Polymer-assisted synthesis of aligned amorphous silicon
nanowires and their core/shell structures with Au nanoparticles
Xing-bin Yan
a,b
, Tao Xu
a
, Shan Xu
a,b
, Gang Chen
a,b
,
Qun-ji Xue
a
, Sheng-rong Yang
a,
*
a
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
b
Graduate School of the Chinese Academy of Sciences, Beijing, 100083, China
Received 13 August 2004; in final form 23 August 2004
Available online 11 September 2004
Abstract
Aligned amorphous Si nanowires (SiNWs) were synthesized directly from Si substrates with the assistance of a new carbon-based
network polymer, poly(phenylcarbyne), during the heat-treatment in Ar atmosphere at 1120 °C. A core/shell structure of SiNWs
wrapped with Au nanoparticles was simply fabricated as well. The analytic results of the morphology and microstructure confirmed
the orientation and the amorphous nature of the SiNWs, and the high dispersion of Au nanoparticles on the surface of the SiNWs
without any aggregation. The formation of the SiNWs was explained on the basis of the reaction of carbon with the native silica
layer covering Si substrates.
Ó 2004 Elsevier B.V. All rights reserved.
1. Introduction

important for the potential applications in future micro-
electronic and optoelectronic devices.
In this communication, we report that aligned amor-
phous SiNWs can be synthesized directly from Si sub-
strates with the assistance of a new carbon-based
network polymer, poly(phenylcarbyne). Moreover, a
core/shell structure of SiNWs wrapped with highly dis-
persed Au nanoparticles is simply fabricated as well.
The methods significantly simplify the preparation of
0009-2614/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.cplett.2004.08.099
*
Corresponding author. Fax: +86 931 8277088.
E-mail address: (S. Yang).
www.elsevier.com/locate/cplett
Chemical Physics Letters 397 (2004) 128–132
aligned SiNWs and the metal–SiNWs composite materi-
als, and make the processes more cost-effective.
2. Experimental
The poly(phenylcarbyne), PPC, was inexpensively
synthesized by the procedure: the reduction of the
appropriate PhCCl
3
monomer, with an ultrasonically
generated emulsion of Na–K alloy and an ethereal sol-
vent, tetrahydrofuran (THF), reported in detail else-
where [14,15]. This polymer is composed of a
randomly constructed network of tetrahedral hybridized
phenylcarbyne units and can be converted into dia-
mond-like carbon by pyrolysis [15]. Freshly prepared

copy (XPS, Perkin–Elmer PHI-5702).
3. Results and discussion
After pyrolysis of the polymer/Si, a blue tinted gray
colored wool-like film was all deposited on the different
type Si sub strates, which indica tes that the type of Si
substrate does not affect the formation of the SiNWs.
The SEM images in Fig. 1a reveal that the nanowires
(NWs) are highly aligned perpendicular to the Si sub-
strate. As is seen form the cross-sectional view along
the edge of the scratched film, the orientation of the
NWs is widespread over the whole substrate. The homo-
geneous thickne ss of the NWs film is easily obtained to
be about 500 lm. Thus, the growth rate of the NWs is
estimated to be about 70 nm/s. The magnified SEM im-
age in the right inset shows that the NWs appear dense
and parallel to each other. More interestingly, the SEM
images in Fig. 1b reveal some dandelion-like wires. As is
seen form the top view of the NWs film, the relatively
straight nanowire spli ts into several curly sub-branche s
to different orientation. The magnified image in the right
inset shows these sub-branches are similar to wire-like
spherical particle agglomerates with the width range
from nanoscale to micron-scale.
The EDX spectrum of aligned NWs on the cross-
section of the SiNWs film, shown in Fig. 2a, reveals
these NWs are mainly composed Si. The remaining
oxygen peak comes from the surfa ce oxidation of the
nanowires and the atomic rate for Si:O in these nano-
wires is 7:1 on average. While, the ED X spectrum of
particle-linked wires on the tip of SiNWs film, shown

particle size of the wrapped Au nanoparticles in the
composite SiNWs is 5 ± 1.5 nm. It is noted that the
Au nanoparticles are well dispersed on the surface of
the SiNWs without any aggregation. The SAED pattern
(a)
Si
O
Intensity (a.u.)
Intensity (a.u.)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
(b)
Si
C
O
Energy (KeV)
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Energy (KeV)
Fig. 2. EDX spectra of the aligned nanowires (a) and the particle-linked wires (b).
Fig. 3. (a) Low magnification TEM image of SiNWs; (b) TEM image of a single particle-linked wire; (c) TEM image of a single straight SiNWs and
the corresponding highly dispersed selected area electron diffraction (SAED) pattern; (d) and (e) TEM images of SiNWs wrapped Au nanoparticles
and the corresponding SAED pattern.
130 X. Yan et al. / Chemical Physics Letters 397 (2004) 128–132
in the inset of the TEM image of individual Au–SiNW
shows diffraction rings, which is corresponded to Au
crystal. Moreover, the content of the Au nanoparticles
in the Au–SiNWs is 5 at.%, which is determined by
EDS.
Part of the SiNWs film was peeled off from Si sub-
strate and used to measure the Raman. Two peaks
around 301 and 519 cm

the carbon pha se was composed of small carbon nanopar-
ticles [14]. Moreover, when the temperature is below
1050 °C, the product is amorphous carbon film coated
on Si substrate; when the temperature is 1050–1100 °C,
the surface of the carbon film changes very rough and
there are some erodible taints on Si substrate, which indi-
cates that chemical reaction may take place; when the
temperature is above 1100 °C, aligned amorphous SiNWs
film is main product. Thus, we think that the higher pyro-
lysis temperature (1120 °C) will lead to a large amount of
carbon nanoparticles having high chemical activity. The
growth of SiNWs may start from the reaction of the active
carbon nanoparticles with the native oxide layer on Si
substrate [11,16,17]. This native oxide layer is reduced
by carbon nanoparticles to yield silicon monoxide, and
then the nucleation site of the Si nanostructures is formed
by the decomposition of silicon monoxide. The above
reactions are proposed as below:
Si
x
O
2
! Si
x
O þ CO ðx > 1Þð1Þ
Si
x
O ! Si
xÀ1
þ SiO ð2Þ

4
are uni-
formly absorbed on the surface of the SiNWs. Because
of the high standard electrode potential of the
Au
3+
/Au
0
couple, Au
3+
has high polarization and high
chemical reactivity. Au
3+
could be easily reduced to
Au
0
in air at 200 °C [19]. Thus, the Au–SiNWs can be
obtained by heat-treatment of the SiNWs and
HAuCl
4
Æ H
2
O at 300 °C in Ar atmosphere. It is believed
that all chlorin have been evaporated during the thermal
200 300 400 500 600 700 800 900
2TA
Intensity (a.u.)
Raman shift (cm
-1
)

be found, in the online version at doi:10.1016/
j.cplett.2004.08.099.
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