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 38 (2007) 27–30
Flower-like silicon nanostructures Zhihong Liua, Jia Shaa,b, Qing Yanga, Zixue Sua,b, Hui Zhanga, Deren Yanga,
a State Key Laboratory of Silicon Materials, Zhejiang University, Zheda Road 38, Hangzhou 310027, PR China
b Department of Physics, Zhejiang University, Zheda Road 38, Hangzhou 310027, PR China
Available online 17 December 2006
Abstract
In this paper we present a flower-like silicon nanostructure grown by combining the oxidation-assisted growth (OAG) mechanism and the vapor–liquid–solid (VLS) growth mechanism It is found that the flower-like silicon nanostructures are nucleated initially via the VLS mechanism and then grown on silicon wafer via the OAG mechanism Furthermore, light emission was observed, which is considered to
be the enhanced photothermal effect
r2007 Elsevier B.V All rights reserved
PACS: 68.65 k; 78.20.Nv; 78.67 n
Keywords: Silicon; Flower-like; Photothermal; Nanowires
1 Introduction
During recent years, silicon nanostructures have attracted
much attention due to their potential applications in
interconnection and basic blocks for future nanoscale
electronic and optoelectronics devices [1–3], and sensor
applications[4–6] There are two major synthesis methods:
vapor–liquid–solid (VLS) and oxide-assisted growth (OAG)
The VLS process was originally developed by Wagner [7]
and co-workers, recently Lieber, Yang, and many other
research groups used it to generate silicon nanowires and
other nanowires[8–11] The VLS process is a well-controlled
method, while the OAG method[12–15]can produce large
quantity SiNWs by the simple thermal evaporation of
silicon monoxide powders Furthermore, different
morphol-ogies such as wires, rods, chains, coaxial cables, and ribbon
structures can be produced in the OAG process
In this paper we present a flower-like silicon
nanos-tructures grown by combining the thermal evaporation of
silicon monoxide (SiO) powders with the VLS growth
mechanism Enhanced photothermal effect is observed
2 Experiment The flower-like silicon nanostructure was synthesized by thermal evaporation SiO powders at 1100 1C in an evacuated quartz tube SiO powders (99.99%, Shanghai Chemical Co.) were put in the center of the furnace, and several n-type (1 1 1) silicon wafers with a resistivity of about 0.01 O cm were placed in the downstream The silicon wafers were cleaned by the standard RCA process, then covered with a 10 nm thick Au film The furnace was evacuated to 30 Pa by a mechanical pump, meanwhile the temperature of the furnace was raised up to 1100 1C at a heating rate of 20 1C/s Then a mixed gas of Ar (80%) and
H2(20%) at 104Pa was kept flowing at a flow rate of 250 standard cubic centimeters per minute (sccm) through the tube After 3 h of growth, the flower-like silicon nanos-tructure was formed on the silicon substrates of the downstream at the area of about 700 1C For comparison, the silicon wafers without Au film deposition were also prepared, and the same experiments were carried out The as-grown specimens were analyzed by a field emission scanning electronic microscope (FESEM, FEI, Sirion), a transmission electronic microscope (TEM, JEM-2010, JEOL), and a fiber optical spectrometer (Tensail TS100A)
www.elsevier.com/locate/physe
1386-9477/$ - see front matter r 2007 Elsevier B.V All rights reserved.
doi: 10.1016/j.physe.2006.12.028
Corresponding author Tel.: +86 571 87951667;
fax: +86 571 87952322.
E-mail address: mseyang@zju.edu.cn (D Yang).
Trang 23 Result and discussion
Fig 1 is the SEM image of an as-grown specimen The
flower-like nanostructures with the diameter of
500–1000 nm and the length of 3–5 mm on the silicon
substrate can be observed A typical flower is composed of
an intertwined stem, a bulbous head consisting of a tight bundle of several nanowires, and a single catalyst particle attached at the top end of the flower-like nanostructures The TEM image of a flower-like silicon nanostructure on
a holey carbon grid is given inFig 2 The upper right inset
of Fig 2 is the selected area electron diffraction (SAED)
Fig 2 TEM image of a flower-like nanostructure The upper right inset is the SAED pattern of the stem, which is marked with an arrow b Fig 1 SEM image of an as-grown specimen The surface of the silicon substrate is covered with flower-like silicon nanostructures The white arrow reveals a single catalyst particle attached at the top end of a flower-like nanostructure.
Trang 3pattern of the stem, which is marked as b with an arrow It
indicates that the flower-like silicon nanostructures are
crystalline in nature.Figs 3a and bare the corresponding
energy dispersive X-ray spectroscopy (EDX) data of the
head (marked as a with an arrow inFig 2) and the stem
(marked as b with an arrow in Fig 2) of the flower-like
silicon nanostructure The EDX spectra show that the stem
only contains Si and O elements, while the head contains
2.8 at% Au besides Si and O
On the basis of the results of SEM and TEM, it is
considered that the growth of those flower-like silicon
nanostructures is via both of the VLS process and the
OAG process In the initial stage, the Au film is dissolved
as liquid drops on silicon substrate, and then those Au
drops act as catalysts to enhance the nucleation of silicon
nanostructures, which is described as the VLS process[8]
Later, silicon nanostructures are grown up on the
nucleation sites via SiO vapor, which is the so-called OAG process [16] The growth may take place at the periphery of the Au liquid drops As a result, the Au ball is pushed away from the silicon substrate and lifts upward by the growing nanowires In the silicon substrate without Au film, no flower-like structures were observed besides individual nanowires
Under the irradiation of a 980 nm laser of 100 mW, the as-grown specimen emits a visible light.Fig 4is the optical spectrum It can be seen that the wavelength of the light is mainly from 520 to 860 nm It is believed that the emitting
of the light is due to the enhanced photothermal effect of silicon nanostructures which was reported by N Wang et
al [17] The special structure of flower-like silicon nanostructures enhances the optical absorption, and raises the temperature of the nanostructures, so that the silicon nanostructures emit visible light
Spectrum 3 Atomic%
Element Weight% Atomic%
0 Ca O
AuSi a
b
Au Au
Au
Au Au
Ca Ca
Full Scale 368 cts Cursor: -0.102 keV (0 cts) 1 2 3 4 5 6 7 8 9 10
keV
0 O Si
Full Scale 368 cts Cursor: -0.102 keV (0 cts) 1 2 3 4 5 6 7 8 9 10
keV
65.69
Spectrum 2
Fig 3 (a) is the corresponding EDX data of the head (marked as a with an arrow in Fig 2 ) and (b) is the corresponding EDX data of the stem (marked as
b with an arrow in Fig 2 ) The upper right insets in the spectra are the element rate table, respectively.
Trang 44 Conclusions
We have demonstrated the synthesis of flower-like silicon
nanostructures The synthesis can be controlled at optimal
experimental condition consistent with a VLS growth
mechanism The optical characterization of the as-prepared
flower-like silicon nanostructures has been carried out, and
light emission into visible range was observed, which is
believed to be due to the enhanced photothermal effect
Acknowledgments The authors would like to thank the Natural Science Foundation of China (Grant No 60225010) for financial support
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0
100
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λ nm
Fig 4 Optical spectrum of flower-like nanostructure excited by a 980 nm
laser under a power of 100 mW.