Quantitative chemical analysis by energy-dispersive X-ray
spectrometry (EDS) in the environmental scanning electron microscope
(ESEM) is difficult. This analysis is complicated by the spread of the
electron beam by chamber gas molecules and the necessity for surface
charge neutralization. Without charge neutralization, errors in
quantitative analysis can range up to 15–20% relative. It is
possible to achieve the error expected of traditional EDS, ±5%
relative error, using a newly developed surface charge neutralization
scheme for the ESEM. Estimates of accuracy and precision are based on
studies of the National Bureau of Standards (now National Institutes
for Science and Technology) Standard Reference Material 482, a series
of certified copper–gold alloys. The scheme for charge
neutralization requires an independent path to ground at or near the
surface of the specimen. The current through the ground path must be
maintained at zero by adjusting the voltage on the Gaseous Secondary
Electron DetectorTM when the sample chamber is at a gas
pressure of 1–2 torr. This procedure forms the exact number of
chamber gas positive ions to neutralize negative electrical charge on
the specimen surface from electron bombardment.