Probe current stability in electron-probe microanalysis

Abstract

Quantitative electron-probe microanalysis requires a stable probe current. With adequately stable supply voltages, the main cause of instability in the conventional triode electron gun is movement of the tip of the tungsten hairpin filament forming the cathode. The sensitivity of the probe current to small displacements of the filament of the electron gun of a Cambridge Instrument Company `Geoscan' microanalyser has been measured, with various gun geometries and bias conditions. This enables gun parameters to be optimized with respect to stability and probe current.