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Journal of Alloys and Compounds
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Facile route to straight SnO
2
nanowires and their optical properties
P.G. Li
a,∗
,M.Lei
a
, W.H. Tang
a
,X.Guo
a
,X.Wang
b
a
Department of Physics, Center for Optoelectronics Materials and Devices, Zhejiang Sci-Tech University, Xiasha College Park, Hangzhou 310018, China
b
Department of Electronic Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, China
article info
Article history:
Received 19 September 2008
Received in revised form 8 October 2008
Accepted 15 October 2008
Available online xxx

[4–10].Recently,one-dimensional nanowire structure has attracted
increasing attentions, owing to its enhanced surface to volume
ratio and promising applications for gas sensors [11,12] and
electronic nanodevices [13] Up to now, various methods includ-
ing direct-oxidized growth [14–16], molten-salt synthesis [17,18],
hydrothermal method [19,20], laser-ablation synthesis [21], car-
bothermal reduction [22,23], and template method [24], etc. have
been developed to fabricate SnO
2
nanowires. However, the as-
synthesized nanowires easily bend and length and diameter is
not uniform, which limits their promising applications. So, fabri-
cation of straight SnO
2
nanowires with uniform size and smooth
surface is still a challenge up to now. In this work, we devel-
oped a novel chemical vapor method to synthesize large-scale
SnO
2
nanowires with uniform size using SnO
2
nanoparticles as
starting materials. The structure property and growth mecha-
nism were investigated in detail. In addition, some interesting
∗
Corresponding author. Tel.: +86 571 86843468; fax: +86 571 86843222.
E-mail address: [email protected] (P.G. Li).
optical features of the SnO
2
nanowires were presented in the

at RT using the 325 nm line of a He–Cd laser as the excitation source.
3. Results and discussion
Fig. 1a shows the SEM image of the SnO
2
nanoparticles syn-
thesized by a hydrothermal method. The average size of these
nanoparticles is about 5 nm, indicating the SnO
2
nanoparticles
can be decomposed at relatively low temperature comparing with
micropowders. SEM images of the product deposited on 6H-SiC
substrate are shown Fig. 1b and c. Fig. 1b shows that straight
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Fig. 1. (a) SEM image of the SnO
2
nanoparticles synthesized by hydrothermal method. (b and c) SEM images of the SnO
2
nanowires. (d) EDS analysis of the SnO
2
nanowires.
nanowires with high density are distributed over the entire sur-
face of the substrate. SEM image with higher magnification (Fig. 1c)
clearly indicates that these nanowires are of uniform size and
smooth surface, and the average diameter and length of these

2
nanowires: (a) O1s region, (b) Sn3d region.
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Fig. 4. (a) TEM image of the SnO
2
nanowires. (b) TEM image of a single nanowire. The corresponding FFT pattern is shown in the inset. (c) TEM-based EDS spectrum of the
single nanowire. (d) HRTEM image of the nanowire.
TEM image (Fig. 4a) clearly indicates that nanowires are of
smooth surface and rather uniform size along the growth direction.
Fig. 4b shows a typical nanowire with a clear surface. TEM-
based EDS analysis of the nanowire (Fig. 4c) confirms that the
nanowire mainly consists of Sn and O element, and average Sn/O
atomic ratio of 1:1.94, which exhibits the O-deficient condition of
the nanowire. The corresponding FFT pattern and HRTEM image
clearly show that the nanowire is single crystalline and grows
along [12-1] direction, which is different from common [1 0 1]
and [1 1 0] growth direction [26,27]. No obvious defects and dis-
locations are observed, and the interplanar space is 0.356 nm
and 0.236 nm, which corresponds to the (101) and (200) plane
of the rutile crystalline SnO
2
(Fig. 4d), further confirming rutile
structure of the nanowire. Based on the experimental results, con-
ventional vapor–liquid–solid (VLS) cannot dominate the growth
of the nanowires due to no metal catalyst such as tin particle
attached on the tip of nanowire. Vapor–solid (VS) mechanism also

), etc. It is interesting to observe
that the orange emission disappears after annealing in air at 850
◦
C
for 3 h, whereas no change happens as annealing at Ar and N
2
atmo-
sphere. These results indicate that the yellow emission is related to
the V
o
, whereas orange emission originates from Sn
i
[29,30]. Due to
the synthesis process is in the O-deficient condition, V
o
is unavoid-
able exist. As a native defect of the n-type SnO
2
, The V
o
cannot
be eliminated during the above annealing process. Nevertheless,
Sn
i
can be oxidized and thus removed by annealing in air or oxy-
gen atmosphere. So, orange emission is not commonly detected in
Fig. 5. Room-temperature photoluminescence spectrum of the SnO
2
nanowires.
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A
1g
and B
2g
modes vibrate in the plane perpendicular to the c-axis
while the E
g
mode vibrates in the direction of the c-axis [33].As
shown in Fig. 5, three active Raman scattering peaks at 482.3, 638.3
and 779.1cm
−1
can be assigned to E
g
,A
1g
and B
2g
mode, respec-
tively, in good agreement with those of rutile SnO
2
single crystal
[34]. Nevertheless, the four additional modes are also observed,
all of which are not allowed by rutile-type structure in first-order
Raman-scattering at the zone center. Among them, the mode peak
at 699.7 cm
−1
reported in previous article [27] is caused by the
finite-size effects of SnO
2
. The other additional peaks at 548.7, 591.1

and 733.8 cm
−1
, respectively, were related to the defect-induced
phonon modes due to the surface disorder and large amount of O
vacancies and Sn interstitial.
Acknowledgements
This work was supported by the key project of the National Nat-
ural Science Foundation of China (60571029, 50672088) and the
Zhejiang Provincial Natural Science Foundation (Z605131).
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