Chapter
3 Spectrometer
The PHOIBOS spectrometer consists of a vacuum housing and four major internal com-
ponents, which are shown in figures 3 - 5. All the parts must be contained within an Ul-
tra High Vacuum (UHV) environment, as particles emitted from the sample surface can
collide with the gas molecules changing their energy and momentum.
The internal components are:
● input lens system for receiving charged particles;
● 180° hemispherical analyzer (HSA) with 100 / 150 mm nominal radius for per-
forming spectroscopic energy measurements;
● detector assembly for single particle detection;
● Slit Orbit mechanism with an external rotary feedthrough.
● Iris aperture with an external rotary feedthrough
The excitation source is dependent upon the technique to be used, but is commonly x-
rays or other photons, electrons or ions. Before the particles pass into the hemispherical
analyzer, they first pass through an electron lens system and a slit. Both the electron
lens system and the slits sizes (entrance and exit) have an effect on the energy spread
detected by the analyzer.
The input lens system (Figure 5: Analyzer Main Components and Voltage Principle page
10) includes ten lens tubes. For undisturbed image quality, the input lens system is grid-
free. The lens stages define the analysis area and angular acceptance by imaging the
emitted particles onto the entrance slit of the analyzer. Particles passing through the
lenses are focused onto the input slit S1 and are retarded in the lens for subsequent en-
ergy analysis. In addition the lens stages define the acceptance angles and area for a
given magnification entrance slit (see table 2 on page 16).
The lens system may be operated in several different modes for angular and spatially
resolved studies to adapt the analyzer to different tasks. All lens modes can be set elec-
tronically.
For small spot analysis a lateral resolution down to 100 m is available using the Highμ
Magnification Mode and the special Iris aperture. In the various Magnification Modes,
PHOIBOS 11
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