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Optimisation of the S.E. Signal to Background Ratio in ESEM

Published online by Cambridge University Press:  02 July 2020

T.H. Keller ,
B.L. Thiel  and
A.M. Donald
T.H. Keller
Affiliation:
Polymers and Colloids Groups, Cavendish Laboratory, Department of Physics, University of Cambridge, Madingley Road, Cambridge, CB3 0HE, U.K.
B.L. Thiel
Affiliation:
Polymers and Colloids Groups, Cavendish Laboratory, Department of Physics, University of Cambridge, Madingley Road, Cambridge, CB3 0HE, U.K.
A.M. Donald
Affiliation:
Polymers and Colloids Groups, Cavendish Laboratory, Department of Physics, University of Cambridge, Madingley Road, Cambridge, CB3 0HE, U.K.
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Extract

We have performed a theoretical and experimental study of the signal composition in the Environmental SEM (ESEM) with the intention of forming a set of general guidelines for optimising the signal to background ratio. In the ElectroScan ESEM, a gas ionisation cascade is used to amplify the secondary electron signals emanating from the specimen surface. The presence of gas in the chamber also gives rise to a pressure dependent background signal derived from ionisation events between gas molecules and high energy primary beam and backscattered electrons, as well as secondary electrons generated by the probe skirt.

The signal collected by an environmental secondary detector (ESD) (ElectroScan, 1991) or a gaseous secondary detector (GSED) (ElectroScan, 1994) is an amplified signal which is a composite of at least three contributions. These are the amplified currents arising from the ionisation of the gas by high energy electrons from the primary (Ipe) and backscattered electrons (Ihse).

Type
New Trends in Scanning Electron Microscopy and Microanalysis
Information
Microscopy and Microanalysis , Volume 4 , Issue S2: Proceedings: Microscopy & Microanalysis '98, Microscopy Society of America 56th Annual Meeting, Microbeam Analysis Society 32nd Annual Meeting, Atlanta, Georgia July 12-16, 1998 , July 1998 , pp. 296 - 297
Copyright
Copyright © Microscopy Society of America

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References

1) Thiel, B.L. et al., J. Microscopy, 187 (1997) 143.CrossRefGoogle Scholar

2) Fletcher, A.L. et al., J.Phys.D 30 (1997) 2249.CrossRefGoogle Scholar

3) Joy, D.C., GASSEM (1996).Google Scholar

4) The authors would like to thank the BBSRC and EPSRC for their financial support.Google Scholar