The Surface-ionization Source

The operation principle of this source is very simple. When a beam of vaporized metal hits a hot surface such as Ta, W, Ir, the metal atoms are ionized due to an interaction with the surface. This may take place in a tube consisting of the ionizing metal. 

An acceleration electrode extracts the ions from the end of the tube. The ionization efficiency 17 is given by the Saha-Langmuir formula  

CO = statistical weight ratio of atoms/ions adsorbed 1 1. gJe(i-0)/kT] at the surface 

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With the surface ionization source it is generally assumed that the reactant ion internal state distribution is characterized by the source temperature and that the majority of the reactant ions are in their ground electronic state. This contrasts with the uncertainty in reactant state distributions when transition metal ions are generated by electron impact fragmentation of volatile organometallic precursors (10) or by laser evaporation and ionization of solid metal targets (11). Many examples... 

Ionization of tertiary amines was shown to be favored over that of secondary amines, which were more efficiently ionized than primary amines. Compared with a conventional Ni source, the surface ionization source was reported to have a relatively large dynamic range, a selective response to certain types of compounds, and none of the regulatory problems associated with radioactive ionization sources. 

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