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Physica E 24 (2004) 278–281
Sulfide-assisted growth of silicon nano-wires by
thermal evaporation of sulfur powders
Junjie Niu
a
, Jian Sha
a,b
, Deren Yang
a,
*
a
State Key Lab of Silicon Materials, Zhejiang University, Hangzhou 310027, People’s Republic of China
b
Department of Physics, Zhejiang University, Hangzhou 310027, People’s Republic of China
Received 23 March 2004; accepted 11 May 2004
Available online 10 July 2004
Abstract
Silicon nanowires (SiNWs) with a diameter of B20 nm were synthesized by the thermal evaporation of
sulfur powders on silicon wafers. The source of the SiNWs came from the silicon substrates. It is considered
that the generated SiS compound assisted the formation of SiNWs. Finally, the Raman shift of SiNWs was
discussed.
r 2004 Elsevier B.V. All rights reserved.
PACS: 71.55.Cn; 81.05.Ys
Keywords: Silicon; Nanowires; Sulfide assisted
1. Introduction
Recently the one-dimensional nano-materials,
especially silicon nanowires (SiNWs), have stimu-
lated much interest because of their different

SiNWs were produced on p-type (1 1 1) silicon
wafers with a resistivity of about 0.001 O cm by
means of a low-vacuum CVD system. First,
several pieces of silicon wafers and plenty of sulfur
powders were placed in a semi-sealed alumina boat
which was put at the center of a horizontal quartz
tube furnace. Then the furnace was evacuated to
reach 30 Pa by a mechanical pump. The tempera-
ture of the system was then raised to 900

Cata
heating rate of 25

C min
À1
and continually up to
1250

C at a heating rate of 10

C min
À1
, and held
at 1250

C for 30 min at a constant pressure of
30 Pa. After reaction, the weak black and yellow
substrates with the as-grown materials were
removed from the furnace and characterized by
FESEM (FEI, Sirion), TEM (JEOL, JEM200CX),

data as shown in Fig. 3. The sharp peaks of Si
(1 1 1), Si (3 1 1), Si (4 0 0), and Si (3 3 1) indicates
that the SiNWs were crystalline. Some crystal Al
peaks and low-intensity peaks of SiS
2
(3 0 1) and
SiS
2
(2 1 3) are simultaneously observed. Al peaks
ARTICLE IN PRESS
Fig. 1. FESEM image of the SiNWs on a silicon wafer. The
lower left inset is the EDX taken from the corresponding
sample.
Fig. 2. TEM image of the SiNWs. The top right inset is the
SAED taken from one of the SiNWs. On top left is the
magnified TEM image of a SiNW with tip.
J. Niu et al. / Physica E 24 (2004) 278–281 279
come from the sample preparation process for
the XRD analysis, while SiS
2
comes mainly from
the decomposition of SiS. The discussion of the
growth mechanism is displayed below.
As the function of silicon oxide in the oxygen-
assisted mechanism [15,16], in our experiments,
the silicon sulfide (SiS) also played a key role
in assisting the growth of SiNWs. Therefore, a
sulfide-assisted model for SiNW growth is sug-
gested here.
The reaction procedure mainly took two steps.

þ 2H
2
O ¼ SiO
2
þ2H
2
Sm: ð4Þ
When the temperature reached B900

C, Eq. (2)
happened and the SiS film was produced. Con-
tinually, the SiS is decomposed into Si and SiS
2
at
higher temperature (B1000

C), which could be
confirmed by the XRD spectrum in Fig. 3.
Therefore, it is believed that the SiNWs generated
from the SiS acted as nucleation centers which
were located at the tip of the SiNWs, as shown in
the top left of Fig. 2. Thus, the tip should contain
SiS
2
. But there was no S signal in the EDX
spectrum (the inset of Fig. 1) and only weak SiS
2
peaks are displayed in XRD data (Fig. 3). This is
because the SiS
2

(Fig. 4(b)). Usually, the peak of 510.5 cm
À1
was
regarded to be the first-order transverse optical
phonon mode (TO). The downshift might be
ARTICLE IN PRESS
30 40 50 60 70 80
0
500
1000
1500
2000
Al(111)
Al(200)
SiS
2
(213)
SiS
2
(301)
Al(220)
Al(311)
Si(331)
Si(400)
Si(311)
Si(111)
Intensity (CPS)
2θ (degrees)
Fig. 3. XRD spectrum of the as-grown SiNWs.
400 450 500 550 600 650 700 750

Natural Science Foundation of China (Nos.
50272057 and 60225010) and the Key Project
of Chinese Ministry of Education. The authors
would like to thank Prof. Youwen Wang and
Mr. Z.C. Chen for their great help in the
measurements of TEM and Raman spectroscopy.
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