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A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 1 5
3 2
A comparison of the XPS survey
spectrum taken from the Ta2O5 sample in
its as-received state and cluster-cleaned
state is shown in Fig. 4. Although the
two spectra are similar, the as-received
spectrum shows noticeable carbon con-
tamination on the surface, evidenced by
the large peak at 285 eV. After the sam-
ple was cleaned using the argon cluster
beam, contamination is greatly reduced.
Quantifying the spectrum shows that
the surface is Ta 2O5.
Table 2 shows atomic concentra-
tions for the two spectra shown in Fig. 3.
It is apparent that after cluster-cleaning,
surface contamination was removed.
Figure 4 compares Ta 4f spectra
from the three areas on the surface—
as-received, after a 200-eV monatomic
ion clean, and after cluster ion clean-
ing. The monatomic ion beam cleaned
surface shows clear signs of reduction,
as seen by the shoulder on the low
binding energy side of the doublet,
compared to the as-received spectrum.
This corresponds to approximately 30%
of the surface being reduced due to
ion-induced chemical changes. A 200-
eV monatomic ion beam provides low
beam energy, yet still causes reduction.
Using more common monatomic ion
beam energies, such as 1000 eV, would
cause considerably more damage. The
cluster-cleaned surface does not dis-
play this reduction, ensuring that the
stoichiometry of the surface is pre-
served following carbon removal. Sur-
face compositions are shown in Table 3.
Even using low-energy monatomic
Ar+ ion sputter-cleaning causes a signif-
icant amount of Ta2O5 reduction, prov-
ing cluster ions can be vital in metal ox-
ide analysis. Gas cluster ion beams are
proven to successfully clean inorganic
samples without any visible signs of
oxide reduction and without inducing
chemical changes to the surface being
measured.
SUMMARY
The utility of cluster ion beams
for XPS analysis is just beginning to be
explored, making a range of materials
accessible that previously could not be
analyzed. When combined with a mon-
atomic source, these cluster ion beams
will become an essential tool for any
materials analysis laboratory. ~AM&P
Acknowledgment
The authors would like to thank
Dietrich R.T. Zahn, Daniel Lehmann, and
Iulia Korodi from Chemnitz University
of Technology for use of the organic FET
sample.
For more information: Tim Nunney
is surface analysis product manager,
Thermo Fisher Scientific, Birches Indus-
trial Estate, East Grinstead RH19 1UB,
UK, +44 (0)1342 310290,
, .