Field emission ion source of molecular cesium ions

Molecular cesium ions are formed by field ionization from a liquid-cesium droplet suspended on a tungsten needle. An ion beam containing typically 87% Cs+, 10% Cs+2, 2% Cs+3, and 1% heavier molecular ions Cs+n (n>3) can be extracted from the liquid surface. We identified molecular ions in the beam up to Cs+9 by photodissociation with a krypton ion laser. The source operates with reliable long-term stability and shows a conversion efficiency of liquid metal into gas-phase ions of >25%.