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3 Product and Functional Description | 3.3 Detectors ZEISS
§ 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.
Fig. 17: Comparison of surface information at different acceleration voltages: Acceleration voltage = 1 kV: Good, sur-
face-sensitive imaging (left); Acceleration voltage = 10 kV: Thin layers are not seen (right)
Fig. 18: Comparison of surface information at different acceleration voltages: Acceleration voltage = 5 kV: Good, sur-
face-sensitive imaging (left); Acceleration voltage = 15 kV: Transparent surface caused by increased penetration
depth (right)
The working distance has a significant effect on the efficiency of the SE detector. Shadowing ef-
fects occur when the working distance is too short. If the specimen is too close to the objective
lens, most of the electrons will be deflected by the field of the electrostatic lens or move to the
objective lens itself. This means they cannot be detected by the SE detector.
Depending on the specimen material and on the specimen geometry, a minimum working dis-
tance of approximately 4 mm should be used. Extreme signal loss is likely to occur if shorter work-
ing distances than this are used. Conversely, the SE detector is very good when used for imaging
34 Instruction Manual ZEISS EVO | en-US | Rev. 10 | 354706-0780-006