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Transpector MPS Operating Manual
Material Factor
The material factor for a chemical substance is that part of the
proportionality constant between the partial pressure of that substance
and the resulting mass filtered ion current which depends on the chemical
nature of that substance but not the particular instrument used for that
measurement. The material factor is a function of the ionization probability
and fragmentation factor for the specified substance.
Mean-Free-Path
The mean-free-path is the average distance an ion, electron, atom, or
molecule can travel before colliding with an ambient gas molecule. The
mean free path is inversely proportional to the pressure.
Molecular Flow
Molecular flow is that motion of gas molecules wherein the collisional
mean free path is greater than the critical dimension of a flow constraining
element such as an orifice of tube diameter.
The gas flow characteristics
are dominated by collisions between the gas molecules and the
appropriate surfaces of the vacuum system.
Natural Abundance
The natural abundance of an isotope is the average percentage of all
atoms of a given element which have the same number of neutrons. For
example, 99.985% of all naturally occurring hydrogen atoms have no
neutrons, giving an atomic mass of approximately 1, while 0.015% have
one neutron, giving an atomic mass of approximately 2. There is a third
isotope of hydrogen which contains two neutrons, giving an atomic mass
of 3, but this isotope is unstable with such a short radioactive half life that it
is not normally naturally occurring in any significant quantity on earth.
There are occasions when an observed isotopic abundance will not reflect
the natural abundance. For instance, in semiconductor processing tools
know as ion implanters, it is not unusual for the BF
3
boron dopant source
to be isotopically enriched to 99%+ of the boron-11 isotope (instead of the
naturally occurring 80.22%).
Open Ion Source (OIS)
An open ion source is an ion source constructed with an open grid
structure with high conductance between the ionization region and the
vacuum region surrounding it. Residual gas analyzers are typically
equipped with this type of ion source.
Outgassing
Outgassing is the evolution of gas which was dissolved in or adsorbed on
solid surfaces inside a vacuum chamber.
Parent Ion
A parent ion is an ion made by removing a single electron from the
original, or parent, gas molecule, and therefore has the same mass.
