0FS Cambridge, United Kingdom
| | - S Ghosh
- Department of Materials Science and Metallurgy, University of Cambridge, CB3 0FS Cambridge, United Kingdom
| | - M J Kappers
- Department of Materials Science and Metallurgy, University of Cambridge, CB3 0FS Cambridge, United Kingdom
| | - R A Oliver
- Department of Materials Science and Metallurgy, University of Cambridge, CB3 0FS Cambridge, United Kingdom
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6
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Zheng L, Dang Z, Ding D, Liu Z, Dai Y, Lu J, Fang Z. Electron-Induced Chirality-Selective Routing of Valley Photons via Metallic Nanostructure. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2204908. [PMID: 36877955 DOI: 10.1002/adma.202204908] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Revised: 02/13/2023] [Indexed: 06/18/2023]
Abstract
Valleytronics in 2D transition metal dichalcogenides has raised a great impact in nanophotonic information processing and transport as it provides the pseudospin degree of freedom for carrier control. The imbalance of carrier occupation in inequivalent valleys can be achieved by external stimulations such as helical light and electric field. With metasurfaces, it is feasible to separate the valley exciton in real space and momentum space, which is significant for logical nanophotonic circuits. However, the control of valley-separated far-field emission by a single nanostructure is rarely reported, despite the fact that it is crucial for subwavelength research of valley-dependent directional emission. Here, it is demonstrated that the electron beam permits the chirality-selective routing of valley photons in a monolayer WS2 with Au nanostructures. The electron beam can locally excite valley excitons and regulate the coupling between excitons and nanostructures, hence controlling the interference effect of multipolar electric modes in nanostructures. Therefore, the separation degree can be modified by steering the electron beam, exhibiting the capability of subwavelength control of valley separation. This work provides a novel method to create and resolve the variation of valley emission distribution in momentum space, paving the way for the design of future nanophotonic integrated devices.
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Affiliation(s)
- Liheng Zheng
- School of Physics, State Key Lab for Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Collaborative Innovation Center of Quantum Matter, and Nano-optoelectronics Frontier Center of Ministry of Education, Peking University, Beijing, 100871, P. R. China
| | - Zhibo Dang
- School of Physics, State Key Lab for Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Collaborative Innovation Center of Quantum Matter, and Nano-optoelectronics Frontier Center of Ministry of Education, Peking University, Beijing, 100871, P. R. China
| | - Dongdong Ding
- School of Physics, State Key Lab for Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Collaborative Innovation Center of Quantum Matter, and Nano-optoelectronics Frontier Center of Ministry of Education, Peking University, Beijing, 100871, P. R. China
| | - Zhixin Liu
- School of Physics, State Key Lab for Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Collaborative Innovation Center of Quantum Matter, and Nano-optoelectronics Frontier Center of Ministry of Education, Peking University, Beijing, 100871, P. R. China
| | - Yuchen Dai
- School of Physics, State Key Lab for Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Collaborative Innovation Center of Quantum Matter, and Nano-optoelectronics Frontier Center of Ministry of Education, Peking University, Beijing, 100871, P. R. China
| | - Jianming Lu
- School of Physics, State Key Lab for Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Collaborative Innovation Center of Quantum Matter, and Nano-optoelectronics Frontier Center of Ministry of Education, Peking University, Beijing, 100871, P. R. China
| | - Zheyu Fang
- School of Physics, State Key Lab for Mesoscopic Physics, Academy for Advanced Interdisciplinary Studies, Collaborative Innovation Center of Quantum Matter, and Nano-optoelectronics Frontier Center of Ministry of Education, Peking University, Beijing, 100871, P. R. China
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7
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Discrimination of coherent and incoherent cathodoluminescence using temporal photon correlations. Ultramicroscopy 2022; 241:113594. [DOI: 10.1016/j.ultramic.2022.113594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Revised: 07/12/2022] [Accepted: 07/21/2022] [Indexed: 11/17/2022]
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Cai Q, You H, Hou Q, Tao T, Xie Z, Cao X, Liu B, Chen D, Lu H, Zhang R, Zheng Y. Self-Assembly Nanopillar/Superlattice Hierarchical Structure: Boosting AlGaN Crystalline Quality and Achieving High-Performance Ultraviolet Avalanche Photodetector. ACS APPLIED MATERIALS & INTERFACES 2022; 14:33525-33537. [PMID: 35830680 DOI: 10.1021/acsami.2c06417] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
As a burgeoning wide-band gap semiconductor material, AlxGa1-xN alloy has attracted great attention for versatile applications due to its superior properties. However, its poor crystalline quality has restricted the employment of AlGaN on electronic devices for a long time. Herein, we proposed a nanopillar/superlattice hierarchical structure for AlGaN epitaxy to boost the crystalline quality. The scale-controllable AlN nanopillar template is fabricated from a nickel self-assembly process. AlGaN initiates the epitaxial laterally overgrowth mode based on the nanopatterned template. In addition, the AlxGa1-xN/AlyGa1-yN superlattice structure could effectively block the propagation of threading dislocation segments. The kinetics of the dislocation and epitaxy process in the hierarchical structure is intuitively demonstrated and analyzed. Consequently, the dislocation density of AlGaN grown by this method is significantly reduced by more than 30 times compared to the AlN template. No threading dislocation segments were observed in the 4 μm TEM field of view. Moreover, based on the hierarchical structure, we also fabricated an AlGaN ultraviolet avalanche photodiode (APD). The APD exhibits superior performance, achieving a maximum gain of 1.3 × 105 and high responsivity of 1.46 A/W at 324 nm. The reliability of the nanopillar/superlattice AlGaN epitaxial procedure is anticipated to shed new light on the nitride semiconductor material, further bringing a breakthrough to wide-band gap electronic devices.
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Affiliation(s)
- Qing Cai
- Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
| | - Haifan You
- Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
| | - Qianyu Hou
- Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
| | - Tao Tao
- Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
| | - Zili Xie
- Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
| | - Xun Cao
- Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
| | - Bin Liu
- Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
| | - Dunjun Chen
- Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
| | - Hai Lu
- Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
| | - Rong Zhang
- Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
- Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Physics, Xiamen University, Xiamen 361005, China
- Institute of Future Display Technology, Tan Kah Kee Innovation Laboratory, Xiamen 361102, China
| | - Youdou Zheng
- Key Laboratory of Advanced Photonic and Electronic Materials, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
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9
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Wang L, Li C, Li J, Zhang X, Li X, Cui Y, Xia Y, Zhang Y, Mao S, Ji Y, Sheng W, Han X. Liquid-phase scanning electron microscopy for single membrane protein imaging. Biochem Biophys Res Commun 2022; 590:163-168. [PMID: 34979317 DOI: 10.1016/j.bbrc.2021.12.081] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2021] [Accepted: 12/22/2021] [Indexed: 11/02/2022]
Abstract
Liquid-phase electron microscopy is highly desirable for observing biological samples in their native liquid state at high resolution. We developed liquid imaging approaches for biological cells using scanning electron microscopy. Novel approaches included scanning transmission electron imaging using a liquid-cell apparatus (LC-STEM), as well as correlative cathodoluminescence and electron microscopy (CCLEM) imaging. LC-STEM enabled imaging at a ∼2 nm resolution and excellent contrast for the precise recognition of localization, distribution, and configuration of individually labeled membrane proteins on the native cells in solution. CCLEM improved the resolution of fluorescent images down to 10 nm. Liquid SEM technologies will bring unique and wide applications to the study of the structure and function of cells and membrane proteins in their near-native states at the monomolecular level.
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Affiliation(s)
- Li Wang
- Beijing Key Laboratory of Microstructure and Property of Solids, Institute of Microstructure and Property of Advanced Materials, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing, 100124, China
| | - Changshuo Li
- Beijing Key Laboratory of Microstructure and Property of Solids, Institute of Microstructure and Property of Advanced Materials, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing, 100124, China
| | - Jintao Li
- Beijing Key Laboratory of Environmental and Viral Oncology, Beijing International Science and Technology, Cooperation Base of Antivirus Drug, College of Life Science and Bioengineering, Beijing University of Technology, Beijing, 100124, China
| | - Xiaofei Zhang
- Beijing Key Laboratory of Microstructure and Property of Solids, Institute of Microstructure and Property of Advanced Materials, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing, 100124, China
| | - Xiaochen Li
- Beijing Key Laboratory of Microstructure and Property of Solids, Institute of Microstructure and Property of Advanced Materials, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing, 100124, China
| | - Yiran Cui
- Beijing Key Laboratory of Microstructure and Property of Solids, Institute of Microstructure and Property of Advanced Materials, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing, 100124, China
| | - Yang Xia
- Beijing Key Laboratory of Environmental and Viral Oncology, Beijing International Science and Technology, Cooperation Base of Antivirus Drug, College of Life Science and Bioengineering, Beijing University of Technology, Beijing, 100124, China
| | - Yinqi Zhang
- Beijing Key Laboratory of Microstructure and Property of Solids, Institute of Microstructure and Property of Advanced Materials, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing, 100124, China
| | - Shengcheng Mao
- Beijing Key Laboratory of Microstructure and Property of Solids, Institute of Microstructure and Property of Advanced Materials, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing, 100124, China
| | - Yuan Ji
- Beijing Key Laboratory of Microstructure and Property of Solids, Institute of Microstructure and Property of Advanced Materials, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing, 100124, China.
| | - Wang Sheng
- Beijing Key Laboratory of Environmental and Viral Oncology, Beijing International Science and Technology, Cooperation Base of Antivirus Drug, College of Life Science and Bioengineering, Beijing University of Technology, Beijing, 100124, China.
| | - Xiaodong Han
- Beijing Key Laboratory of Microstructure and Property of Solids, Institute of Microstructure and Property of Advanced Materials, Faculty of Materials and Manufacturing, Beijing University of Technology, Beijing, 100124, China.
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10
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Abstract
Implementing the modern technologies of light-emitting devices, light harvesting, and quantum information processing requires the understanding of the structure-function relations at spatial scales below the optical diffraction limit and time scales of energy and information flows. Here, we distinctively combine cathodoluminescence (CL) with ultrafast electron microscopy (UEM), termed CL-UEM, because CL and UEM synergetically afford the required spectral and spatiotemporal sensitivities, respectively. For color centers in nanodiamonds, we demonstrate the measurement of CL lifetime with a local sensitivity of 50 nm and a time resolution of 100 ps. It is revealed that the emitting states of the color centers can be populated through charge transfer among the color centers across diamond lattices upon high-energy electron beam excitation. The technical advance achieved in this study will facilitate the specific control over energy conversion at nanoscales, relevant to quantum dots and single-photon sources.
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Affiliation(s)
- Ye-Jin Kim
- Department of Chemistry, College of Natural Sciences, Ulsan National Institute of Science and Technology, Ulsan 44919, Korea
- Center for Soft and Living Matter, Institute for Basic Science (IBS), Ulsan 44919, Korea
| | - Oh-Hoon Kwon
- Department of Chemistry, College of Natural Sciences, Ulsan National Institute of Science and Technology, Ulsan 44919, Korea
- Center for Soft and Living Matter, Institute for Basic Science (IBS), Ulsan 44919, Korea
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11
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Ferrer Orri J, Tennyson EM, Kusch G, Divitini G, Macpherson S, Oliver RA, Ducati C, Stranks SD. Using pulsed mode scanning electron microscopy for cathodoluminescence studies on hybrid perovskite films. NANO EXPRESS 2021. [DOI: 10.1088/2632-959x/abfe3c] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Abstract
The use of pulsed mode scanning electron microscopy cathodoluminescence (CL) for both hyperspectral mapping and time-resolved measurements is found to be useful for the study of hybrid perovskite films, a class of ionic semiconductors that have been shown to be beam sensitive. A range of acquisition parameters is analysed, including beam current and beam mode (either continuous or pulsed operation), and their effect on the CL emission is discussed. Under optimized acquisition conditions, using a pulsed electron beam, the heterogeneity of the emission properties of hybrid perovskite films can be resolved via the acquisition of CL hyperspectral maps. These optimized parameters also enable the acquisition of time-resolved CL of polycrystalline films, showing significantly shorter lived charge carriers dynamics compared to the photoluminescence analogue, hinting at additional electron beam-specimen interactions to be further investigated. This work represents a promising step to investigate hybrid perovskite semiconductors at the nanoscale with CL.
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12
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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.
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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
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13
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Solà-Garcia M, Mauser KW, Liebtrau M, Coenen T, Christiansen S, Meuret S, Polman A. Photon Statistics of Incoherent Cathodoluminescence with Continuous and Pulsed Electron Beams. ACS PHOTONICS 2021; 8:916-925. [PMID: 33763505 PMCID: PMC7976602 DOI: 10.1021/acsphotonics.0c01939] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Indexed: 06/12/2023]
Abstract
Photon bunching in incoherent cathodoluminescence (CL) spectroscopy originates from the fact that a single high-energy electron can generate multiple photons when interacting with a material, thus, revealing key properties of electron-matter excitation. Contrary to previous works based on Monte Carlo modeling, here we present a fully analytical model describing the amplitude and shape of the second order autocorrelation function (g (2)(τ)) for continuous and pulsed electron beams. Moreover, we extend the analysis of photon bunching to ultrashort electron pulses, in which up to 500 electrons per pulse excite the sample within a few picoseconds. We obtain a simple equation relating the bunching strength (g (2)(0)) to the electron beam current, emitter decay lifetime, pulse duration, in the case of pulsed electron beams, and electron excitation efficiency (γ), defined as the probability that an electron creates at least one interaction with the emitter. The analytical model shows good agreement with the experimental data obtained on InGaN/GaN quantum wells using continuous, ns-pulsed (using beam blanker) and ultrashort ps-pulsed (using photoemission) electron beams. We extract excitation efficiencies of 0.13 and 0.05 for 10 and 8 keV electron beams, respectively, and we observe that nonlinear effects play no compelling role, even after excitation with ultrashort and dense electron cascades in the quantum wells.
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Affiliation(s)
- Magdalena Solà-Garcia
- Center
for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
| | - Kelly W. Mauser
- Center
for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
| | - Matthias Liebtrau
- Center
for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
| | - Toon Coenen
- Center
for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
- Delmic
BV, Kanaalweg 4, 2628 EB, Delft, The Netherlands
| | - Silke Christiansen
- Fraunhofer
Institute for Ceramic Technologies and Systems IKTS, Äußere Nürnberger Strasse 62, 91301 Forchheim, Germany
| | - Sophie Meuret
- CEMES-CNRS, 29 Rue Jeanne Marvig, 31055 Toulouse, France
| | - Albert Polman
- Center
for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
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14
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Time-resolved cathodoluminescence of DNA triggered by picosecond electron bunches. Sci Rep 2020; 10:5071. [PMID: 32193504 PMCID: PMC7081262 DOI: 10.1038/s41598-020-61711-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Accepted: 03/01/2020] [Indexed: 11/30/2022] Open
Abstract
Despite the tremendous importance of so-called ionizing radiations (X-rays, accelerated electrons and ions) in cancer treatment, most studies on their effects have focused on the ionization process itself, and neglect the excitation events the radiations can induce. Here, we show that the excited states of DNA exposed to accelerated electrons can be studied in the picosecond time domain using a recently developed cathodoluminescence system with high temporal resolution. Our study uses a table-top ultrafast, UV laser-triggered electron gun delivering picosecond electron bunches of keV energy. This scheme makes it possible to directly compare time-resolved cathodoluminescence with photoluminescence measurements. This comparison revealed qualitative differences, as well as quantitative similarities between excited states of DNA upon exposure to electrons or photons.
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15
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Solà-Garcia M, Meuret S, Coenen T, Polman A. Electron-Induced State Conversion in Diamond NV Centers Measured with Pump-Probe Cathodoluminescence Spectroscopy. ACS PHOTONICS 2020; 7:232-240. [PMID: 31976357 PMCID: PMC6967233 DOI: 10.1021/acsphotonics.9b01463] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Indexed: 05/20/2023]
Abstract
Nitrogen-vacancy (NV) centers in diamond are reliable single-photon emitters, with applications in quantum technologies and metrology. Two charge states are known for NV centers, NV0 and NV-, with the latter being mostly studied due to its long electron spin coherence time. Therefore, control over the charge state of the NV centers is essential. However, an understanding of the dynamics between the different states still remains challenging. Here, conversion from NV- to NV0 due to electron-induced carrier generation is shown. Ultrafast pump-probe cathodoluminescence spectroscopy is presented for the first time, with electron pulses as pump and laser pulses as probe, to prepare and read out the NV states. The experimental data are explained with a model considering carrier dynamics (0.8 ns), NV0 spontaneous emission (20 ns), and NV0 → NV- back transfer (500 ms). The results provide new insights into the NV- → NV0 conversion dynamics and into the use of pump-probe cathodoluminescence as a nanoscale NV characterization tool.
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Affiliation(s)
- Magdalena Solà-Garcia
- Center
for Nanophotonics, AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands
- E-mail:
| | - Sophie Meuret
- Center
for Nanophotonics, AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands
| | - Toon Coenen
- Center
for Nanophotonics, AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands
- Delmic
BV, Kanaalweg 4, 2628 EB, Delft, The Netherlands
| | - Albert Polman
- Center
for Nanophotonics, AMOLF, Science Park 104, 1098 XG, Amsterdam, The Netherlands
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16
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Polman A, Kociak M, García de Abajo FJ. Electron-beam spectroscopy for nanophotonics. NATURE MATERIALS 2019; 18:1158-1171. [PMID: 31308514 DOI: 10.1038/s41563-019-0409-1] [Citation(s) in RCA: 98] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/28/2018] [Revised: 05/04/2019] [Accepted: 05/14/2019] [Indexed: 05/22/2023]
Abstract
Progress in electron-beam spectroscopies has recently enabled the study of optical excitations with combined space, energy and time resolution in the nanometre, millielectronvolt and femtosecond domain, thus providing unique access into nanophotonic structures and their detailed optical responses. These techniques rely on ~1-300 keV electron beams focused at the sample down to sub-nanometre spots, temporally compressed in wavepackets a few femtoseconds long, and in some cases controlled by ultrafast light pulses. The electrons undergo energy losses and gains (also giving rise to cathodoluminescence light emission), which are recorded to reveal the optical landscape along the beam path. This Review portraits these advances, with a focus on coherent excitations, emphasizing the increasing level of control over the electron wavefunctions and ensuing applications in the study and technological use of optically resonant modes and polaritons in nanoparticles, 2D materials and engineered nanostructures.
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Affiliation(s)
- Albert Polman
- Center for Nanophotonics, AMOLF, Amsterdam, the Netherlands.
| | - Mathieu Kociak
- Laboratoire de Physique des Solides, Université de Paris-Sud, Orsay, France
| | - F Javier García de Abajo
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, Castelldefels (Barcelona), Spain
- ICREA-Institució Catalana de Reserca I Estudis Avançats, Barcelona, Spain
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17
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Planck's generalised radiation law and its implications for cathodoluminescence spectra. Ultramicroscopy 2019; 204:73-80. [PMID: 31129495 DOI: 10.1016/j.ultramic.2019.05.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Revised: 05/09/2019] [Accepted: 05/19/2019] [Indexed: 11/24/2022]
Abstract
Cathodoluminescence (CL) is an important analytical technique for probing the optical properties of materials at high spatial resolution. Interpretation of CL spectra is however complicated by the fact that the spectrum depends on the carrier injection density of the incident electron beam. Here a generalised version of Planck's radiation law is used to uncover the evolution of CL spectra with injection under steady-state conditions. The importance of the quasi-Fermi level is highlighted and it is shown that steady-state luminescence is suppressed when the carrier distributions undergo a population inversion. The theory is consistent with some well-known luminescence phenomena, such as the blue shifting of donor-acceptor pair transitions with increased injection, and its predictions are experimentally verified on CdTe and GaN, which are exemplar thin-film solar cell and light emitting diode materials respectively. Furthermore, the discussion is broadened to include pulsed illumination in time resolved CL, where the carrier distribution is dynamically evolving with time.
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18
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Bach N, Domröse T, Feist A, Rittmann T, Strauch S, Ropers C, Schäfer S. Coulomb interactions in high-coherence femtosecond electron pulses from tip emitters. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2019; 6:014301. [PMID: 30868085 PMCID: PMC6404915 DOI: 10.1063/1.5066093] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2018] [Accepted: 01/08/2019] [Indexed: 05/26/2023]
Abstract
Tip-based photoemission electron sources offer unique properties for ultrafast imaging, diffraction, and spectroscopy experiments with highly coherent few-electron pulses. Extending this approach to increased bunch-charges requires a comprehensive experimental study on Coulomb interactions in nanoscale electron pulses and their impact on beam quality. For a laser-driven Schottky field emitter, we assess the transverse and longitudinal electron pulse properties in an ultrafast transmission electron microscope at a high photoemission current density. A quantitative characterization of electron beam emittance, pulse duration, spectral bandwidth, and chirp is performed. Due to the cathode geometry, Coulomb interactions in the pulse predominantly occur in the direct vicinity to the tip apex, resulting in a well-defined pulse chirp and limited emittance growth. Strategies for optimizing electron source parameters are identified, enabling advanced ultrafast transmission electron microscopy approaches, such as phase-resolved imaging and holography.
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Affiliation(s)
- Nora Bach
- 4th Physical Institute - Solids and Nanostructures, University of Goettingen, Goettingen, Germany
| | - Till Domröse
- 4th Physical Institute - Solids and Nanostructures, University of Goettingen, Goettingen, Germany
| | - Armin Feist
- 4th Physical Institute - Solids and Nanostructures, University of Goettingen, Goettingen, Germany
| | - Thomas Rittmann
- 4th Physical Institute - Solids and Nanostructures, University of Goettingen, Goettingen, Germany
| | - Stefanie Strauch
- 4th Physical Institute - Solids and Nanostructures, University of Goettingen, Goettingen, Germany
| | - Claus Ropers
- 4th Physical Institute - Solids and Nanostructures, University of Goettingen, Goettingen, Germany
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19
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Meuret S, Solà Garcia M, Coenen T, Kieft E, Zeijlemaker H, Lätzel M, Christiansen S, Woo SY, Ra YH, Mi Z, Polman A. Complementary cathodoluminescence lifetime imaging configurations in a scanning electron microscope. Ultramicroscopy 2018; 197:28-38. [PMID: 30476703 DOI: 10.1016/j.ultramic.2018.11.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2018] [Revised: 11/09/2018] [Accepted: 11/13/2018] [Indexed: 11/29/2022]
Abstract
Cathodoluminescence (CL) spectroscopy provides a powerful way to characterize optical properties of materials with deep-subwavelength spatial resolution. While CL imaging to obtain optical spectra is a well-developed technology, imaging CL lifetimes with nanoscale resolution has only been explored in a few studies. In this paper we compare three different time-resolved CL techniques and compare their characteristics. Two configurations are based on the acquisition of CL decay traces using a pulsed electron beam that is generated either with an ultra-fast beam blanker, which is placed in the electron column, or by photoemission from a laser-driven electron cathode. The third configuration uses measurements of the autocorrelation function g(2) of the CL signal using either a continuous or a pulsed electron beam. The three techniques are compared in terms of complexity of implementation, spatial and temporal resolution, and measurement accuracy as a function of electron dose. A single sample of InGaN/GaN quantum wells is investigated to enable a direct comparison of lifetime measurement characteristics of the three techniques. The g(2)-based method provides decay measurements at the best spatial resolution, as it leaves the electron column configuration unaffected. The pulsed-beam methods provide better detail on the temporal excitation and decay dynamics. The ultra-fast blanker configuration delivers electron pulses as short as 30 ps at 5 keV and 250 ps at 30 keV. The repetition rate can be chosen arbitrarily up to 80 MHz and requires a conjugate plane geometry in the electron column that reduces the spatial resolution in our microscope. The photoemission configuration, pumped with 250 fs 257 nm pulses at a repetition rate from 10 kHz to 25 MHz, allows creation of electron pulses down to a few ps, with some loss in spatial resolution.
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Affiliation(s)
- S Meuret
- Center for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands.
| | - M Solà Garcia
- Center for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
| | - T Coenen
- Center for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands; Delmic BV, Kanaalweg 4, 2628 EB Delft, The Netherlands
| | - E Kieft
- Thermo Fisher Scientific, Achtseweg Noord 5, 5651 GG Eindhoven, The Netherlands
| | - H Zeijlemaker
- Center for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
| | - M Lätzel
- Max Planck Institute for the Science of Light, Staudtstrasse 2, 91058 Erlangen, Germany
| | - S Christiansen
- Max Planck Institute for the Science of Light, Staudtstrasse 2, 91058 Erlangen, Germany
| | - S Y Woo
- Department of Materials Science and Engineering, Canadian Centre for Electron Microscopy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1, Canada
| | - Y H Ra
- Department of Electrical and Computer Engineering, McGill University, 3480 University Street, Montreal, Quebec H3A 0E9, Canada
| | - Z Mi
- Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109, USA
| | - A Polman
- Center for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
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20
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Meuret S, Coenen T, Woo SY, Ra YH, Mi Z, Polman A. Nanoscale Relative Emission Efficiency Mapping Using Cathodoluminescence g (2) Imaging. NANO LETTERS 2018; 18:2288-2293. [PMID: 29546762 PMCID: PMC5897862 DOI: 10.1021/acs.nanolett.7b04891] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2017] [Revised: 03/15/2018] [Indexed: 05/25/2023]
Abstract
Cathodoluminescence (CL) imaging spectroscopy provides two-dimensional optical excitation images of photonic nanostructures with a deep-subwavelength spatial resolution. So far, CL imaging was unable to provide a direct measurement of the excitation and emission probabilities of photonic nanostructures in a spatially resolved manner. Here, we demonstrate that by mapping the cathodoluminescence autocorrelation function g(2) together with the CL spectral distribution the excitation and emission rates can be disentangled at every excitation position. We use InGaN/GaN quantum wells in GaN nanowires with diameters in the range 200-500 nm as a model system to test our new g(2) mapping methodology and find characteristic differences in excitation and emission rates both between wires and within wires. Strong differences in the average CL intensity between the wires are the result of differences in the emission efficiencies. At the highest spatial resolution, intensity variations observed within wires are the result of excitation rates that vary with the nanoscale geometry of the structures. The fact that strong spatial variations observed in the CL intensity are not only uniquely linked to variations in emission efficiency but also linked to excitation efficiency has profound implications for the interpretation of the CL data for nanostructured geometries in general.
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Affiliation(s)
- Sophie Meuret
- Center
for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
| | - Toon Coenen
- Center
for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
- The
Netherlands Delmic BV, Kanaalweg 4, 2628 EB Delft, The Netherlands
| | - Steffi Y. Woo
- Department
of Materials Science and Engineering, Canadian Centre for Electron
Microscopy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1, Canada
| | - Yong-Ho Ra
- Department
of Electrical and Computer Engineering, McGill University, 3480
University Street, Montreal, Quebec H3A 0E9, Canada
- Optic &
Display Material Center, Korea Institute
of Ceramic Engineering & Technology, Jinju 52851, Republic
of Korea
| | - Zetian Mi
- Department
of Electrical and Computer Engineering, McGill University, 3480
University Street, Montreal, Quebec H3A 0E9, Canada
- Department
of Electrical Engineering and Computer Science, Center for Photonics
and Multiscale Nanomaterials, University
of Michigan, Ann Arbor, Michigan 48109, United
States
| | - Albert Polman
- Center
for Nanophotonics, AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
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21
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Cohen M, Salomon A. Secondary Electron Cloaking with Broadband Plasmonic Resonant Absorbers. J Phys Chem Lett 2017; 8:3912-3916. [PMID: 28745891 DOI: 10.1021/acs.jpclett.7b00869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Scanning electron microscopy (SEM) is one of the most powerful tools for nanoscale inspection and imaging. It is broadly used for biomedicine, materials science, and nanotechnology, enabling spatial resolution beyond the optical diffraction limit. In SEM, a high-energy electron beam illuminates a specimen, and the emitted secondary electrons are routed to a positively biased, synchronized detector for image creation. Here, for the first time, we experimentally demonstrate a cloaking of metallic objects from a secondary electron image. We make a metallic disc with a diameter of 300 nm almost invisible to a secondary electron detector with <5 nm spatial resolution. The secondary electron cloaking is based on broadband optical radiation absorption in the near field. Our secondary electron images are in good agreement with full-wave numerical solution of Maxwell's equations at optical frequencies, confirming the concept of secondary electron cloaking based on broadband optical radiation absorption.
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Affiliation(s)
- Moshik Cohen
- Faculty of Engineering, Bar-Ilan University , Ramat-Gan 52900, Israel
- Bar-Ilan Institute for Nanotechnology & Advanced Materials , Ramat-Gan 52900, Israel
| | - Adi Salomon
- Department of Chemistry, Bar-Ilan University , Ramat-Gan 52900, Israel
- Bar-Ilan Institute for Nanotechnology & Advanced Materials , Ramat-Gan 52900, Israel
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22
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Shaheen BS, Sun J, Yang DS, Mohammed OF. Spatiotemporal Observation of Electron-Impact Dynamics in Photovoltaic Materials Using 4D Electron Microscopy. J Phys Chem Lett 2017; 8:2455-2462. [PMID: 28514160 DOI: 10.1021/acs.jpclett.7b01116] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Understanding light-triggered charge carrier dynamics near photovoltaic-material surfaces and at interfaces has been a key element and one of the major challenges for the development of real-world energy devices. Visualization of such dynamics information can be obtained using the one-of-a-kind methodology of scanning ultrafast electron microscopy (S-UEM). Here, we address the fundamental issue of how the thickness of the absorber layer may significantly affect the charge carrier dynamics on material surfaces. Time-resolved snapshots indicate that the dynamics of charge carriers generated by electron impact in the electron-photon dynamical probing regime is highly sensitive to the thickness of the absorber layer, as demonstrated using CdSe films of different thicknesses as a model system. This finding not only provides the foundation for potential applications of S-UEM to a wide range of devices in the fields of chemical and materials research, but also has impact on the use and interpretation of electron beam-induced current for optimization of photoactive materials in these devices.
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Affiliation(s)
- Basamat S Shaheen
- KAUST Solar Center, King Abdullah University of Science and Technology , Thuwal 23955-6900, Saudi Arabia
| | - Jingya Sun
- KAUST Solar Center, King Abdullah University of Science and Technology , Thuwal 23955-6900, Saudi Arabia
| | - Ding-Shyue Yang
- Department of Chemistry, University of Houston , Houston, Texas 77204, United States
| | - Omar F Mohammed
- KAUST Solar Center, King Abdullah University of Science and Technology , Thuwal 23955-6900, Saudi Arabia
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23
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Cathodoluminescence in the scanning transmission electron microscope. Ultramicroscopy 2017; 176:112-131. [DOI: 10.1016/j.ultramic.2017.03.014] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Revised: 11/16/2016] [Accepted: 11/18/2016] [Indexed: 01/18/2023]
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24
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Kociak M, Gloter A, Stéphan O. A spectromicroscope for nanophysics. Ultramicroscopy 2017; 180:81-92. [PMID: 28377215 DOI: 10.1016/j.ultramic.2017.02.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Revised: 02/05/2017] [Accepted: 02/18/2017] [Indexed: 12/01/2022]
Abstract
The new generation of spectromicroscopes opens up new fields of nanophysics. Beyond the impressive spatial and spectral resolutions delivered by these new instruments - an obvious example being the Hermes machine conceived, designed and built by O. L. Krivanek, who is honoured in this journal issue - here we wish to address the motivations and conditions required to get the best out of them. We first coarsely sketch the panorama of physical excitations worth motivating the use of ultra-high resolution spectroscopy techniques in STEMs. We then give general considerations on the use of combined spectroscopy techniques, reciprocal space measurements and additional time-resolved experiments to complement the wealth of the physical insights provided by the new-generation spectromicroscopes. We then comment on the newly enhanced mechanical and high voltage stabilities and their effects on the accuracy of spectroscopic measurements. The use of temperature-dependent experiments, to bring electron spectroscopy techniques to the standard of other condensed matter physics techniques such as optical and X-ray spectroscopy, is also described. We finish by evaluating the impact of other breakthrough developments, such as energy gain electron spectroscopy or electron-phase manipulation, on the use of ultra-high resolution spectromicroscopes.
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Affiliation(s)
- M Kociak
- Laboratoire de Physique des Solides, Université Paris-Sud, CNRS-UMR 8502, Orsay 91405, France.
| | - A Gloter
- Laboratoire de Physique des Solides, Université Paris-Sud, CNRS-UMR 8502, Orsay 91405, France
| | - O Stéphan
- Laboratoire de Physique des Solides, Université Paris-Sud, CNRS-UMR 8502, Orsay 91405, France
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25
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Cohen M, Abulafia Y, Shavit R, Zalevsky Z. Secondary Electron Imaging of Light at the Nanoscale. ACS NANO 2017; 11:3274-3281. [PMID: 28264151 DOI: 10.1021/acsnano.7b00548] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The interaction of fast electrons with metal atoms may lead to optical excitations. This exciting phenomenon forms the basis for the most powerful inspection methods in nanotechnology, such as cathodoluminescence and electron-energy loss spectroscopy. However, direct nanoimaging of light based on electrons is yet to be introduced. Here, we experimentally demonstrate simultaneous excitation and nanoimaging of optical signals using unmodified scanning electron microscope. We use high-energy electron beam for plasmon excitation and rapidly image the optical near fields using the emitted secondary electrons. We analyze dipole nanoantennas coupled with channel nanoplasmonic waveguides and observe both surface plasmons and surface plasmon polaritons with spatial resolution of 25 nm. Our experimental results are confirmed by rigorous numerical calculations based on full-wave solution of Maxwell's equations, showing high correlation between optical near fields and secondary electrons images. This demonstration of optical near-field mapping using direct electron imaging provides essential insights to the exciting relations between electrons plasmons and photons, paving the way toward secondary electron-based plasmon analysis at the nanoscale.
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Affiliation(s)
- Moshik Cohen
- Department of Electrical and Computer Engineering, Ben-Gurion University of the Negev , Beer-Sheva 84105, Israel
| | | | - Reuven Shavit
- Department of Electrical and Computer Engineering, Ben-Gurion University of the Negev , Beer-Sheva 84105, Israel
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26
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Kociak M, Zagonel LF. Cathodoluminescence in the scanning transmission electron microscope. Ultramicroscopy 2016; 174:50-69. [PMID: 28040579 DOI: 10.1016/j.ultramic.2016.11.018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Revised: 11/16/2016] [Accepted: 11/18/2016] [Indexed: 01/18/2023]
Abstract
Cathodoluminescence (CL) is a powerful tool for the investigation of optical properties of materials. In recent years, its combination with scanning transmission electron microscopy (STEM) has demonstrated great success in unveiling new physics in the field of plasmonics and quantum emitters. Most of these results were not imaginable even twenty years ago, due to conceptual and technical limitations. The purpose of this review is to present the recent advances that broke these limitations, and the new possibilities offered by the modern STEM-CL technique. We first introduce the different STEM-CL operating modes and the technical specificities in STEM-CL instrumentation. Two main classes of optical excitations, namely the coherent one (typically plasmons) and the incoherent one (typically light emission from quantum emitters) are investigated with STEM-CL. For these two main classes, we describe both the physics of light production under electron beam irradiation and the physical basis for interpreting STEM-CL experiments. We then compare STEM-CL with its better known sister techniques: scanning electron microscope CL, photoluminescence, and electron energy-loss spectroscopy. We finish by comprehensively reviewing recent STEM-CL applications.
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Affiliation(s)
- M Kociak
- Laboratoire de Physique des Solides, Université Paris-SudParis-Sud, CNRS-UMR 8502, Orsay 91405, France.
| | - L F Zagonel
- "Gleb Wataghin" Institute of Physics University of Campinas - UNICAMP, 13083-859 Campinas, São Paulo, Brazil
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27
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Feist A, Bach N, Rubiano da Silva N, Danz T, Möller M, Priebe KE, Domröse T, Gatzmann JG, Rost S, Schauss J, Strauch S, Bormann R, Sivis M, Schäfer S, Ropers C. Ultrafast transmission electron microscopy using a laser-driven field emitter: Femtosecond resolution with a high coherence electron beam. Ultramicroscopy 2016; 176:63-73. [PMID: 28139341 DOI: 10.1016/j.ultramic.2016.12.005] [Citation(s) in RCA: 123] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2016] [Revised: 11/30/2016] [Accepted: 12/02/2016] [Indexed: 10/20/2022]
Abstract
We present the development of the first ultrafast transmission electron microscope (UTEM) driven by localized photoemission from a field emitter cathode. We describe the implementation of the instrument, the photoemitter concept and the quantitative electron beam parameters achieved. Establishing a new source for ultrafast TEM, the Göttingen UTEM employs nano-localized linear photoemission from a Schottky emitter, which enables operation with freely tunable temporal structure, from continuous wave to femtosecond pulsed mode. Using this emission mechanism, we achieve record pulse properties in ultrafast electron microscopy of 9Å focused beam diameter, 200fs pulse duration and 0.6eV energy width. We illustrate the possibility to conduct ultrafast imaging, diffraction, holography and spectroscopy with this instrument and also discuss opportunities to harness quantum coherent interactions between intense laser fields and free-electron beams.
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Affiliation(s)
- Armin Feist
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany
| | - Nora Bach
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany
| | - Nara Rubiano da Silva
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany
| | - Thomas Danz
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany
| | - Marcel Möller
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany
| | - Katharina E Priebe
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany
| | - Till Domröse
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany
| | - J Gregor Gatzmann
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany
| | - Stefan Rost
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany
| | - Jakob Schauss
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany
| | - Stefanie Strauch
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany
| | - Reiner Bormann
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany
| | - Murat Sivis
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany
| | - Sascha Schäfer
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany.
| | - Claus Ropers
- 4th Physical Institute - Solids and Nanostructures, University of Göttingen, Göttingen, Germany.
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28
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Abstract
Recent advances in the physics and technology of light generation via free-electron proximity and impact interactions with nanostructures (gratings, photonic crystals, nano-undulators, metamaterials and antenna arrays) have enabled the development of nanoscale-resolution techniques for such applications as mapping plasmons, studying nanoparticle structural transformations and characterizing luminescent materials (including time-resolved measurements). Here, we introduce a universal approach allowing generation of light with prescribed wavelength, direction, divergence and topological charge via point-excitation of holographic plasmonic metasurfaces. It is illustrated using medium-energy free-electron injection to generate highly-directional visible to near-infrared light beams, at selected wavelengths in prescribed azimuthal and polar directions, with brightness two orders of magnitude higher than that from an unstructured surface, and vortex beams with topological charge up to ten. Such emitters, with micron-scale dimensions and the freedom to fully control radiation parameters, offer novel applications in nano-spectroscopy, nano-chemistry and sensing. Controlling the generation of light in nano-scale systems is a challenging task and is of growing importance. Here, Li et al. propose a means of controlling the wavefront of light emanating from a single nano scale emitter by holographic principles using a plasmonic metasurface.
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29
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Moerland RJ, Weppelman IGC, Garming MWH, Kruit P, Hoogenboom JP. Time-resolved cathodoluminescence microscopy with sub-nanosecond beam blanking for direct evaluation of the local density of states. OPTICS EXPRESS 2016; 24:24760-24772. [PMID: 27828196 DOI: 10.1364/oe.24.024760] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
We show cathodoluminescence-based time-resolved electron beam spectroscopy in order to directly probe the spontaneous emission decay rate that is modified by the local density of states in a nanoscale environment. In contrast to dedicated laser-triggered electron-microscopy setups, we use commercial hardware in a standard SEM, which allows us to easily switch from pulsed to continuous operation of the SEM. Electron pulses of 80-90 ps duration are generated by conjugate blanking of a high-brightness electron beam, which allows probing emitters within a large range of decay rates. Moreover, we simultaneously attain a resolution better than λ/10, which ensures details at deep-subwavelength scales can be retrieved. As a proof-of-principle, we employ the pulsed electron beam to spatially measure excited-state lifetime modifications in a phosphor material across the edge of an aluminum half-plane, coated on top of the phosphor. The measured emission dynamics can be directly related to the structure of the sample by recording photon arrival histograms together with the secondary-electron signal. Our results show that time-resolved electron cathodoluminescence spectroscopy is a powerful tool of choice for nanophotonics, within reach of a large audience.
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30
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Talebi N. Spectral Interferometry with Electron Microscopes. Sci Rep 2016; 6:33874. [PMID: 27649932 PMCID: PMC5030644 DOI: 10.1038/srep33874] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Accepted: 09/05/2016] [Indexed: 11/14/2022] Open
Abstract
Interference patterns are not only a defining characteristic of waves, but also have several applications; characterization of coherent processes and holography. Spatial holography with electron waves, has paved the way towards space-resolved characterization of magnetic domains and electrostatic potentials with angstrom spatial resolution. Another impetus in electron microscopy has been introduced by ultrafast electron microscopy which uses pulses of sub-picosecond durations for probing a laser induced excitation of the sample. However, attosecond temporal resolution has not yet been reported, merely due to the statistical distribution of arrival times of electrons at the sample, with respect to the laser time reference. This is however, the very time resolution which will be needed for performing time-frequency analysis. These difficulties are addressed here by proposing a new methodology to improve the synchronization between electron and optical excitations through introducing an efficient electron-driven photon source. We use focused transition radiation of the electron as a pump for the sample. Due to the nature of transition radiation, the process is coherent. This technique allows us to perform spectral interferometry with electron microscopes, with applications in retrieving the phase of electron-induced polarizations and reconstructing dynamics of the induced vector potential.
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Affiliation(s)
- Nahid Talebi
- Stuttgart Center for Electron Microscopy, Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany
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31
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Segal E, Weissman A, Gachet D, Salomon A. Hybridization between nanocavities for a polarimetric color sorter at the sub-micron scale. NANOSCALE 2016; 8:15296-15302. [PMID: 27500634 DOI: 10.1039/c6nr03528k] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Metallic hole arrays have been recently used for color generation and filtering due to their reliability and color tunability. However, color generation is still limited to several microns. Understanding the interaction between the individual elements of the whole nanostructure may push the resolution to the sub-micron level. Herein, we study the hybridization between silver nanocavities in order to obtain active color generation at the micron scale. To do so, we use five identical triangular cavities which are separated by hundreds of nanometers from each other. By tuning either the distance between the cavities or the optical polarization state of the incoming field, the transmitted light through the cavities is actively enhanced at specific frequencies. Consequently, a rainbow of colors is observed from a sub-micron scale unit. The reason for this is that the metallic surface plays a vital role in the hybridization between the cavities and contributes to higher frequency modes. Cathodoluminescence measurements have confirmed this assumption and have revealed that these five triangular cavities act as a unified entity surrounded by the propagated surface plasmons. In such plasmonic structures, multi-color tuning can be accomplished and may open the possibility to improve color generation and high-quality pixel fabrication.
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Affiliation(s)
- Elad Segal
- Department of Chemistry, Institute of Nanotechnology and Advanced Materials (BINA), Bar-Ilan University, Ramat-Gan 5290002, Israel.
| | - Adam Weissman
- Department of Chemistry, Institute of Nanotechnology and Advanced Materials (BINA), Bar-Ilan University, Ramat-Gan 5290002, Israel.
| | - David Gachet
- Attolight AG, EPFL Innovation Park, Building D, 1015 Lausanne, Switzerland
| | - Adi Salomon
- Department of Chemistry, Institute of Nanotechnology and Advanced Materials (BINA), Bar-Ilan University, Ramat-Gan 5290002, Israel.
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32
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Operating organic light-emitting diodes imaged by super-resolution spectroscopy. Nat Commun 2016; 7:11691. [PMID: 27325212 PMCID: PMC5512612 DOI: 10.1038/ncomms11691] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Accepted: 04/19/2016] [Indexed: 11/09/2022] Open
Abstract
Super-resolution stimulated emission depletion (STED) microscopy is adapted here for materials characterization that would not otherwise be possible. With the example of organic light-emitting diodes (OLEDs), spectral imaging with pixel-by-pixel wavelength discrimination allows us to resolve local-chain environment encoded in the spectral response of the semiconducting polymer, and correlate chain packing with local electroluminescence by using externally applied current as the excitation source. We observe nanoscopic defects that would be unresolvable by traditional microscopy. They are revealed in electroluminescence maps in operating OLEDs with 50 nm spatial resolution. We find that brightest emission comes from regions with more densely packed chains. Conventional microscopy of an operating OLED would lack the resolution needed to discriminate these features, while traditional methods to resolve nanoscale features generally cannot be performed when the device is operating. This points the way towards real-time analysis of materials design principles in devices as they actually operate. There is a need to characterize devices during operation in real-time and at nanoscopic length scales. Here, King et al. perform electroluminescence-STED imaging with a polymer based light-emitting diode, revealing nanoscopic defects that would be unresolvable with traditional optical microscopy.
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33
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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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34
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Ultrafast strong-field photoelectron emission from biased metal surfaces: exact solution to time-dependent Schrödinger Equation. Sci Rep 2016; 6:19894. [PMID: 26818710 PMCID: PMC4730214 DOI: 10.1038/srep19894] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2015] [Accepted: 12/21/2015] [Indexed: 11/08/2022] Open
Abstract
Laser-driven ultrafast electron emission offers the possibility of manipulation and control of coherent electron motion in ultrashort spatiotemporal scales. Here, an analytical solution is constructed for the highly nonlinear electron emission from a dc biased metal surface illuminated by a single frequency laser, by solving the time-dependent Schrödinger equation exactly. The solution is valid for arbitrary combinations of dc electric field, laser electric field, laser frequency, metal work function and Fermi level. Various emission mechanisms, such as multiphoton absorption or emission, optical or dc field emission, are all included in this single formulation. The transition between different emission processes is analyzed in detail. The time-dependent emission current reveals that intense current modulation may be possible even with a low intensity laser, by merely increasing the applied dc bias. The results provide insights into the electron pulse generation and manipulation for many novel applications based on ultrafast laser-induced electron emission.
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35
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Shahmohammadi M, Ganière JD, Zhang H, Ciechonski R, Vescovi G, Kryliouk O, Tchernycheva M, Jacopin G. Excitonic Diffusion in InGaN/GaN Core-Shell Nanowires. NANO LETTERS 2016; 16:243-9. [PMID: 26674850 DOI: 10.1021/acs.nanolett.5b03611] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We report on the direct observation of the diffusion of carriers in graded InGaN/GaN quantum wells in a nanowire. By probing the local dynamics at the nanoscale, along the wire for different temperatures between 4 and 250 K, we conclude that this diffusion process is thermally activated. In addition, the analysis of the cathodoluminescence lifetime for different temperatures shows that the carrier motion is isotropic and does not follow the indium gradient. Our observations are interpreted in terms of a hopping process between localized states. We find that the random alloy fluctuations prevent any directional drift of excitons along the In gradient and therefore any carrier accumulation. Our results therefore confirm the potential of core-shell nanowires for lighting devices. Indeed, the short lifetime of m-plane quantum wells together with their large active area and the homogeneous distribution of carrier along the quantum well will decrease influence of any high carrier density effect on the efficiency of these light-emitting diodes.
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Affiliation(s)
- M Shahmohammadi
- Laboratory of Quantum Optoelectronics, Ecole Polytechnique Fédérale de Lausanne (EPFL) , 1015 Lausanne, Switzerland
| | - J-D Ganière
- Laboratory of Quantum Optoelectronics, Ecole Polytechnique Fédérale de Lausanne (EPFL) , 1015 Lausanne, Switzerland
| | - H Zhang
- Institut d'Electronique Fondamentale, UMR 8622 CNRS, Université Paris-Saclay , 91405 Orsay cedex, France
| | - R Ciechonski
- GLO AB , Ideon Science Park, Scheelevägen 17, S-223 70 Lund, Sweden
| | - G Vescovi
- GLO AB , Ideon Science Park, Scheelevägen 17, S-223 70 Lund, Sweden
| | - O Kryliouk
- GLO-USA , 1225 Bordeaux Drive, Sunnyvale, California 94086, United States
| | - M Tchernycheva
- Institut d'Electronique Fondamentale, UMR 8622 CNRS, Université Paris-Saclay , 91405 Orsay cedex, France
| | - G Jacopin
- Laboratory of Quantum Optoelectronics, Ecole Polytechnique Fédérale de Lausanne (EPFL) , 1015 Lausanne, Switzerland
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36
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Mendis BG, Gachet D, Major JD, Durose K. Long Lifetime Hole Traps at Grain Boundaries in CdTe Thin-Film Photovoltaics. PHYSICAL REVIEW LETTERS 2015; 115:218701. [PMID: 26636877 DOI: 10.1103/physrevlett.115.218701] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Indexed: 06/05/2023]
Abstract
A novel time-resolved cathodoluminescence method, where a pulsed electron beam is generated via the photoelectric effect, is used to probe individual CdTe grain boundaries. Excitons have a short lifetime (≤100 ps) within the grains and are rapidly quenched at the grain boundary. However, a ~47 meV shallow acceptor, believed to be due to oxygen, can act as a long lifetime hole trap, even at the grain boundaries where their concentration is higher. This provides direct evidence supporting recent observations of hopping conduction across grain boundaries in highly doped CdTe at low temperature.
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Affiliation(s)
- B G Mendis
- Deptartment of Physics, Durham University, South Road, Durham DH1 3LE, United Kingdom
| | - D Gachet
- Attolight AG, EPFL Innovation Square, Building D, 1015 Lausanne, Switzerland
| | - J D Major
- Stephenson Institute for Renewable Energy, University of Liverpool, Chadwick Building, Liverpool L69 7ZF, United Kingdom
| | - K Durose
- Stephenson Institute for Renewable Energy, University of Liverpool, Chadwick Building, Liverpool L69 7ZF, United Kingdom
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37
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Griffiths JT, Zhang S, Rouet-Leduc B, Fu WY, Bao A, Zhu D, Wallis DJ, Howkins A, Boyd I, Stowe D, Kappers MJ, Humphreys CJ, Oliver RA. Nanocathodoluminescence Reveals Mitigation of the Stark Shift in InGaN Quantum Wells by Si Doping. NANO LETTERS 2015; 15:7639-43. [PMID: 26488912 PMCID: PMC4682848 DOI: 10.1021/acs.nanolett.5b03531] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Revised: 10/19/2015] [Indexed: 05/24/2023]
Abstract
Nanocathodoluminescence reveals the spectral properties of individual InGaN quantum wells in high efficiency light emitting diodes. We observe a variation in the emission wavelength of each quantum well, in correlation with the Si dopant concentration in the quantum barriers. This is reproduced by band profile simulations, which reveal the reduction of the Stark shift in the quantum wells by Si doping. We demonstrate nanocathodoluminescence is a powerful technique to optimize doping in optoelectronic devices.
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Affiliation(s)
- James T. Griffiths
- Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
| | - Siyuan Zhang
- Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
| | - Bertrand Rouet-Leduc
- Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
| | - Wai Yuen Fu
- Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
| | - An Bao
- Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
| | - Dandan Zhu
- Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
- Plessey Semiconductors, Tamerton Road, Plymouth PL6 7BQ, United Kingdom
| | - David J. Wallis
- Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
- Plessey Semiconductors, Tamerton Road, Plymouth PL6 7BQ, United Kingdom
| | - Ashley Howkins
- Experimental
Techniques Centre, Brunel University, Uxbridge UB8 3PH, United Kingdom
| | - Ian Boyd
- Experimental
Techniques Centre, Brunel University, Uxbridge UB8 3PH, United Kingdom
| | - David Stowe
- Gatan U.K., 25 Nuffield Way, Abingdon, Oxon OX14 1RL, United Kingdom
| | - Menno J. Kappers
- Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
| | - Colin J. Humphreys
- Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
| | - Rachel A. Oliver
- Department of Materials Science and Metallurgy, University of Cambridge, Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
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38
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Ogletree DF, Schuck PJ, Weber-Bargioni AF, Borys NJ, Aloni S, Bao W, Barja S, Lee J, Melli M, Munechika K, Whitelam S, Wickenburg S. Revealing Optical Properties of Reduced-Dimensionality Materials at Relevant Length Scales. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2015; 27:5693-5719. [PMID: 26332202 DOI: 10.1002/adma.201500930] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Revised: 05/26/2015] [Indexed: 06/05/2023]
Abstract
Reduced-dimensionality materials for photonic and optoelectronic applications including energy conversion, solid-state lighting, sensing, and information technology are undergoing rapid development. The search for novel materials based on reduced-dimensionality is driven by new physics. Understanding and optimizing material properties requires characterization at the relevant length scale, which is often below the diffraction limit. Three important material systems are chosen for review here, all of which are under investigation at the Molecular Foundry, to illustrate the current state of the art in nanoscale optical characterization: 2D semiconducting transition metal dichalcogenides; 1D semiconducting nanowires; and energy-transfer in assemblies of 0D semiconducting nanocrystals. For each system, the key optical properties, the principal experimental techniques, and important recent results are discussed. Applications and new developments in near-field optical microscopy and spectroscopy, scanning probe microscopy, and cathodoluminescence in the electron microscope are given detailed attention. Work done at the Molecular Foundry is placed in context within the fields under review. A discussion of emerging opportunities and directions for the future closes the review.
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Affiliation(s)
- D Frank Ogletree
- Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
| | - P James Schuck
- Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
| | - Alexander F Weber-Bargioni
- Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
| | - Nicholas J Borys
- Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
| | - Shaul Aloni
- Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
| | - Wei Bao
- Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
- Materials Science and Engineering, University of California, Berkeley, California, 94720, USA
| | - Sara Barja
- Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
| | - Jiye Lee
- Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
| | - Mauro Melli
- Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
| | - Keiko Munechika
- Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
| | - Stephan Whitelam
- Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
| | - Sebastian Wickenburg
- Molecular Foundry, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, 94720, USA
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39
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Sun J, Melnikov VA, Khan JI, Mohammed OF. Real-Space Imaging of Carrier Dynamics of Materials Surfaces by Second-Generation Four-Dimensional Scanning Ultrafast Electron Microscopy. J Phys Chem Lett 2015; 6:3884-3890. [PMID: 26722888 DOI: 10.1021/acs.jpclett.5b01867] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
In the fields of photocatalysis and photovoltaics, ultrafast dynamical processes, including carrier trapping and recombination on material surfaces, are among the key factors that determine the overall energy conversion efficiency. A precise knowledge of these dynamical events on the nanometer (nm) and femtosecond (fs) scales was not accessible until recently. The only way to access such fundamental processes fully is to map the surface dynamics selectively in real space and time. In this study, we establish a second generation of four-dimensional scanning ultrafast electron microscopy (4D S-UEM) and demonstrate the ability to record time-resolved images (snapshots) of material surfaces with 650 fs and ∼5 nm temporal and spatial resolutions, respectively. In this method, the surface of a specimen is excited by a clocking optical pulse and imaged using a pulsed primary electron beam as a probe pulse, generating secondary electrons (SEs), which are emitted from the surface of the specimen in a manner that is sensitive to the local electron/hole density. This method provides direct and controllable information regarding surface dynamics. We clearly demonstrate how the surface morphology, grains, defects, and nanostructured features can significantly impact the overall dynamical processes on the surface of photoactive-materials. In addition, the ability to access two regimes of dynamical probing in a single experiment and the energy loss of SEs in semiconductor-nanoscale materials will also be discussed.
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Affiliation(s)
- Jingya Sun
- Solar and Photovoltaics Engineering Research Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Vasily A Melnikov
- Solar and Photovoltaics Engineering Research Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Jafar I Khan
- Solar and Photovoltaics Engineering Research Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Omar F Mohammed
- Solar and Photovoltaics Engineering Research Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia
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40
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Bischak CG, Sanehira EM, Precht JT, Luther JM, Ginsberg NS. Heterogeneous Charge Carrier Dynamics in Organic-Inorganic Hybrid Materials: Nanoscale Lateral and Depth-Dependent Variation of Recombination Rates in Methylammonium Lead Halide Perovskite Thin Films. NANO LETTERS 2015; 15:4799-4807. [PMID: 26098220 DOI: 10.1021/acs.nanolett.5b01917] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We reveal substantial luminescence yield heterogeneity among individual subdiffraction grains of high-performing methylammonium lead halide perovskite films by using high-resolution cathodoluminescence microscopy. Using considerably lower accelerating voltages than is conventional in scanning electron microscopy, we image the electron beam-induced luminescence of the films and statistically characterize the depth-dependent role of defects that promote nonradiative recombination losses. The highest variability in the luminescence intensity is observed at the exposed grain surfaces, which we attribute to surface defects. By probing deeper into the film, it appears that bulk defects are more homogeneously distributed. By identifying the origin and variability of a surface-specific loss mechanism that deleteriously impacts device efficiency, we suggest that producing films homogeneously composed of the highest-luminescence grains found in this study could result in a dramatic improvement of overall device efficiency. We also show that although cathodoluminescence microscopy is generally used only to image inorganic materials it can be a powerful tool to investigate radiative and nonradiative charge carrier recombination on the nanoscale in organic-inorganic hybrid materials.
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Affiliation(s)
| | - Erin M Sanehira
- ⊥National Renewable Energy Laboratory, Golden, Colorado 80401, United States
- #Department of Electrical Engineering, University of Washington, Seattle, Washington 98195, United States
| | | | - Joseph M Luther
- ⊥National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Naomi S Ginsberg
- ∇Kavli Energy NanoSciences Institute, Berkeley, California 94720, United States
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41
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Three-dimensional Aerographite-GaN hybrid networks: single step fabrication of porous and mechanically flexible materials for multifunctional applications. Sci Rep 2015; 5:8839. [PMID: 25744694 PMCID: PMC4351516 DOI: 10.1038/srep08839] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Accepted: 02/06/2015] [Indexed: 02/01/2023] Open
Abstract
Three dimensional (3D) elastic hybrid networks built from interconnected nano- and microstructure building units, in the form of semiconducting-carbonaceous materials, are potential candidates for advanced technological applications. However, fabrication of these 3D hybrid networks by simple and versatile methods is a challenging task due to the involvement of complex and multiple synthesis processes. In this paper, we demonstrate the growth of Aerographite-GaN 3D hybrid networks using ultralight and extremely porous carbon based Aerographite material as templates by a single step hydride vapor phase epitaxy process. The GaN nano- and microstructures grow on the surface of Aerographite tubes and follow the network architecture of the Aerographite template without agglomeration. The synthesized 3D networks are integrated with the properties from both, i.e., nanoscale GaN structures and Aerographite in the form of flexible and semiconducting composites which could be exploited as next generation materials for electronic, photonic, and sensors applications.
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42
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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
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43
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Fu X, Jacopin G, Shahmohammadi M, Liu R, Benameur M, Ganière JD, Feng J, Guo W, Liao ZM, Deveaud B, Yu D. Exciton drift in semiconductors under uniform strain gradients: application to bent ZnO microwires. ACS NANO 2014; 8:3412-20. [PMID: 24654837 DOI: 10.1021/nn4062353] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Optimizing the electronic structures and carrier dynamics in semiconductors at atomic scale is an essential issue for innovative device applications. Besides the traditional chemical doping and the use of homo/heterostructures, elastic strain has been proposed as a promising possibility. Here, we report on the direct observation of the dynamics of exciton transport in a ZnO microwire under pure elastic bending deformation, by using cathodoluminescence with high temporal, spatial, and energy resolutions. We demonstrate that excitons can be effectively drifted by the strain gradient in inhomogeneous strain fields. Our observations are well reproduced by a drift-diffusion model taking into account the strain gradient and allow us to deduce an exciton mobility of 1400 ± 100 cm(2)/(eV s) in the ZnO wire. These results propose a way to tune the exciton dynamics in semiconductors and imply the possible role of strain gradient in optoelectronic and sensing nano/microdevices.
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Affiliation(s)
- Xuewen Fu
- State Key Laboratory for Mesoscopic Physics, and Electron Microscopy Laboratory, Department of Physics, Peking University , 209 Chengfu Road, Beijing 100871, China
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44
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Tizei LHG, Kociak M. Spatially resolved quantum nano-optics of single photons using an electron microscope. PHYSICAL REVIEW LETTERS 2013; 110:153604. [PMID: 25167267 DOI: 10.1103/physrevlett.110.153604] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Revised: 02/15/2013] [Indexed: 05/25/2023]
Abstract
We report on the experimental demonstration of single-photon state generation and characterization in an electron microscope. In this aim we have used low intensity relativistic (energy between 60 and 100 keV) electrons beams focused in a ca. 1 nm probe to excite diamond nanoparticles. This triggered individual neutral nitrogen-vacancy centers to emit photons which could be gathered and sent to a Hanbury Brown-Twiss intensity interferometer. The detection of a dip in the correlation function at small time delays clearly demonstrates antibunching and thus the creation of nonclassical light states. Specifically, we have also demonstrated single-photon states detection. We unveil the mechanism behind quantum states generation in an electron microscope, and show that it clearly makes cathodoluminescence the nanometer scale analog of photoluminescence. By using an extremely small electron probe size and the ability to monitor its position with subnanometer resolution, we also show the possibility of measuring the quantum character of the emitted beam with deep subwavelength resolution.
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Affiliation(s)
- L H G Tizei
- Laboratoire de Physique des Solides, Université Paris-Sud, CNRS-UMR 8502, Orsay 91405, France
| | - M Kociak
- Laboratoire de Physique des Solides, Université Paris-Sud, CNRS-UMR 8502, Orsay 91405, France
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45
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Padilha LA, Bae WK, Klimov VI, Pietryga JM, Schaller RD. Response of semiconductor nanocrystals to extremely energetic excitation. NANO LETTERS 2013; 13:925-932. [PMID: 23373470 DOI: 10.1021/nl400141w] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Using a combination of transient photoluminescence and transient cathodoluminescence (trCL) we, for the first time, identify and quantify the distribution of electronic excitations in colloidal semiconductor nanocrystals (NCs) under high-energy excitation. Specifically, we compare the temporally and spectrally resolved radiative recombination produced following excitation with 3.1 eV, subpicosecond photon pulses, or with ionizing radiation in the form of 20 keV picosecond electron pulses. Using this approach, we derive excitation branching ratios produced in the scenario of energetic excitation of NCs typical of X-ray, neutron, or gamma-ray detectors. Resultant trCL spectra and dynamics for CdSe NCs indicate that all observable emission can be attributed to recombination between states within the quantum-confined nanostructure with particularly significant yields of trions and multiexcitons produced by carrier multiplication. Our observations offer direct insight into the transduction of atomic excitation into quantum-confined states within NCs, explain that the root cause of poor performance in previous scintillation studies arises from efficient nonradiative Auger recombination, and suggest routes for improved detector materials.
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Affiliation(s)
- Lazaro A Padilha
- Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
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46
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Onuma T, Kagamitani Y, Hazu K, Ishiguro T, Fukuda T, Chichibu SF. Femtosecond-laser-driven photoelectron-gun for time-resolved cathodoluminescence measurement of GaN. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2012; 83:043905. [PMID: 22559547 DOI: 10.1063/1.3701368] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
A rear-excitation femtosecond-laser-driven photoelectron gun (PE-gun) is developed for measuring time-resolved cathodoluminescence (TRCL) spectrum of wide bandgap materials and structures such as semiconductors and phosphors. The maximum quantum efficiency of a 20-nm-thick Au photocathode excited using a frequency-tripled Al(2)O(3):Ti laser under a rear-excitation configuration is 3.6×10(-6), which is a reasonable value for a PE-gun. When the distance between the front edge of the PE-gun and the observation point is 10 mm, the narrowest electron-beam (e-beam) diameter is 19 μm, which corresponds to one tenth of the laser-beam diameter and is comparable to the initial e-beam diameter of a typical W hair-pin filament of thermionic electron-gun. From the results of TRCL measurements on the freestanding GaN grown by the ammonothermal method and a GaN homoepitaxial film grown by metalorganic vapor phase epitaxy, overall response time for the present TRCL system is estimated to be 8 ps. The value is the same as that of time-resolved photoluminescence measurement using the same excitation laser pulses, meaning that the time-resolution is simply limited by the streak-camera, not by the PE-gun performance. The result of numerical simulation on the temporal e-beam broadening caused by the space-charge-effect suggests that the present PE-gun can be used as a pulsed e-beam source for spatio-time-resolved cathodoluminescence, when equipped in a scanning electron microscope.
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Affiliation(s)
- T Onuma
- Center for Advanced Nitride Technology (CANTech), Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan
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47
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Lindquist NC, Nagpal P, McPeak KM, Norris DJ, Oh SH. Engineering metallic nanostructures for plasmonics and nanophotonics. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2012; 75:036501. [PMID: 22790420 PMCID: PMC3396886 DOI: 10.1088/0034-4885/75/3/036501] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Metallic nanostructures now play an important role in many applications. In particular, for the emerging fields of plasmonics and nanophotonics, the ability to engineer metals on nanometric scales allows the development of new devices and the study of exciting physics. This review focuses on top-down nanofabrication techniques for engineering metallic nanostructures, along with computational and experimental characterization techniques. A variety of current and emerging applications are also covered.
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Affiliation(s)
- Nathan C Lindquist
- Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, U.S.A
- Physics Department, Bethel University, St. Paul, MN, U.S.A
| | | | - Kevin M McPeak
- Optical Materials Engineering Laboratory, ETH Zürich, Zürich, Switzerland
| | - David J Norris
- Optical Materials Engineering Laboratory, ETH Zürich, Zürich, Switzerland
| | - Sang-Hyun Oh
- Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN, U.S.A
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48
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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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49
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Bok J, Schauer P. LabVIEW-based control and data acquisition system for cathodoluminescence experiments. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2011; 82:113109. [PMID: 22128968 DOI: 10.1063/1.3662203] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Computer automation of cathodoluminescence (CL) experiments using equipment developed in our laboratory is described. The equipment provides various experiments for CL efficiency, CL spectra, and CL time response studies. The automation was realized utilizing the graphical programming environment LabVIEW. The developed application software with procedures for equipment control and data acquisition during various CL experiments is presented. As the measured CL data are distorted by technical limitations of the equipment, such as equipment spectral sensitivity and time response, data correction algorithms were incorporated into the procedures. Some examples of measured data corrections are presented.
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Affiliation(s)
- J Bok
- Institute of Scientific Instruments of the ASCR, v.v.i., Department of Electron Optics, Královopolská 147, CZ-61264 Brno, Czech Republic.
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50
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Corfdir P, Abid M, Mouti A, Stadelmann PA, Papa E, Ansermet JP, Ganière JD, Deveaud-Plédran B. Biexciton emission and crystalline quality of ZnO nano-objects. NANOTECHNOLOGY 2011; 22:285710. [PMID: 21659685 DOI: 10.1088/0957-4484/22/28/285710] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The design of cost-effective standards for the quality of nano-objects is currently a key issue toward their massive use for optoelectronic applications. The observation by photoluminescence of narrow excitonic and biexcitonic emission lines in semiconductor nanowires is usually accepted as evidence for high structural quality. Here, we perform time-resolved cathodoluminescence experiments on isolated ZnO nanobelts grown by chemical vapor deposition. We observe narrow emission lines at low temperature, together with a clear biexciton line. Still, drastic alterations in both the CL intensity and lifetime are observed locally along the nano-object. We attribute these to non-radiative recombinations at edge dislocations, closing basal plane stacking faults, inhomogeneously distributed along the NB length. This leads us to the conclusion that the observation of narrow excitonic and biexcitonic emission lines is far from sufficient to grade the quality of a nano-object.
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Affiliation(s)
- Pierre Corfdir
- Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.
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