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Comparison of Amplification and Imaging Behaviours of Several Gases In The Environmental Sem

Published online by Cambridge University Press:  02 July 2020

B.L. Thiel
Affiliation:
Polymers and Colloids Group, Cavendish Laboratory, Department of Physics, University of Cambridge, Madingley Road, Cambridge, , CB3 OHE, U.K.
A.L. Fletcher
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.

Extract

We have investigated the amplification properties of several imaging gases in the Environmental SEM (ESEM) with the intent of forming a set of general guidelines for the selection of gases. 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. The fraction of secondary electron signal decreases as the pressure is raised. This point is illustrated in figures la and lb which show the calculated fraction of signal contributed by secondary, backscattered, and primary electrons as a function of pressure in helium and water vapour. Helium yields a very pure secondary electron signal over the entire range of pressures shown. Unfortunately, helium does not provide a great deal of signal amplification compared to water vapour (figure 2).

Type
Environmental SEM
Copyright
Copyright © Microscopy Society of America 1997

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References

1)Thiel, B.L., et al., (accepted) J. Microscopy (1997).Google Scholar
2)Fletcher, A.L., et al., (accepted) J. Phys. D (1997).Google Scholar
3)This work was sponsored by the BBSRC and Unilever.Google Scholar
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