On the preferential crystallographic orientation of Au nanoparticles: Effect of electrodeposition time

Article abstract of DOI:10.1016/j.electacta.2009.01.054

The crystallographic orientation of Au nanoparticles electrodeposited at glassy carbon (nano-Au/GC) electrodes (prepared by potential step electrolysis) is markedly influenced by the width of the potential step. The oxygen reduction reaction (ORR) and the

Full text of DOI:10.1016/j.electacta.2009.01.054

Electrochimica Acta 54 (2009) 3720–3725
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
On the preferential crystallographic orientation of Au nanoparticles: Effect of
electrodeposition time
∗
Mohamed S. El-Deab
Department of Chemistry, Faculty of Science, Cairo University, Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
The crystallographic orientation of Au nanoparticles electrodeposited at glassy carbon (nano-Au/GC) elec-
trodes (prepared by potential step electrolysis) is markedly influenced by the width of the potential step.
The oxygen reduction reaction (ORR) and the reductive desorption of cysteine have been studied on nano-
Au/GC electrodes. Furthermore, electron backscatter diffraction (EBSD) technique has been used to probe
the crystallographic orientation of the electrodeposited Au nanoparticles. That is, Au nanoparticles pre-
pared in short time (5–60 s) have been found rich in the Au(1 1 1) facet orientation and are characterized
by a relatively small particle size (ca. 10–50 nm) as well as high particle density (number of particles per
unit area) as revealed by SEM images. Whereas Au nanoparticles prepared by longer electrolysis time
Received 12 November 2008
Received in revised form 20 January 2009
Accepted 20 January 2009
Available online 29 January 2009
Keywords:
Electrodeposition
Preferential orientation
ORR
(>60 s) are found to be much enriched in the Au(1 0 0) and Au(1 1 0) facets and are characterized by a
Nanostructures
Electron back scatter diffraction (EBSD)
relatively large particle size (>100 nm). EBSD patterns provided definitive information about the crystal
orientations mapping of Au nanoparticles prepared at various deposition times.
©
2009 Elsevier Ltd. All rights reserved.
1
. Introduction
This paper addresses the influence of the electrodeposition time
on the crystallographic orientation of Au nanoparticles deposited
on glassy carbon (nano-Au/GC) electrodes. SEM, XRD and electron
backscatter diffraction (EBSD) techniques are used to characterize
the electrodeposited Au nanoparticles in terms of size and prefer-
ential facet orientation. Furthermore, the reductive desorption of
cysteine and the oxygen reduction reactions in alkaline medium
are used as probing electrochemical reactions to monitor the vari-
ation of the crystallographic orientation of the electrodeposited Au
nanoparticles with time.
Nanometer-scale materials are continuously attracting consid-
erable attention due to their unusual and fascinating properties
[
1–5]. The decrease of the size of materials down to the nanometer
range leads to a tremendous change of their surface, electronic and
optoelectronic properties compared with their bulk metal counter-
parts [6,7]. The use of gold nanoparticles has been rapidly extended
to several applications in electronics, optoelectronics, electroanaly-
sis [8,9] as well as chemical and electrochemical catalysis [4,10–13].
In this regard, the preparation of tailored design nanostructures in
terms of size and crystallographic structure is a subject of unequiv-
ocal importance [14–17].
2. Experimental
Electrodeposition is among the most familiar binder-free tech-
nique used for the preparation of nanoparticles. It is a facile
technique which results in the direct attachment of the nanopar-
ticles to the substrate in addition to the facile control of the
characteristics of the metal (or metal oxide) (e.g., size, crystal-
lographic orientation, mass, thickness and morphology of the
nanostructured materials) by adjusting the operating conditions
and bath chemistry [17–21] in contrast to other techniques which
require several steps and consume relatively longer time, such as
sol–gel [22,23], micelle-based cluster generation [24,25] and metal
vapor synthesis routes [26,27].
The working electrode was a GC rod of 3.0 mm diameter sealed
in a Teflon jacket leaving an exposed geometric surface area of
2
0
.07 cm . A spiral Pt wire and an Ag/AgCl/KCl (sat) were the counter
and the reference electrodes, respectively. Prior to the electrode-
position of Au nanoparticles, the GC electrode was polished with
aqueous slurries of alumina powder (particle size down to 0.06 ␮m)
with the help of a polishing microcloth then sonicated for 10 min in
Milli-Q water. Au nanoparticles were electrodeposited from 0.5 M
H SO + 1.0 mM Na[AuCl ] solution by applying potential step elec-
2
4
4
trolysis from 1.1 to 0.0 V vs. Ag/AgCl/KCl(sat) [20,28]. The duration
of the potential step electrolysis was varied from 5 to 900 s to
obtain Au deposits with different characteristics (cf. Table 1). The
thus-prepared Au nanoparticles-electrodeposited GC electrodes
were characterized electrochemically in a deoxygenated (i.e., N2-
∗ Tel.: +202 3567 6603; fax: +202 3572 7556.
E-mail address: msaada68@yahoo.com.
saturated) 0.5 M H SO4 solution (cf. Fig. 1). The self-assembled
2
0
013-4686/$ – see front matter © 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2009.01.054

M.S. El-Deab / Electrochimica Acta 54 (2009) 3720–3725
3721
Fig. 1. SEM micrographs of Au nanoparticles electrodeposited onto GC electrodes from 0.5 M H2SO4 containing 1.0 mM Na[AuCl4] by applying potential step electrolysis from
ꢀ ꢀ ꢀ ꢀ ꢀ ◦
.1 to 0 V vs. Ag/AgCl/KCl(sat) with a step width of (a) 5, (b) 10, (c,c ) 60, (d,d ) 300, (e,e ) 900 s. Note that images c –e are taken at an inclination of 70 of the sample.
1
monolayer (SAM) of cysteine [HS-CH -CH(NH )-COOH] was pre-
directly into the cell containing 0.5 M KOH to obtain an O -saturated
2
2
2
pared by immersing the nano-Au/GC electrodes into an aqueous
solution of 1.0 mM cysteine for 20 min. The reductive desorption
experiments were carried out in a deoxygenated 0.5 M KOH solu-
tion. For the oxygen reduction measurements, O2 gas was bubbled
solution and during the measurements O2 gas was flushed over
the cell solution. Electrochemical measurements were performed
in a three-electrode cell using EG&G potentiostat (model 273A) at
room temperature. The current densities were calculated on the

3722
M.S. El-Deab / Electrochimica Acta 54 (2009) 3720–3725
Table 1
Variation of QAu(1 1 1) of Au nanoparticles with electrodeposition time (td). The nano-Au/GC electrodes were prepared as described in the caption of Fig. 1.
td (s)
Amount of deposited Au
Equivalent film thicknessb
(nm)
QAu(1 1 1)c (%)
Particle size range (nm)
Particle densityd
nanoparticlesa (␮g cm
−2
)
5
1.53
1.94
3.11
5.37
8.12
0.79
1.01
1.61
2.78
4.21
9.46
22.91
90
85
75
55
48
35
30
5–20
10–50
15–60
∼100
∼75
∼70
∼55
∼55
∼50
∼30
1
0
3
6
0
0
20–80
1
3
9
20
00
00
50–120
50–200
100–500
18.26
43.12
a
b
c
Calculated from the Q–t curves during the potential step electrolysis.
The thickness of a homogeneous Au film that covers the entire surface area of GC electrode and with the same Au loading as that of electrodeposited Au nanoparticles.
QAu(1 1 1) represent the ratio of the amount of charge consumed during the reductive desorption of cysteine SAMs from the Au(1 1 1) and Au(1 0 0) + Au(1 1 0) surface
domains, respectively at −700 and −1000 mV vs. Ag/AgCl/KCl(sat)) [33–37].
d
2
The number of particles per 1 ␮m .
basis of the geometric surface areas of the electrodes. All chem-
icals used in this study were of analytical grade and were used
without further purification. XRD measurements were performed
on PANalytical X’Pert PRO MRD X-ray Diffractometer, using Cu
K␣1 radiation (ꢀ = 1.54056 Å) with a Ni filter working at 45 kV and
results are given in Table 1. This table shows that, Au nanoparticles
with different sizes are present: the size of Au particles increases
with increasing electrodeposition time (t ). At long t , a noticeable
d
d
decrease in particle density is observed which is attributed to the
growth and coalescence of the neighboring Au particles. Generally,
the first step of metal deposition is the formation of nuclei of the
depositing metal. Subsequently, two processes take place, i.e., the
growth of the initially formed nuclei and progressive nucleation
[31]. The characteristics of the deposit (e.g., granularity, thickness,
preferential crystallographic orientation) are determined by sev-
eral parameters including the overpotential, concentration of active
species and the electrodeposition time [20]. For the sake of simplic-
ity, the electrodeposition of Au nanoclusters has been carried out
4
0 mA. Scanning electron microscopy (SEM) and electron backscat-
ter diffraction analyses of the Au nanoparticles electrodeposited
onto GC electrodes were carried out using an JSM-6500F scanning
electron microscope (JEOL Optical Laboratory, Japan) equipped with
a backscatter camera.
3. Results and discussion
from a solution of 0.5 M H SO + 1.0 mM Na[AuCl ] and one value
3.1. Morphological characterization of Au nanoparticles
2
4
4
of overpotential has been used (the potential was stepped from 1.1
to 0 V vs. Ag/AgCl/KCl(sat), corresponding to an overpotential (ꢁ) of
−800 mV [20], and the electrodeposition time is the only parameter
that is being tested.
Fig. 2 represents a current transient recorded during the elec-
trodeposition of Au nanoparticles by applying a potential step from
Fig. 1 shows typical SEM images of Au nanoparticles electrode-
ꢀ
ꢀ
posited onto GC (nano-Au/GC) for different times. Images c –e are
◦
obtained at an inclined angle of 70 of the sample to allow for the
observation of the height and morphology of the electrodeposited
Au nanoparticles. These images show an approximately hemispher-
ical shapes of the electrodeposited Au nanoparticles similarly to
those in the previous reports [20,29,30]. Particle size distribution
and the particle density of the Au nanoparticles electrodeposited
on GC electrodes were estimated based on the data in Fig. 1 and the
1.1 to 0 V vs. Ag/AgCl/KCl(sat). The initial sharp high current is due
−
1
Fig. 3. CVs measured at 100 mV s for the various nano-Au/GC electrodes in 0.5 M
H2SO4. The nano-Au/GC electrodes have been prepared as described in the caption
of Fig. 1 with a step width of (a) 5, (b) 10, (c) 30, (d) 60, (e) 300 and (f) 900 s.
Fig. 2. Current transient recorded during a potential step from 1.1 to 0 V vs.
Ag/AgCl/KCl(sat) for a GC electrode in 0.5 M H2SO4 + 1.0 mM Na[AuCl4].

M.S. El-Deab / Electrochimica Acta 54 (2009) 3720–3725
3723
Fig. 6. XRD patterns of nano-Au/GC electrodes prepared in the same way as in Fig. 1
with a step width of (a) 60, (b) 300 and (c) 900 s.
−1
3.2. Electrochemical characterization of Au nanoparticles
Fig. 4. CVs measured at 50 mV s for the reductive desorption of cysteine-SAM
formed at various nano-Au/GC electrodes in N2-saturated 0.5 M KOH. The nano-
Au/GC electrodes are prepared as described in the caption of Fig. 1 with a step width
of (a) 5, (b) 10, (c) 30, (d) 60, (e) 120, (f) 300 and (g) 900 s.
3.2.1. Characteristic CVs
Fig. 3 shows cyclic voltammetric (CV) curves of the various nano-
Au/GC electrodes in 0.5 M H SO solution at a potential scan rate
2
4
−
1
of 100 mV s . This figure shows that the peak current at around
0.9 V (corresponding to the reduction of the Au-oxide monolayer
formed during the positive-going potential scan) increases with td
reflecting the increase of the Au surface area. Table 1 summarizes
the loading and surface characteristics of the Au nanoparticles elec-
to the charging of the double layer. A current decay is observed
−1/2
which is linear with t
indicating a planar diffusion regime which
arises due to the overlapping of the growing hemispherical diffu-
sion layers which provide mass transport for nanocrystal growth
[
20,32].
trodeposited on GC electrodes for different t . The appearance of
d
different patterns (positive to 1.1 V) for the formation of the gold
oxide layer indicates a difference of the compositional ratios of the
different facets covering the Au nanoparticles at each case. How-
ever, no quantitative estimation for each facet can be given.
3
.2.2. Reductive desorption of cysteine
It has been reported that the polycrystalline Au surfaces are
composed, mainly, of three facets of low index crystallographic
orientations, i.e., domains of Au(1 1 1), Au(1 0 0) and Au(1 1 0) ori-
entations [33,34]. Each single crystalline domain exhibits different
binding strength towards an attached thiol. For instance, for a short
chain thiol species like cysteine, a multiple reductive desorption CV
pattern was observed at potentials of −700, −1000 and −1100 mV
vs. Ag/AgCl/KCl(sat) [33,34], corresponding to the reductive des-
orption of cysteine from the (QAu(1 1 1)), Au(1 0 0) and Au(1 1 0)
domains of a polycrystalline Au electrode [33–37]. The ratio of the
peak current intensities reflects the proportion of the low index
facets. In order to assess the ratio of the different Au facets, the
reductive desorption of cysteine was followed at various nano-
Au/GC electrodes.
Fig. 4 shows the CV patterns, measured in 0.5 M KOH solution
−
1
at potential scan rate of 50 mV s , for the reductive desorption of
cysteine-SAM formed at the various nano-Au/GC electrodes. This
figure shows the existence of multiple reductive desorption peaks
at each electrode with different heights depending on t . Table 1
d
summarizes the variation of the ratio of the amount of charge
consumed during the reductive desorption of cysteine from the
Au(1 1 1), Au(1 0 0) and Au(1 1 1) surface domains (QAu(1 1 1)). It
reveals two points:
Fig. 5. CVs measured at 100 mV s−1 for the oxygen reduction at (a) bare GC, (b–d)
nano-Au/GC and (e) bare polycrystalline Au electrodes in O2-saturated 0.5 M KOH.
The nano-Au/GC electrodes are prepared as described in the caption of Fig. 1 with a
step width of (b) 60, (c) 300 and (d) 900 s.

3724
M.S. El-Deab / Electrochimica Acta 54 (2009) 3720–3725
Fig. 7. Electron backscatter diffraction (EBSD) patterns of Au nanoparticles electrodeposited onto GC electrodes (at magnification factor of 80k, S = 500 nm). Electrodeposition
time: (A) 60, (B) 300 and (C) 900 s. (D) is a color coding to identify the crystallographic orientation of Au nanoparticles (Colour online: blue = 1 1 1, red = 0 0 1 and green = 1 0 1
facets).
(
i) Au nanoparticles electrodeposited at short time are enriched in
the Au(1 1 1) facet orientation (cf. Fig. 7A). It is worth to mention
here that the Au(1 1 1) facet is thermodynamically more stable
than the Au(1 0 0) and Au(1 1 0) ones of Au [31].
(ii) The ORR proceeds irreversibly at the nano-Au/GC electrodes
(curves c and d) prepared for 300 and 900 s with about 1.7
times higher peak current density compared with electrode
marked b. The increase in the peak current density is attributed
to the increase in the number of exchanged electron during the
course of the ORR [33,17]. The behavior of electrodes marked c
and d is similar to that observed at the polycrystalline Au elec-
trode (curve e) reflecting the polycrystalline nature of the Au
nanoparticles electrodeposited at longer deposition time.
(
ii) The percentage of QAu(1 1 1) decreases with td and reaches about
0% for Au nanoparticles electrodeposited for 900 s (close to
the natural ratio obtained at the polycrystalline Au electrodes
25 %) [17]). This reflects the polycrystalline nature of the Au
3
(
nanoparticles electrodeposited at longer td (cf. Fig. 7C).
It is worthy to mention here that each nano-Au/GC electrode is
considered as a micro disk array-type electrode at which the diffu-
sion layers at individual Au nanoparticles overlap each other to form
3
.2.3. Oxygen reduction
The oxygen reduction reaction (ORR) was taken as a probing
reaction to further assign the facets of the prepared nano-Au/GC
electrodes. This reaction has been extensively studied at Au sin-
gle crystal electrodes [38,39], Au nanoparticles-based electrodes
a linearly expanding diffusion region as can be expected by com-
√
parison of the diffusion layer thickness (ı = (ꢂDO2 t) ≈ 0.021 cm;
D
is the diffusion coefficient of O in alkaline aqueous medium
2
O
2
[
[
11,40–42] as well as on thin Au films coated carbon substrates
13,43]. The ORR is well known to depend on the crystallographic
−
5
2
−1
(≈10 cm s ) and t is the electrolysis time (s)) and the average
distance between Au nanoparticles (≈50–200 nm). As can be read-
ily seen that ı is much larger than the average distance between the
Au nanoparticles prepared in all cases. Thus, the particle size is of
insignificant role towards the ORR and the crystallographic orien-
tation of the Au nanoparticles is believed to play the primary role
in determining the electrocatalytic activity towards the ORR.
orientation of the Au surface in alkaline media [33,38]. Fig. 5 shows
CVs measured in O -saturated 0.5 M KOH at (a) bare GC, (b–d) nano-
Au/GC and (e) bulk Au electrodes. Inspection of this figure reveals
some interesting points:
2
(
i) The ORR proceeds quasi-reversibly at the nano-Au/GC elec-
trode prepared at 60 s (curve b) This behavior is similar to that
obtained at Au(1 1 1) single crystal electrode [33], indicating the
enrichment of this nano-Au/GC electrode with Au(1 1 1). Fur-
thermore, the peak current density of the ORR at this electrode
3
.3. XRD and electron backscatter diffraction (EBSD) patterns
The determination of microstructure of Au nanoparticles is
important because it determines many of their physical and elec-
trocatalytic properties. Fig. 6 shows the XRD patterns of the Au
nanoparticles electrodeposited onto GC electrodes for various dura-
tions. The diffraction peaks located at 2ꢃ values of ca. 45 and 80 are
attributed to the (0 1 1) and (1 1 0) planes of the carbon substrate,
(
curve b) is very close to that obtained at the bare GC (curve a).
The latter is know to support a two-electron reduction path-
way of O2 to hydrogen peroxide in alkaline media [40,44,45]
and similarly electrode marked b supports the two electron
reduction of O2 as well [33,40].
◦
respectively [46]. This figure reveals the existence of two peaks at 2ꢃ

M.S. El-Deab / Electrochimica Acta 54 (2009) 3720–3725
3725
Table 2
found rich in the Au(1 1 1) facet orientation. At longer deposition
time (>60 s), the Au nanoparticle’s surface consist more Au(1 0 0)
and Au(1 1 0) with a relatively big particle size (>100 nm) and low
particle density (number of particles per unit area) as depicted from
the SEM images.
Variation of the total fraction of the (0 0 1), (1 0 1) and (1 1 1) facet domains for the
Au nanoparticles electrodeposited for various durations.
td (s)
Total fraction
0 0 1)
% of (1 1 1)
(
(1 0 1)
(1 1 1)
6
00
00
0
0.010
0.055
0.089
0.026
0.097
0.210
0.030
0.069
0.108
45
31
26
References
3
9
[1] A. Wieckowski, E.R. Savinova, C.G. Vayenas (Eds.), Catalysis and Electrocatalysis
at Nanoparticle Surfaces, Marcel Dekker, Inc., New York, 2003.
[2] G. Ozin, A. Arsenault, Nanochemistry: A Chemistry Approach to Nanomaterials,
Springer Verlag, New York, 2005.
3] M.-C. Daniel, D. Astruc, Chem. Rev. 104 (2004) 293.
[4] D.M. Kolb, F.C. Simeone, Electrochim. Acta 50 (2005 2989).
5] F.M. Bayoumi, B.G. Ateya, Electrochem. Commun. 8 (2006) 38.
6] R.E. Cavicchi, R.H. Silsbe, Phys. Rev. Lett. 52 (1984) 16.
7] P. Ball, G. Li, Nature 761 (1992) 355.
[8] R. Raj, T. Okajima, T. Ohsaka, J. Electroanal. Chem. 543 (2003) 127.
9] C.M. Welch, R.G. Compton, Anal. Bioanal. Chem. 384 (2006) 601.
10] M.S. El-Deab, T. Ohsaka, Electrochem. Commun. 4 (2002) 288.
◦
◦
of ≈38 and 64 corresponding to the Au(1 1 1) and Au(2 2 0) facet
domains of the Au nanoparticles, respectively [47]. For the present
case, the substrate is glassy carbon, which is of less ordered surface
structure and the quantitative estimation of the preferential crys-
tallographic orientation of Au nanoparticles is difficult due to the
noisy background of the XRD patterns caused by the interference
from the GC substrate.
[
[
[
[
[
[
EBSD is a powerful technique which advantageously allows
for obtaining crystallographic information (i.e., crystal orientation
mapping) of samples (e.g., particles, clusters, aggregates). Fig. 7
shows typical crystal orientation maps obtained for the same sam-
ples in Fig. 1(c–e). Note that particles of the similar orientations
are in similar colors. Black regions of the mapping image represent
areas undetected by electron backscattering due to roughness of
the GC substrate [48]. This figure reveals the following points: (i)
Au nanoparticles electrodeposited at short time (60 s, image A) are
rich in the (1 1 1) orientation (as indicated from the predominance
of the blue color) and (ii) longer electrodeposition time (≥300 s)
leads to enrichment of Au nanoparticles with the (1 0 0) and (1 1 0)
orientations as reflected from the high intensity of the red and
green colors of images B and C consistently with the observations
of the electrochemical measurements (Fig. 4). This observation
is consistent with the theoretical studies of the equilibrium and
growth forms of three-dimensional crystals, in which the growth
forms of three-dimensional crystals contain closely packed crys-
tallographic orientation (the most thermodynamically stable facet,
i.e., the (1 1 1) facet for Au) at the early stage of electrodeposition
[
11] N. Alexeyeva, T. Laaksonen, K. Kontturi, F. Mirkhalaf, D.J. Schiffrin, K. Tam-
meveski, Electrochem. Commun. 8 (2006) 1475.
[12] M. Haruta, Catal. Today 72 (1997) 63.
[13] A. Sarapuu, M. Nurmik, H. Mander, A. Rosental, T. Laaksonen, K. Kontturi, D.J.
Schiffrin, K. Tammeveski, J. Electroanal. Chem. 612 (2008) 78.
[
14] D.L. Feldheim, C.A. Foss, Metal Nanoparticles; Synthesis, Characterization and
Applications, Marcel Dekker, New York, 2002.
[
[
15] J. Rockenberger, E.C. Scher, A.P. Alivisatos, J. Am. Chem. Soc. 121 (1999) 11595.
16] Q. Song, Z.J. Zhang, J. Am. Chem. Soc. 126 (2004) 6164.
[
17] M.S. El-Deab, T. Sotomura, T. Ohsaka, J. Electrochem. Soc. 152 (2005) C1.
[18] D.-L. Lu, K.-I. Tanaka, J. Phys. Chem. 100 (1996 1833).
19] H. Huang, X. Yang, Colloids Surf. A: Physicochem. Eng. Aspects 255 (2005) 11.
20] M.O. Finot, G.D. Braybrook, M.T. McDermott, J. Electranal. Chem. 466 (1999)
34.
[21] V. Srinivasan, J.W. Weidner, J. Electrochem. Soc. 144 (1997) L210.
[
[
2
[22] H.Y. Lee, S.W. Kim, H.Y. Lee, Electrochem. Solid-State Lett. 4 (2001) A19.
[23] M.S. Hong, S.H. Lee, S.W. Kim, Electrochem. Solid-State Lett. 5 (2002) A227.
[24] J. Spatz, S. Mossmer, M. Moller, Chem. Eur. J. 2 (1996) 1552.
[25] R. Glass, M. Moller, J.P. Spatz, Nanotechnology 14 (2003) 1153.
[
26] M. Magnusson, K. Deppet, J.-O. Malm, J.-O. Bovin, L. Samuelson, Nanostruct.
Mater. 12 (1999) 45.
[27] P.J. Collier, J.A. Iggo, R. Whyman, J. Mol. Catal. A: Chem. 146 (1999) 149.
[28] M.S. El-Deab, T. Okajima, T. Ohsaka, J. Electrochem. Soc. 150 (2003) A851.
[29] L. Komsiyska, G. Staikov, Electrochim. Acta 54 (2008) 168.
[
30] M.S. El-Deab, T. Okajima, T. Ohsaka, J. Electrochem. Soc. 153 (2006) E201.
[
31] E. Budevski, G. Staikov, W.J. Lorenz, Electrochemical Phase Formation and
Growth, VCH, Weinheim, 1996 (Chapter 4).
[
31]. On the other hand, at longer electrodeposition times the per-
centage of (1 0 0) and (1 1 0) increases probably due to the more
complex mechanism of growth and coalescence of the neighbor-
ing Au nanoclusters [31]. The fractions for the (0 0 1), (1 0 1) and
[32] G. Gunawardena, G. Hills, I. Montenegro, B. Scarifker, J. Electroanal. Chem. 138
1982) 225.
(
[
[
33] M.S. El-Deab, K. Arihara, T. Ohsaka, J. Electrochem. Soc. 151 (2004) E213.
34] K. Arihara, T. Ariga, N. Takashima, K. Arihara, T. Okajima, F. Kitamura, K. Tokuda,
T. Ohsaka, Phys. Chem. Chem. Phys. 5 (2003) 3758.
(
1 1 1) orientations corresponding to the three samples are given
[
35] M.M. Walczak, C.A. Alves, B.D. Lamp, M.D. Porter, J. Electroanal. Chem. 396
in Table 2. The total fraction of a specific facet is the percentage
of a specific orientation relative to the total area of the analyzed
region of the surface [49]. This table shows that the increase of td
resulted in: (i) increase in the total fraction of the three low index
facets of Au nanoparticles and (ii) a decrease in the percent of the
(
1995) 103.
[
36] C.-J. Zhong, J. Zak, M.D. Porter, J. Electroanal. Chem. 421 (1997) 9.
[37] D.-F. Yang, C.P. Wilde, M. Morin, Langmuir 12 (1996) 6570.
[
[
[
38] S. Strbac, R. Adzic, Electrochim. Acta 41 (1996) 2903.
39] C. Paliteiro, N. Martins, Electrochim. Acta 44 (1998) 1359.
40] M.S. El-Deab, T. Sotomura, T. Ohsaka, Electrochem. Commun. 7 (2005) 29.
(1 1 1) orientation. It should be mentioned here that the analysis of
[41] F. Gao, M.S. El-Deab, T. Okajima, T. Ohsaka, J. Electrochem. Soc. 152 (2005)
A1226.
the EBSD images (given in Table 2) provided the relative percent-
age of the three low index facet orientations of the electrodeposited
Au nanoparticles and cannot be used to estimate the total surface
coverage of GC.
[
[
42] M.S. El-Deab, T. Ohsaka, Electrochim. Acta 52 (2007) 2166.
43] A. Sarapuu, K. Tammeveski, T.T. Tenno, V. Sammelselg, K. Kontturi, D.J. Schiffrin,
Electrochem. Commun. 3 (2001) 446.
[44] A. Sarapuu, K. Vaik, D.J. Schiffrin, K. Tammeveski, J. Electroanal. Chem. 541
2003) 23.
(
[
45] K. Vaik, A. Sarapuu, K. Tammeveski, F. Mirkhalaf, D.J. Schiffrin, J. Electroanal.
Chem. 564 (2004) 159.
46] W.F. McClune (Ed.), Powder Diffraction File, International Centre for Diffraction
Data (ICDD), USA, 2003.
4
. Conclusions
[
In this study, the influence of the electrodeposition time on the
[
47] T. Kinoshita, S. Seino, K. Okitsu, T. Nakayama, T. Nakagawa, T.A. Yamamoto, J.
preferential crystallographic orientation of Au nanoparticles is fol-
lowed by electrochemical and EBSD techniques. Au nanoparticles
electrodeposited at relatively short potential step width (5–60 s) are
Alloys Compd. 359 (2003) 46.
[48] K. Nogita, A.K. Dahle, Mater. Charact. 46 (2001) 305.
[49] A.K. Veneva, M.R. Koblischka, Mater. Sci. Eng. B 151 (2008) 60.