Quadropole Mass Spectrometer
The Quadropole Mass Spectrometer (QMS) on this experiment is used to measure;
-
constituents of the vacuum
-
exact concentrations of molecules dosed into the UHV chamber
-
molecules scattering/desorbing off the sample
(the QMS is mounted in a liquid N2 cooled shroud, with a
line-of-sight tube directed at the sample)
-
reaction products originating from the surface
Typical mass spectra of the UHV chamber are shown below, illustrating the
cleanliness of the vacuum
and confirming that H2 is the major species present at UHV.
The QMS is equipped with a Secondary Electron Multiplier (SEM) detector
which measures the number of electrons reaching the detecting element per
second, rather than counting the ions directly. The amplified electron
signal is much greater than the total number of ions reaching the quadropole,
and this instrument is consequently very sensitive.
The mass spectrometer was purchased from 
Hiden Analytical
The Surface Astrophysics experiment is part of 
Nottingham Astronomy Research Forum
and is based in the Surface
Science Group in the School
of Chemistry at the University
of Nottingham
These pages were last updated 14/10/01