Đây là một bài báo khoa học về dây nano silic trong lĩnh vực nghiên cứu công nghệ nano dành cho những người nghiên cứu sâu về vật lý và khoa học vật liệu.Tài liệu có thể dùng tham khảo cho sinh viên các nghành vật lý và công nghệ có đam mê về khoa học
Trang 1Physica E 23 (2004) 1–4
www.elsevier.com/locate/physe
Junjie Niua, Jian Shaa;b, Niansheng Zhangb, Yujie Jia, Xiangyang Maa, Deren Yanga;∗
a State Key Lab of Silicon Materials, Department of Material Science and Engineering, Zhejiang University, Zheda Lu 38,
Hangzhou 310027, People’s Republic of China
b Department of Physics, Zhejiang University, Hangzhou 310027, People’s Republic of China
Received 8 November 2003; accepted 27 November 2003
Abstract
Tiny SiO2nano-wires (SiO2-NWs) were synthesized on a p-Si (1 1 1) wafer by the chemical-vapor-deposition method The minimum diameter of the nano-wires was around 9 nm, and the length was longer than 10 m The results of transmission electron microscopy shows that the amorphous nano-wires were composed of Si and O with an approximate atomic ratio of 1:2 Furthermore, the photoluminescence behavior of the SiO2-NWs has been also checked
? 2004 Elsevier B.V All rights reserved
PACS: 71.55.Cn; 81.05.Ys; 81.15.Gh
Keywords: Tiny SiO2 nano-wires; Synthesis; PL spectrum
1 Introduction
Quasi-one dimensional nano-materials have
stim-ulated much interest for their potential applications
in nano-electronics, optics, Bat face display, etc
con-Fnement eGect, the diameter of the one-dimensional
nano-materials should be very small (e.g 1 nm) It
has been reported that the minimum diameter of
car-bon tubes could be 0:4 nm [10], and that of silicon
potential photoluminescence and wave-guide
attention [12] Several techniques have been used to
fabricate SiO2-NWs, such as sol–gel, laser ablation,
∗Corresponding author Tel.: 571-8795-1667; fax:
+86-571-8795-2322.
E-mail address: mseyang@dial.zju.edu.cn (D Yang).
catalyzed thermal decomposition, carbothermal re-duction, chemical-vapor-deposition (CVD) and so on [13–17] By means of CVD method, it was reported
50 nm [18]
In this paper, we report the synthesis of the large
scale tiny (about 9 nm in diameter) and long (∼ m)
of compatibility with integrated circuits, silicon sub-strates were used in our experiments The nano-wires were checked by means of a scanning electron mi-croscopy (SEM), transmission electron mimi-croscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and photoluminescence (PL) spectroscopy
2 Experiment The heavily boron-doped p-type Si (1 1 1) wafers as substrates was Frst cleaned for 30 min in the acetone
1386-9477/$ - see front matter ? 2004 Elsevier B.V All rights reserved.
doi:10.1016/j.physe.2003.11.274
Trang 22 J Niu et al / Physica E 23 (2004) 1–4
by ultrasound The substrates were about 20 mm in
width and 40 mm in length Next, a magnetic
sputter-ing method was used to deposit Ni as a catalyst on the
substrates Then the substrates were placed in a quartz
tube furnace The furnace chamber was pumped down
to 10 Pa and heated When the temperature reached
1000◦C, a mixture gas of argon, hydrogen, and silane
(Bow ratio 100:20:15) was allowed into the chamber
The pressure and temperature in the chamber were
kept at 2000 Pa and 1000◦C during the deposition
After that, the substrates were removed from the
fur-nace for the SEM (JSM-T20, JEOL) and PL (F-4500,
Hitachi) measurement, respectively The PL spectra
of the deposited matters on the substrates were
mea-sured at room temperature in the spectral range of
200–900 nm using a general Xe-light source with a
wavelength 206 nm as the excitation source
Further-more, the deposited matters on the substrates were
dis-solved in an ethanol solution, and then the dropwise
was placed on a copper grid covered with a very thin
carbon Flm, so that the deposited materials could be
analyzed with a TEM (Phillip CM200) equipped with
an EDX
3 Results and discussion
Top view of the large-scale entangled tiny
nano-wires synthesized on the silicon substrates is
shown in Fig.1 The as-grown nano-wires have length
Fig 1 Top view SEM image of the densely tiny nano-wires that
grew on a silicon substrate.
Fig 2 TEM image of the as-grown SiO2 -NWs Most of the smooth SiO2-NWs have uniform diameter of about 9 nm, while the others have a diameter of 20 nm The corresponding EDX data (upper right inset) of the SiO2-NWs shows that they are composed of Si and O with an approximate atomic ratio of 1:2 C and Cu peaks originated from Cu grid for TEM analysis.
up to tens of micrometers, and most of them have di-ameter around 9 nm and a few of them have diam-eter around 20 nm, as shown in Fig 2 The smooth
ob-served The EDX spectrum (Fig.2, upper right) shows that the nano-wires were composed of Si and O with
an approximate atomic ratio of 1:2 C and Cu peaks
in the spectrum originated from the Cu grid used for TEM analysis The high-magniFcation TEM image of
a SiO2-NW is given in Fig 3 A clear Ni particle can be seen as the catalyst attached to the tip of the SiO2-NW The SAED pattern (inset of Fig.3) shows
no diGraction spots, indicating the amorphous nature
of the SiO2-NW, which was of the same nature as that
in the previous work [18]
The PL measurements at an excitation wave-length of 206 nm were carried out with a general Xe-light source Fig.4shows the PL spectrum of the
a normal emission band at around 544 nm, which
is believed to be due to neutral oxygen vacancies
of SiO2-NWs [18,19] Furthermore, a new emission band at 595 nm with very weak density could be also observed At present, the exact mechanism of
experiments will be needed
According to the vapor–liquid–solid (VLS) mecha-nism, the catalyst as islands can induce the deposition
Trang 3J Niu et al / Physica E 23 (2004) 1–4 3
Fig 3 TEM image of a single SiO2-NWs A Ni–Si droplet attached
to the tip of the SiO2-NW (the white arrow, lower inset) The
SAED pattern in the upper right indicates the amorphous nature
of the SiO2-NW.
Fig 4 PL spectrum of SiO2 -NWs measured at room temperature.
atoms to form droplets so that nano-wires can grow
[20] The diameter of the nanowires is dependent on
the size of the catalyst In most of the cases these two
sizes are very close In our experiments, the size of the
catalyst was uniform and very small (¡ 10 nm in
di-Fig 5 The sketch graphs of the SiO2-NWs growth.
ameter as shown in Fig.3) Those small catalyst par-ticles could easily form nuclei so that the nano-wires with smaller diameter could be grown on them
In the beginning of the nano-wire growth, the round
Ni particle and the Si atoms deposited from silane form
with more and more Si atoms melting, the droplets gradually reach supersaturation The Si atoms in the droplet will segregate when more Si atoms joined The segregation has an equal probability in the 360◦area around the droplets that place on the smooth silicon substrates Therefore, the segregated Si atoms would grow around the droplet with the crystal directions Si (1 1 1), Si (2 2 0), Si (3 1 1), etc (Fig.5b) According
to the lowest energy theory, the Si (1 1 1) direction will dominate the Fnal growth, for it is the lowest en-ergy Because the consumed Si atoms, due to the earli-est growth of Si (1 1 1) direction, gradually to reach a homeostasis with the deposited Si atoms, the growth of other new Si (1 1 1) directions will not appear around the droplet (Fig.5c) Thus with the prolonged grow-ing time, the Si atoms along with (1 1 1) direction
moved forward slowly accompanying the growth of the SiNWs One thing must be mentioned: the newly formed SiNWs will be oxidized rapidly to amorphous
degree and the impure reaction gases in the quartz
tube Since the temperature (∼ 1000 ◦C) is much lower than the crystalline temperature of the SiO2-NWs, this
Trang 44 J Niu et al / Physica E 23 (2004) 1–4
induces the original nano-silicon structure to an
amor-phous SiO2-NWs and round-belt SiO2 structure (see
the TEM image in Fig.3)
In the primary phase of the SiNWs, the droplets are
pushed forward slowly with the continued growth If
only one droplet exists on the silicon wafer, the droplet
will be pushed to one direction straightly Therefore,
the SiNWs will be uniform and straight growing under
this condition (Fig 5d) In fact, hundreds and
thou-sands of droplets on the substrates collide unavoidably
during the co-instantaneous growth When a moving
droplet encounters another moving droplet, the two
droplets will commix to a bigger droplet (Fig.5e,
be-cause the outside silicon ring is very thin, we ignore
its very weak eGect) When Si atoms drop in, the new
droplet will reach supersaturation again to segregate
and will keep the former SiNWs to grow continually
But the growth velocity (Fig.5f) has been slower in
comparison with the original SiNWs (Fig.5c) A
cer-tain angle (in Fig.5f) between the two diGerent
di-rectional SiNWs induces the SiNWs to grow curly (see
Fig.5g) The SiNWs formed under this condition are
commonly curving (see the circular regions in Fig.2)
Obviously, the number of commixed SiNWs droplets
is very small Even the encountering of three or more
than three droplets is much less (Fig.5h) The
major-ity is that one droplet forms a SiNW and its diameter
is relatively straight, as shown Fig.2 A deeper
might contribute to the successful synthesis and
de-vice application of one-dimensional quantum wires
4 Conclusions
about 9 nm and a length of more than 10 m were
synthesized on a p-Si (1 1 1) wafer The experiments
of SEM and TEM found that nano-wires were
com-posed of Si and O with an approximate atomic ratio
of 1:2 and were of amorphous nature Besides the
nor-mal emission band at 544 nm, a new weak emission
also observed
Acknowledgements This work was supported by the National Natu-ral Science Foundation of China (No 50272057 and 60225010) and Zhejiang Provincial Natural Science Foundation (No 601092) The authors also express their gratitude to Prof Youwen Wang for the TEM measurement
References
[1] D.D.D Ma, C.S Lee, Y Lifshitz, S.T Lee, Appl Phys Lett.
81 (2002) 3233.
[2] S Nihonyanagi, Y Kanemitsa, Physica E 17 (2003) 183 [3] J.J Niu, J Sha, Y.W Wang, X.Y Ma, D.R Yang, Microelectron Eng 66 (2003) 65.
[4] D.P Yu, Y.J Xing, Q.L Hang, H.F Yan, J Xu, Z.H Xi, S.Q Feng, Physica E 9 (2001) 305.
[5] J Sha, J.J Niu, X.Y Ma, J Xu, X.B Zhang, Q Yang, D.R Yang, Adv Mater 14 (2002) 1219.
[6] J.J Niu, J Sha, X.Y Ma, J Xu, D.R Yang, Chem Phys Lett 367 (2003) 528.
[7] H Zhang, X.Y Ma, J Xu, J.J Niu, J Sha, D.R Yang,
J Cryst Growth 246 (2002) 108.
[8] T.I Kamins, R Stanley Williams, T Hesjedal, J.S Harris, Physica E 13 (2002) 995.
[9] Y Cui, C.M Lieber, Science 291 (2001) 851.
[10] N Wang, Z.K Tang, G.D Li, J.S Chen, Nature 408 (2000) 50.
[11] D.D.D Ma, C.S Lee, F.C.K Au, S.Y Tong, S.T Lee, Science 299 (2003) 1874.
[12] D.P Yu, Q.L Hang, Y Ding, H.Z Zhang, Z.G Bai, J.J Wang, Y.H Zou, Appl Phys Lett 73 (1998) 3076 [13] M Zhang, Y Bando, K Wada, K Kubashima, J Mater Sci Lett 18 (1999) 1911.
[14] M Zhang, Y Bando, K Wada, J Mater Res 15 (2000) 387 [15] Z.Q Liu, S.S Xie, L.F Sun, D.S Tang, W.Y Zhou, C.Y Wang, W Liu, Y.B Li, X.P Zou, G Wang, J Mater Res.
16 (2001) 683.
[16] J.C Wang, G.Z Zhan, F.G Li, Solid State Commun 125 (2003) 629.
[17] Z.W Pan, Z.R Dai, C Ma, Z.L Wang, J Am Chem Soc.
124 (2002) 1817.
[18] J.Q Hu, Y Jiang, X.M Meng, C.S Lee, S.T Lee, Chem Phys Lett 367 (2003) 339.
[19] H Nishikawa, T Shiroyama, R Nakamura, Y Ohiki,
K Nagaswa, Y Hama, Phys Rev B 45 (1992) 586 [20] R.S Wangner, W.C Ellis, Appl Phys Lett 4 (1964) 89.