Volume 6 Preprint 31
Structures of Metal-benzotriazole Films on Copper and Other Metals
T. Notoya, M. Satake, T. Ohtsuka, H. Yashiro, M. Sato, T. Yamauchi and D. P. Schweinsberg
Keywords: BTA, ToF SIMS, inhibitor, copper, silver, gold, iron, nickel, chromium, zinc
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Volume 6 Paper C076
Structures of Metal-benzotriazole Films on
Copper and Other Metals
T. Notoya1, M. Satake1, T. Ohtsuka1, H. Yashiro2, M. Sato2, T. Yamauchi3
and D. P. Schweinsberg4
school of Engineering, Hokkaido University, Sapporo,
of Engineering, Iwate University, Morioka, 020-8551, Japan
R&D, Co., Ltd., Tokyo, 103-0025, Japan
of Chemistry, Queensland University of Technology, Brisbane
The chemical states of benzotriazole (BTA) on copper and six other
metals were investigated by measurements of time-of-flight secondary
ion mass spectroscopy (ToF SIMS) of BTA-pretreated metals. The
results were discussed in terms of the relationship between the degree
of polymerization of BTA-metal compounds formed and corrosion
inhibition efficiency determined by polarization resistance
measurements for metals in a mixed solution of BTA and NaCl. The
order of inhibition efficiency corresponded to the degree of
polymerisation; the higher the degree of polymerization, the higher the
Keywords: BTA, ToF SIMS, inhibitor, copper, silver, gold, iron, nickel,
In recent years, time-of-flight secondary ion mass spectroscopy (ToF
SIMS) has been used extensively in the field of surface analytical science.
ToF SIMS enables extremely sensitive detection of molecular ions as well
as atomic ones without causing significant damage to the surface
because of the very small doses of primary ions used in ToF SIMS .
Among the many fields to which ToF SIMS can be applied, organicinhibitor films such as BTA on copper are most interesting targets
because ToF SIMS gives direct information on polymeric structure. This
polymeric structure of BTA films on Cu was confirmed by various
analyses [2-9]. Swift  reported that ToF SIMS is a powerful tool for
investigating the polymeric structure of a BTA film on Cu. Although
BTA films on Cu have been studied extensively, little is known about the
chemical state of BTA on other metals. In this study, the chemical
states of BTA on several kinds of metals were assessed by
measurements of ToF SIMS of BTA-treated metals and their polarization
resistance in an NaCl solution in order to determine the relationship
between degree of polymerization and corrosion inhibition efficiency.
The metal specimens used for ToF SIMS analyses were Cu (99.9% purity),
Ag (99.99%), Au (99.95%), Cr (99.9%), Fe (99.5%), Ni (99.7%) and Zn
(99.99%). Five of those metals (Cu, Ag, Fe, Ni and Zn) were also used
for polarization resistance measurements. The metal specimens were
ultrasonically degreased in acetone for 10 min before pretreatment in a
BTA solution. Pretreatment was carried out by immersion in 0.01
mol/dm3 BTA solution at 298 K for 10 min followed by drying in air.
The corrosion test solution used for polarization resistance
measurements was 0.1 mol/dm3 NaCl with or without 0.01 mol/dm3
BTA. The pH of the corrosion test solution was adjusted with HCl or
2.3 Polarization resistance measurements
An electrochemical cell fitted with one of the above metals as a working
electrode, a saturated calomel electrode as a reference electrode, and a
Pt counter electrode were used to determine polarization resistance.
The volume of the corrosion test solution was 200 cm3, and ±10 mV of
polarization at 0.1 Hz was applied to the specimen using a Corrosion
Monitor (Model 7655, Tohogiken Co., Ltd.) to follow the current
response at 298 K.
2.4 Time-of-Flight Secondary Ion Mass Spectroscopy
The TOF SIMS (Physical Electronics TFS 2000) spectra were recorded
under the following conditions: primary ions,
(15 kV); area of
analysis, 40 to 80 µm2; total dose of primary ions, less than 5 x 10
3. Results and Discussion
3.1 Polarization resistance of metals in 0.1 mol/dm3 NaCl with and
Polarization resistance (Rp) of 5 different metals was determined in 0.1
mol/dm3 NaCl with and without 0.01 mol/dm3 BTA after immersion for
20 minutes at 298 K. The ratio of Rp with BTA to Rp without BTA is shown
in Fig.1. The greater the ratio is, the greater is the inhibitory action of
BTA. Therefore, the inhibitory action of BTA toward these metals was in
the following order:
Cu ≫ Ag
Since the ratios for Ni and Fe were less than 2, BTA is not an effective
inhibitor for these metals.
Rp(with BTA)/Rp(without BTA)
Fig. 1 Ratio of polarization resistance in 0.1 M NaCl + 0.01 M BTA to
that in 0.1 M NaCl for various metals after 20-minutes immersion at 298
3.2 Effect of pH on the polarization resistance of copper
Polarization resistance of copper was measured in pH-adjusted 0.1
mol/dm3 NaCl with and without 0.01mol/dm3 BTA after immersion for
20 minutes at 298 K. The ratio of Rp (with BTA) to Rp (without BTA) as a
function of pH is shown in Fig.2. The inhibitory action of BTA was
highest at pH 6, while its inhibitory action in both acidic and alkaline
solutions was weak.
Rp(with BTA)/Rp(without BTA)
Fig. 2 Effect of pH on the inhibition efficiency of BTA (0.01 M) for Cu in
0.1 M NaCl at 298 K.
3.3 ToF SIMS analysis of BTA films formed on metals
Fig.3 shows typical ToF SIMS spectra of Cu pretreated in 0.01 mol/dm3
BTA for 10 min. Ion fragments originating in BTA were all negative ions
such as CN- (26 amu), C3N- (50 amu), C6H4N- (90 amu) and C6H4N3- (118
amu). Typical positive-ion fragments attributed to a compound of Cu
and BTA are expressed as [(Cu+)n(C6H4N3-)n-1]+. Positive ions in which
the part (C6H4N3-)n-1 in [(Cu+)n(C6H4N3-)n-1]+ had been replaced by CN-,
C3N- or C6H4N- were also observed. The n values of assigned positive
ions ranged from 1 to 5. Negative-ion fragments attributed to a
compound of Cu and BTA are expressed as [(Cu+)m(C6H4N3-)m+1]-. Those
with m values ranging from 0 to 3 were observed. Among the negative
ions, the part (C6H4N3-)m+1 in the negative ion [(Cu+)m(C6H4N3-)m+1]- had
been replaced by CN-, C3N- or C6H4N-.
Fig. 3 Typical secondary ion mass spectra for BTA-pretreated Cu.
Fig.4 shows the relative intensities of secondary positive-ion and
negative-ion fragments from BTA-pretreated Cu at three different pH
values. The relative intensity is the intensity of each ion divided by that
of Cu+ for positive ions and by that of C6H4N3- for negative ions. The
relative intensity did not decrease monotonically with an increase in the
number of monomers; that of 4 monomers (n=4) was greater than that
of 3 monomers (n=3). The relative intensity of the negative-ion
fragments dropped abruptly at m=3, and no negative ion fragments
with more than m=4 were observed. In acidic (pH=1) and alkaline
(pH=13) solutions, negative ion fragments of n=4 or 5 and m=3 or 4
were not observed in the SIMS spectra for BTA-pretreated Cu. These
results indicate that a Cu(I)-BTA film formed on Cu is a short polymeric
structure in neutral solution and that only monomers and dimers of
Cu(I)-BTA formed on Cu in highly acidic and alkaline solutions.
Fig. 4 Relative intensities of secondary ions from BTA-pretreated Cu at
various pH values. The intensities have been normalized with respect to
Cu+ for positive ions and with respect to C6H4N3- for negative ions.
3.3.2 Silver and gold
SIMS spectra for metal-BTA films formed on Ag and Au can be described
as [(M+)n(C6H4N3-)n-1]+ for positive-ion fragments and
[(M+)m(C6H4N3-)m+1]- for negative-ion fragments, where M is Ag or Au.
The number of monomers was in the range of 1 to 4 and m ranged from
0 to 2 for Ag. For Au, n was 1 and m was 0, 1 or 2. The relative
intensities for these positive- and negative-ion fragments are shown in
Fig.5 together with those of Cu for comparison. Much less polymerized
metal-BTA species were observed on Ag and Au.
Fig. 5 Relative intensities of secondary ions from BTA-pretreated Cu,
Ag and Au. The intensities have been normalized with respect to M+ for
positive ions and to C6H4N3- for negative ions.
As shown in Fig. 6, the zinc positive-ion fragments were Zn+ and
[(Zn2+)n(C6H4N3-)2n-1]+ (n=1 or 2). The negative-ion fragments were
[(Zn2+)m(C6H4N3-)2m+1]- (m=0,1 or 2).
Fig. 6 Relative intensities of secondary ions from BTA-pretreated Zn
and Ni. The intensities have been normalized with respect to M+ for
positive ions and with respect to C6H4N3- for negative ions.
Only Ni+ was observed as a positive ion on Ni. Negative-ion fragments
on Ni were [(Ni+)m(C6H4N3-)m+1]- (m=0 or 1) and [(Ni2+)m(C6H4N3-)2m+1]-
(m=0, 1 or 2).
3.3.5 Iron and Chromium
No positive- or negative-ion fragment with its origin in the BTA
compound was detected in the SIMS spectra of BTA-pretreated Fe or Cr.
This is consistent with the results presented in Fig. 1 showing almost no
improvement in corrosion resistance for iron by the BTA pretreatment.
(1) ToF SIMS spectra show that the surface films on BTA-treated metals
are composed of relatively short metal-BTA polymers.
(2) For copper, the longest positive-ion fragment attributed to the
Cu(I)-BTA complex was a tetramer and the longest negative-ion
fragment was a trimer. For silver, the longest positive-ion fragment
attributed to silver-BTA complex was a tetramer and the longest
negative-ion fragment was a dimmer. For zinc, the longest
positive- and negative-on fragments were dimmers. For gold and
nickel, positive- and negative-ion fragments attributed to those
metal complexes were much shorter origomers than those of zinc.
Neither positive- nor negative-ion fragments attributed to iron- or
chromium-BTA complex were detected.
(3) The inhibitory actions of the BTA-treated metals was in the
decreasing order of Cu>> Ag>>Zn>Ni, Fe. This order reflects the
BTA molecular chain length on the metal surfaces.
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Mass Spectrometry”, John Wiley &Sons, 1992.
2 A. J. Swift, Mikrokim. Acta, 120, pp149, 1995.
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