Synthesis of In/InP core-shell nanospheres and their transformation into InP hollow nanospheres

Article abstract of DOI:10.1016/j.jallcom.2008.04.076

Polycrystalline InP hollow nanospheres with an average size of 520 nm and shell thickness of about 110 nm were obtained by acid treatment of In/InP core-shell nanospheres which were solvothermally synthesized in ethanolamine-water binary solution at 180 °

Full text of DOI:10.1016/j.jallcom.2008.04.076

Journal of Alloys and Compounds 472 (2009) 59–64
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Synthesis of In/InP core–shell nanospheres and their transformation into InP
hollow nanospheres
∗
Keyan Bao, Liang Shi, Shuzhen Liu, Shenglin Xiong, Xiaobo Hu, Yitai Qian
Hefei National Laboratory for Physical Sciences at Microscale and Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Polycrystalline InP hollow nanospheres with an average size of 520 nm and shell thickness of about 110 nm
were obtained by acid treatment of In/InP core–shell nanospheres which were solvothermally synthesized
in ethanolamine–water binary solution at 180 C. The sizes of InP hollow nanospheres increased with the
Received 10 March 2008
Received in revised form 21 April 2008
Accepted 22 April 2008
◦
increasing reactants quantities. Meanwhile the shell thicknesses of InP hollow nanospheres could be
controlled by varying the quantity of yellow phosphorus. The process of In/InP core–shell nanospheres
transforming into InP hollow nanospheres was also investigated. The InP products prepared in our experi-
ments can emit blue light, which is different from previous reports and increases the potential application
of InP nanomaterial.
Available online 3 June 2008
Keywords:
Nanostructures
Crystal growth
X-ray diffraction
Luminescence
©
2008 Elsevier B.V. All rights reserved.
1. Introduction
using InCl ·4H O, yellow phosphorus and NaBH as reactants and
3
2
4
employing C17
H CO K as surfactant in aqueous ammonia [17].
35 2
InP, an important III–V semiconductor with a direct band gap
of 1.35 eV at room temperature, has a wide range of applications
in electronic and optoelectronic devices such as high-speed logic
circuits, millimetre-wave sources and amplifiers, and optical fibre
communications [1–3]. Many reports showed that the shape, size
and crystalline structure of semiconductors could greatly affect
their physical and chemical properties [4,5]. Recently, hollow inor-
ganicnanostructureshave attracted considerableattentionbecause
of their promising applications, for example, nanoscale chemical
reactors, efficient catalysts, and photonic building blocks [6,7].
A series of high temperature synthetic methods such as laser-
assisted catalytic growth (LCG) [8–10], vapor–liquid–solid (VLS)
However, the synthesis of InP 3D nanostructures such as hollow
nanospheres, and flowerlike architectures has rarely been reported.
Traditionally, the classic approaches for preparation of hollow
spheres have focused on various sacrificial templates, includ-
ing polystyrene spheres [18,19], silica spheres [20], resin spheres
[21,22], vesicles [23] and liquid droplets [24,25]. Recently, some
III–V semiconductors have also been prepared using the tem-
plate method. For instance, Ga O3 and GaN hollow spheres
2
were obtained by using carbon spheres as templates [26]; InP
honeycomb-like macroporous frameworks were fabricated from
the reaction between InCl ·4H O and yellow phosphorus employ-
3
2
ing Au as template in ethylenediamine solvent [27].
[
11] and thermal chemical process [12,13] were used to prepare InP
In this study, InP hollow nanospheres were obtained by acid
treatment of In/InP core–shell nanospheres. The In/InP core–shell
nanospheres were prepared in ethanolamine–water binary solu-
tion at 180 C for 12 h. InP hollow nanospheres with different
diameters and shell thicknesses could be prepared by varying the
nanostructures. And most of them are one-dimensional (1D) nanos-
tructures. Meanwhile, InP nanostructures can also be synthesized
in solution systems. For instance, InP nanocrystals were obtained
under ultrasonic irradiation from the reaction of InCl ·4H O, yellow
◦
3
2
phosphorus and KBH4 in a mixed solvents of ethanol and ben-
zene [14], monodispersed InP quantum dots were synthesized via
quantities of InCl ·4H O and P . Furthermore, solid nanospheres
3
2
4
and flowerlike architectures were also synthesized by controlling
the reaction conditions.
the reaction between In O3 and yellow phosphorus in alkali aque-
2
ous [15], InP wires were prepared from the reaction of In O3 and
2
yellow phosphorus with CTAB as surfactant in aqueous solution
2. Experimental
[
16], InP nanocrystals with rod-like morphologies were obtained
2.1. Synthesis of In/InP core–shell composite
In a typical synthesis, 2 mmol of InCl3·4H2O was dissolved in 5 mL of distilled
∗ Corresponding author. Tel.: +86 551 3601589; fax: +86 551 3607402.
E-mail address: bkeyan@mail.ustc.edu.cn (Y. Qian).
water, and 40 mL of ethanolamine was added under stirring. Then 8 mmol of NaBH4
and 10 mmol of yellow phosphorus (P4) were added into the solution. The mix-
0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2008.04.076

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K. Bao et al. / Journal of Alloys and Compounds 472 (2009) 59–64
standard data (JCPDS PDF No. 32-0452, a = 5.869 A˚ ). The two small
◦
diffraction peaks marked with stars at 32.9 and 39.4 can be indexed
as (1 0 1) and (1 1 0) diffractions of metallic In (JCPDS PDF No.
0
5–0642, a = 3.251 A˚ ). This indicates that the sample is a mixture of
InP and metallic In. Fig. 1b is the XRD pattern of the above product
treated by 0.3 M HCl for 20 h. It is obvious that after acid treatment
only InP phase exists in the product. Fig. 1c and d shows the XRD
patterns of InP solid nanospheres and InP flowerlike architectures.
All the reflection peaks can be indexed as zinc blende phase of InP.
Fig. 2a shows the field-emission scanning electron microscopy
(FESEM) image of the sample synthesized via the reaction between
2
mmol InCl ·4H O of and 10 mmol of P with VEA : VH2O = 8 : 1. It
3
2
4
is found that the sample is composed of nanospheres with sizes in
the range of 500–550 nm and the surfaces of the nanospheres con-
structed out of small nanoparticles with an average size of 15 nm.
Fig. 2b is the transmission electron microscopy (TEM) image of
the sample, revealing that the sample consists of relatively uni-
form solid nanospheres. The corresponding selected-area electron
diffraction (SAED) pattern (Fig. 2b, inset) indicates that the sample
is polycrystalline and the diffraction rings from inside to outside
can be indexed to (1 1 1), (2 2 0) and (3 1 1) diffractions of InP. How-
ever, the energy dispersive spectrometer (EDS) spectrum (Fig. 2c)
reveals the presence of excess In in the nanospheres (In/P atomic
ratio of 1.68:1; the signals of Cu, C and Cr come from the copper grid
used for the HRTEM observation). And the XRD pattern (Fig. 1a) also
suggests that the product consists of InP and metallic In. Namely,
the product is In/InP composite.
Fig. 2d shows the FESEM image of the product obtained from
acid treatment of In/InP composite for 20 h. From Fig. 2d many
nanospheres and their inner cavities can be observed clearly, con-
firming the hollow structure of the as-obtained product. The TEM
image (Fig. 2e) also reveals that the as-obtained product is hol-
low nanospheres with sizes in the range of 500–600 nm and shell
thickness of about 100 nm. The corresponding SAED pattern (Fig. 2e,
inset) indicates that the sample is polycrystalline and the diffrac-
tion rings from inside to outside can be indexed as (1 1 1), (2 2 0)
and (3 1 1) diffractions of InP. The EDS spectrum (Fig. 2f) reveals
the presence of In and P elements at an In/P atomic ratio of 1.03:1
Fig. 1. XRD patterns of: (a) In/InP core–shell composite synthesized from the reac-
tion between 2 mmol of InCl3·4H2O and 10 mmol of P4 with VEA : VH2O = 8 : 1. (*the
excess metallic In). (b) InP hollow nanospheres obtained by acid treatment of In/InP
core–shell composite at ambient temperature for 20 h. (c) InP solid nanospheres
prepared by using 2 mmol of InCl3·4H2O and 25 mmol of P4 as reaction materials
with VEA : VH O = 8 : 1. (d) InP flowerlike architectures obtained via the reaction
2
between 2 mmol of InCl3·4H2O and 25 mmol of P4 with VEA : VH O = 2 : 7.
2
(the signals of Cu, C and Cr come from the copper grid used for
the HRTEM observation). The XRD pattern also confirms that only
InP phase exists in the product (Fig. 1b). That is to say, the prod-
uct is InP hollow nanospheres. Now, it is clear that the product
was In/InP core–shell nanospheres and InP hollow nanospheres
could be obtained by acid treatment of In/InP core–shell
nanospheres.
◦
ture was transferred into a 50 ml Teflon-sealed autoclave and maintained at 180
C
for 12 h, and then cooled to room temperature naturally. The product was filtered
and washed with distilled water and absolute alcohol several times, finally dried in
◦
vacuum at 60 C for 2 h.
2.2. Synthesis of InP hollow nanospheres
In addition, InP hollow nanospheres prepared under different
reaction conditions were also studied. It was found that the reactant
quantities had a dramatic effect on the diameters and shell thick-
nesses of InP hollow nanospheres. For example, when the quantities
of InCl ·4H O and P were increased to 4 mmol and 16 mmol,
InP hollow nanospheres were obtained by treating In/InP core–shell compos-
ite with dilute HCl (0.3 M) for 20 h at ambient temperature. The final product was
washed with distilled water and absolute alcohol several times, and then dried in
◦
vacuum at 60 C for 2 h.
3
2
4
2
.3. Characterization
respectively, InP hollow nanospheres with diameters in the range
of 700–900 nm and shell thickness of about 90 nm were prepared
Powder X-ray diffraction (XRD) measurements were carried out with a Philips
X’Pert diffractmeter (Cu K␣ ꢀ = 1.541874 A˚ ; Nickel filter; 40 kV, 40 mA). FESEM
images were taken on a JEOL JSM-6300F SEM. HRTEM images were performed on
JEOL JEM-2010 microscope operating at 200 kV. PL measurements were taken at
room temperature using a Fluorolog-3-TAU spectrofluorimeter (Jobin Yvon Com-
pany of France).
(
Fig. 3a). As shown in Fig. 3b, when the quantities of InCl ·4H O
3
2
and P were decreased to 1 mmol and 7 mmol respectively, small
4
InP hollow nanospheres with an average size of 430 nm and wall
thicknesses of 80–90 nm were obtained. Meanwhile, the shell thick-
nessesofInPhollownanospheres could becontrolled byvarying the
quantity of yellow phosphorus when the quantity of InCl ·4H O
3
2
3
. Results and discussion
was fixed at 2 mmol. For instance, InP hollow nanospheres with
diameters in the range of 500–600 nm and shell thickness of about
70 nm (Fig. 3c) were synthesized with a low quantity of yellow
phosphorus (8 mmol P4). When the quantity of yellow phosphorus
was increased to 13 mmol, InP hollow nanospheres with an average
size of 560 nm and wall thickness of about 150 nm were prepared
(Fig. 3d).
Fig. 1a shows the X-ray diffraction (XRD) pattern of the as-
prepared product synthesized from the reaction of 2 mmol of
InCl ·4H O and 10 mmol of P with VEA : VH2O = 8 : 1. The main
3
2
4
reflection peaks can be indexed as zinc blende phase of InP with
lattice constant a = 5.873 A˚ , which is in good agreement with the

K. Bao et al. / Journal of Alloys and Compounds 472 (2009) 59–64
61
Fig. 2. (a) FESEM image; (b) TEM image and corresponding SAED pattern; (c) EDS spectrum (In:P = 1.68:1) of In/InP core–shell nanospheres. (d) FESEM image; (e) TEM image
and corresponding SAED pattern; (f) EDS spectrum (In:P = 1.03:1) of InP hollow nanospheres prepared by treatment of In/InP core–shell composite with dilute HCl at ambient
temperature for 20 h.
Interestingly, InP solid spheres were obtained without acid
treatment when the quantity of yellow phosphorus was increased
to 25 mmol (InCl ·4H O: 2 mmol). The corresponding XRD patterns
The process of In/InP core–shell nanospheres transformation
into InP hollow nanospheres was also investigated. Fig. 5a–c shows
the TEM images of the products which were obtained via acid treat-
ment of In/InP core–shell nanospheres for 2, 10 and 20 h. Fig. 5a
reveals that dilute HCl has slightly corroded the product. As shown
in Fig. 5b, more and more metallic In was dissolved and some
interstitial spaces appeared when the acid treatment time was
prolonged to 10 h. But there was still some metallic In remain-
ing in the centres of the nanospheres. When the treatment time
was increased to 20 h, the obvious contrast between the dark edges
and the relatively bright centres verified their hollow structures
(Fig. 5c).
3
2
(
Fig. 1c and d) confirm that the products are pure InP. Two kinds
of morphologies of InP were obtained by controlling the volume
ratio of EA/H O. Fig. 4a and b shows the FESEM and TEM images
2
of the sample synthesized via the reaction between 2 mmol of
InCl ·4H O and 25 mmol of P with VEA : VH2O = 8 : 1. It is found
3
2
4
that the sample consists of solid nanospheres with sizes in the
range of 500–600 nm and the surfaces of the solid nanospheres
constructed out of small nanoparticles about 12 nm. InP flower-
like architectures were synthesized when the ratio of EA/H O was
2
decreased to 7:2. As shown in Fig. 4c, the sample is composed of a
large quantity of flowerlike patterns with an average size of about
Based on the above investigations, the formation process of InP
hollow nanospheres can be proposed as follows. At the first step,
3+
1
mm and the flowers are composed of nanodollops with an average
In was reduced to metallic In by NaBH . The reaction temperature
4
◦ ◦
(180 C) was higher than the melting points of In and P (157 C and
4
size of 160 nm. The flowerlike structure of the product was further
investigated by SAED and HRTEM. Fig. 4d exhibits the TEM image
of a single nanodollop about 150 nm in size. The inset of Fig. 4e
shows the SAED pattern of the nanodollop, which indicates that
the nanodollop is single crystal. The high-resolution transmission
electron microscopy (HRTEM) image in Fig. 4f also indicates the
◦
◦
44.1 C, respectively), but lower than their boiling points (2080 C
◦
and 280 C, respectively). A little amount of InP was formed via the
reaction of the reduced liquid metallic In and liquid P . The newly
4
formed InP coated on the outer surfaces of aggregated metallic In
particles. When P4 was exhausted, In/InP core–shell structure was
formed. The reaction can be suggests as follows:
good crystallinity of the nanodollop. The crystal planes have lattice
spacing of about 2.06 A˚ corresponding to (2 2 0) plane of the InP
crystal.
2InCl + 6NaBH → 2In + 6NaCl + 6BH + 3H
3
4
3
2

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K. Bao et al. / Journal of Alloys and Compounds 472 (2009) 59–64
Fig. 3. (a–d) SEM images of InP hollow nanospheres prepared with VEA : VH2O = 8 : 1 and different quantities of InCl3·4H2O and P4 (mmol): (a) 4 and 16; (b) 1 and 6; (c) 2
and 8; (d) 2 and 13.
flowerlike architectures were measured. InP hollow nanospheres
4
In + P → 4InP
show an emission band at 433 nm (Fig. 6a). InP solid nanospheres
exhibit an emission peak near 432 nm and flowerlike architec-
tures reveal an emission peak at 412 nm, as shown in Fig. 6b and
c, respectively. These peaks indicate that the samples have pro-
nounced blueshift in contrast to the bulk InP (direct band gap
4
When removing the unreacted In by treatment with dilute HCl,
the inner In disappeared and InP hollow nanospheres were formed.
The growth process of InP hollow nanospheres is simply described
in Scheme 1.
918 nm, 1.35 eV, 300 K) [28]. One possible cause for this blueshift
is the compressive stress that results from lattice distortion of
these ethanolamine-capping nanoparticles. The exact mechanism
of luminescence is not clear at present and further study is under
way. Previous reports had shown that InP nanostructures usually
emitted red light [13,16,29,30]. However, the InP products prepared
4
. Optical property
The room-temperature photoluminescence (PL) spectra of the
as-synthesized InP hollow nanospheres, solid nanospheres and
Fig. 4. (a) SEM and (b) TEM images of InP solid nanospheres prepared with VEA : VH2O = 8 : 1. (c) SEM; (d) TEM and (e) HRTEM images of InP flowerlike architectures
synthesized with VEA : VH2O = 7 : 2.

K. Bao et al. / Journal of Alloys and Compounds 472 (2009) 59–64
63
Fig. 5. TEM images of the product in the formation of InP hollow nanospheres by treatment of In/InP core–shell composite with dilute HCl under different reaction time (h):
a) 2; (b) 10; (c) 20.
(
Scheme 1. Schematic illustration of the formation process of InP hollow nanosphere. (A) A In nanoparticle was formed in the initial solvothermal process. (B) The metallic
In reacted with P4 and formed In/InP core–shell structure. (C) A final InP hollow nanosphere was obtained by treatment In/InP core–shell composite with 0.3 M HCl.
InP hollow nanospheres could be controlled by varying the quanti-
ties of InCl ·4H O and P . When yellow phosphorus was abundant,
3
2
4
InP solid spheres were prepared without acid treatment. InP solid
nanospheres and flowerlike architectures could be obtained by
changing the volume ratio of EA/H O. The optical properties of
2
InP hollow nanospheres, solid nanospheres and flowerlike archi-
tectures were also investigated by the photoluminescence spectra.
Acknowledgements
The financial support of this work, by National Natural Science
Foundation of China (No. 20431020), the 973 Project of China (No.
2
005CB623601) and the China Postdoctoral Science Foundation
(No. 20070420124), is gratefully acknowledged.
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