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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: 06 December 2021

Scanning Electron Microscopy

Scanning Electron Microscopy

(p.693) 10 Scanning Electron Microscopy
Principles of Materials Characterization and Metrology

Kannan M. Krishnan

Oxford University Press

A scanning electron microscope (SEM) focuses an electron beam to a sharp probe, with its diameter, which depends on the acceleration voltage and the aberration coefficients of the probe-forming lens, determining SEM resolution. This electron beam is scanned over the specimen and signals arising from a variety of beam-specimen interactions are recorded to form images using different detectors positioned in the specimen chamber. Secondary electrons, detected with the Everton-Thornley detector, reveal the topography and electrical properties; back-scattered electrons provide information about the average atomic number and local crystallography of the specimen. Ferromagnetic materials alter the trajectory of secondary (Type I) and back-scattered (Type II) electrons to provide magnetic contrast. The magnetic polarization of the secondary electrons can also be analyzed directly (SEMPA) to image domains. The electron beam also excites characteristic X-rays for chemical microanalysis. Luminescent specimens produce light (Cathodoluminescence); these photons provide information on the electronic structure, particularly the defect states, of the specimen. Environmental SEMs, with differential pumping, image the specimen in a gaseous environment and/or under hydration for biological materials. A SEM combined with a focused ion beam (FIB) column is used for nano-fabrication, including preparation of electron-transparent TEM specimens.

Keywords:   Scanning electron microscope, Everton-Thornley detector, Secondary and back-scattered electrons, Beam-specimen interactions, Electron back-scattered diffraction (EBSD), Type I and Type II magnetic contrats, Cathodoluminescence, Environmental SEM, Focussed ion beam milling, Nanofabrication

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