1
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Perez C, Ellis SR, Alcorn FM, Smoll EJ, Fuller EJ, Leonard F, Chandler D, Talin AA, Bisht RS, Ramanathan S, Goodson KE, Kumar S. Picosecond carrier dynamics in InAs and GaAs revealed by ultrafast electron microscopy. SCIENCE ADVANCES 2024; 10:eadn8980. [PMID: 38748793 PMCID: PMC11095486 DOI: 10.1126/sciadv.adn8980] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/05/2024] [Accepted: 04/10/2024] [Indexed: 05/19/2024]
Abstract
Understanding the limits of spatiotemporal carrier dynamics, especially in III-V semiconductors, is key to designing ultrafast and ultrasmall optoelectronic components. However, identifying such limits and the properties controlling them has been elusive. Here, using scanning ultrafast electron microscopy, in bulk n-GaAs and p-InAs, we simultaneously measure picosecond carrier dynamics along with three related quantities: subsurface band bending, above-surface vacuum potentials, and surface trap densities. We make two unexpected observations. First, we uncover a negative-time contrast in secondary electrons resulting from an interplay among these quantities. Second, despite dopant concentrations and surface state densities differing by many orders of magnitude between the two materials, their carrier dynamics, measured by photoexcited band bending and filling of surface states, occur at a seemingly common timescale of about 100 ps. This observation may indicate fundamental kinetic limits tied to a multitude of material and surface properties of optoelectronic III-V semiconductors and highlights the need for techniques that simultaneously measure electro-optical kinetic properties.
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Affiliation(s)
- Christopher Perez
- Sandia National Laboratories, Livermore, CA, USA
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Scott R. Ellis
- Sandia National Laboratories, Livermore, CA, USA
- Intel Corporation, San Jose, CA, USA
| | | | | | | | | | | | | | - Ravindra Singh Bisht
- Department of Electrical and Computer Engineering, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Shriram Ramanathan
- Department of Electrical and Computer Engineering, Rutgers, The State University of New Jersey, Piscataway, NJ, USA
| | - Kenneth E. Goodson
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Suhas Kumar
- Sandia National Laboratories, Livermore, CA, USA
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2
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Katayama K. Pattern-illumination time-resolved phase microscopy and its applications for photocatalytic and photovoltaic materials. Phys Chem Chem Phys 2024; 26:9783-9815. [PMID: 38497609 DOI: 10.1039/d3cp06211b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/19/2024]
Abstract
Pattern-illumination time-resolved phase microscopy (PI-PM) is a technique used to study the microscopic charge carrier dynamics in photocatalytic and photovoltaic materials. The method involves illuminating a sample with a pump light pattern, which generates charge carriers and they decay subsequently due to trapping, recombination, and transfer processes. The distribution of photo-excited charge carriers is observed through refractive index changes using phase-contrast imaging. In the PI-PM method, the sensitivity of the refractive index change is enhanced by adjusting the focus position, the method takes advantage of photo-excited charge carriers to observe non-radiative processes, such as charge diffusion, trapping in defect/surface states, and interfacial charge transfer of photocatalytic and photovoltaic reactions. The quality of the image sequence is recovered using various informatics calculations. Categorizing and mapping different types of charge carriers based on their response profiles using clustering analysis provides spatial information on charge carrier types and the identification of local sites for efficient and inefficient photo-induced reactions, providing valuable information for the design and optimization of photocatalytic materials such as the cocatalyst effect.
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Affiliation(s)
- Kenji Katayama
- Department of Applied Chemistry, Chuo University, Tokyo 112-8551, Japan.
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3
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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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4
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Wang L, Wang H, Nughays R, Ogieglo W, Yin J, Gutiérrez-Arzaluz L, Zhang X, Wang JX, Pinnau I, Bakr OM, Mohammed OF. Phonon-driven transient bandgap renormalization in perovskite single crystals. MATERIALS HORIZONS 2023; 10:4192-4201. [PMID: 37431707 DOI: 10.1039/d3mh00570d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/12/2023]
Abstract
Tailoring the electronic structure of perovskite materials on ultrafast timescales is expected to shed light on optimizing optoelectronic applications. However, the transient bandgap renormalization observed upon photoexcitation is commonly explained by many-body interactions of optically created electrons and holes, which shrink the original bandgap by a few tens of millielectronvolts with a sub-picosecond time constant, while the accompanying phonon-induced effect remains hitherto unexplored. Here we unravel a significant contribution of hot phonons in the photo-induced transient bandgap renormalization in MAPbBr3 single crystals, as evidenced by asymmetric spectral evolutions and transient reflection spectral shifts in the picosecond timescale. Moreover, we performed a spatiotemporal study upon optical excitation with time-resolved scanning electron microscopy and identified that the surface charge carrier diffusion and transient bandgap renormalization are strongly correlated in time. These findings highlight the need to re-evaluate current theories on photo-induced bandgap renormalization and provide a new approach for precisely controlling the optical and electronic properties of perovskite materials, enabling the design and fabrication of high-performance optoelectronic devices with exceptional efficiency and unique properties.
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Affiliation(s)
- Lijie Wang
- Advanced Membranes and Porous Materials Centre (AMPM), Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
| | - Hong Wang
- Advanced Membranes and Porous Materials Centre (AMPM), Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
- KAUST Catalysis Centre, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Razan Nughays
- Advanced Membranes and Porous Materials Centre (AMPM), Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
| | - Wojciech Ogieglo
- Advanced Membranes and Porous Materials Centre (AMPM), Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
| | - Jun Yin
- Department of Applied Physics, The Hong Kong Polytechnic University, Kowloon 999077, Hong Kong, P. R. China
| | - Luis Gutiérrez-Arzaluz
- Advanced Membranes and Porous Materials Centre (AMPM), Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
- KAUST Catalysis Centre, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Xinyuan Zhang
- KAUST Catalysis Centre, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Jian-Xin Wang
- Advanced Membranes and Porous Materials Centre (AMPM), Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
| | - Ingo Pinnau
- Advanced Membranes and Porous Materials Centre (AMPM), Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
| | - Osman M Bakr
- KAUST Catalysis Centre, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Omar F Mohammed
- Advanced Membranes and Porous Materials Centre (AMPM), Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
- KAUST Catalysis Centre, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
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5
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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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6
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Zhang Z, Martis J, Xu X, Li HK, Xie C, Takasuka B, Lee J, Roy AK, Majumdar A. Photoabsorption Imaging at Nanometer Scales Using Secondary Electron Analysis. NANO LETTERS 2021; 21:1935-1942. [PMID: 33635654 DOI: 10.1021/acs.nanolett.0c03993] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Optical imaging with nanometer resolution offers fundamental insights into light-matter interactions. Traditional optical techniques are diffraction limited with a spatial resolution >100 nm. Optical super-resolution and cathodoluminescence techniques have higher spatial resolutions, but these approaches require the sample to fluoresce, which many materials lack. Here, we introduce photoabsorption microscopy using electron analysis, which involves spectrally specific photoabsorption that is locally probed using a scanning electron microscope, whereby a photoabsorption-induced surface photovoltage modulates the secondary electron emission. We demonstrate spectrally specific photoabsorption imaging with sub-20 nm spatial resolution using silicon, germanium, and gold nanoparticles. Theoretical analysis and Monte Carlo simulations are used to explain the basic trends of the photoabsorption-induced secondary electron signal. Based on our current experiments and this analysis, we expect that the spatial resolution can be further improved to a few nanometers, thereby offering a general approach for nanometer-scale optical spectroscopic imaging and material characterization.
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Affiliation(s)
- Ze Zhang
- Department of Mechanical Engineering, Stanford University, Stanford, California 94305, United States
| | - Joel Martis
- Department of Mechanical Engineering, Stanford University, Stanford, California 94305, United States
| | - Xintong Xu
- Department of Mechanical Engineering, Stanford University, Stanford, California 94305, United States
| | - Hao-Kun Li
- Department of Mechanical Engineering, Stanford University, Stanford, California 94305, United States
| | - Chenlu Xie
- Department of Mechanical Engineering, Stanford University, Stanford, California 94305, United States
| | - Brad Takasuka
- Silicon Valley Peripherals Inc., San Jose, California 95117, United States
| | - Jonghoon Lee
- Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, WPAFB, Ohio 45433, United States
| | - Ajit K Roy
- Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, WPAFB, Ohio 45433, United States
| | - Arun Majumdar
- Department of Mechanical Engineering, Stanford University, Stanford, California 94305, United States
- Department of Photon Science, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
- Precourt Institute for Energy, Stanford University, Stanford, California 94305, United States
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7
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Garming MWH, Bolhuis M, Conesa-Boj S, Kruit P, Hoogenboom JP. Lock-in Ultrafast Electron Microscopy Simultaneously Visualizes Carrier Recombination and Interface-Mediated Trapping. J Phys Chem Lett 2020; 11:8880-8886. [PMID: 32909435 PMCID: PMC7569669 DOI: 10.1021/acs.jpclett.0c02345] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Accepted: 09/10/2020] [Indexed: 06/11/2023]
Abstract
Visualizing charge carrier flow over interfaces or near surfaces meets great challenges concerning resolution and vastly different time scales of bulk and surface dynamics. Ultrafast or four-dimensional scanning electron microscopy (USEM) using a laser pump electron probe scheme circumvents the optical diffraction limit, but disentangling surface-mediated trapping and ultrafast carrier dynamics in a single measurement scheme has not yet been demonstrated. Here, we present lock-in USEM, which simultaneously visualizes fast bulk recombination and slow trapping. As a proof of concept, we show that the surface termination on GaAs, i.e., Ga or As, profoundly influences ultrafast movies. We demonstrate the differences can be attributed to trapping-induced surface voltages of approximately 100-200 mV, which is further supported by secondary electron particle tracing calculations. The simultaneous visualization of both competing processes opens new perspectives for studying carrier transport in layered, nanostructured, and two-dimensional semiconductors, where carrier trapping constitutes a major bottleneck for device efficiency.
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Affiliation(s)
- Mathijs W. H. Garming
- Department
of Imaging Physics, Delft University of
Technology, 2628 CN Delft, The Netherlands
| | - Maarten Bolhuis
- Kavli
Institute of Nanoscience, Delft University
of Technology, 2628 CJ Delft, The Netherlands
| | - Sonia Conesa-Boj
- Kavli
Institute of Nanoscience, Delft University
of Technology, 2628 CJ Delft, The Netherlands
| | - Pieter Kruit
- Department
of Imaging Physics, Delft University of
Technology, 2628 CN Delft, The Netherlands
| | - Jacob P. Hoogenboom
- Department
of Imaging Physics, Delft University of
Technology, 2628 CN Delft, The Netherlands
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8
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Gao Y, Nie W, Wang X, Fan F, Li C. Advanced space- and time-resolved techniques for photocatalyst studies. Chem Commun (Camb) 2020; 56:1007-1021. [DOI: 10.1039/c9cc07128h] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Nanoparticle photocatalysts present the obvious characteristic of heterogeneity in structure, energy, and function at spatial and temporal scales.
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Affiliation(s)
- Yuying Gao
- State Key Laboratory of Catalysis
- Dalian National Laboratory for Clean Energy
- The Collaborative Innovation Centre of Chemistry for Energy Materials (iChEM)
- Dalian Institute of Chemical Physics
- Chinese Academy of Sciences
| | - Wei Nie
- State Key Laboratory of Catalysis
- Dalian National Laboratory for Clean Energy
- The Collaborative Innovation Centre of Chemistry for Energy Materials (iChEM)
- Dalian Institute of Chemical Physics
- Chinese Academy of Sciences
| | - Xiuli Wang
- State Key Laboratory of Catalysis
- Dalian National Laboratory for Clean Energy
- The Collaborative Innovation Centre of Chemistry for Energy Materials (iChEM)
- Dalian Institute of Chemical Physics
- Chinese Academy of Sciences
| | - Fengtao Fan
- State Key Laboratory of Catalysis
- Dalian National Laboratory for Clean Energy
- The Collaborative Innovation Centre of Chemistry for Energy Materials (iChEM)
- Dalian Institute of Chemical Physics
- Chinese Academy of Sciences
| | - Can Li
- State Key Laboratory of Catalysis
- Dalian National Laboratory for Clean Energy
- The Collaborative Innovation Centre of Chemistry for Energy Materials (iChEM)
- Dalian Institute of Chemical Physics
- Chinese Academy of Sciences
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9
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Zhang L, Hoogenboom JP, Cook B, Kruit P. Photoemission sources and beam blankers for ultrafast electron microscopy. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2019; 6:051501. [PMID: 31592440 PMCID: PMC6764838 DOI: 10.1063/1.5117058] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2019] [Accepted: 09/03/2019] [Indexed: 06/01/2023]
Abstract
Observing atomic motions as they occur is the dream goal of ultrafast electron microscopy (UEM). Great progress has been made so far thanks to the efforts of many scientists in developing the photoemission sources and beam blankers needed to create short pulses of electrons for the UEM experiments. While details on these setups have typically been reported, a systematic overview of methods used to obtain a pulsed beam and a comparison of relevant source parameters have not yet been conducted. In this report, we outline the basic requirements and parameters that are important for UEM. Different types of imaging modes in UEM are analyzed and summarized. After reviewing and analyzing the different kinds of photoemission sources and beam blankers that have been reported in the literature, we estimate the reduced brightness for all the photoemission sources reviewed and compare this to the brightness in the continuous and blanked beams. As for the problem of pulse broadening caused by the repulsive forces between electrons, four main methods available to mitigate the dispersion are summarized. We anticipate that the analysis and conclusions provided in this manuscript will be instructive for designing an UEM setup and could thus push the further development of UEM.
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Affiliation(s)
| | - Jacob P Hoogenboom
- Department of Imaging Physics, Delft University of Technology, Lorentzweg 1, 2628CJ Delft, The Netherlands
| | - Ben Cook
- Department of Imaging Physics, Delft University of Technology, Lorentzweg 1, 2628CJ Delft, The Netherlands
| | - Pieter Kruit
- Department of Imaging Physics, Delft University of Technology, Lorentzweg 1, 2628CJ Delft, The Netherlands
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10
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Ebihara M, Sohn WY, Katayama K. Lifetime mapping of photo-excited charge carriers by the transient grating imaging technique for nano-particulate semiconductor films. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2019; 90:073905. [PMID: 31370435 DOI: 10.1063/1.5111418] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2019] [Accepted: 07/10/2019] [Indexed: 06/10/2023]
Abstract
The transient grating (TG) imaging technique has been developed, where the refractive index change due to the photoexcited charge carriers excited with a stripe patterned light can be visualized. The spatiotemporal imaging of photoexcited charge carriers was demonstrated for a nanoparticulate TiO2 film. In the analytical procedures to map out the time constant distribution, the averaged response of photoexcited carriers in each image was obtained from the Fourier transform of the TG images since the image has a spatial modulation with a stripe pattern of light. The oscillation response due to the acoustic grating, the decay of the surface trapped electrons (until 1 μs), and thermal diffusion (until 100 µs) were observed. In order to obtain the lifetime imaging of the photoexcited electrons, the target time region (0-1 µs) for the response was selected and fitted with an exponential function, and the time constants were mapped out. We found that the time constants showed a wide range of distribution (68-920 ns), dependent on the sample positions.
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Affiliation(s)
- Makoto Ebihara
- Department of Applied Chemistry, Chuo University, Tokyo 112-8551, Japan
| | - Woon Yong Sohn
- Department of Applied Chemistry, Chuo University, Tokyo 112-8551, Japan
| | - Kenji Katayama
- Department of Applied Chemistry, Chuo University, Tokyo 112-8551, Japan
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11
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Shaheen BS, El-Zohry AM, Yin J, De Bastiani M, De Wolf S, Bakr OM, Mohammed OF. Visualization of Charge Carrier Trapping in Silicon at the Atomic Surface Level Using Four-Dimensional Electron Imaging. J Phys Chem Lett 2019; 10:1960-1966. [PMID: 30942595 DOI: 10.1021/acs.jpclett.9b00598] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The ultrathin thickness (∼1-2 nm) of the native oxide layer on silicon surfaces, which acts as efficient trapping centers, precludes the possibility of studying its impact on the surface-charge carrier dynamics by conventional time-resolved laser spectroscopic techniques because of the large penetration depth of the pump and probe pulses. Here, we use four-dimensional scanning ultrafast electron microscopy (4D S-UEM) with unique surface sensitivity to directly visualize the charge carrier dynamics on Si(100) crystals before and after surface treatment (which removes the native oxide layer) in real space and time simultaneously. Our time-resolved snapshots of the top surface and Kelvin probe-force microscopy results demonstrate that the oxide layer can be formed within minutes after surface treatment, creating undesirable surface-trap states that destroy the population of photogenerated charge carriers on the surface and possibly at the device interface. This new surface observation provides critical photophysical insights into how a few atomic layers of oxide can dramatically influence charge carrier recombination dynamics in silicon solar cells.
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Affiliation(s)
- Basamat S Shaheen
- King Abdullah University of Science and Technology (KAUST) , Division of Physical Sciences and Engineering , Thuwal 23955-6900 , Kingdom of Saudi Arabia
| | - Ahmed M El-Zohry
- King Abdullah University of Science and Technology (KAUST) , Division of Physical Sciences and Engineering , Thuwal 23955-6900 , Kingdom of Saudi Arabia
| | - Jun Yin
- King Abdullah University of Science and Technology (KAUST) , Division of Physical Sciences and Engineering , Thuwal 23955-6900 , Kingdom of Saudi Arabia
| | - Michele De Bastiani
- King Abdullah University of Science and Technology (KAUST) , Division of Physical Sciences and Engineering , Thuwal 23955-6900 , Kingdom of Saudi Arabia
| | - Stefaan De Wolf
- King Abdullah University of Science and Technology (KAUST) , Division of Physical Sciences and Engineering , Thuwal 23955-6900 , Kingdom of Saudi Arabia
| | - Osman M Bakr
- King Abdullah University of Science and Technology (KAUST) , Division of Physical Sciences and Engineering , Thuwal 23955-6900 , Kingdom of Saudi Arabia
| | - Omar F Mohammed
- King Abdullah University of Science and Technology (KAUST) , Division of Physical Sciences and Engineering , Thuwal 23955-6900 , Kingdom of Saudi Arabia
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12
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El-Zohry AM, Shaheen BS, Burlakov VM, Yin J, Hedhili MN, Shikin S, Ooi B, Bakr OM, Mohammed OF. Extraordinary Carrier Diffusion on CdTe Surfaces Uncovered by 4D Electron Microscopy. Chem 2019. [DOI: 10.1016/j.chempr.2018.12.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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13
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Adhikari A, Kwon OH. Surface versus Bulk: Charge Carriers Play by Different Rules. Chem 2019. [DOI: 10.1016/j.chempr.2019.02.020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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14
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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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15
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Cho J, Tang J, Hwang TY, Zewail AH. Observation of dynamical crater-shaped charge distribution in the space-time imaging of monolayer graphene. NANOSCALE 2018; 10:10343-10350. [PMID: 29737349 DOI: 10.1039/c8nr00789f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
A better understanding of charge carrier dynamics in graphene is key to improvement of its electronic performance. Here, we present direct space-time visualization of carrier relaxation and diffusion in monolayer graphene using time-resolved scanning electron microscopy techniques. We observed striking fluence-dependent dynamic images, changing from a Gaussian shape to a novel crater-shaped pattern with increasing laser fluence. Such direct observation of dynamic changes in spatial charge distribution is not readily available from the conventional spectroscopic approaches, which reflect essentially overall effective carrier temperature and density. According to our analysis, for this crater-shaped carrier density to occur in aggregated electron-hole pairs in the high fluence regime there exists an unconventional Auger-assisted carrier recombination process to provide effective relaxation channels, most likely involving emission of optical phonons and plasmons, which is dynamically accessible due to a strong temporal overlap among them. The presented model allows us to successfully account for these unexpected phenomena and to quantitatively analyze the observed spatiotemporal behavior.
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Affiliation(s)
- Jongweon Cho
- Physical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, USA
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16
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Zani M, Sala V, Irde G, Pietralunga SM, Manzoni C, Cerullo G, Lanzani G, Tagliaferri A. Charge dynamics in aluminum oxide thin film studied by ultrafast scanning electron microscopy. Ultramicroscopy 2018; 187:93-97. [DOI: 10.1016/j.ultramic.2018.01.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Revised: 01/16/2018] [Accepted: 01/17/2018] [Indexed: 11/29/2022]
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17
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Imaging surface acoustic wave dynamics in semiconducting polymers by scanning ultrafast electron microscopy. Ultramicroscopy 2018; 184:46-50. [DOI: 10.1016/j.ultramic.2017.08.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Revised: 08/14/2017] [Accepted: 08/20/2017] [Indexed: 11/21/2022]
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18
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Lee YM, Kim YJ, Kim YJ, Kwon OH. Ultrafast electron microscopy integrated with a direct electron detection camera. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2017; 4:044023. [PMID: 28529964 PMCID: PMC5422204 DOI: 10.1063/1.4983226] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Accepted: 04/27/2017] [Indexed: 05/14/2023]
Abstract
In the past decade, we have witnessed the rapid growth of the field of ultrafast electron microscopy (UEM), which provides intuitive means to watch atomic and molecular motions of matter. Yet, because of the limited current of the pulsed electron beam resulting from space-charge effects, observations have been mainly made to periodic motions of the crystalline structure of hundreds of nanometers or higher by stroboscopic imaging at high repetition rates. Here, we develop an advanced UEM with robust capabilities for circumventing the present limitations by integrating a direct electron detection camera for the first time which allows for imaging at low repetition rates. This approach is expected to promote UEM to a more powerful platform to visualize molecular and collective motions and dissect fundamental physical, chemical, and materials phenomena in space and time.
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Affiliation(s)
- Young Min Lee
- Department of Chemistry, School of Natural Science, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulsan 44919, South Korea
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19
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Liao B, Zhao H, Najafi E, Yan X, Tian H, Tice J, Minnich AJ, Wang H, Zewail AH. Spatial-Temporal Imaging of Anisotropic Photocarrier Dynamics in Black Phosphorus. NANO LETTERS 2017; 17:3675-3680. [PMID: 28505461 DOI: 10.1021/acs.nanolett.7b00897] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
As an emerging single elemental layered material with a low symmetry in-plane crystal lattice, black phosphorus (BP) has attracted significant research interest owing to its unique electronic and optoelectronic properties, including its widely tunable bandgap, polarization-dependent photoresponse and highly anisotropic in-plane charge transport. Despite extensive study of the steady-state charge transport in BP, there has not been direct characterization and visualization of the hot carriers dynamics in BP immediately after photoexcitation, which is crucial to understanding the performance of BP-based optoelectronic devices. Here we use the newly developed scanning ultrafast electron microscopy (SUEM) to directly visualize the motion of photoexcited hot carriers on the surface of BP in both space and time. We observe highly anisotropic in-plane diffusion of hot holes with a 15 times higher diffusivity along the armchair (x-) direction than that along the zigzag (y-) direction. Our results provide direct evidence of anisotropic hot carrier transport in BP and demonstrate the capability of SUEM to resolve ultrafast hot carrier dynamics in layered two-dimensional materials.
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Affiliation(s)
| | - Huan Zhao
- Ming Hsieh Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, United States
| | | | - Xiaodong Yan
- Ming Hsieh Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, United States
| | - He Tian
- Ming Hsieh Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, United States
| | - Jesse Tice
- NG Next, Northrop Grumman, 1 Space Park, Redondo Beach, California 90278, United States
| | - Austin J Minnich
- Division of Engineering and Applied Science, California Institute of Technology , Pasadena, California 91125, United States
| | - Han Wang
- Ming Hsieh Department of Electrical Engineering, University of Southern California , Los Angeles, California 90089, United States
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20
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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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21
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Najafi E, Ivanov V, Zewail A, Bernardi M. Super-diffusion of excited carriers in semiconductors. Nat Commun 2017; 8:15177. [PMID: 28492283 PMCID: PMC5437287 DOI: 10.1038/ncomms15177] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Accepted: 03/03/2017] [Indexed: 12/03/2022] Open
Abstract
The ultrafast spatial and temporal dynamics of excited carriers are important to understanding the response of materials to laser pulses. Here we use scanning ultrafast electron microscopy to image the dynamics of electrons and holes in silicon after excitation with a short laser pulse. We find that the carriers exhibit a diffusive dynamics at times shorter than 200 ps, with a transient diffusivity up to 1,000 times higher than the room temperature value, D0≈30 cm2s−1. The diffusivity then decreases rapidly, reaching a value of D0 roughly 500 ps after the excitation pulse. We attribute the transient super-diffusive behaviour to the rapid expansion of the excited carrier gas, which equilibrates with the environment in 100−150 ps. Numerical solution of the diffusion equation, as well as ab initio calculations, support our interpretation. Our findings provide new insight into the ultrafast spatial dynamics of excited carriers in materials. Determining the spatial dynamics of excited carriers will provide a more complete understanding of ultrafast carrier dynamics in materials. Using scanning ultrafast electron microscopy, Najafi et al. are able to observe the spatiotemporal dynamics of excited electron and hole carriers in silicon.
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Affiliation(s)
- Ebrahim Najafi
- Physical Biology Center for Ultrafast Science and Technology, Arthur Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, USA
| | - Vsevolod Ivanov
- Department of Applied Physics and Materials Science, Steele Laboratory, California Institute of Technology, Pasadena, California 91125, USA.,Department of Physics, California Institute of Technology, Pasadena, California 91125, USA
| | - Ahmed Zewail
- Physical Biology Center for Ultrafast Science and Technology, Arthur Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, USA
| | - Marco Bernardi
- Department of Applied Physics and Materials Science, Steele Laboratory, California Institute of Technology, Pasadena, California 91125, USA
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22
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Adhikari A, Eliason JK, Sun J, Bose R, Flannigan DJ, Mohammed OF. Four-Dimensional Ultrafast Electron Microscopy: Insights into an Emerging Technique. ACS APPLIED MATERIALS & INTERFACES 2017; 9:3-16. [PMID: 27976852 DOI: 10.1021/acsami.6b12301] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Four-dimensional ultrafast electron microscopy (4D-UEM) is a novel analytical technique that aims to fulfill the long-held dream of researchers to investigate materials at extremely short spatial and temporal resolutions by integrating the excellent spatial resolution of electron microscopes with the temporal resolution of ultrafast femtosecond laser-based spectroscopy. The ingenious use of pulsed photoelectrons to probe surfaces and volumes of materials enables time-resolved snapshots of the dynamics to be captured in a way hitherto impossible by other conventional techniques. The flexibility of 4D-UEM lies in the fact that it can be used in both the scanning (S-UEM) and transmission (UEM) modes depending upon the type of electron microscope involved. While UEM can be employed to monitor elementary structural changes and phase transitions in samples using real-space mapping, diffraction, electron energy-loss spectroscopy, and tomography, S-UEM is well suited to map ultrafast dynamical events on materials surfaces in space and time. This review provides an overview of the unique features that distinguish these techniques and also illustrates the applications of both S-UEM and UEM to a multitude of problems relevant to materials science and chemistry.
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Affiliation(s)
- Aniruddha Adhikari
- King Abdullah University of Science and Technology , KAUST Solar Center, Division of Physical Sciences and Engineering, Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Jeffrey K Eliason
- Department of Chemical Engineering and Materials Science, University of Minnesota , 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States
| | - Jingya Sun
- King Abdullah University of Science and Technology , KAUST Solar Center, Division of Physical Sciences and Engineering, Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Riya Bose
- King Abdullah University of Science and Technology , KAUST Solar Center, Division of Physical Sciences and Engineering, Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - David J Flannigan
- Department of Chemical Engineering and Materials Science, University of Minnesota , 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States
| | - Omar F Mohammed
- King Abdullah University of Science and Technology , KAUST Solar Center, Division of Physical Sciences and Engineering, Thuwal 23955-6900, Kingdom of Saudi Arabia
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23
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Bose R, Bera A, Parida MR, Adhikari A, Shaheen BS, Alarousu E, Sun J, Wu T, Bakr OM, Mohammed OF. Real-Space Mapping of Surface Trap States in CIGSe Nanocrystals Using 4D Electron Microscopy. NANO LETTERS 2016; 16:4417-4423. [PMID: 27228321 DOI: 10.1021/acs.nanolett.6b01553] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Surface trap states in copper indium gallium selenide semiconductor nanocrystals (NCs), which serve as undesirable channels for nonradiative carrier recombination, remain a great challenge impeding the development of solar and optoelectronics devices based on these NCs. In order to design efficient passivation techniques to minimize these trap states, a precise knowledge about the charge carrier dynamics on the NCs surface is essential. However, selective mapping of surface traps requires capabilities beyond the reach of conventional laser spectroscopy and static electron microscopy; it can only be accessed by using a one-of-a-kind, second-generation four-dimensional scanning ultrafast electron microscope (4D S-UEM) with subpicosecond temporal and nanometer spatial resolutions. Here, we precisely map the collective surface charge carrier dynamics of copper indium gallium selenide NCs as a function of the surface trap states before and after surface passivation in real space and time using S-UEM. The time-resolved snapshots clearly demonstrate that the density of the trap states is significantly reduced after zinc sulfide (ZnS) shelling. Furthermore, the removal of trap states and elongation of carrier lifetime are confirmed by the increased photocurrent of the self-biased photodetector fabricated using the shelled NCs.
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Affiliation(s)
- Riya Bose
- Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Ashok Bera
- Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Manas R Parida
- Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Aniruddha Adhikari
- Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Basamat S Shaheen
- Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Erkki Alarousu
- Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Jingya Sun
- Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Tom Wu
- Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Osman M Bakr
- Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia
| | - Omar F Mohammed
- Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia
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24
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Bose R, Sun J, Khan JI, Shaheen BS, Adhikari A, Ng TK, Burlakov VM, Parida MR, Priante D, Goriely A, Ooi BS, Bakr OM, Mohammed OF. Real-Space Visualization of Energy Loss and Carrier Diffusion in a Semiconductor Nanowire Array Using 4D Electron Microscopy. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2016; 28:5106-5111. [PMID: 27111855 DOI: 10.1002/adma.201600202] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2016] [Revised: 02/28/2016] [Indexed: 06/05/2023]
Abstract
A breakthrough in the development of 4D scanning ultrafast electron microscopy is described for real-time and space imaging of secondary electron energy loss and carrier diffusion on the surface of an array of nanowires as a model system, providing access to a territory that is beyond the reach of either static electron imaging or any time-resolved laser spectroscopy.
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Affiliation(s)
- Riya Bose
- 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
| | - 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
| | - 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
| | - Basamat S Shaheen
- 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
| | - Aniruddha Adhikari
- 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
| | - Tien Khee Ng
- Photonics Laboratory, Computer, Electrical, and Mathematical Sciences and Engineering, KAUST, Thuwal, 23955-6900, Kingdom of Saudi Arabia
| | - Victor M Burlakov
- Mathematical Institute, University of Oxford, Woodstock Road, Oxford, OX2 6GG, UK
| | - Manas R Parida
- 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
| | - Davide Priante
- Photonics Laboratory, Computer, Electrical, and Mathematical Sciences and Engineering, KAUST, Thuwal, 23955-6900, Kingdom of Saudi Arabia
| | - Alain Goriely
- Mathematical Institute, University of Oxford, Woodstock Road, Oxford, OX2 6GG, UK
| | - Boon S Ooi
- Photonics Laboratory, Computer, Electrical, and Mathematical Sciences and Engineering, KAUST, Thuwal, 23955-6900, Kingdom of Saudi Arabia
| | - Osman M Bakr
- 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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25
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Simpson MJ, Doughty B, Yang B, Xiao K, Ma YZ. Imaging Electronic Trap States in Perovskite Thin Films with Combined Fluorescence and Femtosecond Transient Absorption Microscopy. J Phys Chem Lett 2016; 7:1725-31. [PMID: 27103096 DOI: 10.1021/acs.jpclett.6b00715] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Charge carrier trapping degrades the performance of organometallic halide perovskite solar cells. To characterize the locations of electronic trap states in a heterogeneous photoactive layer, a spatially resolved approach is essential. Here, we report a comparative study on methylammonium lead tri-iodide perovskite thin films subject to different thermal annealing times using a combined photoluminescence (PL) and femtosecond transient absorption microscopy (TAM) approach to spatially map trap states. This approach coregisters the initially populated electronic excited states with the regions that recombine radiatively. Although the TAM images are relatively homogeneous for both samples, the corresponding PL images are highly structured. The remarkable variation in the PL intensities as compared to transient absorption signal amplitude suggests spatially dependent PL quantum efficiency, indicative of trapping events. Detailed analysis enables identification of two trapping regimes: a densely packed trapping region and a sparse trapping area that appear as unique spatial features in scaled PL maps.
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Affiliation(s)
- Mary Jane Simpson
- Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Benjamin Doughty
- Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Bin Yang
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Kai Xiao
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
| | - Ying-Zhong Ma
- Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States
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