Synthesis and characterization of In2S3 nanoparticles

Article abstract of DOI:10.1016/j.jallcom.2008.04.047

In this paper, we report a novel solution route to prepare In₂S₃ nanoparticles through directly dispersing melted indium in a sulfur-dissolved solvent. X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and electr

Full text of DOI:10.1016/j.jallcom.2008.04.047

Journal of Alloys and Compounds 472 (2009) 325–327
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Synthesis and characterization of In2S3 nanoparticles
Guangxiu Caoa, Yanbao Zhaob,∗, Zhishen Wub
a Department of Chemistry, Shangqiu Normal College, Henan Shangqiu 476000, China
b Lab for Special Functional Materials, Henan University, Henan Kaifeng 475004, China
a r t i c l e i n f o
a b s t r a c t
Article history:
In this paper, we report a novel solution route to prepare In2S3 nanoparticles through directly dispers-
ing melted indium in a sulfur-dissolved solvent. X-ray powder diffraction (XRD), transmission electron
microscopy (TEM) and electron diffraction (ED) show the formation of In2S3 nanoparticles possessing
tetragonal structure with an average particle diameter of 30 nm. The as-prepared In2S3 nanoparticles
display strong blue–UV emission, promising for applications in optical devices.
Received 3 September 2007
Received in revised form 14 April 2008
Accepted 16 April 2008
Available online 27 May 2008
© 2008 Elsevier B.V. All rights reserved.
Keywords:
Preparation
In2S3 nanoparticles
Characterization
Optical property
Mechanism
1. Introduction
2. Experimental
2.1. Chemicals and preparation
Over the past decades, there has been increasing interest in
III–VI materials due to their unique physical and chemical proper-
ties and potential applications in diverse areas [1]. Tetragonal In2S3,
an III–VI chalcogenide, is an n-type semiconductor with a band
gap of 2.00–2.20 eV, which has already inspired applications in
optoelectronic, photovoltaic industries and solar cell devices [2,3].
Several physical and chemical methods have been developed to fab-
ricate In2S3 with different morphologies [4,5]. For instance, a direct
reaction of the elements in a quartz container at a high tempera-
ture [6], chemical deposition [7], heat treatment of In2O3 in H2S at
elevated temperatures [8], the metathesis reaction of InCl3 and Li2S
[9], and wet chemical methods [10–12]. In2S3 nanoparticles repre-
sent an important class of materials that are potentially useful for
a wide range of applications such as delivery vehicle systems, pho-
tonic crystals, fillers, and catalysts [13]. However, compared with
In2S3 films and powder, much less work has been performed on
In2S3 nanoparticles [14].
In previous papers, we have successfully produced metal
nanoparticles by solution dispersion route in which the melting
metal can be dispersed into nanosized droplets and converted into
metal nanoparticles when the temperature is reduced to room
temperature [15,16]. In this paper, we report a modified solution
dispersion route to prepare In2S3 nanoparticles through one-step
elemental reactions in paraffin oil.
All materials were used without further purification. Indium granules (99.95%),
sulfur powder (99.9%) and paraffin oil were analytical pure reagents from Shanghai
Chemical Co., Shaoyang Chemical Co., and Luoyang Chemical Co., respectively. In a
typical synthesis, 0.7 g commercial indium granules and 0.3 g sulfur powder were
added to 40 mL of paraffin oil in a flask, and the system was sealed and stirred above
180 ◦C for at least 10 h. Then, the supernatant was cooled, centrifuged, washed with
chloroform, and dried to get gray–black product.
2.2. Characterization
X-ray powder diffraction (XRD) was performed on an X’Pert Philips diffrac-
tometer equipped with Ni-filtered Cu K␣ radiation (ꢀ = 1.5418 A) and operating at
˚
40 kV and 40 mA. Transmission electron microscopy (TEM) was carried out on a
JEOL JEM-2010Ex transmission electron microscope, with a tungsten filament at an
acceleration voltage of 200 kV. Differential thermal analysis and thermogravimetry
(DTA and TG) were conducted on the powders in the 30–500 ◦C temperature range,
with an Exstar 6000 thermal system, a heating rate of 10 ◦C/min and in airflow.
X-ray photoelectron spectra (XPS) were collected on an axis of ultra X-ray photo-
electron spectrometer, and the XPS analyses were corrected with reference to C 1s
(284.6 eV). The room-temperature photoluminescence (PL) spectrum was measured
on a Spex F-212 fluorescence spectrophotometer with a Xe lamp upon excitation at
300 nm.
3. Results and discussion
3.1. XRD studies
Fig. 1 shows an XRD pattern of the In2S3 samples prepared
by solution dispersion. The XRD pattern exhibits multiple intense
peaks that are clearly distinguishable. All the reflection peaks can be
∗
Corresponding author.
E-mail address: zhaoyb902@henu.edu.cn (Y. Zhao).
0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2008.04.047

326
G. Cao et al. / Journal of Alloys and Compounds 472 (2009) 325–327
Fig. 3. TG/DTA curves of as-prepared In2S3 sample.
Fig. 1. XRD pattern of In2S3 nanoparticles prepared.
sample. The ED result is consistent with the XRD results presented
above.
indexed to the tetragonal In2S3, and the peak positions are in good
agreement with the known data (JCPDS: 33–1375). The refraction
peaks represent different crystal planes, which are assigned to the
crystal planes of [2 0 0], [2 1 3], [2 0 6], [2 2 0], [3 1 8], and [4 0 0] of
crystalline In2S3, respectively, implying the formation of tetragonal
In2S3.
3.3. Thermal analysis
The thermal behavior of as-obtained product was investigated
by DTA and TG in airflow. Fig. 3 gives the DTA/TG curves of as-
obtained In2S3 product. It can be seen that the sample shows two
distinct weight-loss steps in the temperature range of 30–500 ◦C
on the TG curve. The first weight-loss process taking place below
100 ◦C can be attributed to the desorption of small molecules from
the sample powder. The second mass loss (above 250 ◦C) might be
assigned to the further releasing of solvent molecules or organic
residuals in the samples. On the DTA curve, the product does not
show the characteristic melting peak of metal In at 156 ◦C, which
indicates that metal In is completely converted into indium sulfide.
3.2. TEM and ED studies
The morphology of the products was further examined by TEM.
Fig. 2 displays a typical TEM image of as-prepared indium sulfide. It
can be seen that the particles present broad size distribution with
the average particle diameter of 30 nm. The large size distribution is
naturally caused by the broad size distribution of the liquid indium
droplets formed by stirring effect. Most particles appear to be nearly
spherical shape. The corresponding electron diffraction (ED) pat-
tern (inset) taken from a single In2S3 particle consists of regular
diffraction spots, which reveals the single crystalline nature of the
3.4. XPS analysis
Further evidence for the quality and composition of the sam-
ples was obtained by the XPS of the products. The binding energies
obtained in the XPS analysis were corrected for specimen charging
by referencing the C 1s to 284.6 eV. The In 3d core level spectrum
(Fig. 4a) shows the observed value of the binding energies for In
3d5/2 (444.8 eV) are in good agreement with those observed in
CdIn2S4, which is indicative of indium as trivalent In3+ ions. The
S2p spectrum (Fig. 4b) appears a broad peak, which indicates that
the particle surface sulfur might exist in form of S2− (161.8 eV) and
element S (163.8 eV). The contents of In and S are quantified by In
3d and S 2p peak areas, and a molar ratio of 1:1.52 for In:S is given.
Thus, the XPS results further prove that the sample is composed of
In2S3.
3.5. Proposed the mechanism for formation of In2S3 nanoparticles
According to the above analysis, the formation mechanism of
In2S3 nanoparticles might be involving the dispersion of melting
indium droplets, surface sulfuration of indium droplets, the dif-
fusion of sulfur from the droplet surface to the inner, as well as
solvent and sulfur adsorption at the droplet surface. A possible
pathway for the formation of In2S3 nanoparticles might be as below.
First, large indium droplets are dispersed into small droplets in sol-
vent by stirring force; then, the fresh surface of indium droplet
forms indium sulfide layer through reaction with sulfur dissolved
in solvent, which should prevent the smaller droplets from coagu-
lating, and the indium sulfide layer can adsorb efficiently solvent
molecules to stabilize the droplets in solvent. With the presence of
Fig. 2. TEM image and ED pattern (inset) of the as-obtained In2S3.

G. Cao et al. / Journal of Alloys and Compounds 472 (2009) 325–327
327
Fig. 4. XPS spectra of the In2S3 samples: (a) In 3d peak; and (b) S 2p peak.
[17]. In addition, the possibility of In2O3 presence should also favor
the existence of surface defect sites. The very broad PL background
signal seems to support this fact. The strong blue–UV emission also
suggests that the In2S3 nanoparticles have potential to be a blue
and a UV light emitter.
4. Conclusion
The In2S3 nanoparticles were prepared from metal indium and
elemental sulfur via the solution dispersion, which might be suit-
able for many low melting point metals. The product through this
technique is cheaper, and the surface properties of nanoparticles
can be greatly modified by changing the composition of the sol-
vent. The as-prepared In2S3 nanoparticles appear to be close to a
spherical shape and have a good crystalline. The obtained In2S3
nanoparticles show strong blue–UV emission, promising for appli-
cations in optical devices.
Fig. 5. PL spectrum of as-prepared In2S3 nanoparticles.
Acknowledgements
an indium sulfide layer, indium droplets should be further crushed
into nanosized droplets. In addition, the indium sulfide layer should
adsorb sulfur from solvent, which can diffuse to the inner droplet
and provide the sulfur source required for the sulfuration of inner
indium, resulting in the formation of In2S3 nanoparticles.
This work was supported by National Science Foundation of
China (NSFC) (No. 20671029) and Excellent Youth Foundation of
Henan Province (No. 0612002900).
References
3.6. Optical properties
[1] P.M. Sirimanne, N. Sonoyama, T. Sakata, Chem. Phys. Lett. 350 (2001) 211.
[2] R. Nomura, S. Inazawa, K. Kanaya, H. Matsuda, Appl. Organomet. Chem. 3 (1989)
195.
[3] E. Dalas, L. Kobotiatis, J. Mater. Sci. 28 (1993) 5456.
[4] M.M. El-Nahass, B.A. Khalifa, H.S. Soliman, M.A.M. Seyam, Thin Solid Films 515
(2006) 1796.
[5] Y. Xiong, Y. Xie, G. Du, X. Tian, Y. Qian, J. Solid State Chem. 166 (2002) 336.
[6] N. Barreau, S. Marsillac, J.C. Bernede, Vacuum 56 (2000) 101.
[7] M.G. Sandoval-Paz, M. Sotelo-Lerma, J.J. Valenzuela-Jauregui, M. Flores-Acosta,
R. Ramırez-Bon, Thin Solid Films 472 (2005) 5.
[8] P.M. Sirimanne, S. Shiozaki, N. Sonoyama, T. Sakata, Sol. Energy Mater. Sol. Cells
62 (2000) 247.
Fig. 5 shows the PL emission spectrum of the In2S3 nanoparti-
cles dissolved in chloroform. The PL feature of In2S3 nanoparticles
shows two strong and broad emission bands centered at 470 nm
(blue emission) and 435 nm (UV emission), with two shoulders at
415 and 390 nm, respectively, which obviously reveals their blue
shift compared with the reported data of 620.6 nm for In2S3 bulk
materials. However, the Bohr radius of the excitation for In2S3 was
known to be ∼34 nm [14], hence, the UV emission may also be
attributed to quantum-confined effects of In2S3 nanoparticles. Gen-
erally, the blue luminescence emission is mainly attributed to the
existence of sulfur vacancies. These sulfur vacancies generally act
as deep defect donors in semiconductors and would induce the for-
mation of new energy levels in the band gap. The blue emission thus
results from the radioactive recombination of a photoexcited hole
with an electron occupying the sulfur vacancies. Since the nanopar-
ticle sample contains a distribution of different sized particles, the
larger particles that have smaller band gaps absorb and emit at
longer wavelengths relative to smaller particles in the distribution
[9] J.C. Fitzmaurice, I.P. Parkin, Main Group Met. Chem. 17 (1994) 481.
[10] Y. Liu, M. Zhang, Y. Gao, R. Zhang, Y. Qian, Mater. Chem. Phys. 101 (2007)
362.
[11] Z.P. Ai, Opt. Mater. 24 (2003) 589.
[12] P.N. Kumta, P.P. Phule, S.H. Risbud, Mater. Lett. 5 (1987) 401.
[13] Y.R. Ma, L.M. Qi, J.M. Ma, H.M. Cheng, Langmuir 19 (2003) 4040.
[14] W. Chen, J.O. Bovin, A.G. Joly, S. Wang, F. Su, G. Li, J. Phys. Chem. B 108 (2004)
11927.
[15] Y.B. Zhao, Z.J. Zhang, H.X. Dang, J. Phys. Chem. B 107 (2003) 7574.
[16] Y.B. Zhao, Z.J. Zhang, H.X. Dang, Mater. Sci. Eng. A359 (2003) 405.
[17] W. Hoheisel, V.L. Colvin, C.S. Johnson, A.P. Alivisatos, J. Chem. Phys. 101 (1994)
8455.