Synthesis of bismuth with various morphologies by electrodeposition

Article abstract of DOI:10.1016/S1387-7003(03)00104-7

Metal bismuth with various morphologies, with particle size from nanometer to micrometer, has been successfully prepared by electrodeposition onto Pt, Au, Al and ITO electrodes at room temperature. The size and morphology of the deposits are strongly dependent on preparation conditions, such as deposition potential, current density, electrode and electrolyte. As observed by scanning and transmission electron microscopes, the deposited Bi particles exhibit plentiful appearances, such as prickly rod, banch, skeleton and strip-like shapes. A significant positive magnetoresistence effect is observed even at room temperature.

Full text of DOI:10.1016/S1387-7003(03)00104-7

Inorganic Chemistry Communications 6 (2003) 781–785
www.elsevier.com/locate/inoche
Synthesis of bismuth with various morphologies by electrodeposition
a
a
b
a,
*
Shan Jiang a,b, Yun-Hui Huang , Feng Luo , Nan Du , Chun-Hua Yan
a
State Key Laboratory of Rare Earth Materials Chemistry and Applications, PKU-HKU Joint Laboratory in Rare Earth Materials and
Bioinorganic Chemistry, Peking University, Beijing 100871, China
b
Department of Materials, Nanchang Institute of Aeronautical Technology, Jiangxi 330034, China
Received 9 December 2002; accepted 8 March 2003
Abstract
Metal bismuth with various morphologies, with particle size from nanometer to micrometer, has been successfully prepared by
electrodeposition onto Pt, Au, Al and ITO electrodes at room temperature. The size and morphology of the deposits are strongly
dependent on preparation conditions, such as deposition potential, current density, electrode and electrolyte. As observed by
scanning and transmission electron microscopes, the deposited Bi particles exhibit plentiful appearances, such as prickly rod, banch,
skeleton and strip-like shapes. A significant positive magnetoresistence effect is observed even at room temperature.
Ó 2003 Elsevier Science B.V. All rights reserved.
Keywords: Bismuth particles; Electrodeposition; Morphologies; Magnetoresistance
1. Introduction
methods have become increasingly popular recently due
to their low processing temperature and environmen-
tally beginning conditions. Among them, metalorganic
electrodeposition, a nonvacuum liquid-based technique,
has been proved to favor the formation of nanoscaled
porous bismuth [9,10]. By electrodeposition, it is con-
venient to control the particle growth rate via changing
electrolyte, concentration, current density and applied
potential. Therefore, electrodeposition is a simple, re-
producible and effective route to manipulate the mi-
crostructure. In this communication, we report the
synthesis of Bi samples by electrodeposition under dif-
ferent conditions to achieve abundant morphologies.
The magnetoresistance effect is typically investigated.
Semimetal bismuth (Bi) has attracted much interest in
recent years due to a range of unique electronic prop-
erties originating from its small effective carrier mass
and high carrier mobilities [1–7]. Very large magneto-
resistance (MR) effect has been observed earlier in Bi
single crystals [2], and recently in Bi thin films [3–5] and
nanowires [6,7], which makes Bi as a good candidate for
the material of magnetic sensor.
The microstructure of Bi is considerably important,
both from a fundamental and a technological point of
view. Different microstructures could give rise to differ-
ent physical properties. The MR effect, for example, is
directly related to the quality of sample. Bi sample with
suitable hybrid structure exhibits a large intrinsic MR
effect, which can be used to detect small magnetic fields
[3]. Bi thin films grown by molecular beam epitaxy ex-
hibit a significantly enhanced MR [5], whereas Bi thin
films made by vaporation and sputtering only show a
weak MR effect because of the small polycrystal grains
[8]. Hitherto, great efforts have been done to obtain Bi
samples with high quality [9–14], and solution-based
2. Experimental
The electrodeposition of Bi was carried out under a
constant potential or under a constant current density in
a four-electrode electrolytic cell. The potential was
controlled by a potentiostat. The electrolyte was
BiðNO3Þ Á 5H2O aqueous solution with the absence or
presence of soluble Na2EDTA. The complexant EDTA,
originating from Na2EDTA, was used to change the
Bi3þ reduction potential through the formation of the
* Corresponding author. Tel./fax: +86-10-62754179.
E-mail address: chyan@chem.pku.edu.cn (C.-H. Yan).
1387-7003/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S1387-7003(03)00104-7

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S. Jiang et al. / Inorganic Chemistry Communications 6 (2003) 781–785
complex. BiðNO3Þ3 Á 5H2O was dissolved in nitric acid
and then diluted by distilled water to a desired concen-
tration. All chemicals used were commercial reagents
with analytical purity. Pt, Al, ITO (indium tin oxide)
coated glass (2 X sheet resistivity) and Si(1 0 0) wafer
with Au-patterned underlayer were served as the work-
ing electrodes, respectively. The electrodes were cleaned
ultrasonically successively in acetone, ethanol and dis-
tilled water. Then they were polished chemically in di-
luted HNO3, and subsequently in acetone, and finally
rinsed with distilled water. After the electrodes were
dried, their back surfaces were masked with an insulat-
ing ‘‘Fevibond’’ synthetic resin. Each electrode had an
active area from 1.5 to 2:0 cm2. Pt plates ð10 Â 20 mmÞ
was used as the two counter electrodes. The reference
electrode was saturated calomel electrode (SCE). All
applied potentials, Vc, are cited with respect to SCE. The
experiments were performed at an ambient temperature.
The electrolyte solutions were purged and stirred with
high-pure N2 gas during the deposition process to avoid
the possible oxidation by the dissolved oxygen. After
deposition, the product on the surface of the working
electrode was rinsed with double distilled water for
several times to eliminate residual BiðNO3Þ3, and sub-
sequently washed with alcohol, and then dried by
blowing air. The final products were stored in an N2-
filled desiccator insulated from air.
X-ray diffraction (XRD) patterns were recorded by
an X-ray diffractometer (Rigaku, D/max-2000, Cu-Ka
radiation). The morphologies were detected using a
scanning electron microscope (SEM, JSM6700F, JEOL)
under a working voltage of 3.0 kV and a transmission
electron microscope (TEM, Hitachi, H-9000NAR) op-
erating at 200 kV accelerating voltage. A small drop of
Bi sample predispersed by ethanol was deposited on a
copper grid which was precoated with a film of carbon,
then dried in the air for TEM characterization. Resis-
tance measurements were performed on a MagLab
System 2000 (Oxford, UK). Resistance was measured
using a standard four-probe technique under zero field
and an applied field of 5 T.
Fig. 1. Cyclic voltammograms for (a) 10À3 mol=l BiðNO3Þ3 and (b)
10À3 mol=l BiðNO3Þ3 þ 10À3 mol=l EDTA aqueous solution. Scan
rate: 50 mV=sÀ1
.
respectively. For Fig. 1(b), only one reduction peak
occurs at )0.5 V. Apparently, the addition of EDTA
makes the reduction of Bi3þ shift to a more negative
potential and the deposition current is also reduced. The
negative shift of the observed reduction potential is as-
cribed to the change in conditional electrode potential
caused by the formation of Bi3þ complex with EDTA.
In addition, for the potentiostatic mode, rapid forma-
tion of precipitate was found on the counter electrodes
when the deposition was executed at Vc < À0:4 V, which
comes from the increase of hydroxy ions caused by the
reduction of Hþ in the solution. Thus the applied de-
position potential was kept at no more negative than
)0.4 V. Oxidation of Bi occurs only when the electro-
deposited electrode is exposed to the air for a long time.
The dependence of electrolysis time on current den-
sity ðicÞ for 10À4 mol=l BiðNO3Þ is shown in Fig. 2. The
working potential was held at )30.4 V. At the beginning,
a fast decrease in ic is observed, which is ascribed to the
3. Results and discussion
First, the cyclic voltammograms (CVs) of 10À3 mol=l
Bi3þ and its EDTA complex were investigated. The CVs
were scanned from 0.5 to )0.7 V at a sweep rate of 50
mV/s. As shown in Fig. 1, obvious cycles of reduction
and oxidation are observed. The zero current is usually
related to the equilibrium potential, and the abrupt in-
crease in cathodic current under Vc < 0:03 V is associ-
ated with the formation of the three-dimensional Bi bulk
phase. For Fig. 1(a), two clear reduction peaks are ob-
served at about 0.0 and )0.2 V, corresponding to the
reductions from Bi3þ to Biþ and finally from Biþ to Bi,
Fig. 2. Typical dependence of electrolysis time on current density. The
electrolyte is 10À4 mol=l BiðNO3Þ3, and the deposition potential is held
at )0.4 V.

S. Jiang et al. / Inorganic Chemistry Communications 6 (2003) 781–785
783
lated to the ion migration in the mass transport and the
reaction rate on the electrode, the constant ic indicates
that the ion migration and the electrodeposition are in a
dynamic equilibrium. The following experimental results
also confirm that the electrolysis time has less influence
on the Bi morphology than some other conditions, such
as the substrate and electrolyte. In order to avoid the
oxidation of Bi on the electrode, the electrolysis time in
our practical deposition process is selected to be 1 h.
Fig. 3 typically displays the XRD patterns of the Bi
samples electrodeposited on different substrates of ITO,
Au, Al and Pt, respectively. Compared with the stan-
dard curve (JCPDS card 01-0688), a single rhombohe-
dral phase is formed without bismuth oxide or any other
impurity phases for all the Bi samples, indicating that all
of these electrodes can be well used as substrates for Bi
electrodeposition. However, from the relative intensity
of (1 0 4) and (1 1 0), it seems that the preferential ori-
entation for Bi deposition is somewhat different.
Fig. 4 shows SEM micrographs of the Bi samples
deposited under different conditions. As we can see,
several different morphologies are achieved, which are
strongly dependent on the substrate and electrolyte. For
the samples in Figs. 4(a) and (b), the deposition condi-
tions are very similar. The electrolyte and current den-
sity are the same, and only the working electrode is
different. Prickly rod-like shape is obtained on ITO sheet
in Fig. 4(a), whereas branch-like shape is obtained on Pt
substrate in Fig. 4(b). These two morphologies are very
similar in the particle shape and size. All the branch-like
Fig. 3. XRD patterns for the Bi samples electrodeposited in 0:03 mol=l
BiðNO3Þ3 solution on different substrates: (a) ITO, (b) Au, (c) Al and
(d) Pt. The top curve is from the standard card (JCPDS No. 01-0688).
adsorption of the electro-active substances on the elec-
trode surface. Then, ic increases rapidly as time in-
creases, showing that metal Bi is deposited onto the
surface of the working electrode. With further increasing
the electrolysis time, ic decreases gradually and reaches a
constant after 130 min. Since the current density is re-
Fig. 4. SEM micrographs of the Bi samples deposited in different conditions. (a) Prickly rod-like shape, 0.01 mol/l BiðNO3Þ3, ITO sheet, ic ¼ 30 mA.
(b) Branch-like shape, 0.01 mol/l BiðNO3Þ3, Pt substrate, ic ¼ 30 mA. (c) Skeleton-like shape, 0.01 mol/l BiðNO3Þ3 þ 0:01 mol=l EDTA, ITO sheet,
Vc ¼ À0:4 V. (d) Strip-like shape, 0:03 mol=l BiðNO3Þ3 þ 0:03 mol=l EDTA, Al substrate, Vc ¼ À0:2 V.

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S. Jiang et al. / Inorganic Chemistry Communications 6 (2003) 781–785
and the prickly rod-like particles are of several mi-
crometers in length and hundreds of nanometers in di-
ameter. Figs. 4(c) and (d) display the SEM images of Bi
samples electrodeposited in the electrolyte containing
the complexant EDTA. Interestingly, we can obtain
skeleton-like shape on ITO sheet and strip-like shape on
Al substrate. Each skeleton-like particle consists of
many squama-like fragments; whereas each strip-like
particle is made up of long strips which are connected
together tightly with each other. The growth of Bi
crystallites gets more uniformly with the existence of
EDTA, which shifts the reduction to a more negative
potential and reduces the ic, slowing the reduction rate
and ameliorate the growth of Bi. Obviously, the mor-
phology is also strongly dependent on the substrates.
However, no matter what substrate is used, it seems that
Bi crystallites grow along some direction, as can be de-
duced from the particle shapes. We suggest that the
anisotropy of Bi crystallite itself plays an important role
in the formation of different shapes. Fig. 5 depicts the
typical TEM images and the selected area electron dif-
fraction (SAED) along [0 0 1] direction. One can see that
the diffractive spots can be organized in an almost pre-
cise hexagon or parallelogram, revealing a rhombohe-
dral lattice structure of the bulk Bi. The results exactly
agree with the XRD patterns, confirming that the Bi
sample is of a single phase. Moreover, energy dispersive
X-ray microanalysis (EDAX) evidently shows that the
particle consists of pure Bi.
Now we typically present the magnetoresistance effect
for Bi sample electrodeposited on Al substrate in Fig. 6.
The resistance decreases monotonously with increasing
temperature within the entire temperature range,
showing a semiconductor behavior. This is because
bismuth is a semi metallic element and thus has many
unusual electronic properties due to its highly aniso-
tropic Fermi surface, low carrier concentrations, small
carrier effective masses, and very long carrier mean free
paths. We investigate the magnetoresistance effect using
MR ratio, defined as ðRH À R0Þ=R0, where R0 and RH are
resistance under zero field and an applied field, respec-
tively. As shown in the inset of Fig. 6, Bi exhibits a
positive MR. MR decreases as temperature increases,
but varies very little from low temperature up to room
temperature. We can still observe a large MR ratio of
about 38% at room temperature. As a comparison, the
epitaxial Bi film exhibits a very large MR at low tem-
perature and dramatically drops with increasing tem-
perature [5]. The weak temperature dependence of MR
in the present case is similar to that in the polycrystalline
manganites [15,16], which may be attributed to an ex-
trinsic magnetotransport behavior. Usually, the positive
MR effect arises from curved orbits in a magnetic field
caused by Lorentz force. The large positive MR of Bi is
related with its peculiar electronic structure, such as
small effective mass and high carrier mobility.
In summary, Bi samples with various morphologies
were synthesized by electrodeposition in an acidic solu-
tion of BiðNO3Þ3 with and without the existence of
EDTA on Au, Al, Pt and ITO substrates. Single phase
Fig. 5. TEM images of Bi dendrites for (a) prickly rod-like shape
electrodeposited on ITO substrate in 0:005 mol=l BiðNO3Þ3 under
Vc ¼ À0:2 V and (b) branch-like shape electrodeposited on ITO sub-
strate in 0:1 mol=l BiðNO3Þ3 under ic ¼ 30 mA. The insets show the
electron diffraction pattern taken from the dendrites.
Fig. 6. Resistance as a function of temperature for the bulk Bi elec-
trodeposited on Al substrate in 0:03 mol=l BiðNO3Þ3 þ 0:03 mol=l
EDTA under 0 and 5 T. The inset shows the temperature dependence
of magnetoresistance (MR).

S. Jiang et al. / Inorganic Chemistry Communications 6 (2003) 781–785
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