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Jerng SK, Hong E, Lee G, Lee B, Jeon JH, Kim J, Chun SH. Integration of Vertical Graphene Onto a Tunnelling Cathode for Digital X-Ray Imaging. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2024:e2403721. [PMID: 39148365 DOI: 10.1002/advs.202403721] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2024] [Revised: 07/08/2024] [Indexed: 08/17/2024]
Abstract
As an alternative to thermionic X-ray generators, cold-cathode X-ray tubes are being developed for portable and multichannel tomography. Field emission propagating from needle structures such as carbon nanotubes or Si tips currently dominates related research and development, but various obstacles prevent the widespread of this technology. An old but simple electron emission design is the planar tunnelling cathode using a metal-oxide-semiconductor (MOS) structure, which achieves narrow beam dispersion and low supplying voltage. Directly grown vertical graphene (VG) is employed as the gate electrode of MOS and tests its potential as a new emission source. The emission efficiency of the device is initially ≈1% because of unavoidable fabrication damage during the patterning processes; it drastically improves to >40% after ozone treatment. The resulting emission current obeys the Fowler-Nordheim tunnelling model, and the enhanced emission is attributed to the effective gate thickness reduction by ozone treatment. As a proof-of-concept experiment, a clustered array of 2140 cells is integrated into a system that provides mA-class emission current for X-ray generation. With pulsed digital excitations, X-ray imaging of a chest phantom, demonstrating the feasibility of using a VG MOS electron emission source as a new and innovative X-ray generator is realized.
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Affiliation(s)
| | - Eunju Hong
- Digital X-ray task, Artificial Intelligence Lab, LG Electronics, Seoul, 07796, South Korea
| | - Giwon Lee
- Digital X-ray task, Artificial Intelligence Lab, LG Electronics, Seoul, 07796, South Korea
| | - Byungkee Lee
- Digital X-ray task, Artificial Intelligence Lab, LG Electronics, Seoul, 07796, South Korea
| | - Jae Ho Jeon
- Department of Physics, Sejong University, Seoul, 05006, South Korea
| | - Jinah Kim
- Digital X-ray task, Artificial Intelligence Lab, LG Electronics, Seoul, 07796, South Korea
| | - Seung-Hyun Chun
- Department of Physics, Sejong University, Seoul, 05006, South Korea
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Neu PS, Geelen D, Tromp RM, van der Molen SJ. Extracting transverse electron mean free paths in graphene at low energy. Ultramicroscopy 2023; 253:113800. [PMID: 37390635 DOI: 10.1016/j.ultramic.2023.113800] [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: 01/23/2023] [Revised: 06/02/2023] [Accepted: 06/19/2023] [Indexed: 07/02/2023]
Abstract
The LEEM-IV spectra of few-layer graphene show characteristic minima at specific energies, which depend on the number of graphene layers. For the same samples, low-energy TEM (eV-TEM) spectra exhibit transmission maxima at energies corresponding to those of the reflection minima in LEEM. Both features can be understood from interferences of the electron wave function in a purely elastic model. Inelastic scattering processes in turn lead to a finite, energy-dependent inelastic Mean Free Path (MFP) and a lower finesse of the interference features. Here we develop a model that introduces both an elastic and inelastic scattering parameter on the wave-function level, thus reconciling the models considered previously. Fitting to published data, we extract the elastic and inelastic MFP self-consistently and compare these to recent reports.
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Affiliation(s)
- Peter S Neu
- Leiden Institute of Physics, Universiteit Leiden, Niels Bohrweg 2, Leiden, the Netherlands
| | - Daniël Geelen
- Leiden Institute of Physics, Universiteit Leiden, Niels Bohrweg 2, Leiden, the Netherlands
| | - Rudolf M Tromp
- Leiden Institute of Physics, Universiteit Leiden, Niels Bohrweg 2, Leiden, the Netherlands; IBM Research, T.J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598, USA
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Gong JM, Khan MSS, Da B, Yoshikawa H, Tanuma S, Ding ZJ. A theoretical characterization method for non-spherical core-shell nanoparticles by XPS. Phys Chem Chem Phys 2023; 25:20917-20932. [PMID: 37492028 DOI: 10.1039/d3cp01413d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/27/2023]
Abstract
Core-shell nanoparticles (NPs) are active research areas for their unique properties and wide applications. By changing the elemental composition in the core and shell, a series of core-shell NPs with specific functions can be obtained, where the sizes of the core and shell also influence the properties. X-ray photoelectron spectroscopy (XPS) is useful in this context as a means of quantitatively analyzing such NPs. The empirical formula proposed by Shard [J. Phys. Chem. C, 2012, 116(31), 16806-16813] for calculating the shell thickness of the spherical core-shell NPs has been verified by Powell et al. [J. Phys. Chem. C, 2016, 120(39), 22730-22738] through a simulation of XPS with Simulation of Electron Spectra for Surface Analysis (SESSA) software. However, real core-shell NPs are not necessarily ideal spheres; such NPs can have rich shapes and uneven thicknesses. This work aims to extend the Shard formula to non-ideal core-shell NPs. We have used a Monte Carlo simulation method to study the XPS signal variation with the shell thickness for several modeled non-spherical shapes of core-shell NPs including some complex geometric structures which are numerically constructed with finite-element triangular meshes. Five types of non-spherical shapes, i.e. egg, ellipsoid, rod, rough-surface, and star shapes, are considered, while the size parameters are varied over a wide range. The equivalent radius and equivalent thickness are defined to characterize the average size of the nanoparticles for the use of the Shard formula. We have thus derived an extended Shard formula for the specific core-shell NPs, with which the relative error between the predicted shell thickness and the real thickness can be reduced to less than 10%.
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Affiliation(s)
- J M Gong
- Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China.
- Center for Basic Research on Materials, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan.
- Materials Data Platform Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
| | - M S S Khan
- Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei, Anhui 230031, People's Republic of China
| | - B Da
- Center for Basic Research on Materials, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan.
| | - H Yoshikawa
- Center for Basic Research on Materials, National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan.
| | - S Tanuma
- Materials Data Platform Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
| | - Z J Ding
- Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China.
- Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China
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Determination of electron backscattering coefficient of beryllium by a high-precision Monte Carlo simulation. NUCLEAR MATERIALS AND ENERGY 2021. [DOI: 10.1016/j.nme.2020.100862] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Chen Y, Li Z, Chen J. Abnormal Electron Emission in a Vertical Graphene/Hexagonal Boron Nitride van der Waals Heterostructure Driven by a Hot Hole-Induced Auger Process. ACS APPLIED MATERIALS & INTERFACES 2020; 12:57505-57513. [PMID: 33258372 DOI: 10.1021/acsami.0c13352] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Understanding the scattering process of field injection hot carriers is important for modulating their behaviors, which is the key for improving the efficiency of charge transfer and energy conversion in hot carrier devices. In this work, a significant electron thermalization induced by Auger scattering between a field injection hot hole and a native cold electron has been observed in a vertical single layer graphene/hexagonal boron nitride/few layer graphene (Gr/hBN/FLG) device by measuring the vacuum electron emission characteristics. For the first time, it is found that vacuum electron emission can be measured under both directions of bias within the device. Furthermore, electrons can be emitted even when the applied bias energy is smaller than the work function of the Gr cathode. Further analysis of the emission electron kinetic energy indicates that the low turn-on bias results from the emission of energetic electrons that are ∼3 eV higher than the Fermi level. A semiquantitative model based on hot hole-induced Auger electron emission is established to reproduce the results. All of these findings not only expand our understanding of the hot carrier scattering process in graphene but also provide insights into the applications of hot carrier devices.
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Affiliation(s)
- Yicong Chen
- State Key Lab of Optoelectronic Materials and Technologies, Guangdong Province Key Lab of Display Material and Technology, Sun Yat-sen University, Guangdong 510275, People's Republic of China
- School of Electronics and Information Technology, Sun Yat-sen University, Guangdong 510275, People's Republic of China
| | - Zhibing Li
- State Key Lab of Optoelectronic Materials and Technologies, Guangdong Province Key Lab of Display Material and Technology, Sun Yat-sen University, Guangdong 510275, People's Republic of China
- School of Physics, Sun Yat-sen University, Guangdong 510275, People's Republic of China
| | - Jun Chen
- State Key Lab of Optoelectronic Materials and Technologies, Guangdong Province Key Lab of Display Material and Technology, Sun Yat-sen University, Guangdong 510275, People's Republic of China
- School of Electronics and Information Technology, Sun Yat-sen University, Guangdong 510275, People's Republic of China
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Da B, Liu J, Harada Y, Cuong NT, Tsukagoshi K, Hu J, Yang L, Ding Z, Yoshikawa H, Tanuma S. Observation of Plasmon Energy Gain for Emitted Secondary Electron in Vacuo. J Phys Chem Lett 2019; 10:5770-5775. [PMID: 31513403 DOI: 10.1021/acs.jpclett.9b02135] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Plasmon gain by core-level electrons or elastic electrons observed in past studies seems to be of no practical value in material characterization, mainly because of their ultralow signal intensities. Nevertheless, in the emission spectra of Au samples, we have observed plasmon gain in secondary electrons. The electrons gain energy from surface plasmons after escaping from the surface and thereby only carry surface-plasmon information in the vacuum above the surface. Because the intensity of the emitted SEs is strong, rivaling that of core-level or elastic electrons, the observed phenomenon has in practice the potential to image directly in space the surface plasmon near but exterior to the metal surface.
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Affiliation(s)
- Bo Da
- Research and Services Division of Materials Data and Integrated System , National Institute for Materials Science , 1-1 Namiki , Tsukuba , Ibaraki 305-0044 Japan
- Research Center for Advanced Measurement and Characterization , National Institute for Materials Science , 1-2-1 Sengen , Tsukuba , Ibaraki 305-0047 , Japan
| | - Jiangwei Liu
- Research Center for Functional Materials , National Institute for Materials Science , 1-2-1 Sengen , Tsukuba , Ibaraki 305-0047 , Japan
| | - Yoshitomo Harada
- Research Center for Advanced Measurement and Characterization , National Institute for Materials Science , 1-2-1 Sengen , Tsukuba , Ibaraki 305-0047 , Japan
| | - Nguyen T Cuong
- International Center for Young Scientists , National Institute for Materials Science , 1-1 Namiki , Tsukuba , Ibaraki 305-0044 , Japan
- International Center for Materials Nanoarchitectonics , National Institute for Materials Science (WPI-MANA) , Tsukuba , Ibaraki 305-0044 , Japan
| | - Kazuhito Tsukagoshi
- International Center for Materials Nanoarchitectonics , National Institute for Materials Science (WPI-MANA) , Tsukuba , Ibaraki 305-0044 , Japan
| | - Jin Hu
- Department of Physics and Institute for Nanoscience and Engineering , University of Arkansas , Fayetteville , Arkansas 72701 , United States
| | - Lihao Yang
- Department of Physics , University of Science and Technology of China , Hefei , Auhui 230026 , P.R. China
| | - Zejun Ding
- Department of Physics , University of Science and Technology of China , Hefei , Auhui 230026 , P.R. China
| | - Hideki Yoshikawa
- Research and Services Division of Materials Data and Integrated System , National Institute for Materials Science , 1-1 Namiki , Tsukuba , Ibaraki 305-0044 Japan
- Research Center for Advanced Measurement and Characterization , National Institute for Materials Science , 1-2-1 Sengen , Tsukuba , Ibaraki 305-0047 , Japan
| | - Shigeo Tanuma
- Research Center for Advanced Measurement and Characterization , National Institute for Materials Science , 1-2-1 Sengen , Tsukuba , Ibaraki 305-0047 , Japan
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Suzuki Y, Lacombe L, Watanabe K, Maitra NT. Exact Time-Dependent Exchange-Correlation Potential in Electron Scattering Processes. PHYSICAL REVIEW LETTERS 2017; 119:263401. [PMID: 29328727 DOI: 10.1103/physrevlett.119.263401] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2017] [Indexed: 06/07/2023]
Abstract
We identify peak and valley structures in the exact exchange-correlation potential of time-dependent density functional theory that are crucial for time-resolved electron scattering in a model one-dimensional system. These structures are completely missed by adiabatic approximations that, consequently, significantly underestimate the scattering probability. A recently proposed nonadiabatic approximation is shown to correctly capture the approach of the electron to the target when the initial Kohn-Sham state is chosen judiciously, and it is more accurate than standard adiabatic functionals but ultimately fails to accurately capture reflection. These results may explain the underestimation of scattering probabilities in some recent studies on molecules and surfaces.
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Affiliation(s)
- Yasumitsu Suzuki
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
| | - Lionel Lacombe
- Department of Physics and Astronomy, Hunter College and the Graduate Center of the City University of New York, 695 Park Avenue, New York, New York 10065, USA
| | - Kazuyuki Watanabe
- Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
| | - Neepa T Maitra
- Department of Physics and Astronomy, Hunter College and the Graduate Center of the City University of New York, 695 Park Avenue, New York, New York 10065, USA
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