Au
nanoparticles with a mean diameter of 20 nm with a coverage
of ∼20% of the surface were distributed on a Si wafer surface
and studied both before and after being annealed (at 100 and 300 °C).
The two types of samples were analyzed using secondary ion mass spectroscopy
(SIMS) with Bi
3
+
clusters as the primary ions
combined with surface etching using Ar
1000
+
clusters.
We observed a substantial difference in the SIMS spectra combined
with a relatively short sputtering time of Ar
1000
+
. In the nonannealed samples, bare Au cluster cations and Si
+
were observed in the SIMS spectra; AuSi
+
clusters
were also observed in the annealed samples. These results indicate
Au-silicide formation at a part of the periphery of the Au nanoparticles
upon annealing. We suggest that SIMS experiments using cluster ions
such as Bi
3
+
can not only be used for surface
elemental analyses but also provide information on local chemical
environments of elements on the surface. This is an important issue
in heterogeneous catalysis (e.g., strong metal–support interactions).
We also advise that one should be careful interpreting the SIMS data
combined with a longer Ar
1000
+
sputtering time
because this can deteriorate the surfaces from their original structures.