Synthesis of uniform CoTe and NiTe semiconductor nanocluster wires through a novel coreduction method

Article abstract of DOI:10.1021/ic0262031

A novel coreduction method was developed to synthesize uniform one-dimensional CoTe and NiTe nanocluster wires. In the synthesis, soluble Na₂TeO₃ was used to supply a highly reactive Te source and N₂H₄·H₂O was used both as reducing agent and as complexing agent. The as-prepared samples were characterized by XRD, TEM, and HRTEM. The probable formation mechanism of the nanowires is discussed.

Full text of DOI:10.1021/ic0262031

Inorg. Chem. 2003, 42, 2174−2175
Synthesis of Uniform CoTe and NiTe Semiconductor Nanocluster Wires
through a Novel Coreduction Method
Qing Peng, Yajie Dong, and Yadong Li*
Department of Chemistry, the Key Laboratory of Atomic and Molecular Nanoscience
(China Ministry of Education), Tsinghua UniVersity, Beijing 100084, P. R. China
Received November 22, 2002
A novel coreduction method was developed to synthesize uniform
one-dimensional CoTe and NiTe nanocluster wires. In the
precursor methods11 are usually used for films and coating.
1
2
Solvothermal methods can also be used to produce tel-
lurides, in which commercial Te powder will combine with
metal salts in ethylenediamine medium. However, none of
them can produce 1-D telluride nanowires. Recently, Sander13
synthesis, soluble Na
2
TeO
3
was used to supply a highly reactive
Te source and N ‚H
2
H
4
2
O was used both as reducing agent and
as complexing agent. The as-prepared samples were characterized
by XRD, TEM, and HRTEM. The probable formation mechanism
of the nanowires is discussed.
2 3
et al. have reported an electrodeposition method to Bi Te
nanowires by using porous anodic alumina templates. On
the basis of the syntheses of selenides in our former work,8
we developed a novel coreduction method to CoTe and NiTe
nanocluster wires. By using the in situ produced highly
reactive Te and Co (or Ni), CoTe and NiTe nanocluster wires
were successfully synthesized on the basis of complex
reaction at 140 °C. It is worthy to note that, as a kind of
low-dimensional assembly of nanoparticles, nanocluster wire
has potential applications and is becoming of increasing
,14
Semiconducting tellurides are being actively researched
due to their distinctive properties and now are widely used
in material fields. For example, Bi
2 3
Te -based compounds
have become major components of the thermoelectric
1
x
industry, Hg1-xCd Te is extensively investigated for fabri-
2
cating IR detector arrays, and CdTe is a promising material
3
15
for electronic and optical devices. Recently, a large mag-
interest because it behaves as quantum dots.
netoresistance (MR) effect was also found in tellurides (Ag
2
-
CoSO
4
‚7H
2
O (1.4 g, 0.005 mol) or NiCl
2
2
‚6H O (1.19 g,
4
Te). Herein, a new type of CoTe and NiTe nanocluster wires
consisting of CoTe and NiTe nanoclusters) is reported. We
0.005 mol) was put into a Teflon-lined autoclave of 100 mL
capacity and dissolved in 50 mL of deionized water. The
(
choose CoTe and NiTe just because they are typical magnetic
semiconductors, which have attracted great interest in current
research for their distinctive electrical transport properties.
Although many nanorods and nanowires of oxides, sul-
fides, and selenides5-8 have been synthesized, up to now,
comparatively few studies of telluride nanowires have been
reported. The traditional method used to prepare tellurides
is the direct combination of the elements in evacuated silica
1.11 g (0.005 mol) of Na
and a precipitation of CoTeO
mediately. After stirring for about 10 min, 20 mL of hydra-
zine hydrate (N ‚H O) was added, and finally the precipi-
tate was dissolved. The autoclave was filled with deionized
water up to 80% of the total volume, sealed, and heated at
140 °C for about 5 h. After that, the system was allowed to
cool to room temperature naturally. Black products (the yield
is about 95%) were collected by filtration, washed with de-
ionized water and absolute ethanol, and then dried at 60 °C.
The obtained samples were characterized on a Bruker D8-
advance X-ray powder diffractometer with Cu KR radiation
2
TeO
3
was added into the autoclave,
3
(or NiTeO ) appeared im-
3
H
2 4
2
9
tubes at very high temperature (about 1000 °C). MOCVD
(
metalorganic vapor chemical deposition)10 and molecular
*
Author to whom correspondence should be addressed. E-mail: ydli@
tsinghua.edu.cn.
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4
2174 Inorganic Chemistry, Vol. 42, No. 7, 2003
10.1021/ic0262031 CCC: $25.00 © 2003 American Chemical Society
Published on Web 03/14/2003

COMMUNICATION
These specific oriented lattice fringes indicate that there is
a predominant direction during the growth of CoTe in the
solution. From the inset ED pattern (in Figure 3b) of NiTe,
it can be considered that NiTe nanowires are also composed
of micro NiTe nanoclusters.
Compared to the reported synthetic methods of tellurides,
the most innovative place in our experiments is the use of
Na
2
TeO
3
to supply a highly reactive Te source. N
2
H
4
2
‚H O
Figure 1. (a) XRD patterns of CoTe and NiTe nanowires. (b) TEM image
of as-prepared CoTe nanowires.
is used both as reducing agent and as complexing agent,
which helps to form a uniform and transparent aqueous
solution before reaction. The reaction to form CoTe (similar
to NiTe) can be formulated as the following equations:
1
40 °C
2
CoSO + 2Na TeO + 3N H
8
4
2
3
2
4
2
Co + 2Te + 3N v + 2Na SO + 6H O (1)
2
2
4
2
1
40 °C
Co + Te
8 CoTe
(2)
2
-
Soluble Na
2
TeO
3
will first dissociate in water into TeO
3
+
2+
and Na , and then react with Co to form CoTeO
3
Figure 2. TEM and HRTEM image of one individual CoTe nanowire.
precipitation. When N
tion is dissolved by the formation of Co -N
ion (and dissociative TeO
2
H
4
‚H
2
O is added, CoTeO
3
precipita-
4
complex
2
+
2
H
2
-
3
is formed again), which
provides an ideal environment for the growth of CoTe
2
-
nanowires. At 140 °C, TeO
3
can easily be reduced by
8
,14
2+
hydrazine to Te and at the same time Co can also be
1
6
reduced to Co (eq 1). These newly produced Te and Co
are highly reactive, and they will react with each other to
form the CoTe product (eq 2). We call this process a
hydrothermal coreduction routine. Another possible routine
is that the newly produced Te will be reduced further to
Figure 3. TEM images of (a) NiTe nanowires and (b) one individual
nanowire.
17
were determined at 200 kV by a Hitachi H-800 transmission
electron microscope (TEM) and a JEOL JEM-2010F high-
resolution transmission electron microscope.
Figure 1a shows the typical XRD patterns of CoTe and
NiTe nanocluster wires. The two as-prepared samples are
pure phase with NiAs structure. All the reflections can be
indexed to hexagonal CoTe (a ) 3.893 Å and c ) 5.375 Å,
the (201), (103), and (112) peaks are overlapped to form a
broad peak) or hexagonal NiTe (a ) 3.9293 Å and c )
2- 18
2-
2+
2 4
Te , and then Te reacts with Co -N H to form the
product. Because of these highly reactive Te and/or Co
sources, the whole reaction rate is expedited and a higher
concentration of CoTe monomer (single CoTe molecule
before its nucleation and growth) will form, which may cause
the fast growth along the predominant direction to form
nanowires. To substantiate our hypothesis, we performed
control experiments. When commercial Te powder instead
2 3
of Na TeO was used as reactant in our experiments, no CoTe
1
9
5.3657 Å). The broad peaks indicate the fine average size
2 2
or NiTe product (we obtained only Co(OH) , Ni(OH) , and
of products.
unreacted Te) could be obtained.
TEM measurement of CoTe (Figure 1b) indicates that the
average length of these nanowires is about 2 µm, with the
diameters ranging from 10 nm to 30 nm. Figure 2 shows a
typical individual nanowire with the diameter of ∼20 nm.
Figure 3a shows the nanowires of NiTe. Their lengths range
from 500 nm to about 2 µm. The diameter of a typical
individual nanowire is about 70 nm (Figure 3b). Unlike the
appearance of single crystallized nanowires, many black
clusters can be found in both CoTe and NiTe nanowires
This coreduction method to CoTe and NiTe nanowires
surely can be used to synthesize other 1-D tellurides. It will
have potential applications in fabricating diluted magnetic
semiconductors and other advanced materials.
Acknowledgment. This work was supported by the
NSFC (20025102, 50028201, 20151001), the Foundation for
the Author of National Excellent Doctoral Dissertation of
P. R. China, and the State Key Project of Fundamental
Research for nanomaterials and nanostructures.
IC0262031
(Figures 1b, 2, 3). In the inset HRTEM image (Figure 2) of
one CoTe nanowire, we can clearly see that a bunch of
nanoclusters, which have discontinuous lattice fringes, are
embedded in the middle of the nanowire and welded by
amorphous substance. It is difficult to calculate the interplane
distances and estimate the accurate size of these nanoclusters.
Almost all of the lattice fringes are perpendicular (or
approximately perpendicular) to the long axes of nanowire.
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