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Effects of Space Charge on ESEM Gas Amplification

Published online by Cambridge University Press:  02 July 2020

B.L. Thiel ,
M.R. Hussein-Ismail  and
A.M. Donald
B.L. Thiel
Affiliation:
Polymers and Colloids Group, Cavendish Laboratory, Department of Physics, University of Cambridge, Madingley Road, Cambridge, CB3 OHE, U.K.
M.R. Hussein-Ismail
Affiliation:
Polymers and Colloids Group, Cavendish Laboratory, Department of Physics, University of Cambridge, Madingley Road, Cambridge, CB3 OHE, U.K.
A.M. Donald
Affiliation:
Polymers and Colloids Group, Cavendish Laboratory, Department of Physics, University of Cambridge, Madingley Road, Cambridge, CB3 OHE, U.K.
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Extract

We have performed a theoretical investigation of the effects of space charges in the Environmental SEM (ESEM). The ElectroScan ESEM uses an electrostatic field to cause gas cascade amplification of secondary electron signals. Previous theoretical descriptions of the gas cascade process in the ESEM have assumed that distortion of the electric field due to space charges can be neglected. This assumption has now been tested and shown to be valid.

In the ElectroScan ESEM, a positively biased detector is located above the sample, creating an electric field on the order of 105 V/m between the detector and sample surface. Secondary electrons leaving the sample are cascaded though the gas, amplifying the signal and creating positive ions. Because the electrons move very quickly through the gas, they do not accumulate in the specimen-to-detector gap. However, the velocity of the positive ions is limited by diffusion.

Type
In Situ Studies in Microscopy
Information
Microscopy and Microanalysis , Volume 3 , Issue S2: Proceedings: Microscopy & Microanalysis '97, Microscopy Society of America 55th Annual Meeting, Microbeam Analysis Society 31st Annual Meeting, Histochemical Society 48th Annual Meeting, Cleveland, Ohio, August 10-14, 1997 , August 1997 , pp. 609 - 610
Copyright
Copyright © Microscopy Society of America 1997

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References

Thiel, B.L., et al., (accepted) J. Microscopy, (1997).Google Scholar
von Engel, A., Ionized Gases, Clarendon Press, Oxford (1965).10.1063/1.3046953CrossRefGoogle Scholar