In situ STM study of underpotential deposition of bismuth on Au(1 1 0) in perchloric acid solution

Article abstract of DOI:10.1016/j.electacta.2005.01.067

The underpotential deposition (UPD) of Bi on Au(1 1 0) was investigated in HClO₄ solution using in situ scanning tunneling microscopy. The UPD of Bi occurred in three steps. A 3011 structure, in which Bi atoms formed dimers, was found for the first UPD adlayer. A (1 × 1) image was obtained by STM at the second UPD peak. For the third UPD peak, Bi atoms formed an incommensurate adlayer, and stripes of Bi were observed on terraces. After the third UPD, a structural reconstruction caused by adsorbed Bi was observed.

Full text of DOI:10.1016/j.electacta.2005.01.067

Electrochimica Acta 51 (2006) 2327–2332
In situ STM study of underpotential deposition of bismuth
on Au(1 1 0) in perchloric acid solution
Masanori Haraa, Yoshiki Nagaharaa, Junji Inukaia,b, Soichiro Yoshimotoa, Kingo Itayaa,c,∗
a
Department of Applied Chemistry, Graduate School of Engineering, Tohoku University, 6-6-04 Aoba, Sendai 980-8579, Japan
b
NICHe, Tohoku University, 6-6-10 Aoba, Sendai 980-8579, Japan
c
CREST, JST, 4-1-8 Kawaguchi, Saitama 332-0012, Japan
Received 3 November 2004; received in revised form 15 January 2005; accepted 17 January 2005
Available online 12 September 2005
Abstract
The underpotential deposition (UPD) of Bi on Au(1 1 0) was investigated in HClO4 solution using in situ scanning tunneling microscopy.
ꢀ
ꢁ
3
0
The UPD of Bi occurred in three steps. A
structure, in which Bi atoms formed dimers, was found for the first UPD adlayer. A
1
1
(1 × 1) image was obtained by STM at the second UPD peak. For the third UPD peak, Bi atoms formed an incommensurate adlayer, and
stripes of Bi were observed on terraces. After the third UPD, a structural reconstruction caused by adsorbed Bi was observed.
© 2005 Published by Elsevier Ltd.
Keywords: Au(1 1 0); Bi; UPD; In situ STM
1. Introduction
ture and electrocatalytic activity. Recently, Li and Gewirth
examined the mechanism of the H2O2 electroreduction on
Bi-submonolayer-modified Au(1 1 1) surface using density
function theory calculations [32]. They suggested that the O
atoms in H2O2 interact strongly with two Bi atoms, and that a
cleavage of the O O bond occurs depending on the distance
between adjacent Bi adatoms on the Au(1 1 1) surface. As
the distance between Bi adatoms decreases with increasing
coverage, H2O2 can be adsorbed on Bi without breakage of
the O O bond.
The process of underpotential deposition (UPD) of metals
is known to be extremely sensitive to the surface structure of
the electrode [1–7]. Among various UPD metals, Bi [7–10],
Pb [7–9,11–15] and Tl [7,9,14–16] have been studied exten-
sively because Au electrodes with fractional coverages of
those metal adlayers were reported to be significantly more
active than either bare or monolayer-covered Au surfaces for
the reduction of H2O2 and O2 [7–13].
Several in situ techniques have been used to understand
the relationship between the electrocatalytic activity and
the structure of UPD adlayers: the adlayer structures of Pb
[17–19], Bi [20–24] and Tl [25,26] on Au(1 1 1), and Pb [27],
Bi [28,29] and Sb [30,31] on Au(1 0 0) have been studied
using in situ scanning tunneling microscopy (STM), atomic
force microscopy (AFM) and surface X-ray scattering (SXS).
The results obtained by those in situ techniques provided
direct insight into the relationship between surface struc-
Among the three admetals, namely Bi, Pb and Tl, which
enhance the H2O2 reduction, Bi allows the reaction to start
at the most positive potential. The adlayer structure of Bi
on Au(1 1 1) in HClO4 solution was determined by Gewirth
and co-workers using in situ AFM [20], STM [21] and SXS
[21]. It was reported that the Bi adlayer exists in two dif-
√
ferent structures, (2 × 2) and (p × 3), at positive and neg-
ative potentials, respectively [20,21]. It was also reported
that the H2O2 reduction proceeds at the highest rate on the
(2 × 2) adlayer [20,24,33]. The rate of H2O2 reduction on
Bi-deposited Au(1 0 0) has been determined by Sayed and
∗
Corresponding author. Tel.: +81 22 795 5868; fax: +81 22 795 5868.
¨
Juttner [10]. Recently, we investigated the underpotential
E-mail address: itaya@atom.che.tohoku.ac.jp (K. Itaya).
0013-4686/$ – see front matter © 2005 Published by Elsevier Ltd.
doi:10.1016/j.electacta.2005.01.067

2328
M. Hara et al. / Electrochimica Acta 51 (2006) 2327–2332
deposition process of Bi on Au(1 0 0) by in situ STM in detail
[28,29]. However, to our knowledge, the structure of the UPD
adlayer of Bi on Au(1 1 0) has not been determined.
In this paper, we report on underpotentially deposited Bi
on Au(1 1 0) in HClO4 investigated by using in situ STM at
various electrode potentials.
2. Experimental
Single-crystal electrodes of gold were prepared by the
method of Clavilier et al. [34] Briefly, a pure Au wire (0.7 mm
in diameter) was melted in a hydrogen flame to form a single-
crystal bead. A well-prepared single-crystal bead showed
eight facets of (1 1 1) in an octahedral configuration and six
facets of (1 0 0) in a hexahedral configuration. These facets
usually exhibited a wide, atomically flat terrace-step struc-
ture. A(1 1 0)surfacewasmechanicallyexposedandpolished
with successively finer grades of Al2O3 powder, from 1 to
0.3 ␮m in diameter. The final treatment, performed to expose
a clean and ordered surface, consisted of flame annealing,
slow cooling in a stream of hydrogen gas, and immersion in
ultrapure water. The Au electrode was then transferred into
the STM or the electrochemical cell with a drop of water
protecting the surface from contamination.
In situ STM imaging was performed with Nanoscope E
(Digital Instruments, Santa Barbara, CA). The STM tip was
made from a W wire (0.25 mm indiameter) electrochemically
etched in 1 M KOH. The tip was then coated with transparent
nail polish to minimize the faradaic current. All STM images
were acquired in the constant-current mode.
All electrolyte solutions were prepared with ultrapure
HClO4 (Cica-Merck), 99.9% Bi2O3 (Wako Pure Chemical
Industries, Ltd.), and ultrapure water (Millipore-Q). Elec-
trode potentials are reported with respect to a reversible
hydrogen electrode (RHE) in 0.1 M HClO4.
Fig. 1. (a) Cyclic voltammogram of Au(1 1 0) electrode in 0.1 M HClO4;
scan rate, 50 mV s−1. (b) Cyclic voltammogram of Au(1 1 0) electrode in
50 ␮M Bi2O3 + 0.1 M HClO4; scan rate, 2 mV s−1
.
3. Results and discussion
2 at 0.35 V and Peak 3 at 0.3 V are associated with the second
and the third UPD of Bi on Au(1 1 0) surface, respectively.
The cathodic current commencing at 0.23 V is due to the bulk
deposition of Bi. The peaks observed in the positive scan
correspond to the dissolution of bulk Bi at 0.28 V and the
successive dissolution of the three UPD layers (Peaks 3ꢀ, 2ꢀ
and 1ꢀ). The shape of the CV indicates that the UPD of Bi on
Au(1 1 0) occurred in three steps. The pair of small cathodic
and anodic peaks at the potential slightly positive to 0.43 V
for Peaks 2 and 2ꢀ may be attributable to the UPD of Bi and
its dissolution at a small portion of surface defects, such as
steps and kinks [10]. The charges consumed during the UPD
of Bi at Peaks 1, 2 and 3 were calculated to be approximately
270, 80 and 30 ␮C cm−2, respectively. The theoretical total
charge corresponding to the deposition of a complete (1 × 1)
monolayer of Bi on Au(1 1 0) is 410 ␮C cm−2, assuming that
Bi3+ in solution is transformed into Bi0 upon adsorption on
Au(1 1 0). By using the above values, the surface coverages of
3.1. Cyclic voltammetry
A cyclic voltammogram (CV) of a well-defined Au(1 1 0)
electrode in 0.1 M HClO4 recorded at the scan rate of
50 mV s−1 is shown in Fig. 1(a). The expanded-scale
voltammogram obtained in the double-layer potential region
(dotted line) and the two characteristic anodic peaks at
1.30 and 1.35 V (solid line) resulting from the oxidation
of Au indicate that a well-defined Au(1 1 0) surface was
exposed to the solution as described in the previous papers
[35,36].
Fig. 1(b) shows a CV of Au(1 1 0) in 50 ␮M Bi2O3 + 0.1 M
HClO4. The electrode potential was initially scanned from
0.8 V in the negative direction at the scan rate of 2 mV s−1
.
The increase in cathodic current at 0.65 V is due to the first
UPD of Bi. Peak 1 for the first UPD of Bi is seen at 0.6 V. Peak

M. Hara et al. / Electrochimica Acta 51 (2006) 2327–2332
2329
Fig. 2. STM top view of Au(1 1 0) surface in 0.1 M HClO4; scan area,
5 nm × 5 nm; electrode potential, 0.75 V; tip potential, 0.4 V; tunneling cur-
rent, 20 nA.
Bi after the first, second and third UPD peaks were estimated
to be 0.7, 0.8 and 0.9, respectively.
3.2. In situ STM measurement
STM measurements of Au(1 1 0) surface were first carried
out in a pure 0.1 M HClO4 solution before investigating the
UPD. Fig. 2 shows a high-resolution STM image of Au(1 1 0)
surface obtained at 0.75 V. The bright spots are seen to form
a rectangular structure. The average distances between the
¯
spots, which are aligned in the [1 1 0] and [0 0 1] directions,
are approximately 0.29 and 0.42 nm, respectively. These
lengths are identical to the Au–Au distances on Au(1 1 0),
suggesting that each bright spot represents an Au atom, and
that there is no reconstruction visible in the STM image of the
Au(1 1 0) surface at 0.75 V. After the well-defined structure
was observed on the well-prepared Au(1 1 0) surface in pure
HClO4, the solution was replaced by 50 ␮M Bi2O3 + 0.1 M
HClO4. Then, STM images were obtained at 0.75 V, a poten-
tial more anodic than that for the first UPD (Fig. 1(b)).
The well-ordered (1 × 1) structure was also observed on the
Au(1 1 0) surface, indicating that Bi3+ ions were not adsorbed
on Au(1 1 0) surface in the potential region more anodic than
that for the UPD.
Fig. 3. (a) STM top view recorded at a potential after the first UPD peak of
Bi on Au(1 1 0) in 50 ␮M Bi2O3 + 0.1 M HClO4; scan area, 30 nm × 30 nm;
electrode potential, 0.5 V; tip potential, 0.45 V; tunneling current, 20 nA.
(b) High-resolution STM image of a Bi adlayer on Au(1 1 0) in 50 ␮M
Bi2O3 + 0.1 M HClO4; scan area, 4 nm × 4 nm; electrode potential, 0.5 V;
tip potential, 0.35 V; tunneling current, 15 nA. (c) Structural model for the
Subsequently, the potential was stepped to a value more
cathodic than that for the first UPD. Fig. 3(a) shows an STM
image acquired at 0.5 V, a potential between Peaks 1 and 2
(Fig. 1(b)). Atomically flat terraces are extended with kinked
winding steps of a monatomic height. The steps were sta-
ꢀ
ꢁ
3
0
Bi adlayer deposited on Au(1 1 0) with a
unit cell.
1
1

2330
M. Hara et al. / Electrochimica Acta 51 (2006) 2327–2332
bly observed without changing their shapes. On the terraces,
bright spots are seen to form an ordered structure with the
same brightness. The rows of bright spots are aligned in the
¯
[1 1 0] direction. A close-look at the image in Fig. 3(a) reveals
¯
that each spot is not circular but elongated in the [1 1 0] direc-
tion of the rows of spots. A high-resolution STM image is
shown in Fig. 3(b). The arrow in the middle of the image
¯
indicates a phase boundary running in the [1 1 0] direction.
The Au(1 1 0) surface is covered with small spots. Detailed
examination of the STM image in Fig. 3(b) revealed that the
small spots are arranged in pairs on the surface as encircled
by ellipses; each elongated spot in Fig. 3(a) consists of a pair
of small spots as seen in Fig. 3(b). The average atomic dis-
tance between the two spots which appear to form a dimer is
approximately 0.34 0.05 nm. This distance is similar to that
between two adjacent Bi atoms in a Bi single crystal, 0.32 nm,
suggesting that each bright spot corresponds to a deposited
Bi atom. A unit cell is outlined in Fig. 3(b) by solid lines with
four Bi dimmers at the corners. The longer sides of the unit
¯
cell are in the [1 1 0] direction, whereas the shorter sides are
◦
¯
tilted by 42 5 with respect to [1 1 0]. The average length of
the longer sides of a unit cell is 0.85 0.07 nm, whereas that
of the shorter sides of a unit cell is 0.52 0.05 nm. Because
the brightness is the same for all Bi atoms, they are thought to
be situated at the same adsorption sites. The results described
above indicate that the Bi adlayer on Au(1 1 0) formed at
Fig. 4. STM top view recorded at a potential of the cathodic peak on
Au(1 1 0) in 50 ␮M Bi2O3 + 0.1 M HClO4; scan area, 15 nm × 15 nm; elec-
trode potential, 0.35 V; tip potential, 0.45 V; tunneling current, 20 nA.
ꢂ
ꢃ
3
0
0.5 V is of a
structure, whose model is depicted in
1
1
The coverage of Bi calculated from the (1 × 1) structure
should be equal to unity. However, this value is larger than
the coverage of 0.8 obtained from the total charge density
for Peaks 1 and 2 in the CV. Actually, because the shortest
distance of Bi atoms in a crystal, 0.32 nm, is much larger than
that of Au atom, 0.289 nm, the (1 × 1) structure observed by
STM would appear to be too dense for Bi atoms on Au(1 1 0).
The difference between the coverage values obtained from
CV (Fig. 1(b)) and from STM (Fig. 4) and the larger size of
Bi atom, appears to suggest that the bright spots in the STM
image in Fig. 4 might not represent Bi atoms but the substrate
Au atoms.
Fig. 3(c). Based on the brightness of Bi atoms and the distance
between them, each Bi atom is assigned to a near four-fold
site. In this model, the lengths of the longer and shorter sides
of the unit cell are 0.87 and 0.51 nm, respectively, which
match the measured distances of 0.85 and 0.52 nm. How-
ever, the angle between the longer and shorter sides of a unit
cell in the model is 58◦, whereas the measured angle was 42◦.
We think that this difference is probably caused by the ther-
mal drift. The coverage of Bi calculated from this structure is
0.66, which agrees well with the value obtained by the charge
density measurement, 0.7, as described in the preceding sec-
tion.
The appearance of a (1 × 1) structure of the Au substrate at
a higher coverage observed in this study does not seem to be a
usual case. For example, the disorder–order phase transition
in an adsorbed sulfate layer is known to occur on Au(1 1 1)
and Pd(1 1 1) surfaces in 0.1 M H2SO4. In the potential region
of the disordered phase, an ideal (1 1 1)–(1 × 1) structure has
been observed by STM even sulfate ions are adsorbed on
the surfaces [37,38]. The same behavior was reported for Br-
and Cl-adsorbed Au(1 0 0) surfaces [39]. However, in those
cases, the (1 × 1) structure has been observed only at low
coverages of the adsorbates. On the other hand, it is impor-
tant to point out again that the step lines were mobile at the
potential for Peak 2. It has been reported that the presence
of a strongly adsorbed layer suppresses the diffusion of Au
atoms [28,31,39]. By comparing the mobility of Au atoms at
step edges at a higher coverage of Bi (Fig. 4) with the stability
The electrode potential was then stepped to 0.35 V, which
is a potential of Peak 2 (Fig. 1(b)). Fig. 4 shows an STM
image. Bright spots aligned in the [1 1 0] and [0 0 1] direc-
¯
tions are seen to form an ordered rectangular structure on
the atomically flat terraces. Interestingly, the step lines were
obscure and mobile at this potential. A unit cell is shown
in Fig. 4. The average atomic distances between the bright
spots that form a unit cell are 0.29 and 0.41 nm, respec-
tively. This unit cell of Bi adlayer is the same as that of the
underlying Au(1 1 0)–(1 × 1) lattice. This (1 × 1) structure
was observed in the potential range for Peak 2 (Fig. 1(b)).
ꢂ
ꢃ
3
0
The structural change between
and (1 × 1), which
1
1
occurred when the electrode potential was changed, was
reversible.

M. Hara et al. / Electrochimica Acta 51 (2006) 2327–2332
2331
the step lines. Fig. 5 shows STM images acquired at 0.3 V
15 min after the potential step. The large-scale STM image
in Fig. 5(a) shows that the rod-like arrays with a monoatomic
height now run parallel to the [0 0 1] direction, or the direc-
tion of the atomic rows of the underlying Au(1 1 0) lattice.
The width of the arrays is 1.8 0.2 nm, approximately six
¯
times the Au–Au distance in the [1 1 0] direction. Weaver
andco-workersfoundanadsorbate-inducedsubstraterestruc-
turing on Br- and I-adsorbed Au(1 1 0) surfaces [40–42].
They observed the erosion of terrace edges especially in
the [0 0 1] direction and the appearance of arrays of sin-
gle atomic layers of ‘nanorods’, 1.8 nm in width oriented
in [0 0 1] on Br-adsorbed Au(1 1 0) [40]. The rod-like steps
might have been formed on the Bi-adsorbed Au(1 1 0) sur-
face to compensate for the surface tension and to lower the
total surface energy [40]. Furthermore, a close examination
of STM images revealed the presence of stripes of Bi on the
terraces. Fig. 5(b) shows a high-resolution STM image, in
which stripes of Bi are seen. The distance between stripes
on the terrace is approximately 1.2 0.1 nm. In this image,
the bright spots form a quadrilateral structure. The rows of
the bright spots are along the atomic rows of the underlying
¯
Au(1 1 0) lattice, in the [1 1 0] and [0 0 1] directions. Those Bi
atoms exhibit different corrugation heights probably because
Biatomsaresituatedatdifferentadsorptionsites. Theaverage
atomic distances between the Bi atoms aligned in the [0 0 1]
direction is 0.41 0.05 nm, which is equal to the Au–Au
distance of Au(1 1 0) surface. On the other hand, the average
atomic distance between Bi atoms aligned in the direction is
0.38 0.05 nm, which is greater than that of Au(1 1 0) sur-
face, 0.289 nm. The striped structures must be caused by the
mismatch between the adlattice of Bi and the substrate lattice
of Au(1 1 0) [1,21,43]. The result described above indicates
that Bi atoms formed an incommensurate adlayer at 0.3 V.
The stripe pattern was observed in the potential range
for the third UPD peak (Fig. 1(b)). All UPD processes
observed in this study were completely reversible with
respect to the electrode potential. No alloy formation
was indicated as in the case on Au(1 1 1) and (1 0 0)
[20,21,28,29].
Fig. 5. (a) STM top view of Bi on Au(1 1 0) in 50 ␮M Bi2O3 + 0.1 M HClO4;
scan area, 30 nm × 30 nm; electrode potential, 0.27 V; tip potential, 0.35 V;
tunneling current, 15 nA. (b) High-resolution STM image of Bi adlayer on
Au(1 1 0) in 50 ␮M Bi2O3 + 0.1 M HClO4; scan area, 10 nm × 10 nm; elec-
trode potential, 0.3 V; tip potential, 0.35 V; tunneling current, 15 nA.
4. Conclusions
The UPD process of Bi on Au(1 1 0) in HClO4 solution
was investigated by electrochemical measurements and in
situ STM. The UPD of Bi occurred in three steps. High-
resolution STM images revealed that the Bi adlayer formed
ꢂ
ꢃ
at a lower coverage (Fig. 3(a)), there seems to be a possibility
that Bi atoms are only weakly adsorbed at Peak 2, forming a
disordered phase on Au(1 1 0) surface.
3
0
after the first UPD peak has a
structure. STM
1
1
The potential was then stepped to 0.27 V, which was in the
potential range where the formation of the third UPD layer
was completed. In the first minute after stepping the poten-
tial, the initially winding steps became straight, and rod-like
images acquired at the second UPD peak showed a (1 × 1)
structure of Au(1 1 0). After the third UPD peak, the adsorbed
Bi atoms formed stripes, and they were incommensurate
with respect to the Au(1 1 0) substrate. All UPD processes
observed in this study were reversible.
¯
arrays began to grow in the [0 0 1] or [0 0 1] direction from

2332
M. Hara et al. / Electrochimica Acta 51 (2006) 2327–2332
[19] N.J. Tao, J. Pan, Y. Li, P.I. Oden, J.A. DeRose, S.M. Lindsay, Surf.
Acknowledgments
Sci. Lett. 271 (1992) L338.
[20] C.-H. Chen, A.A. Gewirth, J. Am. Chem. Soc. 114 (1992) 5439.
[21] C.-H. Chen, K.D. Kepler, A.A. Gewirth, B.M. Ocko, J. Wang, J.
Phys. Chem. 97 (1993) 7290.
[22] I. Oh, M.E. Biggin, A.A. Gewirth, Langmuir 16 (2000) 1397.
[23] T. Solomun, W. Kautek, Electrochim. Acta 47 (2001) 679.
[24] K. Tamura, B.M. Ocko, J.X. Wang, R.R. Adzic, J. Phys. Chem. B
106 (2002) 3896.
This work was supported partially by the COE project,
“Giant Molecules and Complex Systems, 2004”, from the
Ministry of Education, Culture, Sports, Science and Tech-
nology, Japan, and by Core Research for Evolutional Science
and Technology organized by the Japan Science and Technol-
ogy Agency. The authors thank Dr. Y. Okinaka for his help
in writing this manuscript.
[25] W. Polewska, J.X. Wang, B.M. Ocko, R.R. Adzic, J. Electroanal.
Chem. 376 (1994) 41.
[26] R.R. Adzic, J.X. Wang, B.M. Ocko, Electrochim. Acta 40 (1995)
83.
References
[27] U. Schmidt, S. Vinzelberg, G. Staikov, Surf. Sci. 348 (1996) 261.
[28] M. Hara, Y. Nagahara, S. Yoshimoto, J. Inukai, K. Itaya, J. Elec-
trochem. Soc. 151 (2004) 92.
[1] K. Itaya, Prog. Surf. Sci. 58 (1998) 121.
[29] M. Hara, Y. Nagahara, S. Yoshimoto, J. Inukai, K. Itaya, Jpn. J.
Appl. Phys. 43 (2004) 7232.
[30] J.W. Yan, Q. Wu, W.H. Shang, B.W. Mao, Electrochem. Comm. 6
(2004) 843.
[31] M. Hara, J. Inukai, S. Yoshimoto, K. Itaya, J. Phys. Chem. B 108
(2004) 17441.
[2] A.A. Gewirth, B.K. Niece, Chem. Rev. 97 (1997) 1129.
[3] B.E. Conway, Prog. Surf. Sci. 16 (1984) 1.
[4] A.T. Hubbard, Chem. Rev. 88 (1988) 633.
[5] M.P. Soriaga, Prog. Surf. Sci. 39 (1992) 325.
[6] J. Clavilier, A. Rodes, El. K. Achi, M.A. Zamakhchari, J. Chim.
Phys. Phys. Chim. Biol. 88 (1991) 1291.
[32] X. Li, A.A. Gewirth, J. Am. Chem. 125 (2003) 7086.
[33] B.K. Niece, A.A. Gewirth, Langmuir 12 (1996) 4909.
[34] J. Clavilier, R. Faure, G. Guinet, R. Durand, J. Electroanal. Chem.
107 (1980) 205.
[35] A. Hamelin, J. Electroanal. Chem. 407 (1996) 1.
[36] A.S. Dakkouri, D.M. Kolb, in: A. Wieckowski (Ed.), Interfacial Elec-
trochemistry, Marcel Dekker Inc., New York, 1999, p. 151.
[37] L.-J. Wan, T. Suzuki, K. Sashikata, J. Okada, J. Inukai, K. Itaya, J.
Electroanal. Chem. 484 (2000) 189.
[7] G. Kokkindis, J. Electroanal. Chem. 201 (1986) 217.
[8] K. Ju¨ttner, Electrochim. Acta 29 (1984) 1597.
[9] K. Ju¨ttner, Electrochim. Acta 31 (1986) 917.
[10] S.M. Sayed, K. Ju¨ttner, Electrochim. Acta 28 (1983) 1635.
[11] M. Alvarez-Rizatti, K. Ju¨ttner, J. Electroanal. Chem. 144 (1983) 351.
[12] R.R. Adzic, A.V. Tripkovic, N.M. Markovic, J. Electroanal. Chem.
114 (1980) 37.
[13] R. Adzic, A. Tripkovic, R. Atanasoski, J. Electroanal. Chem. 94
(1978) 231.
[38] O.M. Magnussen, J. Hagebock, J. Hotlos, R.J. Behm, Faraday Dis-
cuss. 94 (1992) 329.
[14] G. Kokkinidis, D. Sazou, J. Electroanal. Chem. 199 (1986) 165.
[15] R. Amadelli, J. Molla, P. Bindra, E. Yeager, J. Electrochem. Soc.
128 (1981) 2706.
[16] R. Amadelli, N. Markovic, R. Adzic, E. Yeager, J. Electroanal.
Chem. 159 (1983) 391.
[17] M.P. Green, K.J. Hanson, R. Carr, I. Lindau, J. Electrochem. Soc.
137 (1990) 3493.
[18] M.P. Green, K.J. Hanson, Surf. Sci. Lett. 259 (1991) 743.
[39] A. Cuesta, D.M. Kolb, Surf. Sci. 465 (2000) 310.
[40] S. Zou, X. Gao, M.J. Weaver, Surf. Sci. 452 (2000) 44.
[41] X. Gao, M.J. Weaver, Phys. Rev. Lett. 73 (1994) 846.
[42] X. Gao, G.J. Edens, M.J. Weaver, J. Phys. Chem. B 98 (1994)
8074.
[43] T. Yamada, N. Batina, K. Itaya, J. Phys. Chem. 99 (1995) 8817.