Single crystalline tellurium nanowires were successfully synthesized in large scale by a facile approach of vaporizing tellurium metal and condensing the vapor in an inert atmosphere onto a Si substrate. Tellurium was evaporated by heating at 300 C at 1 torr and condensed on the Si substrate at 100-150 C, in the downstream of argon (Ar) gas at a flow rate of 25 sccm for 30 min. The as-synthesized nanowires have diameters between 100-300 nm and lengths up to several micrometers. The single crystalline nanowires grew in a preferred [0001] direction. The obtained nanowires were highly pure as only tellurium metal was used in the vaporization process, and no other reagent, surfactant, or template were used for the growth. This low temperature and high-yield approach to the tellurium nanowires synthesis may facilitate its industrial production for various applications

Bongsoo Kim

Jeunghee Park

Paritosh Mohanty

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Copyright © 2006 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 6, 1–4, 2006
Large Scale Synthesis of Highly Pure Single
Crystalline Tellurium Nanowires by Thermal
Evaporation Method
Paritosh Mohanty1, Jeunghee Park2, and Bongsoo Kim1∗
1Department of Chemistry, KAIST, Daejeon 305701, Korea
2Department of Chemistry, Korea University, Jochiwon 339700, Korea
Single crystalline tellurium nanowires were successfully synthesized in large scale by a facile
approach of vaporizing tellurium metal and condensing the vapor in an inert atmosphere onto a
Si substrate. Tellurium was evaporated by heating at 300 C at 1 torr and condensed on the Si
substrate at 100–150 C, in the downstream of argon (Ar) gas at a flow rate of 25 sccm for 30 min.
The as-synthesized nanowires have diameters between 100–300 nm and lengths up to several
micrometers. The single crystalline nanowires grew in a preferred [0001] direction. The obtained
nanowires were highly pure as only tellurium metal was used in the vaporization process, and no
other reagent, surfactant, or template were used for the growth. This low temperature and high-yield
approach to the tellurium nanowires synthesis may facilitate its industrial production for various
applications.
Keywords: Single Crystalline Metal Nanowires, Tellurium, Vapor-Phase Synthesis.
1. INTRODUCTION
Owing to their possible novel applications such as fabri-
cation of nanodevices, gas sensors, biosensors etc., single
crystalline one-dimensional (1D) metallic nanostructures
have attracted much interest.1–5 Among the reported meth-
ods for the synthesis of 1D nanostructures, vapour-phase
synthesis is probably one of the most widely used.6–8 But
it is mainly employed for the synthesis of metal oxides,
metal sulfides or other systems, and only a few reports
are available for metal 1D nanostructures.6–8 While sev-
eral approaches have been reported for the synthesis of
metal nanowires, most of these are based on wet chemi-
cal methods.1–5 Tellurium (Te) is a narrow-bandgap semi-
conductor with bandgap energy of 0.35 eV and it has
been considered as an excellent candidate for the future
high-efficiency photoconductors, thermoelectric and piezo-
electric devices.29–19 Many functional materials such as
CdTe, Bi2Te3 etc. can also be synthesized by the reac-
tion of tellurium with other elements. The crystal structure
of Te is highly anisotropic with covalently bonded atoms
forming unique helical chains. These chains are bound
through weak van der Waals interactions and form hexag-
onal lattices. This anisotropic crystal structure induces
∗Author to whom correspondence should be addressed.
tellurium towards a 1D growth leading to nanowires
morphology.29–19
Xia and coworkers reported the synthesis of vari-
ous 1D Te nanostructures in wet chemical methods.29
Recently, several other approaches such as solvothermal
synthesis,10 microwave assisted synthesis,11 biomolecules
assisted synthesis,1213 and other wet chemical synthesis of
1D tellurium nanostructures are also reported.14–16 How-
ever, the vapor phase synthesis of 1D Te nanostructures is
not common. In a particular vapor phase synthesis, tubular
structures of Te with micrometer diameters were formed.17
Using a similar vaporization method, Geng et al. synthe-
sized tellurium nanobelts by reacting Al2Te3 powder with
H2O in a horizontal tube furnace at a high-temperature
of 500 C.18 Metraux and Grobety have demonstrated the
synthesis of Te nanotubes by a physical vapor deposition
method, using an induction furnace.19
In this article, we report the synthesis of single crys-
talline tellurium nanowires by a facile low temperature
(300 C) vaporization method. Most of the reported 1D
tellurium nanostructures were synthesized using surfactant,
biomolecules, other precursors or some special experimen-
tal techniques.29–19 In the present method, we used only
highly pure (99.99%) tellurium powder as precursor for
the growth of the single crystalline nanowires. The nano-
wire morphology of tellurium could potentially improve or
J. Nanosci. Nanotechnol. 2006, Vol. 6, No. 11 1533-4880/2006/6/001/004 doi:10.1166/jnn.2006.015 1
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Large Scale Synthesis of Highly Pure Single Crystalline Tellurium Nanowires Mohanty et al.
modify its fascinating electrical, electronic or thermoelec-
tric properties.
2. EXPERIMENTAL DETAILS
The synthesis of the tellurium nanowires was carried out
in a 1 inch diameter horizontal quartz tube furnace whose
central temperature was held at 300 C. The nanowires
were deposited on the Si substrate placed downstream
(about 2–3 inches) from an alumina boat filled with 0.3 g
of tellurium powder (99.99%, Aldrich). Before the start of
the reaction, the chamber was evacuated to 0.3 torr and
then purged with argon (Ar) gas at a flow rate of 25 stan-
dard cubic centimeters per minute (sccm) for 30 minutes.
In the steady state, the Ar flow rate and the pressure of the
chamber were 25 sccm and 1.0 torr, respectively. Then the
furnace was heated to 300 C at a rate of 20 C per minute.
Grayish-black films were deposited all over the Si sub-
strate after a deposition time of 30 min. The as-synthesized
products were employed for various characterizations.
Field emission scanning electron microscope (FESEM)
images of the as-synthesized Te nanowires were taken
on a Phillips XL30S. Transmission electron microscope
(TEM), high resolution TEM (HRTEM) images, selected
area electron diffraction (SAED) pattern, and energy-
dispersive X-ray spectrum (EDS) were studied on a Jeol
JEM-2100F transmission electron microscope operated at
200 kV. X-ray diffraction (XRD) pattern of the specimen
was recorded on a Rigaku D/max-rc (12kW) diffractome-
ter operated at 40 kV voltage and 80 mA current with
filtered 0.15405 nm CuK radiation. X-ray photoelectron
spectroscopy (XPS) measurements of the specimen were
carried out on an ESCA 2000, V.G. Microtech UK, at a
pressure of 1 × 10−9 torr using the Mg K line with a
photon-energy of 1253.6 eV.
3. RESULTS AND DISCUSSION
Thermal evaporation of Te metal below its melting point
and at a low pressure of 1 torr, and condensation of
the vapor at a suitable temperature onto a substrate led
to highly pure nanowires in high yield. Figure 1 is the
FESEM image showing an overview of the as-synthesized
nanowires. Their diameter varies between 100–300 nm
with lengths extended up to several micrometers. Some of
the nanowires are lying on the substrate where as most of
them are close to vertical to the substrate with an inclined
angle. The crystal structure of the obtained nanowires was
studied with XRD. Figure 1(b) shows a typical XRD pat-
tern of the obtained Te nanowires. All the peaks in the
diffractogram were indexed as being due to the hexagonal
crystal structure of Te (JCPDS file no 36-1452). The peak
positions are fairly matched with the standard values. The
most intense peak at interplanar spacing d = 02343 nm is
due to the reflection from (102) crystal plane. The second
(b)
20 30 40 50 60 70
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0
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2θ (degree)
Fig. 1. (a) FESEM image of tellurium nanowires deposited on Si sub-
strate kept at 100–150 C by heating tellurium powder at 300 C for
30 min. (b) XRD pattern of the as-synthesized tellurium nanowires.
most intense peak at d= 01969 nm is due to the reflection
from (003) crystal plane. In the standard diffraction file
the (003) peak is observed with an intensity of ∼9% with
respect to the most intense peak. But in the present case
it appears as the second most intense peak with an inten-
sity of ∼90% compared to the most intense (102) peak.
This enhancement of the intensity of (003) peak imply
the possibility of growth of the nanowires along [0001]
direction. In the next section of this article, the HRTEM
image and the SAED pattern were used to study the single
crystallinity and growth direction of the obtained tellurium
nanowires.
The elemental composition of the as-synthesized nano-
wires was studied with EDS and the XPS spectrum. The
EDS spectrum shown in Figure 2(a) indicates that the
nanowires were highly pure. A few extra peaks were
observed from copper and carbon because of the use
of carbon coated copper grid for sample preparation. In
the high resolution XPS spectrum shown in Figure 2(b),
the presence of two peaks at 573.06 and 583.46 eV (as
against the standard value of 573.1 and 583.49 eV) due
to 3d5/2, 3d3/2 binding energies, respectively, confirms the
purity of the nanowires. These two peaks have a separation
2 J. Nanosci. Nanotechnol. 6, 1–4, 2006
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Mohanty et al. Large Scale Synthesis of Highly Pure Single Crystalline Tellurium Nanowires
565 570 575 580 585 590
(b)
∆ = 10.4 eV
3d3/2
3d5/2
Binding Energy (eV)
Fig. 2. (a) EDS pattern of the tellurium nanowires demonstrating the
high purity of the specimen. (b) High-resolution XPS spectrum of the
as-synthesized nanowires.
= 104 eV which agrees well with the standard value of
= 1039 eV in the elemental tellurium.20
The TEM and the HRTEM micrographs of a represen-
tative nanowire are shown in Figure 3(a) and (b), respec-
tively. The corresponding SAED pattern is given in the
inset of Figure 3(a). The TEM image shows the mor-
phology, and the HRTEM image and the SAED pattern
were used in order to confirm the structure and the growth
direction of the as-synthesized nanowires. The nanowire
is straight with a diameter of ∼160 nm which can be
seen with the TEM image. The clear lattice fringes in the
HRTEM image in Figure 3b indicate that the nanowire is
structurally uniform and single crystalline. The interplanar
spacing of ∼0.59 nm is consistent with the (001) crys-
tal plane and another interplanar spacing of ∼0.22 nm is
due to the (110) crystal plane which are perpendicular and
parallel to the nanowire axis, respectively. These observa-
tions confirm that the nanowires are grown in the preferred
Fig. 3. (a) TEM and (b) HRTEM micrographs of a representative Te
nanowire. The corresponding SAED pattern is given in the inset to (a).
The nanowire grew along the [0001] direction as demonstrated with the
HRTEM image and the SAED pattern.
direction of [0001]. This is further supported by the SAED
pattern shown in the inset to Figure 3(a).
The formation of the Te nanowires can be explained
through a vapor-solid (VS) growth mechanism. Typically,
in a vapor-phase synthesis, the degree of the supersatura-
tion controls the morphology of the obtained nanostruct-
ures.6 At a low degree of supersaturation nanowires were
formed, and medium or high supersaturation favors growth
of bulk crystal or powder, respectively.6 The supersatura-
tion factor can be controlled by adjusting the experimental
conditions such as temperature, pressure, and the proper
dilution of Ar mixture. In the present case, the nanowires
were formed through a VS mechanism because of the low
degree of supersaturation of the tellurium vapor at the tem-
perature region of 100–150 C, which is much lower than
the melting point (449.51 C) of tellurium metal.6
Furthermore, the anisotropic crystal structure of Te
induces a strong tendency towards the 1D growth. Accord-
ing to the Wulff facets theorem for the shape-control of a
crystal growth, the relative specific surface energy of each
J. Nanosci. Nanotechnol. 6, 1–4, 2006 3
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Large Scale Synthesis of Highly Pure Single Crystalline Tellurium Nanowires Mohanty et al.
[0001]
= Te
Fig. 4. Schematic representation of the tellurium crystal structure show-
ing the anisotropy with a longer c-axis.
crystal facet determines the shape of the crystal, and favors
the configuration with a minimum total surface energy.21
As shown with the schematic diagram in Figure 4, the
crystal structure of Te is highly anisotropic with a longer
c-axis. It has covalently bonded atoms forming unique
helical chains which are bound through weak van der
Waals interactions and form hexagonal lattices. Thus, the
symmetry of basic crystal lattice of Te is reflected in
single-crystalline nanowires with a preferred growth direc-
tion along c-axis.
4. CONCLUSION
In summary, we have successfully synthesized single crys-
talline tellurium nanowires by a vapor phase method. Free
standing nanowires were grown in a regular [0001] direc-
tion on the Si substrate at a deposition temperature of 100–
150 C. The tellurium nanowires were very pure as only
Te metal was involved in the growth process and no tem-
plate or catalyst was used. The obtained nanowires can be
potentially useful for the fabrication of nanodevices with
high performance and novel properties. Further studies on
electrical transport and thermoelectric properties are under
progress.
Acknowledgment: This work was supported by
KOSEF(R01-2005-000-10711-0). TEM analysis was per-
formed at the Korea Basic Science Institute in Daejeon.
References and Notes
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Received: 9 November 2005. Revised/Accepted: 11 February 2006.
4 J. Nanosci. Nanotechnol. 6, 1–4, 2006


Large Scale Synthesis of Highly Pure Single Crystalline Tellurium Nanowires by Thermal Evaporation Method

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Large Scale Synthesis of Highly Pure Single Crystalline Tellurium Nanowires by Thermal Evaporation Method

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