Surface Ionization Sources

Surface Ionization Sources. In this system, a low ionization potential atom (e.g. caesium) is adsorbed on a high work function metal (e.g. iridium). The temperature is raised so that the rate of desorption exceeds the rate of arrival of the atoms at the surface, and the Cs is then desorped as ions with very small energy spread (< 1 eY). The spot size - current characteristics of these sources lie between liquid metal and plasma discharge sources. 

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... 

Figure 1. Schematic view of ion beam apparatus and surface ionization source.

M. G. Inghram and W. A. Chupka. Surface Ionization Source Using Multiple Filaments. Rev. Sci. Instrum., 24(1953) 518-520. 

Thermal ionization mass spectrometry (TIMS) is one of the oldest mass spectrometric techniques, first applied by Dempster in 1918.114 The thermal emission of positivly charged ions emitted from a salt on a heated surface was first observed by Gehrcke and Reichenheim 12 years before.115 The thermal surface ionization source is a very simple ion source and operates under high vacuum conditions. TIMS is mostly useful for elements with relatively low ionization energy ( )) - in... 

Figure 2.26 a) Experimental arrangement of a single-filament thermal surface ionization source b) Schematic diagram of a double-filament arrangement for thermal surface ionization. (H. Kienitz (ed.), Massenspektrometric (1968), Verlag Chemie, Weinheim. Reproduced by permission of Wiley-VCH.)... 

Thermal surface ionization source on a hot filament thermal surface ionization M+, MX" high < 1( 4 Pa single-focusing SFMS isotope ratios isotope dilution geochronology... 

The study of the 0 decay of 0.59s 145Cs was conducted at the TRISTAN mass separator on-line to the high flux reactor at BNL. A detailed description of the TRISTAN facility can be found in reference [GIL81]. The radioactive samples were produced by fissioning a uranium target integrated in a positive surface ionization source.[PI084] In this experiment, the usual Re surface ionizer was replaced with a Ta ionizer. The lower work function of Ta ensured no independent production of Ba from the ion source at a low power operation ( 1200°C). 

Surface ionization sources are commonly used for producing a Cs+ ion beam. Surface ionization is produced in a vacuum by heating a source metal which is adsorbed onto the... 

Another simple means of creating ions is a surface ionization source. This works effectively for species having low ionization energies, which in this work include atomic silicon and atomic transition metals. Typically, a rhenium filament resistively heated to about 2200 K is used. Silane or the vapors of a transition metal complex or salt are directed at the filament, where decomposition and ionization occur. It is generally believed that the electronic state distribution of the ions formed is in equilibrium at the filament temperature. This generally produces ground-state ions, e.g., exclusively Si+( P), with a distribution of spin-orbit levels associated with the filament temperature. 

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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