Zeiss EVO, Инструкция по эксплуатации, Страница: 42 / 180

3 Product and Functional Description | 3.5 Optional Components and Accessories ZEISS
Parameter Description
30 μm The standard aperture is recommended for many applications.
7.0 μm to 20 μm With these apertures, the probe current is frequently too low to ob-
tain a sufficient signal-to-noise ratio and the required contrast.
60 μm Higher probe currents frequently improve the contrast.
120 μm Only recommended for analytical applications.
Specimen tilt Avoid large angles of tilt, if possible. Slight tilting can improve effi-
ciency.
Operation mode The VPSE G4 detector is used mainly in the VP mode.
As the VPSE G4 detector detects light, it can be used as a simple
cathodoluminescence (CL) detector in high-vacuum mode.
3.5.1.2 C2D Detector
Purpose The cascade current detector (C2D) is a special type of detector that you can use instead of the SE
detector to create a secondary electron image under variable pressure conditions.
The SE detector cannot be used under variable pressure conditions: The high potential at the scin-
tillator would cause an electrical breakdown with a lightning flash that runs from the scintillator
to the outer body.
Fig. 29: C2D image of radiolaria
Function On the surface of the specimen, secondary electrons are created. The secondary electrons acceler-
ate towards the C2D detector due to the potential that is applied to the detector electrode.
On their way to the detector, the secondary electrons collide with residual gas molecules (nitro-
gen, air molecules, or water). The collisions ionize the residual gas molecules and create additional
electrons, as well as cations. The additional electrons also accelerate towards the detector and
collide with further gas molecules, which are ionized.
The result is a charge cascade that amplifies the original SE signal by a factor of up to 1000.
The electrons that result from the charge cascade are all collected by the electrode of the C2D de-
tector and the current is further amplified by the detector.
The cations that result from the charge cascade neutralize any negative charge on the specimen
that may have been created by the primary electron beam.
42 Instruction Manual ZEISS EVO | en-US | Rev. 10 | 354706-0780-006