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Imaging the Probe Skirt in the Environmental SEM

Published online by Cambridge University Press:  02 July 2020

B.L. Thiel ,
I.C. Bache  and
P. Smith
B.L. Thiel
Affiliation:
Polymers and Colloids Group, Cavendish Laboratory, University of Cambridge, Cambridge, UK
I.C. Bache
Affiliation:
Polymers and Colloids Group, Cavendish Laboratory, University of Cambridge, Cambridge, UK
P. Smith
Affiliation:
FEI-Philips, 1 Corporation Way #2, Peabody, MA01960-7990 , USA
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Extract

In low vacuum scanning electron microscopes, the primary beam is partially scattered by the gas present in the specimen chamber. The development of these microscopes, in particular the so-called ‘Environmental’ SEM, was initiated when it was realized that this scattering does not necessarily compromise the imaging capabilities of the instrument. Indeed, some modern commercial instruments are capable of better than 2 nanometer resolution at gas pressures of several torr. The accepted explanation for this is as follows: The mean-free-path of the high energy primary electrons is several millimeters in one torr of water vapour (for example). Because the actual pathlength of electrons travelling through the gas is only a few millimeters, most of them do not scatter at all. Those that do scatter are supposedly distributed over a relatively large area. Thus, the probe features a high-intensity central region surrounded by a slowly decaying low-intensity skirt. High resolution imaging is possible because the signal-to-(skirt)background ratio is high.

Type
Working with ESEM and Other Variable Pressure Systems
Information
Microscopy and Microanalysis , Volume 6 , Issue S2: Proceedings: Microscopy & Microanalysis 2000, Microscopy Society of America 58th Annual Meeting, Microbeam Analysis Society 34th Annual Meeting, Microscopical Society of Canada/Societe de Microscopie de Canada 27th Annual Meeting, Philadelphia, Pennsylvania August 13-17, 2000 , August 2000 , pp. 794 - 795
Copyright
Copyright © Microscopy Society of America

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References

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