ZEISS
3 Product and Functional Description | 3.2 Main Components
Function
Electrons moving to the detector are attracted/repelled by the collector grid and directed to the
scintillator. The electrons gain energy from the scintillator and thus are able to interact with a
phosphor layer, which generates photons (light). The light travels up a light pipe to a photomulti-
plier. The photomultiplier multiplies the flashes of light and outputs a signal that can be used for
imaging.
The collector voltage can be varied in the range between −250 V and +400 V.
A positive collector voltage generates an electrical field in front of the detector, thus directing the
low energy SEs towards the scintillator.
A negative collector voltage generates a field deflecting the low energy SEs so that they cannot
reach the scintillator and do not contribute to the signal. Only high-energy BSEs reach the scintil-
lator contributing to the image generation. This produces a pseudo-backscattered image, which
shows pronounced material contrast, but largely cancels surface properties and topography.
Fig. 28: Comparison of
detector images using positive and negative collector bias voltage:
+300 V collector bias: Good display of surface structures and topography (left),
detector using –150 V collector
bias: Extremely strong topography, including shadow generation (right)
§
Positive collector bias voltage
When using a positive collector bias voltage, surfaces that are tilted in the direction of the de-
tector are emphasized, but there are no shadowing effects.
§
Negative collector bias voltage
When using a negative collector bias voltage, the image shows enhanced topographical con-
trast, which arises mainly from the extreme shadowing effects. However, the fine surface de-
tails are less visible.
Info
For all standard applications, the collector bias should be set to +300 V.
Surface images that show enhanced topographical information can also be generated using
BSE detectors, but they do not show the shadows that can be created using the SE detector.
Applications
Unlike the InLens SE detector, which can be used only with acceleration voltages up to 20 kV, the
SE detector can be used in the complete high-voltage range.
Instruction Manual ZEISS SIGMA series | en-US | Rev. 7 | 352102-9344-006
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