Materials Sciences and Applicatio ns, 2010, 1, 8-12
doi:10.4236/msa.2010.11002 Published Online April 2010 (
Copyright © 2010 SciRes. MSA
Temperature Dependence of Current-Voltage
Characteristics in Individual Sb2Se3 Nanowire
Kien-Wen Sun, Ting-Yuan Fan
Department of Applied Chemistry, National Chiao Tung University, Hsinchu, Taiwan, China.
Received February 17th, 2010; revised March 11th, 2010; accepted March 15th, 2010.
We demonstrated techniques toward nanoscale thermometries by using a hydrothermally prepared single Sb2Se3
nanowire. Suitable electrodes were fabrica ted to make electrica l conta ct with a nano wire on a silico n substra te by com-
bining techniques of dielectrophoresis, electron beam (e-beam) lithography, and focused ion beam (FIB). Measure-
ments of temperature-dependent electrical resistivity were carried out from room temperature up to 525 K. The cur-
rent-voltage characteristics showed linear and symmetric behavior through the entire temperature range, which indi-
cated that the contacts are ohmic. The resistance of the single Sb2Se3 nanowire decreased with increasing temperature.
However, a larger thermal activation energy of ~ 4.2 eV was found near a temperature above 420 K. We speculate that
the reduction of resistance at a higher temperature was due to the breakdown of grain boundary barriers.
Keywords: Nanowire, Dielectrophoresis, E-Beam Lithography
1. Introduction
The measurement of temperature on the nanometer scale
is currently a topic of great interest. Advancements in
nano- and biotechnology also demand precise thermome-
try down to the nanoscale. In spatially localized regions
of fluid and solid matter, unexpected heat transfer and
dynamics in confined nanoscale measurements areas bec-
ome important. In particular, the performance of modern
nanodevices, such as fluidic channels, integrated circuits,
and electronic and biologic devices, is often determined
by thermal considerations. The development of nanoscale
thermal sensing devices can meet the requirement for
both accuracy and resolution. Several devices and tech-
niques employing the physical properties of materials,
such as their thermal expansion/contraction of volume,
thermo-optical and electronic properties, have been de-
veloped for the measurement of temperature on the scale
of microns and below. For example, the linear thermal
expansion behavior recorded for a liquid gallium column
confined in the MgO nanotube was used as a nano ther-
mometer in microenviroments [1]. Another common way
to measure local temperature is to use a thermocouple,
which can be fabricated lithographically or can be va-
por-deposited onto nanotips made from another metal
[2-5]. A noncontact thermometer with the support of a
fiber-optic sensor was demonstrated in [6]. Naberhaus et
al. [7,8] reported that certain messenger RNAs change
their conformation in response to temperature. Kotov et
al. developed a reversible nano thermometer comprised
of a dynamic structure with two types of nanoparticles.
These are connected by polymeric spacers acting as a
molecular spring in the aqueous state [9].
In recent years, antimony triselenide (Sb2Se3), a layer-
structured semiconductor of an orthorhombic crystal
structure, has attracted considerable attention due to its
switching effects [10] and good photovoltaic and ther-
moelectric properties [11,12]. Its high thermoelectric
power allows possible applications for optical, thermoe-
lectric cooling, and power conversion devices. In this
work, we demonstrate the temperature dependence of a
single Sb2Se3 nanowire’s transport properties using di-
electrophoresis, E-beam lithography, and focused ion
beam (FIB) technique. The thermal properties of this
device can be effectively used as a nano thermometer in
environments where conventional methods cannot make
2. Experimental Details
Fabrication processes of the single nanowire-based nano
thermometer are given as follows. Our Sb2Se3 nanorod
samples were produced from a single source precursor
Sb[Se2P(OiPr)2]3 and have been studied and demon-
strated elsewhere [13,14] under different solvothermal
temperature conditions. The SEM images of the fabric
Temperature Dependence of Current-Voltage Characteristics in Individual SbSe Nanowire9
2 3
cated nanowire clusters are shown in Figure 1. The nan-
owires have a diameter of 70 nm to 90 nm and an aver-
age length of 3 m to 5 m. EDS indicates that these
nanowires are composed of the element Sb and Se with
the ratio of 1:1.5, as shown in Figure 2. Figure 3 shows
the HRTEM image of an individual nanowire which re-
veals that the nanowire is a single crystal and free from
dislocation. The fringe spacing of ca. 3.9 Å, 5.2 Å, and
3.2 Å corresponding to (001), (120), and (121) planes of
orthorhombic phase Sb2Se3, respectively. It can be seen
that the (001) planes are perpendicular to the surface of
the individual nanowire, from which it can be deduced
that the wire grew along the [001] direction.
We first diluted the 0.001 g of Sb2Se3 nanowire pow-
der in 10 ml deionized (DI) water and ethanol mixture.
The solution was then placed in an ultrasonic bath oper-
ated at a vibration frequency of 185 KHz for 30 min to
Figure 1. SEM images of the fabricated Sb2Se3 nanowire
Figure 2. EDS pattern of the final product (C and Cu sig-
nals can be attributed to the copper microgrid and carbon
film supporting the Se2Se3 nanowires)
Figure 3. HRTEM images of an individual nanowire and
the corresponding crystal planes
prevent the formatio n of clusters. A test drop of the solu-
tion was placed on a bare Si wafer, and after the solution
dried out, scanning electron microscope (SEM) images
were taken to examine the clustering of the nanowires.
The concentration of the solution was continuously di-
luted and adjusted until the nanostructures can be well
dispersed on the Si template.
We designed and fabricated a coordination system on
Si templates for labeling a dispersed single nanowire.
The templates used in the experiments were commer-
cially available 4-inch silicon wafers with (001) crystal
orientation and n-type background doping. The Si wafer
was first diced into 2 cm × 2 cm chips. As shown in Fig-
ure 4(a), a pattern of two-dimensional arrays of cross-
finger-type metal wires with a linewidth of 500 nm, a
pitch of 1 m, and a length of 15 m were defined on the
Si chip using e-beam lithography within an area of 1
A drop of diluted Sb2Se3 nanowire solution was pla-
ced within the inter-digitated electrode patterns. By ap-
plying a bias across the contact pads, the dielectrophore-
sis force [15-18] drove the nanowires to bridge the elec-
trode gap. The SEM images of the Sb2Se3 nanowires’
dielectrophoresis alignment process across the inter-
digitated electrodes are shown in Figures 4(b) and (c).
The sample surface was then scanned by SEM to allocate
a single nanowire. After a single nanowire was selected,
a focus ion beam (FIB) was used to selectively deposit
Platinum (Pt) metal contacts on both ends of the rod, as
shown in Figure 4(d). The surface of the Si substrate
was passivated in advance using a thermally grown SiO2
layer with a thickness of 2000 Å to avoid leakage current
Copyright © 2010 SciRes. MSA
Temperature Dependence of Current-Voltage Characteristics in Individual Sb2Se3 Nanowire
Copyright © 2010 SciRes. MSA
(a) (b)
(c) (d)
Figure 4. The SEM images of (a) two-dimensional cross-finger-type metal wire array, (b)-(c) Sb2Se3 nanowires across the
inter-digitated electrodes, and (d) the two-point electrical contact made on a single Sb2Se3 nanowire
through the substrate during the current–voltage (I-V)
measurements. The temperature dependence of the I-V
characteristics of a single nanorod were probed at a tem-
perature range from 300 K to 525 K with an HP-4145
probe station under a current sensitivity of 1 pA and a
heating stage.
3. Results and Discussion
The electrical contacts were found to be ohmic through-
out the scanned voltage range from –0.5 V to 0.5 V with
a step of 0.001 V. Figure 5 shows the I-V curves of a
single nanowire from 300 K to 448 K. The resistivity of
the nanorod decreased with the increasing temperature
due to the increase in free carriers. A thermal activation
energy of ~ 0.235 eV was found when the curves be-
tween T = 300K to 423K were fitted with the thermally
activated transport model [19,20]:
0exp( )
where is the resistance at T and is the
thermal activation energy for conduction.
R a
Surprisingly, a dramatic reduction in resistivity was
observed when the te mperature was increased above 423
Temperature Dependence of Current-Voltage Characteristics in Individual SbSe Nanowire11
2 3
K, as shown in Figures 5 and 6. Figure 6 shows th at the
electrical current reaches 170
A at the temperature of
523 K and at an applied voltag e of 0.5 V. A th ermal acti-
vation energy larger than 4.0 eV was found when the I-V
curves were fitted with the thermally activated transport
model. In Figure 7 we plot the resistance as a function of
temperature on a log-log scale. A kink in the curve cle-
arly took place at a temperature of ~ 430 K. The experi-
ments were repeatable when the temperature was cycled
from room temperature to 525 K. However, results from
temperature dependent Raman, X-ray diffraction, and
differential scanning calorimeter measurements ruled out
the possibility of phase transition due to the oxidation of
the nanorod at a temperature below 525 K. We speculate
that the reduction of resistance at a high temperature is
due to the escape of trapped charges near the surface. At
a high temperature, the breakdown of potential barrier
leads to the escape of electrons and holes from the sur-
face traps and results to the carrier transport along the
surface and induce an additional quasi-drift current.
Figure 5. I-V curves of a two-point contact single nanowire
at a temperature range from 300 K to 448 K. The scanned
voltage range was from –0.5 V to +0.5 V
Figure 6. I-V curves of a two-point contact single nanowire
at a temperature range from 300 K to 525 K
In Figure 8 a broad PL emission centered at about 700
nm with an FWHM of nearly 150 nm was observed at an
excitation wavelength of 532 nm for the single nanorod.
The features on this broad emission can be fitted with a
single Gaussian peak centered at 675 nm. Although sim-
ilar PL results were reported by Ma et al. [21] on
wire-like microcrystalline Sb2Se3 powder excited with
UV laser light. Their experimental results indicated a PL
peak at 707 nm but with a much narrower FWHM of
only 25 nm. The broad emission peak observed in our
experiment originates from the increasing number of
surface defects, impurities, and dangle bonds attached to
the surface as the dimensions of the nanostructures were
reduced from micrometer to nanometer scale. These sur-
face states are clearly responsible for the dramatic in-
crease of electrical conductance at a high temperature.
Figure 7. Resistance as a function of temperature was plot-
ted on a log-log scale. Thermal activated energies of 0.235
eV and 4.198 eV were obtained at the low and high tem-
perature ranges respectively when the I-V curves were fit-
ted with the thermally activated transport model
Figure 8. Photoluminescence spectrum from a single Sb2Se3
Copyright © 2010 SciRes. MSA
Temperature Dependence of Current-Voltage Characteristics in Individual Sb2Se3 Nanowire
Copyright © 2010 SciRes. MSA
4. Summary
In conclusion, we demonstrated a novel nano thermome-
ter based on a single Sb2Se3 nanorod, which can be used
for the temperature measurement of a temperature range
from 300 K to 525 K, in a micrometer size environment.
The temperature dependence of the nano thermometer’s
transport characteristics shows a dramatic reduction in
electrical resistivity (by more than two orders of magni-
tude) at a temperature near 525 K. The nonlinear electri-
cal behavior of the nanowire is attributed to the grain
boundary barrier mechanisms.
5. Acknowledgement
This work was supported by the National Science Coun-
cil of Republic of China under contract No. NSC 96-
2112-M-009-024–MY3, and NSC 96-2120-M-009-004-,
and the MOE ATU program.
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