PK=aÉëÅêáéíáçå
fåëíêìÅíáçå=j~åì~ä=`êçëëÄÉ~ã=PQM
=
ÉåMOE`loF
=PV=çÑ=NPQ
mêáåÅáéäÉ=çÑ=çéÉê~íáçå
3.3.4.3. VPSE detector
Since the In-lens SE detector and the SE2 detector are both designed for the use in HV mode,
SEs cannot be detected in VP mode with these detectors. Therefore the Variable Pressure Sec-
ondary Electron (VPSE) detector has been developed for SE detection in VP mode.
1
Preamplifier
2
Photomultiplier
3
Objective lens
4
Light guide with collector
electrode
5
Specimen
The VP mode enables imaging of
non-conducting specimens (
5
) with-
out charging artefacts. This is possi-
ble, because positively ionised gas
molecules stabilise local charging.
The collector electrode mounted on the light guide (
4
) is held on a positive potential forming a col-
lecting field for SEs. Thus, SEs move towards the detector. In VP mode gas molecules are present
in the specimen chamber. The accelerated SEs excite gas molecules, which emit a photon when
they de-excite to the ground state. Although BSEs also cause collisions, their contribution is less
than 1 % because of the lower ionising cross section.
The emitted photons are detected by the rod-like light guide pointing at the specimen. The photo-
multiplier (
2
) amplifies the light signal and converts it into an electron current. The degree of am-
plification is depending on the photomultiplier voltage, which regulates the contrast. The pre-
amplifier (
1
) amplifies the signal and regulates the brightness.
IMPORTANT
SE detection in VP mode is pressure-dependent:
The higher the pressure the stronger the signal, but the worse the resolution. Therefore, optimum
pressure (as low as possible, but sufficient to compensate for charging) should always be selected
for every application.
Fig. 3.11: Schematics of the VPSE detector
Содержание Crossbeam 340
Страница 1: ...Crossbeam 340 Crossbeam workstation Instruction Manual ...
Страница 24: ...OQ çÑ NPQ fåëíêìÅíáçå j åì ä êçëëÄÉ ã PQM ÉåMOE loF OK p ÑÉíó p ÑÉíó ÉèìáéãÉåí ...
Страница 60: ...SM çÑ NPQ fåëíêìÅíáçå j åì ä êçëëÄÉ ã PQM ÉåMOE loF RK fåëí ää íáçå ...
Страница 120: ...NOM çÑ NPQ fåëíêìÅíáçå j åì ä êçëëÄÉ ã PQM ÉåMOE loF UK qêçìÄäÉëÜççíáåÖ mçïÉê ÅáêÅìáí ...
Страница 126: ...NOS çÑ NPQ fåëíêìÅíáçå j åì ä êçëëÄÉ ã PQM ÉåMOE loF NNK ÄÄêÉîá íáçåë ...
Страница 130: ...NPM çÑ NPQ fåëíêìÅíáçå j åì ä êçëëÄÉ ã PQM ÉåMOE loF NPK aÉÅä ê íáçå çÑ ÅçåÑçêãáíó ...
Страница 133: ......