Solution-chemical syntheses of nanostructure HgTe via a simple hydrothermal process

Article abstract of DOI:10.1016/j.jallcom.2010.03.135

HgTe rod-shape composed of crystalline particles has been prepared by a hydrothermal method, and characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and transition electron microscopy (TEM). The effects of capping agents, reductants, reaction temperatures, and reaction times on crystal structures and shapes of HgTe have been investigated. The results showed that the CTAB as capping agent plays a crucial role in the hydrothermal process. The synthesis procedure is simple and uses less toxic reagents than the previously reported methods.

Full text of DOI:10.1016/j.jallcom.2010.03.135

Journal of Alloys and Compounds 499 (2010) 121–125
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Solution-chemical syntheses of nanostructure HgTe via a simple hydrothermal
process
a,b,∗
b
a
Masoud Salavati-Niasari
, Mehdi Bazarganipour , Fatemeh Davar
a
Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P.O. Box 87317–51167, I. R. Iran
Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P.O. Box 87317–51167, I. R. Iran
b
a r t i c l e i n f o
a b s t r a c t
Article history:
HgTe rod-shape composed of crystalline particles has been prepared by a hydrothermal method, and
characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and
transition electron microscopy (TEM). The effects of capping agents, reductants, reaction temperatures,
and reaction times on crystal structures and shapes of HgTe have been investigated. The results showed
that the CTAB as capping agent plays a crucial role in the hydrothermal process. The synthesis procedure
is simple and uses less toxic reagents than the previously reported methods.
Received 19 December 2009
Received in revised form 12 March 2010
Accepted 15 March 2010
Available online 23 March 2010
Keywords:
Hydrothermal
HgTe
©
2010 Elsevier B.V. All rights reserved.
Nanostructure
Solution-chemical
1
. Introduction
as a semi-metal with a negative band gap of 20.15 eV [9]. If this
material is made in the form of small particles and quantum con-
finement occurs, the band gap will widen and the material may
exhibit properties of a narrow band gap semiconductor with poten-
tial optical properties at the telecommunications wavelengths.
Also it is worthy to note that excitonic diameter in HgTe is
large.
Due to the population with highly mobile carriers, HgTe is an
ideal material in semiconductor devices such as optical switches,
infrared detectors or photovoltaics [10–12]. Several methods have
been applied for preparation of conventional HgTe materials
including the combination of the elements at elevated tempera-
ture [13], molecular precursor method [14], and organometallic
vapor phase epitaxy growth [15,16]. Recently, vigorous interest
has been intrigued by nanometer-scaled HgTe particle because of
its quantum confinement effect which can dramatically increase
the effective band gap and give rise to near-infrared emission,
suggesting prospective applications in 1.3 and 1.5 ␮m optical
telecommunication devices [17–23].
Li et al. have prepared mercury chalcogenides HgE (E = S, Se, Te)
with spherical morphologies by conversion of HgO with chalco-
gen in ethylenediamine at room temperature [17]. Song et al. have
reported a sonochemical method of synthesizing nanocrystalline
HgTe in which ethylenediamine was used as solvent but mixed with
a complexing agent of 1-thioglycerol [18]. Wet chemical synthetic
routes have also been developed for colloidal HgTe nanoparticles
in aqueous solution at room temperature [19–21].
Recently, nanocrystalline chalcogenides of the late transition
metals and the main group elements have attracted much inter-
est due to their unique thermoelectric, semiconducting and optical
properties. Most studies in this area were focused on cadmium
and zinc compounds [1–3]. On the other hand, only a few publi-
cations have reported the synthesis of mercury sulfides, selenides
and tellurides, mostly due to the high toxicity of mercury. Neverthe-
less, mercury chalcogenides are promising materials for catalysts,
infrared detectors [4], light emitting diodes and electrochemical
cells [5,6]. In particular, nanocrystalline HgTe is one of the candi-
date materials in the area of photoconductive/photovoltaic devices,
IR detectors and IR emitters [7].
While II–VI semiconductor NCs such as CdSe have been prepared
routinely and extensively studied, the synthesis of mercury chalco-
genide QDs have still remained a challenge. Of these chalcogenides,
HgTe is of interest for applications in the optoelectronics indus-
try, since its emission covers the low-loss transmission windows
in silica telecommunication fibers, which lies at around 1300 nm
(
0.95 eV) and 1550 nm (0.79 eV) [8]. As a bulk material, HgTe exists
∗ Corresponding author at: Institute of Nano Science and Nano Technology,
University of Kashan, Kashan, P.O. Box 87317–51167, Islamic Republic of Iran.
Tel.: +98 361 5555 333; fax: +98 361 5552 930.
E-mail address: salavati@kashanu.ac.ir (M. Salavati-Niasari).
0
925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2010.03.135

1
22
M. Salavati-Niasari et al. / Journal of Alloys and Compounds 499 (2010) 121–125
2.
Experimental
2.1. Materials and physical measurements
All of reagents and solvents were purchased from Merck (pro-analysis) and
were dried using molecular sieves (Linde 4 Å). XRD patterns were recorded by a
Rigaku D-max C III, X-ray diffractometer using Ni-filtered Cu K␣ radiation. Scanning
electron microscopy (SEM) images were obtained on Philips XL-30ESEM equipped
with an energy dispersive X-ray (EDX). Transmission electron microscopy (TEM)
images were obtained on a Philips EM208 transmission electron microscope with
an accelerating voltage of 100 kV.
2.2. Nanostructure HgTe prepared by hydrothermal method
Hg(NO3)3·H2O and TeCl4 were used as the simple precursor in the hydrothermal
synthesis. The precursor with stoichiometric ratio of Hg:Te (1:1) was put into a
Teflon-lined autoclave. The autoclave was then filled with water up to 80% of its
volume. After adding sufficient KBH4 as the reductant, NaOH as base and PEG 20,000
◦
as capping agent, the autoclave was sealed immediately and heated to 180 C for the
synthesis reaction. After reaction for 12 h, the autoclave was cooled down to room
temperature naturally. The obtained precipitates were separated by centrifugation,
washed with deionized water followed by ethanol for three times, and dried at
◦
1
00 C under vacuum for 24 h. The structure and morphology of the HgTe powders
were characterized by XRD and TEM.
3
. Results and discussion
The reaction of mercury(II) nitrate with TeCl in presence of PEG
4
2
0,000 and KBH4 as described above resulted in the formation of
nanosized cubic HgTe [space group: F-43m (2 1 6)]. The particles
were crystalline, as determined by powder X-ray diffraction (XRD)
measurements shown in Fig. 1a. The wide-angle peaks indicate the
cubic phase and correspond to diffractions from the 1 1 1, 2 2 0, and
3
1 1 planes of bulk HgTe coloradoite. The peaks are broadened com-
pared to those of bulk HgTe, indicating the small particle size. The
crystallite size diameter (D) of the HgTe nanoparticles has been
calculated by Debye–Scherrer equation:
0
.9ꢀ
D =
ˇ cos ꢁ
where ␤-FWHM (full-width at half-maximum, or half-width) is in
radians and ꢁ is the position of the maximum of diffraction peak
and ꢀ is the X-ray wavelength (1.5406 Å for Cu K␣). The mean size
of the particles was estimated 34 nm (JCPDS 77-2014). No remark-
able diffractions of other phases such as tellurium, mercury or their
other compoundscan be foundin Fig. 1a, indicating that apureHgTe
phase has been formed after the synthesis for the samples.
Meanwhile, influence of capping agent, reductant sort, temper-
ature and time were investigated on the as-prepared nanostructure
HgTe (Fig. 1b–e). With exchange of capping agent from PEG 20,000
to CTAB (cetyltrimethylammoniumbromide) and reductant sort
from KBH4 to N H , particle size of 34–27 nm was decreased,
2
4
respectively (Fig. 1a and b). In other word, with increasing of time
from 12 to 24 h, particle size was increased from 27 to 35 nm,
respectively (Fig. 1b and c). At the same time, with decreasing of
◦
Fig. 1. XRD patterns of prepared HgTe in (a) 180 C and 12 h, at the presence of PEG
◦
temperature from 180 to 120 C, further peaks were observed that
20,000 as capping agent and KBH4 as reductant, (b) CTAB as capping agent and N2H4
as reductant, (c) CTAB as capping agent, N2H4 as reductant and 24 h and (d) CTAB as
capping agent, N2H4 as reductant, 24 h and 120 C.
exhibited impurity in nanostructure HgTe (showed with triangles
in pattern) (Fig. 1d). Obviously, the crystallinity of the as-prepared
HgTe gradually improved with increasing reaction temperature and
time. In general, the resultant particles became bigger with increas-
ing temperature and time.
◦
shape shape is preferential morphology along with agglomeration
of particles (Fig. 2c). Meanwhile, in presence of Zn as reductant,
particles are highly agglomerated (Fig. 2d).
The morphology and size of the as-synthesized products were
characterized by SEM and TEM. Fig. 2a and b depicts SEM and TEM
The strong reductant KBH and N H in combination with stir-
4
2
4
images of sample nanostructure HgTe in presence of KBH as reduc-
tant and PEG 20,000 as capping agent at 180 C and 12 h. From the
ring rapidly created a large number of nuclei and further growth
of the nuclei was limited. As a result, many small particles were
obtained. The reduction at the presence of Zn proceeds only two-
dimensionally, i.e., at the interface of Zn powder with the metal
cation solution. The rate of reduction is further limited by the mass
transport of the metal cation solution to the Zn surface. Therefore,
depletion of metal cations near the interface might occur. As a con-
4
◦
micrograph, it was observed that the nanostructure was slightly
agglomerated. Fig. 2c and d reveals reductant sort effect on mor-
phology of nanostructures in presence of PEG 20,000 as capping
agent. In this study, reductant plays the key role on morphology
of nanostructure HgTe. In presence of N H as reductant, the rod-
2
4

M. Salavati-Niasari et al. / Journal of Alloys and Compounds 499 (2010) 121–125
123
◦
Fig. 2. (a and b) SEM and TEM image of images of HgTe in presence of KBH4 as reductant and PEG 20,000 as capping agent at 180 C and (c and d) SEM images of HgTe in
presence of CTAB as capping agent and N2H4 and Zn as reductant, respectively.
sequence of the rate and surface area limitation, crystal growth is
favored over nucleus formation as the result of larger particles [24].
On the other hand, to reach ideal morphology, we prepared
nanostructure HgTe with various capping agents such as: CTAB
and SDBS (sodium dodecyl-benzene-sulfonate) in the presence of
tion of CTAB, rod-shape is preferential morphology; meanwhile,
utilization of SDBS as capping agent inclines agglomeration of
nanostructure and growing of particle. Experiments showed that
the morphology of the final product could be affected by Hg2+ ion
sources (Fig. 3c and d). Keeping the other experimental conditions
constant, however, SEM observations showed that the morpholo-
N H as reductant (Fig. 3a and b). Fig. 3a and b shows that, utiliza-
2
4
◦
2+
Fig. 3. SEM images of HgTe in presence of (a) CTAB and (b) SDBS as capping agent, in 180 C, 12 h and N2H4 as reductant and (c) HgCl2 and (d) HgSO4 as source of Hg in
presence of CTAB as capping agent 180 C, 12 h and N2H4 as reductant.
◦

1
24
M. Salavati-Niasari et al. / Journal of Alloys and Compounds 499 (2010) 121–125
◦
2+
◦
Fig. 4. TEM images of HgTe of (a) CTAB as capping agent, in 180 C, 12 h and N2H4 as reductant and (b) HgSO4 as source of Hg in presence of CTAB as capping agent 180 C,
1
2 h and N2H4 as reductant.
gies of the products were obviously different. When HgCl was used
ogy of nanostructure exchanged from rod-shape to shuck-like
(Fig. 5a). Meanwhile, with increasing reaction time from 12 to 24 h,
nanostructures showed dense agglomerate and particle size was
increased (Fig. 5b). Fig. 5c shows temperature effect on HgTe mor-
phology. With decreasing temperature from 180 to 120 C some
rod-shape nanostructures together with impurity were obtained
(Figs. 5b and 1d). Also, nanostructure HgTe was prepared at room
2
as Hg2+ ion source, some rod-shape nanostructures were replaced
by particles (Fig. 3c). When HgSO was used, many HgTe irregular
4
particles were produced (Fig. 3d).
◦
In Fig. 4, we illustrated TEM images of HgTe in presence of CTAB
as capping agent, N H as reductant (Fig. 4a) and HgSO as source
2
4
4
of Hg2+ (Fig. 4b).
With variation base from NaOH to NH3 with keeping the
other experimental conditions constant, we observed morphol-
temperature in presence of CTAB as capping agent and N H4
as reductant (Fig. 5d). At room temperature, rod-shape nanos-
2
◦
◦
◦
Fig. 5. SEM images of HgTe: (a) NH3 as base, 12 h and 180 C; (b) 24 h, 180 C; (c) 120 C, 12 h; and (d) room temperature, 12 h in presence of CTAB as capping agent and N2H4
as reductant.

M. Salavati-Niasari et al. / Journal of Alloys and Compounds 499 (2010) 121–125
125
Table 1
Characterization comparison of HgTe nanostructures with other similar works.
Method
Precursors
Size
Morphology
Ref.
Hydrothermal
Sonochemical
Sonochemical
Solution method
HgCl2, Na2TeO3
Diameter of 100–300 nm and length of up to 2–3 ␮m
Diameters of 15 nm and lengths of up to 200 nm
65 nm
2.3 nm
Nanorods
Nanorods
Nanoparticles
Nanocrystals
[25]
[18]
[26]
[27]
Hg(ClO4)2, tellurium powder
Hg(NO3)2, tellurium powder
HgO, Te powder
Acknowledgment
Authors are grateful to Council of Institute of Nano Science and
Nano Technology, University of Kashan and for providing financial
support to undertake this work.
References
[
[
[
1] C.B. Murray, D.J. Norris, M.G. Bawendi, J. Am. Chem. Soc. 115 (1993) 8706–
715.
2] K. Sooklal, B.S. Cullum, S.M. Angel, C.J. Murphy, J. Phys. Chem. 100 (1996)
551–4555.
3] M. Fromment, H. Cachet, H. Essaaidi, G. Maurin, R. Cortes, Pure Appl. Chem. 69
1997) 77–82.
8
4
(
[
[
4] G. Debias, Phys. Status Solid A 83 (1984) 269–278.
5] V.L. Colvin, M.C. Schlamp, A.P. Aliviastors, Nature 370 (1994) 354–357.
Fig. 6. EDX spectrum of the HgTe nanoparticles prepared in the presence of KBH4
as reductant and PEG 20,000 as capping agent at 180 C.
◦
[6] A. Hangfeldt, M. Gratzel, Chem. Rev. 95 (1995) 49–68.
[
[
7] S.S. Kale, C.D. Lockhande, Mater. Chem. Phys. 59 (1999) 242–246.
8] M.T. Harrison, S.V. Kershaw, M.G. Burt, A.L. Rogach, A. Kornowski, A. Eych-
müller, H. Weller, Pure Appl. Chem. 72 (2000) 295–307.
tructures are broken down and agglomerated similar to HgTe
bulk.
[9] Landolt-Börnstein, Numerical Data and Functional Relationships in Science and
Technology: New Series, vol. 17b: Semiconductors, Springer, Berlin, 1982.
10] A. Delin, T. Klüner, Phys. Rev. B 66 (2002) 035117–035124.
11] N.G. Wright, M.I. McMahon, R.J. Nelmes, Phys. Rev. B 48 (1993) 13111–
13114.
12] V. Daumer, L. Golombek, M. Gbordzoe, E.G. Novik, V. Hock, C.R. Becker, H.
Buhmann, L.W. Molenkamp, Appl. Phys. Lett. 83 (2003) 1376–1378.
13] T. Nath, S. Roy, P. Saxena, P.C. Mathur, J. Appl. Phys. 67 (1990) 826–831.
[14] M.L. Steigerwald, C.R. Sprinkle, J. Am. Chem. Soc. 109 (1987) 7200–7201.
[15] R. Korenstein, W.E. Hoke, P.J. Lemonias, J. Appl. Phys. 62 (1987) 4929–4931.
16] S.K. Ghandhi, I.B. Bhat, H. Ehsani, D. Nucciarone, G. Miller, Appl. Phys. Lett. 55
1989) 137–139.
17] Y.D. Li, Y. Ding, H.W. Liao, Y.T. Qian, J. Phys. Chem. Solids 60 (1999) 965–968.
The EDX analysis of the product, prepared HgTe in the presence
[
[
◦
of KBH as reductant and PEG 20,000 as capping agent at 180 C, is
4
shown in Fig. 6, in which only Hg and Te-related peaks are present
with the atomic ratio close to 1 [18]. The EDX spectra for other
samples were similar as with the spectra shown in Fig. 6.
In comparison to other similar works that illustrated in Table 1,
our method is simple and has low cost and scale-up route. Also,
we have used nontoxic precursors and solvent. In this route, we
apply various capping agents and sort of reductants which are rare
in preparation of nanostructure HgTe and rod-shape morphology
was obtained. The sizes of nanostructure HgTe seem convenient
than similar works.
[
[
[
(
[
[18] H. Song, K. Cho, H. Kim, J.S. Lee, B. Min, H.S. Kim, S.W. Kim, T. Noh, S. Kim, J.
Cryst. Growth 269 (2004) 317–323.
19] M.T. Harrrison, S.V. Kershaw, A.L. Rogach, A. Kornowski, A. Eychmüller, H.
Weller, Adv. Mater. 12 (2000) 123–125.
[
[
[
20] M. Green, G. Wakefield, P.J. Dobson, J. Mater. Chem. 13 (2003) 1076–1078.
21] H. Kim, K. Cho, H. Song, B. Min, J.-S. Lee, G.-T. Kim, S. Kim, Appl. Phys. Lett. 83
4
. Conclusion
(
2003) 4619–4621.
[
[
[
22] P. Olk, B.C. Buchler, V. Sandoghdar, N. Gaponik, A. Eychmüller, A.L. Rogach1,
Appl. Phys. Lett. 84 (2004) 4732–4734.
23] M. Kazes, D.Y. Lewis, Y. Ebenstein, T. Mokari, U. Banin, Adv. Mater. 14 (2002)
In summary, this work has demonstrated a new approach for
the controllable growth of HgTe rod-shape via exchange reduc-
tant and capping agent. This route to HgTe nanostructure is simple,
convenient, effective, and holds potential for large-scale synthesis
needed for commercial applications. Most important of all, the new
approach can yield rod-shape morphology of HgTe directly with-
out the mechanical crushing and the sieving needed for a solidified
melt which may exhibit enhanced near-infrared properties.
317–321.
24] A. Trifonova, M. Wachtler, M.R. Wagner, H. Schroettner, C. Mitterbauer, F.
Hofer, K.-C. Möller, M. Winter, J.O. Besenhard, Solid State Ionics 168 (2004) 51–
59.
[
[
25] A.-M. Qin, Y.-P. Fang, C.-Y. Su, Mater. Lett. 61 (2007) 126–129.
26] M. Kristl, M. Drofenik, Ultrasonics Sonochem 15 (2008) 695–699.
[27] L.S. Li, H. Wang, Y. Liu, S. Lou, Y. Wang, Z. Du, J. Colloid Interface Sci. 308 (2007)
54–257.
2