Charge neutralization in the ESEM for quantitative X-ray microanalysis.
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 Detector 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.
Carlton
Robert A
RA
Rhone-Poulenc Rorer, Collegeville, PA 19426, USA. robert.a.carlton@gsk.com
Lyman
Charles E
CE
Roberts
James E
JE