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Laboratory
for ChemoMetrics,
Vienna (Austria) MS - Chemometrics - COSIMA |
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Summary of Results: Software Simulation of TOF-SIMS |
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Method |
Generation of secondary
ions
The simulation of TOF-SIMS uses a Monte Carlo approach
for generating a large number of single secondary ions.
The properties of a secondary ion are taken from pre-defined
probability distributions by pseudo random numbers. For each generated
secondary ion the flight time is computed.
Parameters considered are for instance:
(1) Temporal intensity distribution of the
primary ion pulses
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Example for an intensity distribution of a primary ion pulse.
(2) Fragmentation pattern as defined by an
experimental SIMS spectrum
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Na K C3H3 136.06 |
20 30 10 100 |
Example for a peak list defining relative intensities of secondary
ions.
(3) Initial kinetic energy distribution of
secondary ions
Example for a distribution of the initial kinetic energies of secondary
ions.
E0 is typical between 1 to 10 eV.
(4) Time interval for ion counting.
Typical time intervals are
between 0.1 and 50 ns.
Geometry of the virtual TOF
instrument
The default geometry contains a two-stage ion reflector and
corresponds to the COSIMA instrument. All drift lengths and potentials can be
easily changed by the user. A TOF without reflector is optional. For simplicity
only axial movements of ions and only homogenous electrical fields are
considered.
Geometry and electric potentials of the COSIMA instrument
(simplified).
Simulation of TOF-SIMS data
Simulation of 10000 secondary ions typically needs 1 s computing
time (PC, 500 MHz). Results can be graphically displayed or stored on text
files. See Software
and examples 1, 2, 3.
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Last update 2000-12-03 |
