Scanning Electron Microscopy


A theoretical study on the ion transmission through the laser microprobe mass analyzer LAMMA 500 was made using ray-tracing computer programs. The calculations reveal that the ion transmission is strongly affected by the initial conditions of ion formation. Chromatic and spherical aberrations give rise to considerable discrimination in the univoltage lens.

A correlation is attempted between measured and theoretical transmission curves. For the latter a physically plausible plasma model was initially assumed to generate the input parameters, i.e., locus of ion formation and angular and energy distributions of the ions (atomic and cluster ions).

The model needs correction for aberration and space-charge effects : comparison of experimental and calculated ion transmission curves suggests, indeed, a more important contribution of particles with high energy and emitted under large angles, than initially assumed.

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