FEI Quanta FEG 250, Руководство пользователя

Страница: 167 / 228

System Options: Energy Dispersive X-ray (EDX) Analysis
9-19
LFD EDX ANALYSIS
EDX analysis should be performed at the lowest possible gas
pressure, so it should be done with the LFD. Normally, X-ray analysis
is performed with a relatively high beam current so that there is
enough signal for a good LFD image even at very low gas pressure.
The Hot Stage cone can also be used with the LFD for X-ray analysis
and has a field of view twice as large as the X-ray PLA.
FIGURE 9-15 LFD CONFIGURATION FOR THE EDX ANALYSIS
GSED EDX ANALYSIS
The ESEM mode allows observation of electrically insulating samples,
but care must be taken when using this mode to collect X-ray results.
FIGURE 9-16 X-RAY IMAGING WITH THE GSED
Some of the electrons are deflected due to interaction with the
chamber gas. The deflected electrons form a “skirt” around the main
beam. The skirt electrons will hit the sample at points that are remote
from the area of interest, and generate X-rays from these points.
The number of skirt electrons increases with chamber pressure and
the distance that the beam travels through the gas. The effect of these
skirt electrons can be minimized by reducing gas pressure, or by
shortening the distance between the sample and the final PLA.
The X-ray detector is designed for the sample to be at 10 mm WD,
which is too long for optimum imaging with a high pressure detector
such as the GSED. For this reason, the ESEM is supplied with a
special X-ray PLA which is used in conjunction with the LFD to give
the best results.