SEMs are frequently equipped with two detectors for secondary
electrons: an
in-lens detector and a conventional secondary electron detector.
The
in-lens detector is located inside the electron column of the
microscope and is arranged rotationally symmetric around
the optical axis. Due to a sophisticated magnetic field at
the pole piece, the secondary electrons are collected with
high efficiency. In particular at low voltages and small working
distances, images with high contrast can be obtained. Besides
information about morphology and surface topography, the in-lens
detector
images differences in the work function (e.g., electronic variations)
on the sample with high lateral resolution. On the other hand,
in the images recorded by the conventional secondary electron
detector,
the
topographic information is dominant. |
| Example |
|
Secondary
electron images of graphite electrode material obtained with the
conventional secondary electron detector (left) and the in-lens
detector (right) (LEO 1530 Gemini, operated at 1 keV). While the
contrast is rather homogeneous in the left image, pronounced differences
are present in the in-lens image: the conducting graphite (low
work function) appears with bright contrast whereas the separator,
a fibrous polymer, appears black (high work functions; almost
no electrons are leaving the surface there at the selected conditions).
Sample: H. Buqa, P. Novak, PSI
|
SEM
basics | SE imaging | Dependence
on voltage |
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