ABSTRACT
The advantages of surface ionization ion source are stable surface for ion extraction, suited for usually difficult elements such as halogens and alkalines and highly element selective. Ionization at hot surfaces was first investigated by Langmuir and others in 1923. Surface ionization can be a very efficient way of ionizing elements with low ionization potentials such as the alkalines or high electron affinities to form negative ions such as the halogens. Surface ionization ion sources consist of a high-temperature ionizer made of high-work-function material, such as tungsten, rhenium, iridium, or zeolite for positive-ion production, or low-work-function material, such as tungsten with a Cs monolayer, platinum coated with C, or lanthanum hexaboride for the generation of negative ions. The advantage of thermoionization ion source is high ionization efficiency. Thermoionization is, in principle, the same as surface ionization but is used in connection with a hot cavity as ionizer.
