Characterization of Tin-catalyzed silicon nanowires synthesized by the hydrogen
radical-assisted deposition method
Minsung Jeon
⁎
, Hisashi Uchiyama, Koichi Kamisako
Department of Electronic and Information Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan
abstractarticle info
Article history:
Received 11 September 2008
Accepted 2 October 2008
Available online 9 October 2008
Keywords:
Tin catalyst
Silicon nanowires
Hydrogen radicals
VLS mechanism
Phase diagram
Tin-catalyzed silicon nanowires (SiNWs) were synthesized at various hydrogen gas flow rates using the
hydrogen radical-assisted deposition method. Large quantities of SiNWs with various crystal phases were
synthesized and their characteristics were estimated. Tin-capped SiNWs were straightly grown and their
structures were changed with increasing hydrogen gas flow rates. Their diameters on the bottom side were
increased ranging from approximately 50 to 200 nm and their lengths extended up to ~2 µm with increasing
hydrogen gas flow rates.
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
Since the synthesis of carbon nanotubes [1], much attempt has
been devoted to synthesizing one-dimensional nanostructure materi-
als, such as nanowires, nanorods, nanotubes and nanoribbons [2].
These nanomaterials provide a good system to research the depen-
dence of electrical, optical and magnetic properties [3–8]. They are
also expected to play an important role as both interconnections and

vacuum chamber with a pressure of 2×10
− 5
Torr. Hydrogen (H
2
) gas is
introduced into the 1/2-inch diameter trumpet-like quartz tube, which
is surrounded by microwave cavity. Then, the hydrogen radicals
generated by 2.45 GHz microwave are irradiated for 1 min onto the
samples to fabricate nanosize metal particles. To fabricate nanoparticles,
aH
2
gas flow, microwave power and working p ressure are selected to
100 sccm, 40 W and 0.5 Torr, respectively. For synthesizing silicon
nanowires (SiNWs), silane (SiH
4
) gas as Si source is introduced into the
experimental chamber from a ring-type copper tube that has many
orifices, and it is reacted with hydrogen radicals generated by
microwave in the quartz discharge tube. In order to investigate the
effect of synthesis conditions, SiNWs are synthesized using the
hydrogen radical-assisted deposition method [19] at various hydrogen
gas flow rates ranging from 130 to 180 sccm. Detailed other synthesis
conditions are summarized in Table 1 .
SiNWs are syn thesized for 1 0 min, and t heir characteristics a r e
estimated by Field Emission Scanning Electron Microscopy (FE-SEM) and
X -ra y diffractometer (XRD). For further investigation, the sy nthesized
Materials Letters 63 (2009) 246–248
⁎ Corresponding author. Tel./fax: +81 42 388 7446.
E-mail address: (M. Jeon).
0167-577X/$ – see front matter © 2008 Elsevier B.V. All rights reserved.

straightly gr own a s shown in insets of Fig. 1 (b) a nd (c). How ever, their si zes became thicker
with increasing H
2
gas flo w. The diameters of SiNWs on the bottom side were gradually
increased ranging from approximat ely 50 t o 200 nm with increasing H
2
gas flow rates.
Moreover , their lengths extended up to ~2 µm. It indicates that the H
2
gas flow affect the
growth of SiNWs. Moreover, the high-magnification FE-SEM images explained that th e
SiNWs were tapered and that Sn catalysts r emained on the tip of Si NWs (see r ed c ircles i n
inset of Fig. 1 (a)). It means that the SiNWs a r e synthesized via vapor–liq uid–solid (VLS)
mechanism [9, 13]. The detailed explanation of the VLS mechanism will be followed later .
Above mentioned sampl es w ere also e xamined b y XRD measurement. Fig. 1 (d) s hows the
XRD p att erns of S iNWs synthesized a t varied H
2
gas flow r at es. The XRD patterns indicate that
the syn thesized SiNWs ar e highl y crystallized sil icon with di ffraction peaks of (111), (220)and
(3 11). Mor e over, the Snmetal peaks of (200) and (1 0 1) were also w eakly detected at 30.66 and
32.044 deg., r espectively (see black arrows in Fig. 1 ( d)). These peaks were reveal ed because
theSncatalystswerelocatedonthetopofSiNWsasshownininsetofFig. 1(a). Such SiNWs
grew randomly wi th different crystal orientations.
Fig. 2 shows a schematic of the Sn–Si alloy binary phase diagram [18]. SiNWs are
typically synthesized via the VLS growth mechanism at temperatures higher than the Sn–
Si eutectic temperature. This VLS mechanism has been introduced by Wagner et al. to
growth single crystalline silicon [9]. A typical VLS growth starts with the dissolution of
gaseous reactants into a nano-size metal liquid droplet, followed by nucleation and growth
Table 1
Synthesis conditions for silicon nanowires (SiNWs)

spectra taken for the nanoparticle shown in inset of Fig. 3(a). It indicates that the
nanoparticle comprises Sn and Si elements. The Sn nanoparticle located on the top of Si
nanowire implies that a Sn catalyst assisted VLS mechanism is typically related in the
growth of SiNWs. These results denote that the as-synthesized SiNWs by ourexperimental
method are pure crystalline silicon without oxygen and other impurities.
4. Conclusion
Tin-catalyzed silicon nanowires (SiNWs) were synthesized atvarious
hydrogen gas flow rates using the hydrogen radical-assisted deposition
method. Voluminous SiNWs, which have various crystal phases, were
whisker-likely synthesized at all growth condition. Their structures
were gradually changed with increasing hydrogen gas flow rate. The
diameters of SiNWs on the bottom side were increased ranging from
approximately 50 to 200 nm and their lengths extended up to ~2 µm. It
indicates that the SiNWs can be controlled by the introduced hydrogen
gas flow rates.
References
[1] Iijima S. Nature 1991;354:56.
[2] Wang ZL. Nanowires and Nanobelts: Materials, Properties and Devices. Kluwer
Academic Publishers; 2003.
[3] Westwater J, Gosain DP, Usui S. Jpn J Appl Phys 1997;36:6204.
[4] Alivisatos AP. Science 1996;271:933.
[5] Kang SH, Kim JY, Kim HS, Sung YE. J Ind Eng Chem 2008;14:52.
[6] Cui Y, Lieber CM. Science 2001;291:851.
[7] Chung SW, Yu JY, Heath JR. Appl Phys Lett 2000;76:2068.
[8] Duan X, Niu C, Sahi V, Chen J, Parce JW, Empedocles S, et al. Nature 2003;425:274.
[9] Wagner RS, Ellis WC. Appl Phys Lett 1964;4:89.
[10] Wang N, Tang YH, Zhang YH, Lee CS, Bello I, Lee ST. Chem Phys Lett 1999;299:237.
[11] Zhang XY, Zhang L, Meng GW, Li GH, Phillipp NY, Phillipp F. Adv Mater 2001;13:1238.
[12] Morals AM, Lieber CM. Science 1998;279:208.
[13] Givargizov EI. J Cryst Growth 1975;31:20.