Self-pulsing emission of a liquid metal ion source

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Abstract
Needle‐type liquid metal ion sources are found to exhibit self‐sustained, pulsed emission for very smooth emitter surfaces and/or incomplete wetting. A distinct dependence on extraction voltage is found both for the length and height of individual pulses as well as for the interval between pulses. These observations are explained by an insufficient flow of liquid along the shank of the needle. Therefore, the emitting cone collapses and rebuilds only after some time delay necessary for the liquid to flow to the apex. The experimental results are described by a hydrodynamic model that incorporates liquid flow impedance. Liquid film thicknesses, as derived from these results, are found to be ≤1000 Å for self‐pulsing emitters. This figure is in agreement with Auger electron spectroscopy sputter depth profiles of those emitters.

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