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4.
Electrochemistry
of
Diamond:
Semiconductor and Structural Aspects
Yuri V. Pleskov
4.1. Introduction
Being extraordinarily stable and corrosion-resistant, diamond is
an attractive electrode material for use in theoretical and applied
electrochemistry [1]. In particular, diamond electrodes have been
reported to be stable and effective electrodes for environmentallyoriented [2] and analytical [3,4] purposes.
As with many insulators, diamond can be transformed into a
wide-gap semiconductor by appropriate doping. Boron practically
is the only “shallow” acceptor dopant that makes diamond
conducting at room temperature (most other dopants have too
large an ionization energy) [5]. Recently, sulfur was suggested as
an equally shallow donor dopant [6].
Depending on the doping level, diamond exhibits properties
either of a semiconductor (e.g., at boron content from 10 to 1000
ppm) or a “poor metal” (with up to 10,000 ppm of B or even higher).
It is the heavily doped diamond that is used as an electrode
material in electrosynthesis, electroanalysis, etc.
However, in this chapter we shall focus our attention on
moderately doped diamond, because it is most suitable for
revealing effects of the semiconductor nature and crystal structure
on the electrochemical properties of this material.
4.2. Effects of the Semiconductor Nature of
Diamond
4.2.1. Current—Voltage Curves
It
is
known
that
one
of
the
characteristic
features
of
semiconductor/metal contacts is the rectification of electric current.
The
asymmetry
of
current—voltage
semiconductor/metal contact is
curves
at
a
quite pronounced: the “direct”
current passing the contact can be rather large, while the reverse
(blocking)
current
is
very
small.
The
current—voltage
characteristics at some “ideal” semiconductor electrodes do follow
this law (e.g., anodic dissolution of n-type germanium, etc.) [7].
For p-type boron-doped diamond electrodes, the blocking
direction of current is cathodic; for n-type sulfur-treated diamond,
anodic. The asymmetrical current—voltage characteristics have
indeed occasionally been observed in redox electrolytes with lightly
doped diamond samples [1, 8 , 9 ] (Fig. 4.1). However, more
abundant are symmetrical cyclic voltammograms, the more so for
heavily doped diamond (Fig. 4.2 [10]).
Different redox systems differ in their peak-to-peak potential
difference Ep on the cyclic voltammograms: the faster is the
electrochemical reaction, the smaller isEp. For reversible
reactions, Ep ≈ 59 mV [11]. An extensive qualitative study of the
dependence of Ep on the
Fig. 4.1. a - Cyclic voltammogram for a boron-doped diamond
electrode in 0.008 M K3Fe(CN)6 solution [1]; b - potentiodynamic
curves for a sulfur-treated diamond electrode: cathodic in 0.1 M
K3Fe(CN)6, anodic in 0.1 M K4Fe(CN)6 solution, at a potential scan
rate of (1) 5, (2) 10, (3) 20, (4) 50, and (5) 100 mV s -1 [9]. Supporting
electrolyte: 0.5 M H2SO4.
Fig. 4.2. Cyclic voltammogram for a {111} face of a HTHP
single
crystal in 0.5 M H2SO4 + 0.01 M Fe(CN)63- + 0.01 M Fe(CN)64
solution. The potential scan rate was 5 mV s-1 [10].
properties of diamond and electrolyte [12] showed that (1) outersphere reactions are more reversible than inner-sphere ones1; (2)
redox systems with more positive equilibrium potentials are more
reversible than those having negative equilibrium potentials,
which is but natural for a p-type semiconductor electrode (see [7]);
and (3) on heavily doped (metal-like) diamond electrodes, the
We recall that outer-sphere reactions involve the outer
coordination sphere of reacting ions; thus, little if any change
occurs inside the ion solvate shell. These reactions proceed without
breaking up intramolecular bonds,whereas in inner-sphere
reactions, involving the inner coordination sphere, the electron
transfer is accompanied by the breaking up or formation of such
bonds. Inner-sphere reactions are often complicated by the
adsorption of reactants and/or reaction products on the electrode
surface.
1
reactions proceed in a more reversible manner than on moderately
doped electrodes (which demonstrate semiconductor behavior). The
latter statement was corroborated quantitatively [ 13 ] by
juxtaposing the charge-transfer (faradaic) resistance RF of
diamond/redox electrolyte interfaces and the diamond bulk
resistivity . This resistance can be measured using the
electrochemical-impedance method, as a low-frequency cut-off on
the real-component axis in the complex-plane presentation of
impedance
spectra
taken
in
redox
solutions
of
different
concentrations (Fig. 4.3a [13])2. It can be also determined from the
slope of the current—voltage curves recorded in these solutions.
We emphasize that both the impedance spectra and the
voltammetric curves should be taken at or near the reversible
potential of the redox systems. The faradaic resistance is
essentially equal to the reciprocal of the exchange current j0 (up to
a factor of RT / F), which is a measure of the reaction rate:
RF = RT / (nFj0)
(4.1)
Here R is the gas constant, T is the absolute temperature, and F is
the Faraday constant. The RF vs.  dependence is presented in Fig.
4.4. We conclude that the reaction proceeds at a higher rate at
readily conducting diamond electrodes.
More precisely, the low-frequency cut-off equals RF + Rs where Rs
is the “series” (Ohmic) resistance in the equivalent circuit of the
electrode (Fig. 4.6 below).
2
Fig. 4.3. (a) Complex-plane plots of impedance spectra measured for
a polycrystalline diamond electrode at the equilibrium potential in 1
M KCl + x M K3Fe(CN)6 + x M K4Fe(CN)6 solution at a value of x: (1)
3.3 10-3; (2) 10-2; (3) 5 10-2; (4) 10-1; (5) 2 10-1. Frequency f (Hz) is
shown in the figure. (b) Dependence of the faradaic resistance on the
K4Fe(CN)6 concentration (the K3Fe(CN)6 concentration being kept
constant) [13].
Fig. 4.4. Dependence of the faradaic resistance measured at the
equilibrium redox potential for polycrystalline diamond electrodes on
their resistivity for (1) Fe(CN)63-/4- and (2) quinone/hydroquinone
redox systems [13].
At first glance, the proportionality between RF and  reflects
the
fundamental
law
of
the
electrochemical
kinetics
at
semiconductor electrodes, namely, the exchange current of a
semiconductor electrode must be proportional to the surface
concentration of charge carriers participating in the redox reaction.
However, a closer look into the problem, based on reference [14],
allows one to conclude that it is the potential distribution at the
diamond/redox electrolyte solution interface, rather than the
surface concentration of the charge carriers, that depends on the
diamond doping level, the more so, for more heavily doped samples.
More precisely, the potential drop in the Helmholtz layer in a
redox electrolyte increases with increasing doping. Therefore, the
reaction rate reflects the Helmholtz potential drop, rather than the
charge carrier concentration. This is the reason why the behavior
of semiconductor diamond is far from “ideal”; in particular, no
current rectification is typically observed on (rather heavily doped)
diamond electrodes, as mentioned above.
In addition to the Ep quantity, the electrode kinetics can be
characterized by the transfer coefficients  (for cathodic reactions)
and  (for anodic reactions). The transfer coefficients can be found,
e.g., from the slope of the dependence of the voltammetric current
peak potential Ep on the logarithm of the potential scanning rate v
(compare Fig. 4.1b):
Ep = const - (RT / 2nF) ln v
(4.2)
They can also be obtained from the slope of the dependence of the
faradaic resistance on the logarithm of the redox electrolyte
concentration at the equilibrium potential (see Fig. 4.3b). Indeed,
as shown above, the faradaic resistance RF, measured in a redox
solution at its equilibrium potential, equals the reciprocal of the
exchange current j0. By measuring the dependence of j0 on the
concentration of the oxidized form cox in the solution, while the
concentration of the reduced form cred has been kept constant (or
vice versa), the transfer coefficient  (or, respectively, ) can be
calculated by the formula [11]:
j0 = nFk0 cox 1- cred ,
where k0 is the rate constant of the reaction.
(4.3)
On
metal
electrodes, the
transfer
coefficients
typically
approach 0.5. Generally, the transfer coefficients for redox
reactions on moderately doped diamond electrodes are smaller
than 0.5; their sum  +, less than 1. We recall that an ideal
semiconductor electrode must demonstrate a rectification effect; in
particular, on p-type semiconductors, reactions proceeding via the
valence band have the transfer coefficients  = 0,  = 1, and thus, 
+ = 1 [7]. Actually, the ideal behavior is rarely the case even with
single crystal semiconductor materials manufactured by use of
advanced technologies ( like germanium, silicon, gallium arsenide,
etc.). The departure from the “ideal” semiconductor behavior is
likely to be caused by the fact that the interfacial potential drop
appears essentially localized, even in part, in the Helmholtz layer,
due, e.g., to a high density of surface states, or the surface states
directly participate in the electrochemical reactions. As a result,
the transfer coefficients  and  have intermediate values,
between those characteristic of semiconductors (0 or 1) and metals
(0.5). Semiconductor diamond falls in with this peculiarity.
However, for heavily doped electrodes, the redox reactions often
proceed as reversible, and the transfer coefficients approach 0.5
( “metal-like” behavior).
4.2.2. Impedance Spectroscopy
Another specific feature of semiconductor electrodes is the
characteristic
potential
dependence
of
their
differential
capacitance. The measuring procedure is known to consist in
applying a perturbing harmonic voltage signal of frequency f to the
electrochemical cell and measuring the cell response at the same
frequency. The differential capacitance rarely is frequencyindependent. Generally, the complex-plane presentation of an
impedance spectrum (Fig. 4.5a) has a linear high-frequency
segment inclined to a vertical line (Fig. 4.5b [ 15 ]). Such a
dependence can be described by introducing a constant-phase
element (CPE) into the electrode’s equivalent circuit (Fig. 4.6). The
inherent impedance of a CPE is [16]: ZCPE = -1 (i)-a, where i = (1)1/2;  = 2f is the ac angular frequency; the power a determines
the character of the frequency dependence, and the frequencyindependent quantity  is measured in Faa-1cm-2 units. When a
approaches 1, the frequency-independent capacitance C can be
substituted for  with reasonable accuracy. This capacitance can
be used in calculating the acceptor (or donor) concentration NA
(respectively, ND) in the semiconductor diamond, by using the
Schottky theory of semiconductor interfaces [7].
Fig. 4.5. Complex-plane presentation of (a) impedance spectrum for a
HTHP single crystal in 2.5 M H2SO4 solution; (b) its high-frequency
part [15]. The frequencies (kHz) are shown in the figure.
Fig. 4.6. Equivalent circuits for semiconductor electrodes with (a)
frequency-independent capacitance Csc and (b) constant-phase
element CPE. Rs is the series resistance, and RF is the faradaic
resistance.
To determine NA (ND), the reciprocal of differential capacitance
squared has been plotted versus the electrode potential E; such a
graph is called a Mott—Schottky plot (Fig. 4.7). From the slope of
the line, NA (ND) can be calculated:
ND,A =  (2 / e0) [d(C-2) / dE]-1.
(4.4)
Here  and 0 are the permitivity of diamond and free space,
respectively, and e is the electron charge; the “+” and “–” signs
relate to donors and acceptors, respectively. We recall that
equation (4.4) reflects the potential dependence of the thickness of
the space-charge layer in the semiconductor. By extrapolating the
line to C-2  0, the flat-band potential of the diamond electrode
can be found. We note that the slopes of the two lines in Figs. 4.7a
and 4.7b have opposite signs, thus unambiguously evidencing the
p-type and n-type conductance in the boron-doped and sulfurtreated diamond, respectively.
Fig. 4.7. Mott—Schottky plots for (a) {110}-oriented boron-doped ptype and (b) {111}-oriented sulfur-treated n-type CVD epitaxial
diamond thin-film electrodes in 0.5 M H2SO4 solution [8, 29].
The Mott—Schottky-plot approach is now widely applied to
diamond electrodes as a nondestructive method in studying the
bulk and surface properties (through the doping level or flat-band
potential, respectively) of synthetic diamond. It should be noted,
however, that often the doping level in the diamond may be too
high to meet the essential assumption of the Mott—Schottky
analysis (primarily, a non-degenerate semiconductor behavior). If
such is the case, the values of the acceptor (or donor)
concentrations obtained must be referred to as approximations.
It is worth mention that, even being frequency-dependent, the
Mott—Schottky plot usually remainslinear, thus reflecting the
potential dependence of the space-charge layer thickness, for any
particular frequency f [17]. This fact allows one to conclude that,
whatever is the reason for the frequency dependence of the
capacitance, it relates to the space-charge layer, rather than the
diamond surface proper. Thus, a slow ionization, in the space
charge region of a diamond crystal, of atoms with a relatively
deep-lying energy level was assumed [ 18 ] as a tentative
explanation for the frequency dispersion of the capacitance of
diamond electrodes.
In addition to the Mott—Schottky-plot method, based on linear
impedance measurements, the dopant concentration can be
determined using the amplitude demodulation method (ADM), a
version of nonlinear impedance techniques [19]. Unlike the abovediscussed linear-impedance method, here the perturbing signal
applied to the cell is a high-frequency () current signal,
modulated in its amplitude at a low frequency  (Fig. 4.8, inset);
thevoltage response E of the cell is measured at this lower
frequency. According to the theory of the method, the response is
proportional to the d(C-2)/dE value. This allows direct determining
N A:
NA = - I02 / 2e02E ,
(4.5)
where I0 is the amplitude of the applied current signal. The
potential-independent ADM signal (see Fig. 4.8) is the equivalent
of
a
constant-slope
constant(versus
depth)
Mott—Schottky
distribution
plot;
of
the
both
reflect
dopant
in
a
the
semiconductor.
Fig. 4.8. Potential dependence of the ADM signal for a {111} lateral
face of a HTHP single crystal (see Fig. 4.10 below). Inset: form of the
perturbing current signal applied to the cell;  = 0.5 MHz,  = 2 kHz
[10].
The ADM measurements were used in determining the doping
level in numerous semiconductors, including diamond [18]. A
particular application of the ADM method toHTHP (high-
temperature, high-pressure) diamond single crystals will be
touched on below.
4.2.3. Photoelectrochemistry of Diamond
Already in the first paper on the photoelectrochemistry of the
diamond electrode [ 20 ], it was shown that the semiconductor
nature of diamond manifests itself in generating photocurrent and
photopotential. When light is absorbed in diamond, excess charge
carriers (electrons and holes) are generated. The electron—hole
pairs are separated in the electric field of the space-charge layer;
the minority carriers either cross the diamond/solution interface,
provided an appropriate electron or hole acceptor (e.g., hydrogen
ion) is present in the solution, or, when the interface is of a
blocking nature, charge up the electrode surface. Correspondingly,
photocurrent or photopotential is observed in the cell. At the first
stage, the photoelectrochemistry of diamond was studied using
sub-band light, whose quantum energy was less than the diamond
band gap width (~ 5.5 eV); therefore, the excess charge carriers
were generated via photoionization of some light-sensitive
impurities,
rather
than
valence-electron
excitation
to
the
conduction band [20, 21 ]. Later, supraband light with higher
quantum energy was used [22, 23], which provided band-to-band
electron excitation in diamond.
Fig. 4.9. Potential dependence of the photocurrent squared for a
polycrystalline diamond electrode in 1 M KCl solution [20].
When light is absorbed deep in a semiconductor, that is, the
light
penetration
depth
exceeds
the
(potential-dependent)
thickness of the space-charge layer near the electrode surface, the
layer where the charge separation proceeds widens with increasing
potential applied to the electrode. The photocurrent Iph thus varies
with the electrode potential E in much the same way as the
differential capacitance C: the photocurrent squared vs. potential
plot is linear (Fig. 4.9), resembling the Mott—Schottky plot
(compare Fig. 4.7). At the flat-band potential, the electrode is not
charged; hence, no charge separation is possible and the
photocurrent is zero. Therefore, by extrapolating the plot in Fig.
4.9 to Iph2  0, the flat-band potential can be determined, just as
in the Mott—Schottky-plot approach. Other photoelectrochemical
methods for the flat-band potential determination, namely, by
measuring the photocurrent onset potential or the limiting opencircuit photopotential yielded by very intense illumination, are
described in [22].
4.3. Effects of the Crystal Structure
The electrode behavior of diamond can be affected by its crystal
structure. Our comparative studies of chemical-vapor-deposited
(CVD) single-crystal (homoepitaxial) and polycrystalline diamond
thin-film electrodes, as well as amorphous diamond-like carbon
electrodes, gave insight into the role of intercrystalline boundaries
in the electrochemical behavior of diamond. By comparing the
impedance spectra and kinetics of various redox reactions, we
concluded that the single-crystal and polycrystalline diamond
electrodes are similar in their electrochemical properties. Both the
impedance characteristics (the differential capacitance, the CPE
parameters a and ) and the kinetic parameters (the transfer
coefficients  and , the rate constant k0) are similar for the singlecrystal and polycrystalline diamond electrodes. By contrast, the
wide-gap diamond-like carbon (assumed to be a model material for
the intercrystalline boundaries) appeared to be an inactive
electrode in performing the electrochemical redox reactions.
Therefore,
we
concluded
that
the
electrode
behavior
of
polycrystalline diamond films is entirely determined by the
diamond crystallites proper, rather than by the intercrystalline
boundaries, at least, at moderate electrode polarization [ 24 ].
However, at high anodic potentials (just prior to the onset of
oxygen evolution), a minor current peak was observed in the
potentiodynamic curves taken with polycrystalline electrodes in a
supporting electrolyte solution, which cannot be observed with
single-crystal films. The peak was ascribed to the anodic oxidation
of sp2-carbon of the intercrystalline boundaries [25], which turned
out to be less oxidation-resistant than the diamond crystallites.
In the last part of this chapter, our attention will be focused on
the electrochemical properties of individual crystal faces of HTHP
diamond single crystals, as well as single-crystal (homoepitaxial)
CVD-diamond films. Our preliminary studies showed that the
HTHP single crystals, on the whole, are similar to the CVD
polycrystalline films in terms of their electrode behavior. In
particular, both the polycrystalline thin-film electrodes and the
HTHP single crystal electrodes are equally characterized by the
special type of frequency-dependent capacitance described by the
CPE.
We dealt with single crystals grown from a Ni—Fe—C—B melt,
at
pressures
and
temperatures
within
the
diamond
thermodynamic stability range. The growth was performed, using
a seed, by temperature gradient techniques (for details, see ref. 26).
Boron, an acceptor dopant, was added to the source melt as
ferroboron (the boron concentration in the batch was 0.1 wt. %). At
the conclusion of the synthesis, the solidified metal was dissolved
in a Cr2O7 + H2SO4 mixture at 80100oC and the diamond crystals
extracted. This oxidative treatment obviously made the diamond
surface
oxygen-terminated,
unlike
as-grown
CVD-diamond
surfaces which are hydrogen-terminated. The near-seed region of
the crystals was then ground off and polished by pressing the
crystals against the surface of a rotating cast-iron polishing wheel.
One of the crystals is schematically presented in Fig. 4.10. It is
a cubo-octahedron with unevenly developed {111} and {100} faces.
The orientation of the rear (polished) face also approached {111}.
100
100
111
Fig. 4.10. A HTHP-diamond single crystal (top view).
The octahedral and cubic faces (including the polished rear face
of the crystal) were consecutively exposed to the electrolyte
solution, the rest of the crystal’s surface (including the crystal
edges), the ohmic contacts, and the current lead being insulated.
To distinguish between like faces, we designated them as “central”,
“left”, “right”, “bottom” (see Fig. 4.10), and “rear” (polished).
Typical Mott—Schottky plots of the individual faces are given
in Fig. 4.11 [10]. The rather positive flat-band potential is due to
the fact that the diamond surface had been oxidized during its
above-described processing. From the slope of the lines, the
uncompensated acceptor concentration was calculated. The NA
values thus obtained (coinciding with those determined by the
ADM method, see Fig. 4.8) are given in Table 4.1.
Fig. 4.11. Mott—Schottky plots for two faces of the crystal shown
in Fig. 4.10. in 0.5 M H2SO4 solution [10].
We now turn our attention to the kinetic data. Anodic and
cathodic potentiodynamic curves were taken at the faces of the
single crystals in the 0.5 M H2SO4 + 0.01 M Fe(CN)63- (or Fe(CN)64)
solution. The current vs. potential curves passed through a
maximum whose potential depended on the potential scanning
rate v (compare the cathodic curves in Fig. 4.1b). The transfer
coefficients for the cathodic () and anodic () reactions in the
Fe(CN)63-/4- system were determined by using equation (2), as
discussed above. The  and  values are also shown in Table 4.1.
Table 4.1. Properties of individual faces of the single crystal (Fig. 4.10)
[10].
NA (cm-3)


{111} central
2  1019
-
0.11
{111} rear
9  1018
0.5
0.25
1.3  1021
0.6
0.25
{111} lateral (left)
3  1020
0.33
0.43
{100} right
6  1021
-
-
{100} left
4.8  1021
0.6
0.38
Face
{111} lateral (bottom)
From these data the following conclusions were drawn:
(i) The cast-iron-wheel surface polishing does not affect the
capacitance significantly, as no marked difference in C or NA was
found between the central (as-grown) and the rear (polished) {111}
faces of the crystal shown in Fig. 4.10. In this respect, the
semiconductor diamond differs from “traditional” semiconductors
(germanium, silicon, etc.), whose mechanical processing, by using
abrasives, results in the formation of a so-called damaged layer
rich in dislocations, point defects, and other distortions of the
crystal lattice. (Therefore, chemical or electrochemical etching is
required to remove the damaged layer, which is necessary for
revealing the semiconductor properties.) By contrast, the specific
abrasive-free processing of diamond we used, evidently, does not
distort its crystal lattice.
(ii) The {100} faces appeared more heavily doped than the central
{111} face. 3 Interestingly, the lateral {111} faces appeared more
heavily doped than the central {111} face of the crystals. These
peculiarities may reflect the complicated conditions in the source
melt.
(iii) Generally, the higher doping level, the less irreversible is the
redox reaction. On the most heavily doped {100} “left” face, the
reaction kinetics approach that at “metal-like” diamond electrodes.
Thus, the known sectorial character of the HTHP diamond
crystals [ 27 ] well manifests itself in the electrochemical
measurements. On the whole, the difference in the electrochemical
behavior of the individual faces can be primarily ascribed to
different boron concentration in their adjacent growth sectors,
resulting from the different ability of the diamond crystal faces to
incorporate the boron dopant during the growth process, rather
than to different surface atomic densities or other purely surface
properties.
We now turn to the homoepitaxial CVD-diamond films
deposited onto dielectric single crystal diamond substrates. The
three crystal faces, that is, {111}-, {110}-, and {100}-orientated,
were studied by differential capacitance measurements [28]. They
differ in their capacitance markedly. The Mott—Schottky plots (see,
We note that this particular finding is in contrast to the known
ability of the {111} face to incorporate boron, during the growth
process, more intensely than the {100} face.
3
e.g., Fig. 4.7a for the {110}-oriented film) allowed us to estimate
the acceptor concentration in the films (Table 4.2). Their different
doping level can be explained by
Table 4.2. Acceptor concentration
homoepitaxial CVD films [28].
in
differently
oriented
Face
{100}
{110}
{111}
Polycrystalline
NA (cm-3)
(2-3) 
1.3  1020
(5-7) 
5  1020
1019
1020
the above-mentioned different intensity of boron incorporation into
differently orientated diamond crystal faces during the film growth.
The results of the kinetic measurements agree with the
capacitance data. The voltammetric curves for the polycrystalline
film and {111} and {110} faces, taken in Fe(CN)63-/4- and
Ru(NH3)2+/3+ redox solutions, are typical of irreversible, however,
rather fast electrode reactions. By contrast, on the lightly doped
{100} face, the current is very low; the process is under kinetic,
rather than diffusion, control (Fig. 4.12). Thus, the electrochemical
reactions in the Fe(CN)63-/4- and Ru(NH3)62+/3+ systems are slowed
down in the following sequence: polycrystalline ≈ {111} > {110} >
{100}. These findings agree with the above-discussed dependence
of the electrochemical reaction rate on the diamond doping level.
Similar results, for the {111}- and {100}- faces, were obtained in ref.
29. On the whole, the results obtained for the homoepitaxial CVDfilms are in agreement with those found for the individual faces of
the HTHP-single crystals.
Fig. 4.12. Cyclic voltammograms taken for {110}-, {100}-, and {111}oriented crystal faces of homoepitaxial CVD-diamond films in 0.1
MNaCl + 0.005 M Ru(NH3)6Cl2 + 0.005 М MRu(NH3)6Cl3 solution.
The potential scan rate was 10 mV s-1 [28].
4.4. Conclusions
Moderately doped diamond electrodes are well suited for revealing
the semiconductor and structural aspects of the diamond
electrochemistry. The structural effects often boil down to a
difference in the acceptor concentration in the diamond, rather
than reflecting the surface atomic density or other purely surface
properties. To reveal these fine effects, the electrochemical
behavior of individual faces must be compared under the condition
of equal doping level.
Other studies into the
structural
effects involved
the
comparison of the growth and nucleation surfaces of free-standing
polycrystalline diamond films [ 31 ], nanodiamond thin-film
electrodes [ 32 , 33 ], and the electrochemical polishing of
polycrystalline diamond electrode surfaces [34].
4.5. Acknowledgment
The work carried out was financed in part by the NEDO
International Joint
Research Grant Program, Project 01МВ9,
and the Russian Foundation for
Basic Research, Project 04-03-
32034.
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