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A field ion microscope — imaging atom probe study of the underpotential deposition of copper on platinum
Surface Science 145 (1984) North-Holland.
SURFACE
L475
L475--L4XO
Amsterdam
SCIENCE
LETTERS
A FIELD ION MtCROSCOPE - IIMAGiNG ATOM PROBE STUDY OF THE UNDERPOTENTIAL DEPOSITION OF COPPER ON PLATINUM KG.
EVERETT
*, S.D. WALCK,
G.M. SCHMID
Depurtnwntsuf Chetvtistty und Mrrteriri1.v Science
and J.J. HREN
and Engirrrerin,q.Unrwrsi~s of Flwidtt. Gurrtrstille,
Florida 326 I I. USA
Received 6 April
1984
In the course of studies on the initial stages of electrochemical deposition of alloys, we sought a technique that would determine both the location and the composition of clusters consisting of only a few atoms. We utilized the only technique that is capable of sufficient resolution and sensitivity to solve this particular problem, the combination of field ion microscope (FIM) and imaging atom probe (IAP). For our first experiments we studied the underpotential deposition of Cu on Pt, since the electrochemical behavior of this deposition is well known [l-8] and because Cu should be easy to detect. In addition, Pt gives very sturdy and regular images in the FIM-IAP used for the present studies. The FIM alone has been appiied with limited success to a study of anodic film formation on Ir and Pt [9], and to a study of electrodeposited films [lo]. To our knowledge, the present work represents the first application of the FIM-IAP combination to basic electrochemical problems. Since the earlier work of Breiter [l]; the underpotential deposition of Cu on Pt has attracted continued interest [2-71. A consensus of this work suggests that underpotential deposition of Cu starts at approximately 0.8 V (versus NHE) and continues until approximately a monolayer has been formed at about 0.1 V (in 5 x 10e4M Cu2’/0.100M H2S0,) [6]. No Cu(1) is produced in this potential range [S]; the layer is generally considered to consist of uncharged Cu atoms, although an electrosorption valency of 0.83 has been determined, which would indicate some residual charge [8]. Cyclic voltammograms show either three or two distinct anodic current peaks. Nevertheless, the layer is often assumed to be uniform. Only Breiter [l] allows for the formation of thin patches at 0.3 V. At potentials < 0.1 V (in 5 X 10m4M CL?+) bulk Cu deposition occurs and this is accompanied by CufI) formation [S] and by a
* On leave. Department
of Chemistry,
Stetson University.
Deland,
0039-6028/84/$03.00 Q Elsevier Science Publishers (North-Holland Physics Publishing Division)
Florida
B.V.
32720.
USA.
fourth (or third) anodic stripping peak. Fig. 1 shom,s the cyclic \.oltammogram\ we obtained on the Pt specimens used for the present study. Thcv \vere obtained identical The
in 5 x 10 ‘M CUSO~/O.~~~M H,SO, with those of Hammond and Winograd FIM-IAP
suitable
for
Industries) satd.
FIM
used use
by electrolytic
CaCI,
floated
in this were
study
was constructed
prepared
etching
on CCI,.
electrolyte 161.
from
0.13
with alternating
A suitable
after mm
Pt
current
are
Panitz. wire
virtual& Ill].
in water
holder tip and
Tip>
(Engelhardt
in ;I layer of
tip was washed
and its shaft was then spot-welded onto a special diameter Pt wire approximately 0.6 cm long. The
and
and
aquco~~~
ethanol
made from I.6 mm holder combination
was inserted into the FIM, imaged with Ne :md field evaporated until an atomically clean, regular surface of the type shown in fig. 2 was obtained. The assembly inserted
was then into
removed
a Teflon
from
electrode
the FIM. holder.
rinsed
It was
in ethanol again
washed
and
lvater.
with
and
copious
amounts of triply distilled water and inserted into the electrochemical cell. The Pyrex electrochemical cell used for the Cu deposition was of standard design containing the tip assembly. a concentric Pt-wire basket counter electrode, and a saturated The electrolyte was 1 X lO-~‘M CuSO,. distilled, once from
calomel O.lOOM
reference electrode or OSOOM H,SO,
All chemicals were reagent alkaline pern~anganate and
in a separate containing
compartment. 5 x IO ‘RI1 or
grade. all water wab triply twice more in a quartz still.
K.G. Ewrrtt
et ttl. / FIM-
IAP stt&
of Cu on Pt
L477
Instrumentation was a Princeton Applied Research model 370 Electrochemistry System. All potentials are reported with respect to the normal hydrogen electrode (NHE). To remove surface contamination, the electrodes were potential-cycled between +0.2 and + 1.55 V at 100 mV s-’ for 20 min. Three consecutive scans between +0.15 and +0.8 V at either 20 mV ss’ or 100 mV s-’ were then recorded (fig. 1). During the anodic scan four peaks are clearly distinguishable. Peak IV can be ascribed to the removal of bulk Cu. peaks III, II, and I to the removal of underpotential Cu. For the work reported here, the anodic scan was stopped at +0.55 V. i.e., between peaks III and II, and the test electrode withdrawn under applied potential. Only underpotential Cu of the types corresponding to peaks II and I
Fig. 2. Typical field ion microscope image of a Pt tip. Imaging gas: Ne at 1.0 voltage: 9.2 kV; magnification approximately lo6 X.
X
10W5 Ton; imaging
remained, therefore. on the Pt surface. The tips were again and ethanol and inserted into the FIM-IAP. The detector
rinsed with was gated
water for a
mass-to-charge ratio of 32 (Cu” ). A typical image is shown in fig. 3. Other prominent species present appeared at mass-to-charge ratios of 16 ~18 and could have been O+, OH ’ . or H ?O ’ These are shown in fig. 4. Fig. 3 clearly shows patches of some 20 or so Cu atoms over a background of evenly
distributed
underlying
(and
a very early stage remain
during
single
invisible)
Cu atoms Pt lattice.
without It appears
in the underpotential
reoxidation
until
almost
deposition
any obvious as if patch cycle.
relationship formation
or rather.
all of the Cu has been
Fig. 3. Imaging atom probe image of underpotential Cu on Pt. peaks voltage 3.2 kV. desorption pulse 1.75 kV, detector gate 620 ns.
to the occurs
at
as if patches removed.
I and II remaining.
The
Applied
K.G.
Ewrerr
et (II. / FIM-
IAP stu&
of C-u on PI
L479
oxygenated species mentioned above seem to be evenly distributed, again without any relation to the underlying lattice (fig. 4). It must be pointed out that these results are preliminary and should be interpreted with caution. The FIM used here for the initial tip preparation (fig. 2) was not the same as the one in the FIM-IAP used for Cu imaging (fig. 3). Due to differences in design in the two FIM’s, we could not obtain a Pt image after the Cu had been removed, except in a few instances. Thus, the configuration of the underlying lattice, although very similar to the one shown in fig. 2, was not always known. In addition, several days elapsed between the electrochemical treatment and the FIM-IAP application. However. the main purpose of this work was to demonstrate that Pt specimens suitable for the FIM can
Fig. 4. Imaging atom probe image of oxygenated species on Pt. Applied voltage 3.2 kV, desorption pulse 1.75 kV. detector gate 450 ns.
K.G. Everett et al. / FIM-
L480
IAP study ofCu on PI
successfully withstand rather rigorous electrochemical treatments. Furthermore, the possibility exists to obtain answers on a atomic level to questions arising, for instance, in connection with the early stages of electrodeposition. The authors would like to thank Dr. J.A. Panitz and the Surface Physics Group of Sandia National Laboratories for the use of one of their FIM-IAP’s during one of the authors’ (J.J.H.) visit during the summer of 1983,
References [l] [2] [3] [4] [5] [6] [7] [8] [9] [lo] [ll]
M.W. Breiter, J. Electrochem. Sot. 114 (1967) 1125. G.W. Tindall and S. Bruckenstein, Anal. Chem. 40 (1968) 1051, 1637. M.W. Breiter, Trans. Faraday Sot. 65 (1969) 2197. B.J. Bowles, Electrochim. Acta 15 (1970) 589. S.H. Cadle and S. Bruckenstein, Anal. Chem. 43 (1971) 932. J.S. Hammond and N. Winograd, J. Electrochem. Sot. 124 (1977) 826. J.S. Hammond and N. Winograd, J. ElectronaL Chem. 80 (1977) 123. J.W. Schultz, Ber. Bunsenges. Physik. Chem. 74 (1970) 7. C.C. Schubert, C.L. Page and B. Ralph, Electrochim. Acta 18 (1973) 33. K.D. Rendulic and E.W. Miller, J. Appl. Phys. 38 (1967) 550. J.A. Panitz, Rev. Sci. Instr. 44 (1973) 1034.
SURFACE
L475
L475--L4XO
Amsterdam
SCIENCE
LETTERS
A FIELD ION MtCROSCOPE - IIMAGiNG ATOM PROBE STUDY OF THE UNDERPOTENTIAL DEPOSITION OF COPPER ON PLATINUM KG.
EVERETT
*, S.D. WALCK,
G.M. SCHMID
Depurtnwntsuf Chetvtistty und Mrrteriri1.v Science
and J.J. HREN
and Engirrrerin,q.Unrwrsi~s of Flwidtt. Gurrtrstille,
Florida 326 I I. USA
Received 6 April
1984
In the course of studies on the initial stages of electrochemical deposition of alloys, we sought a technique that would determine both the location and the composition of clusters consisting of only a few atoms. We utilized the only technique that is capable of sufficient resolution and sensitivity to solve this particular problem, the combination of field ion microscope (FIM) and imaging atom probe (IAP). For our first experiments we studied the underpotential deposition of Cu on Pt, since the electrochemical behavior of this deposition is well known [l-8] and because Cu should be easy to detect. In addition, Pt gives very sturdy and regular images in the FIM-IAP used for the present studies. The FIM alone has been appiied with limited success to a study of anodic film formation on Ir and Pt [9], and to a study of electrodeposited films [lo]. To our knowledge, the present work represents the first application of the FIM-IAP combination to basic electrochemical problems. Since the earlier work of Breiter [l]; the underpotential deposition of Cu on Pt has attracted continued interest [2-71. A consensus of this work suggests that underpotential deposition of Cu starts at approximately 0.8 V (versus NHE) and continues until approximately a monolayer has been formed at about 0.1 V (in 5 x 10e4M Cu2’/0.100M H2S0,) [6]. No Cu(1) is produced in this potential range [S]; the layer is generally considered to consist of uncharged Cu atoms, although an electrosorption valency of 0.83 has been determined, which would indicate some residual charge [8]. Cyclic voltammograms show either three or two distinct anodic current peaks. Nevertheless, the layer is often assumed to be uniform. Only Breiter [l] allows for the formation of thin patches at 0.3 V. At potentials < 0.1 V (in 5 X 10m4M CL?+) bulk Cu deposition occurs and this is accompanied by CufI) formation [S] and by a
* On leave. Department
of Chemistry,
Stetson University.
Deland,
0039-6028/84/$03.00 Q Elsevier Science Publishers (North-Holland Physics Publishing Division)
Florida
B.V.
32720.
USA.
fourth (or third) anodic stripping peak. Fig. 1 shom,s the cyclic \.oltammogram\ we obtained on the Pt specimens used for the present study. Thcv \vere obtained identical The
in 5 x 10 ‘M CUSO~/O.~~~M H,SO, with those of Hammond and Winograd FIM-IAP
suitable
for
Industries) satd.
FIM
used use
by electrolytic
CaCI,
floated
in this were
study
was constructed
prepared
etching
on CCI,.
electrolyte 161.
from
0.13
with alternating
A suitable
after mm
Pt
current
are
Panitz. wire
virtual& Ill].
in water
holder tip and
Tip>
(Engelhardt
in ;I layer of
tip was washed
and its shaft was then spot-welded onto a special diameter Pt wire approximately 0.6 cm long. The
and
and
aquco~~~
ethanol
made from I.6 mm holder combination
was inserted into the FIM, imaged with Ne :md field evaporated until an atomically clean, regular surface of the type shown in fig. 2 was obtained. The assembly inserted
was then into
removed
a Teflon
from
electrode
the FIM. holder.
rinsed
It was
in ethanol again
washed
and
lvater.
with
and
copious
amounts of triply distilled water and inserted into the electrochemical cell. The Pyrex electrochemical cell used for the Cu deposition was of standard design containing the tip assembly. a concentric Pt-wire basket counter electrode, and a saturated The electrolyte was 1 X lO-~‘M CuSO,. distilled, once from
calomel O.lOOM
reference electrode or OSOOM H,SO,
All chemicals were reagent alkaline pern~anganate and
in a separate containing
compartment. 5 x IO ‘RI1 or
grade. all water wab triply twice more in a quartz still.
K.G. Ewrrtt
et ttl. / FIM-
IAP stt&
of Cu on Pt
L477
Instrumentation was a Princeton Applied Research model 370 Electrochemistry System. All potentials are reported with respect to the normal hydrogen electrode (NHE). To remove surface contamination, the electrodes were potential-cycled between +0.2 and + 1.55 V at 100 mV s-’ for 20 min. Three consecutive scans between +0.15 and +0.8 V at either 20 mV ss’ or 100 mV s-’ were then recorded (fig. 1). During the anodic scan four peaks are clearly distinguishable. Peak IV can be ascribed to the removal of bulk Cu. peaks III, II, and I to the removal of underpotential Cu. For the work reported here, the anodic scan was stopped at +0.55 V. i.e., between peaks III and II, and the test electrode withdrawn under applied potential. Only underpotential Cu of the types corresponding to peaks II and I
Fig. 2. Typical field ion microscope image of a Pt tip. Imaging gas: Ne at 1.0 voltage: 9.2 kV; magnification approximately lo6 X.
X
10W5 Ton; imaging
remained, therefore. on the Pt surface. The tips were again and ethanol and inserted into the FIM-IAP. The detector
rinsed with was gated
water for a
mass-to-charge ratio of 32 (Cu” ). A typical image is shown in fig. 3. Other prominent species present appeared at mass-to-charge ratios of 16 ~18 and could have been O+, OH ’ . or H ?O ’ These are shown in fig. 4. Fig. 3 clearly shows patches of some 20 or so Cu atoms over a background of evenly
distributed
underlying
(and
a very early stage remain
during
single
invisible)
Cu atoms Pt lattice.
without It appears
in the underpotential
reoxidation
until
almost
deposition
any obvious as if patch cycle.
relationship formation
or rather.
all of the Cu has been
Fig. 3. Imaging atom probe image of underpotential Cu on Pt. peaks voltage 3.2 kV. desorption pulse 1.75 kV, detector gate 620 ns.
to the occurs
at
as if patches removed.
I and II remaining.
The
Applied
K.G.
Ewrerr
et (II. / FIM-
IAP stu&
of C-u on PI
L479
oxygenated species mentioned above seem to be evenly distributed, again without any relation to the underlying lattice (fig. 4). It must be pointed out that these results are preliminary and should be interpreted with caution. The FIM used here for the initial tip preparation (fig. 2) was not the same as the one in the FIM-IAP used for Cu imaging (fig. 3). Due to differences in design in the two FIM’s, we could not obtain a Pt image after the Cu had been removed, except in a few instances. Thus, the configuration of the underlying lattice, although very similar to the one shown in fig. 2, was not always known. In addition, several days elapsed between the electrochemical treatment and the FIM-IAP application. However. the main purpose of this work was to demonstrate that Pt specimens suitable for the FIM can
Fig. 4. Imaging atom probe image of oxygenated species on Pt. Applied voltage 3.2 kV, desorption pulse 1.75 kV. detector gate 450 ns.
K.G. Everett et al. / FIM-
L480
IAP study ofCu on PI
successfully withstand rather rigorous electrochemical treatments. Furthermore, the possibility exists to obtain answers on a atomic level to questions arising, for instance, in connection with the early stages of electrodeposition. The authors would like to thank Dr. J.A. Panitz and the Surface Physics Group of Sandia National Laboratories for the use of one of their FIM-IAP’s during one of the authors’ (J.J.H.) visit during the summer of 1983,
References [l] [2] [3] [4] [5] [6] [7] [8] [9] [lo] [ll]
M.W. Breiter, J. Electrochem. Sot. 114 (1967) 1125. G.W. Tindall and S. Bruckenstein, Anal. Chem. 40 (1968) 1051, 1637. M.W. Breiter, Trans. Faraday Sot. 65 (1969) 2197. B.J. Bowles, Electrochim. Acta 15 (1970) 589. S.H. Cadle and S. Bruckenstein, Anal. Chem. 43 (1971) 932. J.S. Hammond and N. Winograd, J. Electrochem. Sot. 124 (1977) 826. J.S. Hammond and N. Winograd, J. ElectronaL Chem. 80 (1977) 123. J.W. Schultz, Ber. Bunsenges. Physik. Chem. 74 (1970) 7. C.C. Schubert, C.L. Page and B. Ralph, Electrochim. Acta 18 (1973) 33. K.D. Rendulic and E.W. Miller, J. Appl. Phys. 38 (1967) 550. J.A. Panitz, Rev. Sci. Instr. 44 (1973) 1034.