Page 265 - Inorganic Mass Spectrometry - Fundamentals and Applications

The Emission of Ions 251

a
of Ea(Re04)2 into a rare earth oxide matrix gave strong Reo,- flux and no evi-
it
dence of Ea volatilizing as either a neutral or an ionic species. Here can be con-
cluded that Ea(ReO,), must be embedded in a matrix to allow Reo,- to migrate
away from the Ea counter ion and to sublime as an anion.
The fourth example, an unpublished study [lo], has demonstrated that silver
a
molten glass ion emitters volatilize considerable neutral silver atom flux accom-
panying the silver ion flux, again leaving open the possibility that this is a
pseudo-S-L type of ion emission process.
Additional evidence, useful in supporting the concept that silver zeolite and
silver molten glass ion emitters are S-L processes, would be that both ions and neu-
trals arise from the same species in the solid state; this issue is addressed in the fol-
lowing section, on high-temperature SIMS.

High-temperature mass spectrometry (HT-SIMS) is a technique currently being
the
developed that bas not yet been described in public literature, and hence is men-
a
tioned here only briefly. Our group has been developing SIMS as technique for
determining chemical speciation of inorganic solids at room temperature [ 1 1-13],
and HT SIMS is an expansion of this effort. Most techniques for the determination
of chemical species in solids (other than various crystallographic methods) rely on
taking the solid material into solution, followed by some analytical technique such
as liquid chromatography inductively coupled plasma mass spectrometry (LC-
ICP-MS) or LC-electrospray-MS. This can be a definitive determination as long
as the chemical species is unchanged by the process of dissolving the solid mate-
rial. If the chemical species are altered by the dissolution process, then the altered
species is determined rather than the original species.
Performing the chemical speciation analysis on the unaltered specimen with
the
SIMS alleviates this uncertainty. However, results are fundamentally more dif-
for
ficult to interpret, for certain species that are more ambiguous, and other species
is
with which the technique cannot be made to work. Each situation obviously quite
different and care must be exercised in choosing a method.
Because the goal is to determine the chemical species present on the surface
it
of ion emitters at high temperatures, is obviously impossible to dissolve the ma-
terial; hence SIMS is used to determine the chemical species. One of our SIMS in-
struments has been modified so the ion emitting surface is at full operating tem-
perature in the sample position, where it can be bombarded with a beam of
perrhenate anions and the resulting sputtered secondary ions measured by mass
spectrometry. This instrument is now operational and is being used to determine
the practicality of this approach. The first study, which is presently being con-
ducted, is an effort to determine the chemical species present on the surface of
a
silver molten glass ion emitter. The iodneutral mass spectrometer results show that