Fabrication and SERS properties of Ag/Cu2S composite micro-nanostructures over Cu foil

Article abstract of DOI:10.1016/j.saa.2011.04.050

A new kind of Ag/Cu₂S composite micro/nanostructures has been prepared via a convenient galvanic reduction method. SEM images of these micro/nanostructures showed that Ag nanoparticles with the size of around 50-100 nm were well deposited on the surface of Cu₂S micro/nanostructures. The SEM images also indicated that the Ag nanoparticles were preferentially grown on the big polygonal Cu₂S microstructures, which could be explained by a localization of the electrons on the surface of the polygonal Cu₂S microstructures after the electron transfer step. Owing to the introduction of Ag nanoparticles on the surface of Cu₂S micro/nanostructures, the resulting Ag/Cu₂S composite micro-nanostructures could be used as a versatile substrate for surface enhanced Raman scattering.

Full text of DOI:10.1016/j.saa.2011.04.050

Spectrochimica Acta Part A 79 (2011) 1247–1250
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Fabrication and SERS properties of Ag/Cu2S composite micro–nanostructures
over Cu foil
Wei Song, Jinjie Wang, Zhu Mao, Weiqing Xu, Bing Zhao∗
State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Qianjin Street 2699, Changchun 130012, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new kind of Ag/Cu2S composite micro/nanostructures has been prepared via a convenient galvanic
reduction method. SEM images of these micro/nanostructures showed that Ag nanoparticles with the
size of around 50–100 nm were well deposited on the surface of Cu2S micro/nanostructures. The SEM
images also indicated that the Ag nanoparticles were preferentially grown on the big polygonal Cu2S
microstructures, which could be explained by a localization of the electrons on the surface of the polygonal
Cu2S microstructures after the electron transfer step. Owing to the introduction of Ag nanoparticles on
the surface of Cu2S micro/nanostructures, the resulting Ag/Cu2S composite micro–nanostructures could
be used as a versatile substrate for surface enhanced Raman scattering.
Received 22 March 2011
Received in revised form 13 April 2011
Accepted 15 April 2011
Keywords:
Surface enhanced Raman scattering
Ag/Cu2S
Composite
Micro–nanostructures
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
ity might be due to the long-range electromagnetic enhancement
for the localized surface plasmonic resonance (LSPR) excited by Ag
In the past few years, various metallic or semiconductorial
nanoparticles with controllable size, shape and composition have
been widely developed and applicable in many kinds of fields such
as catalysis, size quantum effects, luminescence, third-order non-
linearity, surface enhanced Raman scattering (SERS), biomedical
engineering, and so on [1–8]. Among these, SERS have attracted
more and more attention to surface scientists for its simple and
super-sensitive detection of adsorbed molecules on the chemi-
cal, physical, and biological surface and interfaces. Formerly, the
SERS substrates were mainly based on various kinds of rough solid
metal support or metallic colloids. Recently, semiconductors, such
as ZnS, CdS, CuO, CdTe, ZnO, TiO2, etc., have also been used as
the SERS substrates [7,9–13], which could directly produce weak
SERS signals with typical enhancement factor (EF) up to 104. How-
ever, the SERS activities based on such semiconductors were much
lower than that of metal nanoparticles, hampering their practical
applications. Previous reports have announced that combination of
metal nanoparticles with semiconductors is a meaningful approach
to enhance the SERS activity of semiconductors. For example,
Wang et al. fabricated Ag/TiO2 composite particles with nanometer
size by irradiation of an AgNO3 solution with light of wavelength
>330 nm in the presence of TiO2 nanoparticles and observed the
SERS effects [14]. We have fabricated a SERS active Ag/TiO2 compos-
ite nanofibers, exhibiting a high EF of 4-mercaptopyridine (4-Mpy)
adsorbed on their surface [15]. The improvement of SERS activ-
nanoparticles under the irradiation of a suitable laser. The similar
phenomenon was also observed in the system of Ag/ZnO composite
microspheres [16].
For the preparation of metal/semiconductor composite nanos-
tructures, a simple and common method is in situ reduction
of metallic salt on the surface of semiconductor nanostructures
[15,16]. As the reaction is fast, the shape and size of the metal
nanostructures are not well controlled. Recently, we have pro-
posed that metal nanoparticles could be site-specific deposit on
the tip of ZnO nanorod arrays through a simple galvanic reduction
method [17]. By tuning the reaction time and the concentra-
tion of silver nitrate, the density of Ag nanoparticles on the tip
of ZnO nanorods could be controlled. In this paper, we demon-
strate that such method could also be applicable in the fabrication
of metal/sulfide composite micro–nanostructures. Moreover, the
resulted preferential deposition of silver nanoparticles on the big
polygonal Cu2S microstructures further proved the rich localiza-
tion of the electrons on the top surface of semiconductors which
generated by the galvanic reaction. The results also indicated that
the Ag/Cu2S composite micro–nanostructures could be used as a
versatile substrate for SERS.
2. Experimental
2.1. Materials
Cu foil was obtained from Sinopharm Chemical Regent Co.,
Ltd. Ethylenediamine was obtained Tianjin Bodi Chemical Hold-
ing Co., Ltd. Sulphur powder was purchased from Shenyang No.
∗
Corresponding author. Tel.: +86 431 85168473.
E-mail addresses: zhaob@mail.jlu.edu.cn, zhaobing@jlu.edu.cn (B. Zhao).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.04.050

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W. Song et al. / Spectrochimica Acta Part A 79 (2011) 1247–1250
Fig. 1. (a) SEM images of Cu2S micro–nanostructures over copper foil. (b) SEM images of Ag/Cu2S composite micro–nanostructures over copper foil. (c) Proposed deposition
of Ag nanoparticles on the Cu2S micro–nanostructures via a galvanic reduction.
5 Chemical Regent Factory. 4-mercaptopyridine (4-Mpy) and p-
aminothiophenol (PATP) were obtained from Sigma Chemical
Company. AgNO3 and ethanol were obtained from Shanghai Kefeng
Chemical Regent Co., Ltd. and Beijing Chemical works, respectively.
SEM measurements, which were performed on a JEOL JSM-6700F
field emission scanning electron microscope (FE-SEM) operated at
3.0 kV. The X-ray diffraction (XRD) patterns of Ag nanoparticles on
the Cu2S micro–nanostructures over copper foil were recorded in
a Seiemens D5005 diffractometer using Cu K␣ radiation. Raman
spectra of Ag nanoparticles on the Cu2S micro–nanostructures over
copper foil were obtained with a Renishaw Raman system model
1000 spectrometer. The 514.5 nm radiation from a 20 mW air-
cooled argon ion laser was used as an exciting source. The laser
power at the sample position was typically 40 ␮W with an aver-
age spot size of 1 ␮m in diameter. Data acquisition involved the
30-s accumulations for 4-Mpy and PATP adsorbed on Ag nanopar-
ticles on the Cu2S micro–nanostructures over copper foil. To record
the Raman spectrum of 4-Mpy and PATP adsorbed on Ag nanopar-
ticles on the Cu2S micro–nanostructures over copper foil, the
substrate was immersed in 1 ml of a 4-Mpy and PATP ethanol
solution for 20 min and rinsed with an ethanol solution three
times.
2.2. Synthesis of Cu2S micro–nanostructures over copper foil
The fabrication of Cu2S micro–nanostructures was similar with
the previous report [18]. A piece of Cu foil was washed with water
and ethanol for several times and blew with N2. After drying, it was
put into a 40 mL Teflon-lined stainless steel autoclave. Followed, a
30 mL sulphur solution in ethylenediamine with a concentration of
10−3 M was introduced into the above Teflon-lined stainless steel
autoclave. The autoclave was maintained at 130 ◦C for 12 h and sub-
sequently cooled to room temperature. The resulted product was
washed with water and ethanol carefully.
2.3. Deposition of Ag nanoparticles on Cu2S
micro–nanostructures via galvanic reduction route
3. Results and discussion
The prepared Cu2S micro–nanostructures over copper foil were
carefully immersed into an AgNO3 solution with certain concentra-
tion and reaction time. After that, the obtained Ag/Cu2S composite
micro–nanostructures were taken out from the AgNO3 solution,
and washed with deionized water for several times. Finally, the
product was dried under nitrogen atmosphere at room tempera-
ture.
3.1. Morphologies and structure characterization of the obtained
Ag/Cu2S composite micro–nanostructures
Cu2S is widely used as an excellent p-type semiconductor mate-
rial applicable in solar cells, super ionic materials and optical filters
[19,20]. In the present work, Cu2S micro–nanostructures were pre-
pared over copper foil through a solvothermal reaction using Cu
foil and sulphur as sources. Fig. 1a showed representative SEM
images of starting Cu2S micro–nanostructures over copper foil. It
was found that two main structures including big polygonal Cu2S
microstructures and small Cu2S nanoparticles were observed. The
2.4. Materials characterizations
The shape and size of Ag nanoparticles on the Cu2S
micro–nanostructures over copper foil were characterized by

W. Song et al. / Spectrochimica Acta Part A 79 (2011) 1247–1250
1249
5000
10-3
10-4
10-5
10-6
10-7
M
M
M
M
M
1000
Cu
Cu2S
Cu-Cu2S
Ag 111
40
x2
x4
Cu-Cu2s-Ag
1600
1200
800
400
20
30
50
60
70
80
Wavenumber (cm-1)
2θ (degree)
Fig. 2. XRD patterns of Cu2S micro–nanostructures over Cu foil and Ag/Cu2S
Fig. 3. SERS spectra of PATP with different concentrations adsorbed on Ag/Cu2S
micro–nanostructures.
composite micro–nanostructures.
3.2. SERS spectra of PATP and 4-Mpy on Ag/Cu2S composite
micro–nanostructures
size of the big polygonal Cu2S microstructures is about several
micrometers, while that of the small Cu2S nanoparticles is in the
range of 100–800 nm. Fig. 1b showed the deposition of Ag nanopar-
ticles on the surface of Cu2S micro–nanostructures. The deposition
was conducted under a concentration of the silver salt of 10 mM
and the reaction time was 30 s. As can be seen, Ag nanoparticles
with the size of around 50–100 nm were well deposited on the
surface of Cu2S micro/nanostructures. Moreover, the SEM images
indicated that the Ag nanoparticles were preferentially grown on
the top surface of big polygonal Cu2S microstructures, which could
be explained by a localization of the electrons on the top surface
of the polyhedral Cu2S microstructures after the electron transfer
step. The SEM images also showed that the density of Ag nanopar-
ticles on the edge of the polyhedral Cu2S microstructures is much
higher than that of the facet of polyhedral Cu2S microstructures,
indicating that the electrons are apt to localize on the edge of the
polyhedral Cu2S microstructures. Fig. 1c illustrates a generalized
process of the deposition of Ag nanoparticles on the surface of Cu2S
micro–nanostructures. In fact, this reaction is a similar galvanic
reduction of Ag+ by more active copper foil into Ag nanoparti-
cles. Electrons will be generated when copper was oxidized, then
it will transfer into the surface of Cu2S micro–nanostructures,
where the silver ions are reduced by the electrons. Because the
big polyhedral Cu2S microstructures lie on the top of the Cu2S
nanoparticles, electrons tend to localize on that region, resulting
in more Ag nanoparticles are grown on the top surface of Cu2S
microstructures.
In this article, we firstly choose PATP as probe molecules because
it could be well adsorb on the surface of metal and sulfide nanos-
tructures [21,22]. Fig. 3 (top line) shows the SERS spectrum of PATP
(10−3 M) adsorbed on Ag/Cu2S composite micro–nanostructures
over copper foil. From it, two main peaks at 1576 and 1077 cm−1
were observed. The 1576 cm−1 line is the C C stretch, and the
1077 cm−1 line is the C–S stretch for PATP molecules, respec-
tively [23]. These two signals are attributed to the a1 modes of
the PATP molecules. Furthermore, the peaks at 1142, 1188, 1389,
and 1436 cm−1 are also observed. These lines are all ascribed to
the b2 symmetry of PATP molecules. The SERS enhancement of b2
symmetry on Ag/Cu2S composite micro–nanostructures is owing
to the charge-transfer mechanism, which is in accordance with the
Herzberg–Teller selection rule [24]. The SERS properties of PATP
molecules with different concentrations on the surface of Ag/Cu2S
composite micro–nanostructures have also been studied (Fig. 3).
As the concentration of PATP decreases, the SERS intensities of
PATP decrease accordingly. However, the SERS signals could be still
detected even the concentration of PATP molecules was decreased
to 10−6 M.
Besides the PATP, 4-Mpy molecules are also used as probe
to evaluate the SERS enhancement mechanism on the surface
of Ag/Cu2S composite micro–nanostructures. From Fig. 4, it is
found that a strong peak at 1585 cm−1 and a weak shoulder
peak at around 1609 cm−1 are observed. These two peaks could
be ascribed to the ring mode of 4-Mpy molecule with depro-
tonated and protonated nitrogen, respectively [25]. In order to
investigate the SERS effect of 4-Mpy molecules on the surface
of Cu2S micro–nanostructures, the difference spectrum between
the Raman spectra of 4-Mpy adsorbed on Ag/Cu2S composite
micro–nanostructures and Ag mirror is also shown in Fig. 4c. It
is found that three additional obvious peaks at 1034, 1212 and
1589 cm−1 appeared. The peak at 1034 cm−1 is related to the pyri-
dine ring C–H in-plane bending mode, while the band at 1212 cm−1
is ascribed to CH/NH deformation mode of 4-Mpy. Obviously, these
three peaks could be attributed to the SERS of 4-MPy molecules
adsorbed on bare Cu2S micro–nanostructures. Generally, most
of the SERS peaks on Ag/Cu2S composite micro–nanostructures
should be attributed to the Ag nanoparticles with size between
50 and 100 nm. And the enhancement of the SERS signals of
4-Mpy at 1034, 1212 and 1589 cm−1 adsorbed on bare Cu2S
The structure of the as-synthesized Ag/Cu2S compos-
ite micro–nanostructures was supported by powder XRD
measurement. Fig.
2 shows typical XRD patterns of the
as-prepared Cu2S micro–nanostructures and Ag/Cu2S com-
posite micro–nanostructures. In the XRD pattern of Cu2S
micro–nanostructures, all of the main peaks were similar with
the previous reports, which could be indexed to the structures
of Cu2S and ␤-Cu2S except the peaks of copper foil [18]. Even
though the peak intensity of Ag nanoparticles are lower than
the Cu2S micro–nanostructures in the XRD pattern of Ag/Cu2S
composite micro–nanostructures, this does not contradict the
appearance of the peak of Ag (1 1 1), indicating that Ag nanopar-
ticles were deposited on the surface of Ag/Cu2S composite
micro–nanostructures.

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W. Song et al. / Spectrochimica Acta Part A 79 (2011) 1247–1250
Acknowledgments
Cu-Cu2S-Ag
a
c
difference
Ag mirror
The research was supported by the National Natural Sci-
ence Foundation (Grant Nos. 20873050, 20903044, 20921003,
20973074) of P. R. China and the Basic Research Fund of Jilin Uni-
versity.
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4. Conclusions
In summary, we have developed a facile galvanic reduction
route for producing Ag/Cu2S composite micro–nanostructures over
copper foil. The SEM images indicated that Ag nanoparticles are
preferential deposited on the edge of the surface of big polygonal
Cu2S microstructures due to a localization of the electrons at the
edge of Cu2S microstructures as the reducing agent. The Raman
spectra confirm that the SERS effect was attributing to the interac-
tion between the Ag nanoparticles and Cu2S micro–nanostructures.
Meanwhile, a stronger enhanced electromagnetic field was pro-
duced between Ag nanoparticles and Cu2S micro–nanostructures
owing to the long-range electromagnetic enhancement.
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