Stanford Research Systems RGA100, Руководство по эксплуатации и программированию

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4 Glossary of Terms
SRS Residual Gas Analyzer
Mass peak. The ion current pattern in the vicinity of maximum amplitude by scanning
through a small portion of the mass range containing ions of a single mass-to-charge
ratio. Very often, the term ““mass peak”” refers to the signal developed from singly
charged ions. For example, nitrogen is said to have a ““mass 28 peak””.
Mass Range. The range of mass numbers defined by the mass number of the lightest and
the heaviest singly charged ions which can be detected by the RGA.
Mass spectrometer . An instrument which produces a beam of molecular ions from a
sample, separates the resulting mixture of ions according to their mass-to-charge ratios,
and provides output signals which are measures of the realtive abundances of the ionic
species present.
Mass spectrum . A graph of ion abundance vs mass-to-charge ratio.
Minimum Detectable Partial Pressure change (MDPP). The partial pressure change
corresponding to the smallest signal change which can be distinguished from noise. A
common prescription is,
'
p
min
=
V
/S
g
, where
V
is the noise and S
g
is the partial pressure
sensitivity for the gas being measured.
Noise . Random fluctuation in the output signal unrelated to a change in the partial
pressure of the gas from which the signal is derived. The appropriate measure of noise is
the standard deviation
V
N
of N independent determinations of the average output signal
obtained at constant partial pressure.
Open Ion Source (Also Nude Ion Source). An ionizer with electrodes of high
transparency to gases.
Outgassing . The evolution of gas molecules from the internal wall surfaces of the
vacuum system.
Parent ion . An ion of the same mass as that of the original parent molecule.
Partial Pressure . The pressure of a designated component of a gaseous mixture within a
system as it is exerted on the chamber walls. The sum of the partial pressures of all the
kinds of gases gives the total pressure.
Partial Pressure Analyzer (abbreviation: PPA). A compact mass spectrometer used to
analyze the residual gas composition in a vacuum system.
Peak height (also peak intensity). The maximum ion signal developed in the RGA for a
given mass-to-charge ratio peak.
Peak width (
'
M
v%
). The difference between the mass-to-charge ratio values on either
side of a mass peak at which the signal has dropped to v% of the peak height, H. See also
Resolution.
Principal mass peak. The most intense peak in the fragmentation pattern of any
molecule.