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Charge Contrast Imaging of Gibbsite Using the Variable Pressure SEM

Published online by Cambridge University Press:  01 December 2004

Kevin Robertson ,
Raynald Gauvin  and
James Finch
Kevin Robertson
Affiliation:
Department of Mining, Metals and Materials Engineering, McGill University, Montréal, Québec H3A 2B2, Canada
Raynald Gauvin
Affiliation:
Department of Mining, Metals and Materials Engineering, McGill University, Montréal, Québec H3A 2B2, Canada
James Finch
Affiliation:
Department of Mining, Metals and Materials Engineering, McGill University, Montréal, Québec H3A 2B2, Canada
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Abstract

The variable pressure scanning electron microscope (VP-SEM) allows imaging of insulators without the need for a conductive coating, due to charge neutralization at the surface from recombination of positive ions and surface electrons. Varying certain parameters such as pressure, bias, and working distance creates incomplete neutralization, and localized charging develops called charge contrast. Although the exact mechanism creating charge contrast imaging (CCI) is unknown, it is agreed that it is related to an optimum charge compensation. The behavior of the CCI is still vague, which presents a problem for determining the mechanisms. This article provides user-friendly methods of finding the optimum levels of charge contrast in the VP-SEM. We show that the CCI is obtained at optimum operating conditions where the specimen current is between 2.5 nA and 3.5 nA. The specimen current is a function of secondary electrons (SE) emission and ionization potential, producing an ion flux. Therefore an optimum specimen current represents the balanced conditions of SE emission and ion flux. Controlling the pressure, working distance, bias, scan rate, and beam current allows the microscopist to set the specimen current at this optimum level for charge contrast imaging. All the work was performed on gibbsite using the S3000N VP-SEM from Hitachi.

Keywords

variable pressure scanning electron microscopecharge contrast imaginggibbsiteenvironmental secondary electron detectorcontrast measurement
Type
Research Article
Information
Microscopy and Microanalysis , Volume 10 , Issue 6 , December 2004 , pp. 721 - 732
Copyright
© 2004 Microscopy Society of America

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References

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