Underpotential deposition of cadmium adatoms on Te and CdTe

Article abstract of DOI:10.1016/j.electacta.2006.06.038

Underpotential deposition (UPD) of Cd adatoms onto the surface of Te and CdTe films in Cd²⁺-containing solutions has been studied using electrochemical methods and AFM. The electrochemical deposition of Cd adatoms on Te and CdTe begins at potentials 400 mV more positive than the reversible potential of Cd²⁺/Cd couple and proceeds irreversibly. A strong chemical interaction of Cd adatoms with the surface Te atoms is the driving force of the UPD process. The deposition of Cd adatoms on the tellurium surface is accompanied by their stepwise interaction with tellurium to give CdTe nanophase.

Full text of DOI:10.1016/j.electacta.2006.06.038

Electrochimica Acta 52 (2006) 996–1002
Underpotential deposition of cadmium adatoms on Te and CdTe
∗
N.P. Osipovich , S.K. Poznyak
Physico-Chemical Research Institute, Belarusian State University, Leningradskaya str. 14, 220050 Minsk, Belarus
Received 20 February 2006; received in revised form 22 May 2006; accepted 16 June 2006
Available online 8 August 2006
Abstract
2
+
Underpotential deposition (UPD) of Cd adatoms onto the surface of Te and CdTe films in Cd -containing solutions has been studied using
electrochemical methods and AFM. The electrochemical deposition of Cd adatoms on Te and CdTe begins at potentials 400 mV more positive
2
+
than the reversible potential of Cd /Cd couple and proceeds irreversibly. A strong chemical interaction of Cd adatoms with the surface Te atoms
is the driving force of the UPD process. The deposition of Cd adatoms on the tellurium surface is accompanied by their stepwise interaction with
tellurium to give CdTe nanophase.
©
2006 Elsevier Ltd. All rights reserved.
Keywords: Underpotential deposition; Cadmium; Electrodeposition; Cadmium telluride; Tellurium; Adatoms
1
. Introduction
positive than the equilibrium potential EMz+
/M0
. In those works
the electrodeposition potential does not reach the values nec-
essary to reduce chalcogen to chalcogen hydride, and, thus, the
chalcogenide formation must include the step of metal UPD on
semiconductor. AlthoughthepossibilityofCdUPDonCdSeand
Te was reported [26,27], these processes have not been studied in
detail.
The study of the processes of adatom electrodeposition
on foreign substrates at potentials more positive than the
equilibrium Nernst potential (underpotential deposition, UPD)
provides an important information on the mechanism of some
electrochemical processes, such as adsorption, charge transfer,
nucleation and growth of a new phase, etc. [1–4]. Up to now
most of the papers concerning UPD of adatoms dealt with
Here we present the results of a detailed investigation of the
UPD of cadmium adatoms on tellurium and cadmium telluride.
“metallic electrode–foreign metal adatoms” systems and more
than 50 systems of that kind were described [4,5]. But there
is relatively little information on the UPD processes on the
semiconductor surfaces. Electrodeposition of lead monolayers
on the germanium surface [6], copper and silver monolayers on
Hg1−xZnxTe [7], UPD of copper on diamond [8] were studied.
We have found the Pb UPD on Se [9], Te [10], PbSe [11]
and PbTe [12], the Bi UPD on Te [13]. Note that the UPD
of metal adatoms on semiconductors is of importance in the
electrochemical synthesis of binary A B and A B semi-
conductors. In particular, in ECALE (electrochemical atomic
layer epitaxy) method, alternating UPD of metal and non-metal
adatoms is used [14–22]. Also worthy of mention are the works
on electrodeposition of CdTe and CdSe films [23–25], where the
metal and the chalcogen are codeposited at the potentials more
2
. Experimental
2.1. Electrodes
Polycrystalline (according to the XRD analysis) Te and CdTe
filmelectrodeswereobtainedbypotentiostaticelectrodeposition
of these materials onto an Au substrate from solutions contain-
ing 0.002 M TeO2 + 0.1 M HNO3 (deposition potential: −0.2 V;
II VI
III V
◦
T = 70 C), and 1 M CdSO4 + 0.001 M TeO2 + 0.05 M H2SO4
◦
(
deposition potential: −0.3 V; T = 70 C), respectively. Before
the deposition, the Au foil was polished using diamond paste,
treated with hot concentrated HNO3 and H2SO4, then washed
◦
with bidistilled water and finally heated at 700 C for 20 min
in the air. The prepared Te and CdTe films were about 0.5 ␮m
thick; CdTe films had the p-type conductivity.
∗
BeforetheexperimentstheTeelectrodeswerecycledin0.1 M
HNO3 in the potential range from −0.5 to 0.38 V. To get the
Corresponding author.
E-mail address: osipovich@bsu.by (N.P. Osipovich).
0
013-4686/$ – see front matter © 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2006.06.038

N.P. Osipovich, S.K. Poznyak / Electrochimica Acta 52 (2006) 996–1002
997
correct results, each of the voltammograms was measured on an
individual electrode.
3. Experimental results
.1. Cadmium electrodeposition on tellurium
No Faradaic processes are observed on Te electrode in
3
2
.2. Apparatus and chemical reagents
Electrochemical experiments were carried out in a standard
the background electrolyte (0.1 M HNO3) in a wide range of
potentials (Fig. 1a, dotted line). Anodic Te oxidation begins at
E > 0.4 V, while cathodic reduction starts at E < −0.5 V. With
three-electrode two-compartment cell with a platinum counter
electrode and an Ag|AgCl|KCl(sat.) reference electrode. All
potentials were determined with respect to this reference elec-
trode and controlled by a conventional potentiostat with a pro-
grammer. Current densities reported in this work refer to geo-
metric area of the electrodes.
2+
Cd ions present in the solution, a cathodic current peak CTe
is observed at potentials more positive than the equilibrium
E
Cd /Cd0
2+
potential (−0.67 V against Ag|AgCl|KCl(sat.)) for
the negative potential scan. On the subsequent reverse scan,
an anodic A1 peak appears (Fig. 1a). When the cathodic limit
Spectral dependences of the photocurrent were obtained
using a set-up equipped with a high intensity grating monochro-
mator, a 1000 W xenon lamp and a slowly rotating light
chopper (0.3 Hz). The photocurrent spectra were corrected
for the spectral intensity distribution at the monochromator
output. The polychromatic light from 100 W halogen lamp
Te
1
Te
of polarization is negatively shifted, the A peak concurrently
decreases and then disappears and another anodic peak A
2
Te
appears.
Study of the electrochemical processes on Te electrode in
0.01 M Cd(NO3)2 + 0.1 M HNO3 solution revealed the follow-
ing regularities:
−
2
(
j = 4.2 mW cm ) equipped with an infrared filter was also used
for the photoelectrochemical measurements.
AFM images of the electrode surface were obtained with a
Femto-Scan-001 microscope (Advanced Technologies Center,
Moscow) operated in the constant force mode (1.5–5 nN) under
ambient conditions. AFM tips were standard oxide-sharpened
•
•
•
Both of the anodic peaks and the cathodic one are positively
2+
shifted with increasing the Cd concentration in solution.
The A1 peak on the positive scan appears only after the
Te
cathodic CTe peak is recorded on the negative scan.
−
1
Si3N4 cantilevers with spring constants of 0.06 and 0.12 N m
.
−1
At a potential sweep rate of 20 mV s the charge correspond-
ing to the anodic A1 peak is close to the cathodic charge
The computer analysis of the AFM images was performed to
estimate the true surface area (roughness factor) of Te films.
Reagents of the highest purity and doubly distilled water were
used in the electrolyte preparation. All solutions were deaerated
by blowing purified argon through and over the solution. Analy-
sis of the solutions for cadmium was carried out using an atomic
absorption spectroscopy.
Te
passed through the electrode on the potential sweep down to
−
0.36 V (Fig. 1a, curve 1). But when the cathodic polariza-
tion limit is negatively shifted, the cathodic charge becomes
greater than the anodic charge measured on the subsequent
positive scan, which is accompanied by the appearance of
the A2 peak (Fig. 1a, curves 3 and 4). On increasing the
Te
Fig. 1. (a) Voltammograms of Te electrode in 0.1 M HNO3 (dotted line) and in 0.01 M Cd(NO3)2 + 0.1 M HNO3 solutions (solid lines). The potential was scanned from
−
1
open circuit potential EOCP = 0.33 to −0.36 V (1), −0.385 V (2), −0.45 V (3), −0.61 V (4) and then to 0.35 V. Potential sweep rate: 20 mV s . (b) Voltammograms
of Te electrode in 0.01 M Cd(NO3)2 + 0.1 M HNO3 solutions. The potential was scanned from open circuit potential EOCP = 0.33 to −0.35 V (1), −0.4 V (2), −0.46 V
−
1
(
3), −0.52 V (4) and then to 0.35 V. Potential sweep rate: 200 mV s . The inset shows the dependence of the charges corresponding to the cathodic (solid dots) and
anodic (open dots) peaks on the lower potential limit.

9
98
N.P. Osipovich, S.K. Poznyak / Electrochimica Acta 52 (2006) 996–1002
Fig. 2. Anodic voltammograms of Te electrode in 0.01 M Cd(NO3)2 + 0.1 M
HNO3 solution recorded after its potentiostatic polarization at −0.45 V for 5,
−1
Fig. 3. Voltammograms of Te electrode in 0.01 M Cd(NO3)2 + 0.1 M HNO3
solution recorded at modulated polychromatic illumination. Inset shows the
photocurrent spectrum of Te electrode with cadmium deposited on its surface at
polarization to −0.61 V. The spectrum was recorded in 0.1 M HNO3 solution at
1
0, 50 s, and 5 min. Potential sweep rate: 20 mV s
.
sweep rate up to 200 mV s 1 only one anodic A1 peak is
−
Te
−0.4 V.
observed in the voltammograms (Fig. 1b). The charge corre-
sponding to this peak increases initially with increasing the
passed cathodic charge and then reaches the limiting value
with a mean diameter of 20 nm on the background of the initial
surface structure (Fig. 4).
(Fig. 1b, inset).
•
If Cd is deposited on Te electrodes under potentiostatic con-
2
ditions, the subsequent positive scan demonstrates A peak
Te
growing and A1 peak decreasing and then disappearing with
3.2. Electrodeposition of cadmium on cadmium telluride
Te
deposition time (Fig. 2).
To elucidate the nature of the current peaks observed at
2
+
Te electrode in Cd -containing solutions, we also studied the
electrochemical behavior of CdTe film electrodes in the same
solutions.
In order to obtain additional information on the nature of
the A and A2 peaks, we performed the chemical analysis of
1
Te
Te
anodic dissolution products. To do this, the Te electrode after
2+
The surface of the CdTe electrodes, which were withdrawn
from the deposition cell immediately after their preparation,
washed and transferred into another cell filled with 0.01 M
Cd(NO3)2 + 0.1 M HNO3 solution under Ar atmosphere, have
no time to be oxidized appreciably. If the potential of these elec-
its negative polarization in Cd -containing solution was with-
drawn from the cell, rinsed and transferred into another cell with
0
.1 M HNO3 solution. After recording the anodic peaks the solu-
tion in the cell was analyzed for cadmium. The obtained results
showed that the charges corresponding to ATe and A2 peaks
1
Te
trodes (hereafter referred to as as-prepared electrodes) is shifted
are in good agreement with the cadmium amount found in the
solution, indicating that these peaks are associated only with
cadmium stripping.
1
OCP
positively from the open circuit potential (E
= −0.09 V), an
anodic peak A2 is observed at 0.15 ÷ 0.25 V, and at E > 0.4 V
CdTe
Tellurium is a narrow-gap semiconductor (Eg = 0.4 eV) with a
rather high electrical conductivity at room temperature. Hence,
Te electrode behaves as a metallic one in solution. We could
not notice any photoelectrochemical activity of Te electrode
in background electrolyte in the potential range investigated.
there is a drastic current rise due to the dissolution of whole
CdTe film (Fig. 5a, dotted line). On negative potential scan, a
1
cathodic CCdTe peak is observed at −0.4 V and anodic A
CdTe
and A2
peaks are recorded on the subsequent reverse scan
CdTe
(Fig. 5a). The charge corresponding to the anodic peaks in this
case is greater than that for the cathodic peak by the value of
2+
But after the cathodic CTe peak has been recorded in the Cd -
containing solution, a cathodic photocurrent is observed on the
illumination of Te electrode (Fig. 3). The long-wavelength edge
of the photocurrent spectrum (the inset in Fig. 3) correlates
well with the absorption edge of cadmium telluride, indicat-
ing that this compound is formed on the Te electrode during the
Cd UPD.
the charge corresponding to the A2
peak (Fig. 5a, dotted
CdTe
line) recorded at the initial anodic polarization. Furthermore, a
small A1
peak observed at E ≈ 0 V disappears on shifting the
CdTe
cathodic polarization limit into more negative potential region
(Fig. 5a).
If the as-prepared CdTe electrodes are kept in the deposi-
tion electrolyte for several minutes or in air for several tens of
minutes (after having been removed from the deposition cell),
their surface is oxidized strongly and the open circuit potential
becomes more positive (E2 = −0.12 V). There is no A
The CdTe formation is accompanied by a significant change
in the surface morphology of Te electrode. As-prepared Te
film consists of grains of about 100 nm in width (Fig. 4). The
negative polarization of the electrode at −0.45 V in 0.01 M
Cd(NO3)2 + 0.1 M HNO3 solution for several minutes (the
passed charge corresponds to the deposition of 12–15 mono-
layers of cadmium) leads to the appearance of smaller grains
2
OCP
CdTe
peak on the anodic voltammograms of these electrodes (Fig. 5b,
dotted line). On the negative potential scan, a cathodic C
CdTe
peak is observed and anodic A1 and A2 peaks are recorded
CdTe
CdTe

N.P. Osipovich, S.K. Poznyak / Electrochimica Acta 52 (2006) 996–1002
999
Fig. 4. AFM images of the surface of as-prepared Te electrode (a) and the Te electrode with cadmium adatoms deposited potentiostatically at a potential of −0.45 V
for 4 min (b).
on the subsequent positive scan (Fig. 5b). For these electrodes,
the charges corresponding to the cathodic and anodic peaks are
4. Discussion
close, and the anodic A1
peak is higher than the A2
peak
4.1. Electrochemical behavior of CdTe electrodes
The electrochemical deposition of CdTe film in 1 M
CdTe
CdTe
at initial stages of Cd electrodeposition. Moreover, in the case of
strongly oxidized electrodes the A1
peak is markedly higher
CdTe
as compared with that for the as-prepared electrodes (Fig. 5a
and b).
4 2 2 4
CdSO + 0.001 M TeO + 0.05 M H SO electrolyte proceeds in
the regime of UPD of Cdad and overpotential deposition of Te
14]. The Cd adatoms are deposited on the surface Te atoms
[
and the quantity of the deposited Cd is bounded by a monolayer
since the UPD of Cd on Cd is impossible. Only after deposition
of fresh Te atoms on the surface, the Cd UPD becomes again
possible. Immediately after electrodeposition is stopped, both
cadmium and tellurium atoms can be on the CdTe film surface.
When we transfer quickly the electrode into the other cell with
0.01 M Cd(NO3)2 + 0.1 M HNO3 solution and polarize it posi-
tively, cadmium is dissolved from the surface according to the
reaction [28]:
2
+
CdTe → Cd + Te + 2e¯
(1)
giving the anodic A2
peak (Fig. 5a, dotted line). Note that
CdTe
this process proceeds at more negative potentials than the direct
electrooxidation of CdTe into Cd(II) and Te(IV).
On negative polarization of as-prepared CdTe electrode, the
UPD of Cd occurs on Te atoms which are on the telluride surface
Fig. 5. Voltammograms of as-prepared CdTe electrodes (a) and the CdTe elec-
trodes with strongly oxidized surface (b). The potential was scanned from the
open circuit potential (EOCP) in the positive direction (dotted lines) and from the
EOCP in the negative direction with different scan limits (−0.4 V (solid lines),
(cathodic CCdTe peak). On the subsequent positive scan, both the
−
0.5 V (dashed lines) and −0.61 V (dashed-dotted lines)) and then back in the
−1
positive direction. Potential sweep rate: 20 mV s
.
deposited Cd atoms and those, which were initially present on

1
000
N.P. Osipovich, S.K. Poznyak / Electrochimica Acta 52 (2006) 996–1002
the surface of the as-prepared electrode, are dissolved, so that
the charge corresponding to A2
peak is greater than that for
the cathodic CCdTe one (Fig. 5a).
When as-prepared CdTe electrode is exposed to the depo-
sition solution or to air for a long time, cadmium is lost from
the surface and the latter is enriched with tellurium. It may be a
result of its oxidation by oxygen or of displacement processes,
for example:
and tellurium atoms to give CdTe phase on the surface. The
evolution of the stripping voltammograms recorded after poten-
tiostatic polarization of the Te electrode in the potential region of
Cd UPD for different periods of time distinctly demonstrates the
CdTe
changes occurring on the Te surface. With increasing the Cd
ad
1
deposition time, the peak (A ) of Cd dissolution from the Te
Te
ad
2
Te
surface decreases and disappears and the peak A associated
with the CdTe dissolution appears and then increases (Fig. 2).
The fact that the cathodic charge passed during the Cd UPD
becomes greater than that recorded on subsequent positive scan,
is easy to be explained: only Cd atoms from the CdTe surface
are dissolved, while the deeper ones are not oxidized in this
potential region.
CdTe|2Cds + Te(IV) → CdTe|Tes + 2Cd(II)
(2)
where Cds and Tes are the surface cadmium and tellurium
atoms participating in the displacement reaction. Such displace-
ment processes were previously observed for cadmium adatomic
When recording the voltammograms at a sufficiently high
2+
layer on PbSe in Pb -containing solution [29] and for copper
adatomic layer on Au(1 1 1) in Pt(IV)- and Pd(II)-containing
solutions [30]. The formation of a Te layer on the CdTe surface
during its oxidation was shown in a number of works [28,31–34].
It was found that after immersion in an acidic solution (2 M
−1
sweep rate (200 mV s ), cadmium telluride has no time to be
formed because of kinetic limitations. In this case the Cd UPD
on Te is not yet complicated by the CdTe formation and only one
anodic peak related to the stripping of Cd adatoms from the Te
surface is observedin the voltammograms (Fig. 1b). The limiting
4+
H2SO4) with or without Ce ions the stoichiometric surface of
value of the charge corresponding to the A1 peak was used as
0
Te
CdTe is covered with a Te layer with a limiting thickness of
the charge required for the UPD of Cdad monolayer on Te. It
was determined on the Te electrode with a known roughness
about 1–2 nm [32–34]. On the photoelectrochemical oxidation
in acidic medium (HClO4, pH 0) CdTe is first oxidized into Cd2+
and elementary tellurium, the latter forming a passivation layer
at the electrode surface [28]. According to the findings of Lincot
and Vedel, the thickness of this layer does not exceed 1 nm. Tak-
ing into account the covalent radius of Te atom (0.137 nm), this
corresponds to approximately 3–4 monolayers of tellurium. In
addition, the enrichment of the CdTe surface with tellurium was
found to proceed during the photoelectrochemical oxidation of
CdTe electrodes [35,36].
−2
factor and was 400 ± 50 ␮C cm of the real surface. This value
is close to the calculated charge necessary to form a cadmium
monolayer with hexagonal close packing.
Thus, during the Cd UPD on Te the deposition of several
monolayers of cadmium is possible owing to the interaction
of Cd adatoms with tellurium resulting in the CdTe formation,
and to the Cd diffusion into the Te bulk. Although this is not
a classical UPD process, however, it should be noted that this
process is similar to the process of surface alloying observed
during the UPD of some metals onto the other metals. The study
of the UPD of Pb on Au [37–39], Ag [39–46] and Tl on Ag
It is reasonable that the peak of cadmium dissolution, A2
,
CdTe
is absent on positive polarization of the electrode with strongly
oxidized surface (Fig. 5b, dotted line), and cadmium is deposited
all over the surface on negative polarization, so that the charge
corresponding to CCdTe peak is greater than that for the as-
prepared electrode with slightly oxidized surface, a part of the
latter being occupied by cadmium.
[46,47] and Cd on Au [48,49] showed that the surface alloying
is a rather common phenomenon in the UPD systems which are
characterized by a strong adatom–substrate interaction.
There is a large separation on the potential scale between
1
Te
the peaks of deposition (CTe) and stripping (A ) of cadmium
The A1
peak may be associated with the anodic stripping
CdTe
adatoms on tellurium. According to [50], this suggests that the
UPD of Cdad on Te is irreversible. The latter is also evidenced
by the effect of the sweep rate on the potential of these peaks:
of Cd adatoms deposited onto Te-rich surface of the oxidized
CdTe electrodes. This assumption is supported by a close simi-
larity of the A1 and A1
peaks and by the fact that the A1
Te
CdTe
CdTe
increasing sweep rate results in a negative shift of the C peak
Te
peak is significantly higher for strongly oxidized CdTe elec-
trodes in comparison with as-prepared ones.
and in a positive shift of the A1 peak.
Te
An important characteristic of the UPD process is the under-
UPD
potential shift, ꢀE
—the difference in peak potentials of
4
.2. The UPD of Cd adatoms on tellurium
adatomic monolayer adsorption–desorption and equilibrium
UPD
E
z+
/M0
potential [4]. To estimate ꢀE
value for the UPD
M
The results obtained suggest that the CTe, and A1 peaks
of Cdad on Te, we should take into account the process irre-
Te
observed at Te electrodes are related to the UPD of cadmium
adatoms on tellurium and their stripping, respectively. As to the
peaksA2 onTeandA2 onCdTe, theirsimilaritysuggeststhat
they are of the same nature, that is, both are related to the process
of cadmium stripping from the CdTe surface. This fact as well as
the appearance of the photoelectrochemical activity on Te with
the deposited Cd adatoms and the change in the surface mor-
phology evidence strongly that the UPD of Cdad on tellurium is
accompanied by a progressive interaction of cadmium adatoms
versibility. According to [50,51], for an electrochemical reaction
z+
M
+ ze → M with the rate-determining step being the charge
ad
transfer, the differences between the potential of the reversible
process peak (Ep,r) and those of the peaks of cathodic (E
and anodic (E ) processes for an irreversible process depend
Te
CdTe
cat
p,irr
)
an
p,irr
on the potential sweep rate, v, as follows:
RT
RT
cat
p,irr
E
− Ep,r = (
−
(3)
βzF)ln v0
(βzF)ln v

N.P. Osipovich, S.K. Poznyak / Electrochimica Acta 52 (2006) 996–1002
1001
Fig. 6. Voltammograms of Te electrode in 0.01 M Cd(NO3)2 + 0.1 M HNO3 solutions recorded at different potential sweep rates (a) and the dependence of potentials
corresponding to cathodic (1) and anodic (2) peaks on logarithm of the potential sweep rate (b).
RT
RT
in good agreement with the ꢀEUPD value estimated experimen-
tally.
an
p,irr
E
− Ep,r = −
+
(4)
(
(1 − β)zF)ln v0
where v0 is the reversibility parameter, β is the symmetry factor
((1 − β)zF)ln v
for the surface process. From Eqs. (3) and (4) it follows that
5. Conclusions
cat
an
the slopes for the plots of E
versus ln v and E
versus ln v
p,irr
p,irr
are RT/βzF and RT/(1 − β)zF, respectively, and the intersection
The present study showed that the UPD of cadmium adatoms
can be performed on Te electrode, with the UPD shift being
about 0.5 V. This process is accompanied by a progressive inter-
action of cadmium adatoms and tellurium atoms to give CdTe
nanophase, resulting in a noticeable photoelectrochemical activ-
ity of the Te electrode. A characteristic feature of the UPD of
Cdad on tellurium surface is the irreversibility of the process,
whichmayberelatedtoastronginteractionofcadmiumadatoms
with surface tellurium atoms.
The Cd UPD on CdTe electrodes occurs at the same poten-
tials as on Te electrodes and Cd adatoms are deposited only
on the surface Te atoms. However, the anodic stripping of the
Cd adatoms from CdTe is observed at 200 mV more positive
potentials in comparison with that from Te.
of the plots gives the values of ln v0 and Ep,r. The potential
UPD
difference EMz+
/M0
− Ep,r gives the value of ꢀE
.
The following aspects should be taken into account when
UPD
determining the ꢀE
for the Cd–Te system. It is necessary to
deposit a Cdad monolayer avoiding the CdTe formation because
the latter process leads to a change of the surface nature. Fur-
thermore, for definiteness sake the measurements should be
performed at the same degree of surface coverage. These condi-
tions can be met owing to the cathodic potential limit, the value
of which should be changed with changing the potential sweep
rate. The corresponding voltammograms and the dependence of
1
Te
potentials of the adsorption (CTe) and desorption (A ) peaks
of Cdad monolayer on Te are shown in Fig. 6. For the UPD of
UPD
Cdad on Te, the estimated ꢀE
value was about 0.47 V. The
The phenomenon of the UPD of cadmium adatomic layers
on tellurium is of interest for understanding the mechanism of
CdTe electrosynthesis and directs the possible ways of preparing
semiconductor structures including monolayers or nanoparticles
of cadmium telluride.
exact value is difficult to determine, because the potential of the
anodic A1 peak depends slightly on the potential of the cathodic
Te
polarization limit.
In the works [52,53] from a thermodynamic point of view,
the following expression was derived for the UPD shift:
1
UPD
Acknowledgments
ꢀ
E
=
(5)
bind
M–S
bind
ze(E
− E
)
M–M
This work was supported by the NATO Collaborative Link-
age Grant PST.CGL.979631 and the Belarusian state program
“NANOTEKH”.
bind
M–M
where E
is the binding energy per atom of bulk metal M
the binding energy of an atom M when adsorbed on
the substrate S. Going to moles we obtain
bind
M–S
and E
1
bind
M–S
1
UPD
References
ꢀE
=
=
) zF(E
ꢀ
ꢀbind
ꢀbind
ꢀbind
)
M–M
zeNA(E
− E
− E
M–M
M–S
[
1] R.R. Adzic, in: H. Gerischer, C.W. Tobias (Eds.), Advances in Electro-
chemistry and Electrochemical Engineering, vol. 13, Wiley, New York,
(6)
1
978, p. 159.
If for the UPD of Cd on Te we take ꢀ G298 CdTe
ad
f
[
2] D.M. Kolb, in: H. Gerischer, C.W. Tobias (Eds.), Advances in Electrochem-
istry and Electrochemical Engineering, vol. 11, Wiley, New York, 1978, p.
−
1
(
98.55 kJ mol ) as a measure of strengthening of Cd–Te
bond in comparison with Cd–Cd bond, we can obtain
125.
UPD
ꢀ
E
= 98,550/(2 × 96,500) ≈ 0.5 V. This calculated value is
[3] K. J u¨ ttner, W.J. Lorenz, Z. Phys. Chem. 122 (1980) 163.

1
002
N.P. Osipovich, S.K. Poznyak / Electrochimica Acta 52 (2006) 996–1002
[
4] D.M. Kolb, M. Przasnysky, H. Gerischer, J. Electroanal. Chem. 54 (1974)
5.
5] E. Herrero, L. Buller, H.D. Abruna, Chem. Rev. 101 (2001) 1897.
[28] D. Lincot, J. Vedel, J. Cryst. Growth 72 (1985) 426.
[29] E.A. Streltsov, N.P. Osipovich, L.S. Ivashkevich, A.S. Lyakhov, Elec-
trochim. Acta 44 (1999) 2645.
[30] S.R. Brankovic, J.X. Wang, R.R. Ad zˇ i c´ , Surf. Sci. 474 (2001) L173.
[31] Y.-C. Lu, R.S. Feigelson, R.K. Route, J. Appl. Phys. 67 (1990) 2583.
[32] C. Debiemme-Chouvy, F. Iranzo Mar ´ı n, U. Roll, M. Bujor, A. Etcheberry,
Surf. Sci. 352–354 (1996) 495.
[33] F.I. Mar ´ı n, J. Vigneron, D. Lincot, A. Etcheberry, C. Debiemme-Chouvy,
J. Phys. Chem. 99 (1995) 15198.
2
[
[
6] A.B. Ershler, A.V. Kaisin, Kh.Z. Brainina, I.M. Levinson, Elektrokhimiya
2
2 (1986) 203.
[
[
7] C.N. van Huong, P. Lemasson, Phys. Rev. B 40 (1989) 3021.
8] F. Bouamrane, A. Tadjeddine, R. Tenne, J.E. Butler, R. Kalish, C. L e´ vy-
Cl e´ ment, J. Phys. Chem. 102 (1998) 134.
[
9] E.A. Streltsov, S.K. Poznyak, N.P. Osipovich, J. Electroanal. Chem. 518
(
2002) 103.
[34] A. Etcheberry, F.I. Mar ´ı n, E. Novakovic, R. Triboulet, C. Debiemme-
Chouvy, J. Cryst. Growth 184/185 (1998) 213.
[
[
[
[
10] E.A. Streltsov, N.P. Osipovich, L.S. Ivashkevich, A.S. Lyakhov, Elec-
trochim. Acta 44 (1998) 407.
11] E.A. Streltsov, N.P. Osipovich, L.S. Ivashkevich, A.S. Lyakhov, V.V. Sviri-
dov, Electrochim. Acta 43 (1998) 869.
12] E.A. Streltsov, N.P. Osipovich, L.S. Ivashkevich, A.S. Lyakhov, A.N. Vesti,
Belar. Ser. Khim. Nauk 3 (1997) 21 (in Russian).
13] N.P. Osipovich, E.A. Streltsov, A.S. Susha, Electrochem. Commun. 2
[35] H. Gerischer, W. Mindt, Electrochim. Acta 13 (1968) 1239.
[36] P.P. Konorov, S.M. Repinskii, Elektrokhimiya 4 (1968) 226 (in Russian).
[37] U. Schmidt, S. Vinzelberg, G. Staikov, Surf. Sci. 348 (1996) 261.
[38] M.P. Green, K.J. Hanson, R. Carr, I. Lindau, J. Electrochem. Soc. 137
(1990) 3493.
[39] M.P. Green, K.J. Hanson, Surf. Sci. 259 (1991) L743.
[40] H. Siegenthaler, K. J u¨ ttner, Electrochim. Acta 24 (1979) 109.
[41] T. Vitanov, A. Popov, G. Staikov, E. Budevski, W. Lorenz, E. Schmidt,
Electrochim. Acta 31 (1986) 981.
[42] A. Popov, N. Dimitrov, O. Velev, T. Vitanov, E. Budevski, Electrochim.
Acta 34 (1989) 265.
[43] A. Popov, N. Dimitrov, D. Kashchiev, T. Vitanov, E. Budevski, Electrochim.
Acta 34 (1989) 269.
[44] N. Dimitrov, A. Popov, T. Vitanov, E. Budevski, Electrochim. Acta 36
(1991) 2077.
[45] N. Dimitrov, A. Popov, D. Kashchiev, T. Vitanov, E. Budevski, Electrochim.
Acta 36 (1991) 1259.
[46] D. Carnal, P.I. Oden, U. M u¨ ller, E. Schmidt, H. Siegenthaler, Electrochim.
Acta 40 (1995) 1223.
[47] H. Siegenthaler, K. J u¨ ttner, E. Schmidt, W.J. Lorentz, Electrochim. Acta
23 (1978) 1009.
(
2000) 822.
[
[
[
14] B.W. Gregory, J.L. Stickney, J. Electroanal. Chem. 300 (1991) 543.
15] I. Villegas, J.L. Sticney, J. Electrochem. Soc. 139 (1992) 686.
16] B.W. Gregory, D.W. Suggs, J.L. Sticney, J. Electrochem. Soc. 138 (1992)
1
279.
17] F. Loglio, M. Innocenti, G. Pezzatini, M.L. Foresti, J. Electroanal. Chem.
62 (2004) 117.
18] R. Vaidyanathan, J.L. Stickney, U. Happek, Electrochim. Acta 49 (2004)
321.
[
[
[
5
1
19] M. Innocenti, S. Cattarin, M. Cavallini, F. Loglio, M.L. Foresti, J. Elec-
troanal. Chem. 532 (2002) 219.
20] T. Ozn u¨ l u¨ er, U. Demir, J. Electroanal. Chem. 529 (2002) 34.
21] M. Innocenti, F. Forni, G. Pezzatini, R. Raiteri, F. Loglio, M.L. Foresti, J.
Electroanal. Chem. 514 (2001) 75.
¨
¨
[
[
¨
[
22] A. Gichuhi, B.E. Boone, U. Demir, C. Shannon, J. Phys. Chem. B. 102
1998) 6499.
23] M.P.R. Panicker, M. Knaster, F.A. Kroger, J. Electrochem. Soc. 125 (1978)
66.
(
[48] J.W. Schultze, F.D. Koppitz, M.M. Lohrengel, Ber. Bunsen. Phys. Chem.
78 (1974) 693.
[49] R. Vidu, S. Hara, J. Electroanal. Chem. 475 (1999) 171.
[50] B.E. Conway, H. Angerstein-Kozlovska, US Nat. Bur. Stand. Spec. Publ.
455 (1976) 107.
[
5
[
[
[
24] F.A. Kroger, J. Electrochem. Soc. 125 (1978) 2028.
25] Z. Loizos, N. Spyrellis, G. Maurin, Thin Solid Films 204 (1991) 139.
26] Kh.Z. Brainina, V.V. Nikiforov, Elektrokhimiya 25 (1989) 1237 (in Rus-
sian).
[51] H. Angerstein-Kozlowska, B.E. Conway, J. Electroanal. Chem. 95 (1979)
1.
[
27] E.A. Streltsov, N.P. Osipovich, Dokl. Akad. Nauk Belar. 42 (1998) 58 (in
Russian).
[52] C. S a´ nchez, E. Leiva, J. Electroanal. Chem. 458 (1998) 183.
[53] W. Schmickler, Chem. Phys. 141 (1990) 95.