Some comments on the mechanism of emission from liquid metal ion sources

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Abstract
Ion currents of up to 30 mu A are readily obtained from liquid metal ion sources. The high electric field required to create the liquid cone from which emission occurs has given rise to the use of the term liquid metal field ion emission to describe the mechanism. Two candidate processes-field ionisation and field evaporation-are considered in the light of the available experimental data concerning the size of the cone apex, operating voltages etc. It is concluded that field ionisation or any other process requiring ionisation of thermally evaporated neutral atoms is unlikely to be the dominant process because of the absence of a heating mechanism capable of raising a sufficiently large area of the cone surface to the temperatures required. Field evaporation is, however, seen to be a possible mechanism provided an emitting feature of a few tens of angstroms is present. Alternatively, emission may be due to a moving asperity on the apex of a blunter emitting cone.

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