Fabrication of metal cadmium nanowires by an assistant thermal decomposition method

Article abstract of DOI:10.1246/cl.2005.1482

Using a simple assistant thermal decomposition method, metal cadmium nanowires were large-scale fabricated from CdS powders in an argon atmosphere. Investigation results demonstrate that the Cd nanowires have lengths of several microns and diameter of about 70-150 nm. Copyright

Full text of DOI:10.1246/cl.2005.1482

1482
Chemistry Letters Vol.34, No.11 (2005)
Fabrication of Metal Cadmium Nanowires by an Assistant Thermal Decomposition Method
Jian-wei Zhao,ꢀ Chang-hui Ye, Xiao-sheng Fang, Peng Yan, and Li-de Zhang
Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences,
Hefei, Anhui 230031, P. R. China
(Received July 22, 2005; CL-050949)
Using a simple assistant thermal decomposition method,
metal cadmium nanowires were large-scale fabricated from
CdS powders in an argon atmosphere. Investigation results dem-
onstrate that the Cd nanowires have lengths of several microns
and diameter of about 70–150 nm.
radiation], and transmission electron microscopy [(TEM) JEOL
2010, operated at 200 kV].
Figure 1 shows the XRD pattern of the as-prepared products.
All of its peaks can be indexed to those of hexagonal-phased
ꢀ
cadmium with lattice constants of a ¼ 2:963 A and c ¼ 5:591
ꢀ
A. It should be noted that no diffraction peaks from CdO or other
impurities have been found in our samples. Different from the
XRD pattern of the Cd nanosheets, the (002) peak was not sharp
and strong and it suggests that Cd nanowires may have different
plane of the surface. The morphology of the products was exam-
ined using SEM. A typical SEM image for cadmium nanowires
is shown in Figure 2a. The image shows that the products consist
of a large quantity of wire-like nanostructure with lengths in the
range of several to several tens of micrometers. As shown in
Figure 2b, it is a high-magnification SEM image and reveals that
the wires have a diameter of about 70–150 nm.
Over the past decade, numerous efforts have been employed
in controlling the sizes and shapes of inorganic nanomaterials
because these parameters represent key elements that determine
their electrical and optical properties.1,2 In particular, different
morphologies, such as wire-like, rod-like, belt-like, tube-like,
and scroll-like, may have different properties with unique appli-
cations.3–5 Thus, one of the most important researches on nano-
materials is to develop the techniques for the fabrication of qua-
si-one dimensional (1D) nanomaterials. It is well known that
cadmium metal is an important material used in metal plating
and coating operations. Cadmium is also used extensively in
nickel–cadmium and solar batteries and in pigments. Although
cadmium metal is an important material but most research about
cadmium nanomaterials were focused on the cadmium chalcoge-
nides.6–11 Because of the relatively low melting point, cadmium
metal (melting point: 321 ꢁC) nanostructrue is difficult to prepare
by vapor process. Recently, Hu et al. have prepared single-
crystalline cadmium nanotubes by the pyrolysis of CdS powder
in inert gas.12 In our previous works, we fabricated cadmium
nanosheets and a polycrystalline CdS thin layer on surface was
found as the determining factor for its formation.13 But if this
thin layer is lost at the formation process, what would be formed
finally? Herein, some zinc powder was used to adsorb sulfur
chemically in experiment and single crystal cadmium nanowires
were fabricated. Their growth process and mechanism have also
been discussed.
The apparatus used for the thermal decomposition of CdS
powers is also the conventional horizontal tube furnace with a
2-cm inner-diameter alumina tube mounted inside. CdS powders
(ca. 50 nm, 6 g, self-made by the direct reaction of CdCl and
Na2S in aqueous solution) were placed in an alumina boat that
covered with a quartz plate and then put into the center of the
alumina tube. A little of zinc powders were placed in another
boat and put downstream in the alumina tube (12 cm away from
the source materials). The tube furnace was purged with high-
purity argon for 2 h prior to heating to eliminate oxygen in the
furnace. Under a constant flow of Ar (20 sccm), the furnace
was rapidly heated to 1000 ꢁC in 8 min and kept at this temper-
ature for 40 min. After the system was cooled down to room tem-
perature, a soft and silvery-white product was collected on the
inner wall of the alumina tube at a temperature of 200–300 ꢁC.
The as-prepared products were characterized and analyzed
by scanning electron microscopy [(SEM) JEOL JSM 6700F],
X-ray diffraction [(XRD) PW1710 instrument with Cu Kꢀ
20
30
40
50
60
70
80
2θ (degree)
Figure 1. XRD pattern of as prepared products.
The morphology and structure of individual Cd nanowires
have been characterized in further detail using TEM and selected
area electron diffraction (SAED). A representative TEM image
shown in Figure 3a reveals that the produced Cd nanowires
are curved and similar with the reported Cd nanotubes.10 Some
linear nanowires with a diameter of about 100 nm were also
found as shown in Figure 3b. The SAED pattern (Figure 3c)
recorded perpendicular to the nanowire long axis could be
(a)
(b)
Figure 2. The morphology of the Cd nanowires. (a) A low-
magnification SEM image, (b) a high-magnification SEM image.
Copyright Ó 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.11 (2005)
1483
(a)
(b)
(c)
(a)
(b)
Figure 4. The morphology of the Cd microwires. (a) A low-
magnification SEM image, (b) a high-magnification SEM image.
Cu
Cd
(d)
of one to two micrometers. These microwires were the result of
the continued growth of the nanowires. It should be noted that
these microwires were almost linear. That may be the result of
increase of the diameter and so the effect of the temperature
decreased in the experiment.
Cd
Cu
Cd
Cu
0
2
4
6
8
10
12
14
16
18
20
In conclusion, metal cadmium wires were large-scale fabri-
cated from CdS powders by a simple thermal decomposition
method with some zinc powder used to adsorb sulfur chemically
in experiment. The as-prepared Cd nano-wires have lengths of
several microns and diameter of about 70–150 nm. The forma-
tion of the wires could be ascribed to the lost of restriction on
the further growth along [0001] direction. These Cd wires may
be used as precursors to synthesize the cadmium chalcogenides
or other cadmium-related compounds nanostructures.
Energy (keV)
Figure 3. (a) and (b): The TEM images of the Cd nanowires,
(c): the corresponding SAED pattern of Cd nanowires, (d)
EDS data shows that composition of the nanowires is metal
cadmium, the Cu peaks come from the TEM grid.
indexed for the [01 ꢂ 10] zone axis of single crystalline Cd and
suggested that the nanowires growth occurred along the h0002i
direction. EDS attached to TEM analysis demonstrated that
composition of the nanowires is cadmium metal as shown in
Figure 3d. Because some zinc powder was used in experiment,
the trace sulfur element is not seen in the EDS data of Cd nano-
wires.
This work was financially supported by the National
Major Project of Fundamental Research: Nanomaterials and
Nanostructures (Grant No. 2005CB623603).
The formation process of Cd nanowires involves a vapor–
solid mechanism similar to the growth of Cd nanotubes reported
by Hu et al.12 and Cd nanosheets reported by Zhao et al.6 But
different from the formation of the Cd nanosheets, the S2 gas
was generated from the decomposition of the CdS and then
was adsorbed chemically by the Zn powders at high temperature
before reacting with the Cd products in experiment. As a result,
the polycrystalline CdS thin layer on the surface could not be
formed and its restriction on the further growth along [0001] di-
rection was lost. It is known that, from thermodynamic point of
view, the (0002) surface is a high-energy plane for hexagonal
crystal owing to the closed packing effect. As a result, the
[0001] direction would be an optimized growth direction in va-
por growth. So at low gas flow rate and relatively low vapor pres-
sure of Cd, the crystals grow along this optimized direction and
finally form the Cd nanowires. The relatively low melting point
of metal cadmium, small diameters of the wires, and the equiv-
alent growth temperature may explain the curve morphologies of
the nanowires.
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Through controlling the heating time, we can obtain Cd
wires with different diameters. As an example, when the heating
time was extended to 100 min, cadmium microwires would be
formed. A typical SEM image (Figure 4a) shows that the prod-
ucts consist of a large quantity of wire-like structures with
lengths of several hundreds of micrometers. The diameter of
these wires, seen from the image of Figure 4b, was in the range
Published on the web (Advance View) September 28, 2005; DOI 10.1246/cl.2005.1482