# Synthesis and Characterization of Selenium Nanowires

Authors: C. K. Senthil kumaran; S. Agilan; Dhayalan Velauthapillai; N. Muthukumarasamy; M. Thambidurai; T. S. Senthil; R.  Balasundaraprabhu
Journal: ISRN Nanotechnology
 (2011)

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## Abstract

Selenium nanowires have been grown by chemical method. The effect of annealing on
the properties of the prepared selenium nanowires has been studied. The X-ray
diffraction studies indicated the formation of selenium with trigonal phase, and
no secondary phase was observed. The composition analysis results show that
selenium is present in the sample. HRTEM images reveal that selenium nanowires
have diameter ranging from 30–50 nm and length of
1-2μm. The diameter and length of nanowires have
been found to increase with increase in annealing temperature.


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## Body

## 1. Introduction

One-dimensional (1D) nanostructural materials such as nanotubes, nanowires, and
nanorods have recently received much attention due to their interesting properties
and are potential candidates for application in different fields. The
one-dimensional nanostructured selenium nanowires have been widely studied because
of their functional properties in superconductivity [1], high photoconductivity, and catalytic activity. Selenium nanowires
find application in the areas of photoelectric cells, xerography, light-measuring
devices, and solar batteries [2]. Fan et al.
[3] have synthesized Se microrods,
microtubes, and dendrite type microstructure by using Se powder and NaOH as starting
materials under hydrothermal condition. t-Se in the form of nanowires and
nanoribbons or nanobelts have been synthesized using
β-carotene [4] and
cellulose [5] as reducing agent by same method
at 160°C. Zhang et al. have prepared t-Se nanowire arrays by electrodeposition
using anodic porous alumina templates [6]. Li
and Yam’s group has employed ascorbic acid as the reducing agent under the
assistance of β-cyclodextrin to make selenium nanowires
[7]. Chen et al. have prepared t-Se
nanorods through a hydrothermal route [8].
Selenium has a high reactivity towards a variety of chemicals, which can be explored
to transform selenium element into many other important functional materials, such
as PbSe, ZnSe, and CdSe [9–11]. Selenium is extensively known as an
important elemental semiconductor as well as an essential element in biology and
chemistry. Selenium is also one of the essential trace elements for human beings. It
has been confirmed that selenium can improve the activity of the selenoenzyme,
gluthione peroxidase and prevent free radicals from damaging cells and tissues in
vivo. Se nanomaterials have been prepared by different workers using various
techniques such as hydrothermal route, chemical vapor deposition, sonochemical
approaches, refluxing processes, and cellulose-directed growth [12–15].The size and shape of nanomaterials have a major influence on their physical and
chemical properties, and the ability to control these parameters remains a great
technological challenge with important implications for nanoscale science. Special
attention has been directed towards the control of size and morphology of
chalcogenide nanostructures. Recently, synthesis of nanowires with controlled
alignment, size, shape, and compositions based on one-dimensional structure has
triggered great interest due to the fact that these nanowires may provide
opportunities to exploit new phenomena and novel properties. A large number of work
about the preparation of nanowire structures have been reported. Notable examples
including the nanowires of Se via a chemical precipitation method [16], Se nanowires by a hydrothermal technique
[17] have also been reported. These
methods, however, have several major drawbacks, including the use of toxic
chemicals, extreme synthesis conditions involving high-operating temperatures and/or
pressures, and highly acidic or alkaline reaction conditions. The method used in the
present study is simple and is of low cost and scale-up route and less toxic
precursors and solvents have been used. In this paper, we report about the
preparation and characterization of selenium nanowires using chemical method.


## 2. Experimental

Selenium nanowires have been prepared using the required precursors by chemical
method. An aqueous solution of 0.05 M of SeO2 and starch
(50 mg) were dissolved in water and stirred for about one hour at room
temperature. Ascorbic acid (0.025 M) was added dropwise to the above
mentioned solution. The colour of the solution changed into brick-red, indicating
the formation of Se nanoparticles in the solution. The solution was stirred for 5
hours at room temperature. After 5 hours, the suspension was centrifuged and washed
with water and ethanol several times. The samples were then suspended in ethanol and
allowed to age for 2 hours without stirring. After centrifugation, the samples were
dried at room temperature. The Se samples have been annealed at 100°C and
200°C for 1 h using a heating rate of 2°C/min.X-ray diffraction studies have been carried out using PANalytical X-ray
diffractometer, and surface morphology of the samples has been studied using
scanning electron microscope (JEOL JSMS 800-V). Transmission electron microscope
(HRTEM) images of the prepared Se have been recorded using a JEOL JEM2100
microscope. Compositional analysis of the samples has been studied using energy
dispersive analysis of X-rays (JEOL Model JED-2300).


## 3. Results and Discussion

Figure1(a) shows the X-ray diffraction
patterns of as prepared Se. The diffraction peaks at 2θ
(degrees) of 23.57°, 29.73°, 41.28°, 43.68°, 45.43°,
51.72°, 56.07°, 61.62°, 65.24° and 71.60° are,
respectively, indexed as the (100), (101), (110), (102), (111), (201), (112), (103),
(210), and (113) planes of Se. All the diffraction peaks in the
2θ range measured correspond to the trigonal structure of
Se with lattice constants a
=
4.35 Å and c
=
4.93 Å and are in good agreement with those
on the standard data card (JCPDS card No. 06–0362). Figures 1(b) and 1(c) show that the X-ray diffraction patterns of 100°C and
200°C annealed Se. The (100), (101), (110), (102), (111), (201), (112), (210),
and (113) peaks of the 100°C and 200°C annealed selenium are slightly
shifted when compared to the as-prepared selenium because annealed samples are under
a tensile strain, and the amount of strain increases with increase in annealing
temperature. The sharpness of the diffraction peaks suggests that the product is
well crystallized. The crystallite size of selenium is calculated using
Scherrer’s equation, (1)D
=
K
λ
β
cos
⁡
⁡
θ
, where D is the grain size, K is a constant taken to be 0.94,
λ is the wavelength of the X-ray radiation,
β is the full width at half maximum, and
θ is the angle of diffraction. The crystallite size
has been calculated and is found to be in the range 30–50 nm for
as-prepared, 100°C, and 200°C annealed selenium, respectively.Figure 1
X-ray diffraction pattern of Se (a) as prepared, (b) 100°C, and (c)
200°C annealed samples.Figure2 shows the scanning electron
microscope (SEM) image of the as-prepared Se, 100°C and 200°C annealed
selenium samples. Figure 2(a) shows the
image of the as-prepared selenium nanowire. Figure 2(b) shows the SEM image of the 100°C annealed Se nanowires. The
SEM image reveals that the Se nanowires are of uniform size with a mean diameter of
30 nm. SEM image of 200°C annealed Se is shown in Figure 2(c). It can be seen that the nanowires has a
length of several micrometers and diameter ranging from 30 to 50 nm. It can
be clearly seen that the lengths of the Se nanowires increase rapidly with
increasing the annealing temperature; however, the diameters increase slowly.
Therefore, it is understood that the aspect ratios and lengths of the Se nanowires
can also be controlled by annealing temperature. Figure 3 shows the energy dispersive X-ray analysis (EDAX) spectra of
the Se sample. In the EDAX, Se is the only element detected, indicating that the
sample is highly pure.SEM image of Se (a) as prepared, (b) 100°C annealed, and (c) 200°C
annealed.
(a)
(b)
(c)Figure 3
EDAX spectra of as-prepared Se.Figure4(a) shows the transmission electron
microscope (TEM) image of as-prepared Se nanowires. The image shows that the
nanowires are straight and uniform with an average diameter of about 30 nm.
Figure 4(b) shows the selected area electron
diffraction (SAED) pattern of as-prepared Se nanowires. Selected area electron
diffraction image (Figure 4(b)) exhibits
diffraction rings corresponding to the (100), (101), (110), (102), (111), and (201)
directions of the trigonal phase of Se. The d-spacing values
obtained for all the diffraction rings from the SAED pattern match very well with
that of trigonal phase Se. Figure 5(a) shows
the TEM image of 200°C annealed Se nanowires. The TEM image (Figure 5(a)) confirms the formation of Se nanowires
with several micrometers of length and 50 nm diameter. Figure 5(b) shows the SAED pattern of 200°C annealed Se
nanowires. SAED image (Figure 5(b)) exhibits
diffraction rings corresponding to the (100), (101), (110), (102), (111), (201), and
(103) directions of the trigonal phase of Se. The d-spacing values
corresponding to plane (100) for as-prepared and annealed (200°C) samples are
found to be 3.76 Å and 3.73 Å. The
d-spacing values calculated from these Figures (4(b) and 5(b)) are in close agreement with the values obtained from X-ray
diffraction studies.(a) Transmission electron microscope and (b) selected area electron
diffraction images of the as-prepared Se nanowires.
(a)
(b)(a) Transmission electron microscope and (b) selected area electron
diffraction images of the Se nanowires annealed at 200°C.
(a)
(b)


## 4. Conclusion

Selenium nanowires have been prepared by chemical method. X-ray diffraction analysis
reveals that the as-prepared and annealed selenium samples are of trigonal
structure. The composition analysis results show that Se is present in the sample.
TEM images reveal that Se nanowires have diameter ranging from
30–50 nm and length 1-2μm.



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*Source: 589073-2011-07-25.xml*