Synthesis of silicon nanowires after hydrogen radical treatment
Minsung Jeon
⁎
, Koichi Kamisako
Department of Electronic and Information Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, 184-8588 Tokyo, Japan
ABSTRACTARTICLE INFO
Article history:
Received 16 October 2007
Accepted 16 May 2008
Available online 24 May 20 08
Keywords:
Silicon nanowires
Hydrogen radicals
Metal oxide film
Nanoparticles
Silicon nanowires (SiNWs) were synthesized through the hydrogen radical-assisted deposition method.
Voluminous indium (In) metal catalysts with smooth spherical structures were successfully fabricated from
indium oxide films after hydrogen radical treatment for 5 min. Their sizes were widely distributed, ranging
from several nm to about 150 nm. Subsequently, the large quantities of SiNWs were synthesized using the
hydrogen-radical-assisted deposition method. Their diameters typically ranged from several nm to several
hundred nm, and their lengths extended to about 10 μm. The SiNWs were composed of well-crystallized
silicon cores and hydrogenated amorphous outer layers.
© 20 08 Elsevier B.V. All rights reserved.
1. Introduction
Since the initial discovery of carbon nanotubes [1], one-dimen-
sional (1D) nanostructures, including the well-known nanotubes and
nanowires, have been utilized extensively in the various fields of
nanoscale optical and electronic devices [2–5]. In particular, silicon
nanowires (SiNWs) are irresistible materials in the semiconductor
industry because the bulk properties of silicon are well-known.
Several methods, such as the chemical-vapour deposition (CVD)

2
in the
discharge tube. This method is referred to herein as the hydrogen
radical-assisted deposition method. The fabrication of the metal
catalysts from a metal oxide film and the synthesis of SiNWs were
performed using this method. Glass substrates coated with an approx-
imately 150 nm thick indium oxide film was used.
To fabricate the indium particles as metal catalysts, the sub-
strates were heated at a temperature of 400 °C in a vacuum chamber
with a pressure of 2 ×10
− 5
Torr. Then the substrate was exposed to
the hydrogen radicals for 5 min with a gas pressure of 0.4 Torr
by introducing H
2
gas with a flow rate of 120 sccm. The indi-
um nanopa rticle catalysts were fabricated after hydrogen radical
treatment. Their properties, crystal phase pattern, and surface mor-
phology were evaluated using an X-ray diffractometer (XRD), with
Cu Kα radiation and field-emission scanning electron microscopy
(FE-SEM).
For synthesizing the SiNWs, SiH
4
gas was introduced as a Si source
after the fabrication of the metal nanoparticles. The gas pressure and
microwave power were set at 0.4 Torr and 40 W, respectively. The
substrate temperature was kept at 400 °C during the growth of the
SiNWs. The H
2
and SiH

3
film shown in Fig. 1(a) reveal the high relative intensity of the (222)
peak compared with the other peaks. On the other hand, hydrogen radical treatment
was performed on the substrate for 5 min at 400 °C to fabricate the metal nanocrystal
catalysts. As for the XRD results after hydrogen radical treatment, as shown in Fig. 1(b),
only the crystal indium (In) diffraction peaks of (101), (002), (110), (112), and (200) were
observed. In particular, the indium peak of (101) was strongly revealed. The hydrogen
radicals could react with the metal oxide film on the substrate surface to fabricate the
metal nanocrystal catalysts. As a result, only the metal indium nanocrystals remain on
the substrate after hydrogen radical treatment. To estimate the morphologies of the as-
fabricated indium nanoparticles after hydrogen radical treatment, FE-SEM observation
was performed. Fig. 1(c) shows the large quantity of nano-size indium crystals. The
fabricated nanocrystals are shown as having smooth spherical structures, and their
sizes are shown to range from several nm to 150 nm. Based on the above results, it was
realized that hydrogen radical treatment is an essential process that must be performed
when metal nanocrystal catalysts are fabricated from metal oxide films. After the
fabrication of the indium nanocrystal catalysts, the SiNWs were synthesized using
the hydrogen radical-assisted reaction deposition method for 1 h, at the same temper-
ature. The morphologies of the synthesized SiNWs were observed through FE-SEM
measurement.
Fig. 2 shows the low-magnification top-view FE-SEM micrograph of the as-
synthesized SiNWs. The voluminous quantities of SiNWs were grown for 1 h at 400 °C.
The detailed FE-SEM analysis revealed that the SiNWs were tapered and that the In
catalyst remained on top of the SiNWs (Fig. 2 inset). The as-synthesized SiNWs were
approximately several nm to several hundred nm in diameter, and their lengths
extended to about 10 μm. Furthermore, to confirm the crystal structure of the SiNWs,
TEM analysis was carried out. The results of the high-resolution TEM (HR-TEM) analysis
support the structural distinction made above.
Fig. 3 shows the HR-TEM micrograph and SAED pattern of an as-synthesized SiNW.
The lattice fringes correspond to the (-1-11) and (1-11) planes. The crystalline SiNW was

to 150 nm. Subsequently, the SiNWs were synthesized, and large
quantities of them were whisker-likely grown. The diameters of the
as-synthesized SiNWs were approximately several nm to several
hundred nm, and their lengths extended to about 10 μm. The SiNW
was crystalline, and it was sheathed with a hydrogenated amorphous
outer layer that was about 10 nm thick. These results suggest that the
hydrogen radical-assisted deposition method, including the radical
pre-treatment process, is a candidate method. Moreover, the results
indicate that a voluminous quantity of SiNWs, not including oxygen,
can be synthesized in a simple way.
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