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Principles of Materials Characterization and Metrology$
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Kannan M. Krishnan

Print publication date: 2021

Print ISBN-13: 9780198830252

Published to Oxford Scholarship Online: July 2021

DOI: 10.1093/oso/9780198830252.001.0001

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PRINTED FROM OXFORD SCHOLARSHIP ONLINE (oxford.universitypressscholarship.com). (c) Copyright Oxford University Press, 2021. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in OSO for personal use. date: 19 January 2022

Transmission and Analytical Electron Microscopy

Transmission and Analytical Electron Microscopy

(p.552) 9 Transmission and Analytical Electron Microscopy
Principles of Materials Characterization and Metrology

Kannan M. Krishnan

Oxford University Press

Transmission electron microscopy provides information on all aspects of the microstructure — structural, atomic, chemical, electronic, magnetic, etc. — at the highest spatial resolution in physical and biological materials, with applications ranging from fundamental studies to process metrology in the semiconductor industry. Developments in correcting electron-optical aberrations have improved TEM resolution to sub-Å levels. Coherent Bragg scattering (diffraction), incoherent Rutherford scattering (atomic mass), and interference (phase) are some contrast mechanisms in TEM. For phase contrast, optimum imaging is observed at the Scherzer defocus. Magnetic domains are imaged in Fresnel, Foucault, or differential phase contrast (DPC) modes. Off-axis electron holography measures phase shifts of the electron wave, and is affected by magnetic and electrostatic fields of the specimen. In scanning-transmission (STEM) mode, a focused electron beam is scanned across the specimen to sequentially form an image; a high-angle annular dark field detector gives Z-contrast images with elemental specificity and atomic resolution. Series of (S)TEM images, recorded every one or two degrees about a tilt axis, over as large a tilt-range as possible, are back-projected to reconstruct a 3D tomographic image. Inelastically scattered electrons, collected in the forward direction, form the energy-loss spectrum (EELS), and reveal the unoccupied local density of states, partitioned by site symmetry, nature of the chemical species, and the angular momentum of the final state. Energy-lost electrons are imaged by recording them, pixel-by-pixel, as a sequence of spectra (spectrum imaging), or by choosing electrons that have lost a specific energy (energy-filtered TEM). De-excitation processes (characteristic X-ray emission) are detected by energy dispersive methods, providing compositional microanalysis, including chemical maps. Overall, specimen preparation methods, even with many recent developments, including focused ion beam milling, truly limit applications of TEM.

Keywords:   Transmission electron microscopy, Scanning transmission electron microscopy, Analtyical electron microscopy, Reciprocity theorem, Aberration correction, Phase contrast imaging, Fresnel, Focoult and differential phase contrast imaging, Electron energy-loss spectroscopy, Energy-filtered imaging, X-ray microanalysis and mapping, Z-contrast imaging, Electron holography, Electron Tomography, Semiconductor process metrology

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