Liquid metal ion source (LMIS)

A liquid metal ion source is a type of source used in instruments that use a focused ion beam. The ion source consists of a metal that is operated in liquid form.

A liquid metal ion source (LMIS) usually consists of a holder with two connectors, through which the source is connected to a high-voltage potential. There is a tungsten wire between the connectors, which allows, among other things, the heating of the source. The tungsten wire is connected to the actual tungsten tip and reservoir. The reservoir contains the material of the ion source (usually gallium). In the liquid state, the reservoir material wets the tungsten tip thanks to the capillary effect. The end of the tungsten tip has a radius of a few nanometers, which means that the electric field in this area is particularly strong. The applied high voltage leads to the formation of a Taylor cone at the end of the tungsten tip.

At the same time, the atoms in the liquid material are ionized. These ions are moved by the electric field and form a fine protrusion at the end of the Taylor cone. Field evaporation takes place at this protrusion and the ions escape from the material into the vacuum.