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Electron Beam Current Loss at the High-Vacuum– High-Pressure Boundary in the Environmental Scanning Electron Microscope

Published online by Cambridge University Press:  02 February 2002

Gerasimos D. Danilatos ,
Matthew R. Phillips  and
John V. Nailon
Gerasimos D. Danilatos*
Affiliation:
ESEM Research Laboratory, 98 Brighton Boulevard, North Bondi, New South Wales 2026, Australia
Matthew R. Phillips
Affiliation:
Microstructural Analysis Unit, University of Technology, Sydney, PO Box 123, Broadway, New South Wales 2007, Australia
John V. Nailon
Affiliation:
Centre for Microscopy and Microanalysis, The University of Queensland, Brisbane, Queensland 4072, Australia
*
*Corresponding author
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Abstract

A significant loss in electron probe current can occur before the electron beam enters the specimen chamber of an environmental scanning electron microscope (ESEM). This loss results from electron scattering in a gaseous jet formed inside and downstream (above) the pressure-limiting aperture (PLA), which separates the high-pressure and high-vacuum regions of the microscope. The electron beam loss above the PLA has been calculated for three different ESEMs, each with a different PLA geometry: an ElectroScan E3, a Philips XL30 ESEM, and a prototype instrument. The mass thickness of gas above the PLA in each case has been determined by Monte Carlo simulation of the gas density variation in the gas jet. It has been found that the PLA configurations used in the commercial instruments produce considerable loss in the electron probe current that dramatically degrades their performance at high chamber pressure and low accelerating voltage. These detrimental effects are minimized in the prototype instrument, which has an optimized thin-foil PLA design.

Keywords

environmental scanning electron microscopeelectron scatteringelectron lossdifferential pumpinggas jetpressure limiting apertureimage noiseelectron skirt
Type
Research Article
Information
Microscopy and Microanalysis , Volume 7 , Issue 5 , September 2001 , pp. 397 - 406
Copyright
Copyright © Microscopy Society of America 2001

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