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Synthesis and Characterization of silicon nanowires
Wu Shan, Shao Yuanmin, Ye Fengfeng, Nie Tianxiao, and Yang Xinju
Phys. Dept., Fudan Univ., Shanghai, People’s Republic of China
.
1 Instruction
Silicon nanowires (Si NWs) have been considered as building blocks of next generation for novel electronic devices, biological/chemical sensors, optoelectronic
devices, renewable energy devices due to their unique electrical and optical properties, as well as their compatibility with the sophisticated Si technology.
Varieties of methods have been exploited to fabricate SiNWs, including vapor-liquid-solid(VLS) growth method,solution-liquid-solid growth method,laser assisted
catailtic growth and etc.However, some methods such as VLS method are expensive, energy-consuming process that require extreme conditions. A new simple
method of Synthesis large-scale Si nanowires are prepared here by directly annealing Si wafer coated with metallic Fe film with a flow of forming gas. Electrical
properties of a single Si nanowire is measured through Conductive-Atomic Force Microscope.
2.1 Synthesis of Si NWs
Cleaned P-type Si (100) wafer was deposited a 1-2 nm thick Fe film at room temperature by
molecular beam epitaxy (MBE). An annealing furnace equipped with a temperature controller and a
quartz tube was used for the NW synthesis. The Fe-coated Si wafer was then placed to the middle
of the quartz tube and annealed for 30-35 min under the forming gas with a flow rate of 150 L/h at
atmospheric pressure. After the completion of the NWs synthesis, the furnace was cooled naturally
to room temperature.
(a)
10nm
200nm
(c)
(b)
200nm
200nm
-10nm
AFM image of Fe-coated Si wafer after annealing at low temperature(1000)℃,
there are particles at different diameter.
(a)
(b)
Fe Film
SEM Image of Si nanowires growth at different temperature (a)1200℃ (b)1250℃ (c)1300℃.
With the increase of temperature, the quantity and length of nanowires are increased.
Si substrate
Si substrate
(c)
518
504
(a)
(d)
Si nanowires
(b)
Fe-Si alloy
Si substrate
Si substrate
200nm
Schematic diagram of Si NWs growth mechanism: (a)Cleaned Si wafer; (b) Fe film
deposited on the Si wafer; (c) formation of the Fe-Si alloy droplets; (d) continuous
diffusion of Si atoms through the wafer-catalyst interface into the alloy droplets, and the
growth of Si NWs through the catalyst-NW interface; and the finally formed Si NWs.
<321>
290
(c)
20nm
(a)TEM image of Si nanowire (b)-(c)HRTEM image and the
corresponding SAED pattern of nanowire labeled in (a)
SiNW
p+ Si Substrate
100
100nm
(a)
2.2 Electrical property of single SiNW
The synthesized Si NWs were dispersed in ethyl
alcohol by using sonication and then was
dispensed on the p+ Si substrate. We obtain a
random directional Si NWs layer, ConductiveAtomic Force Microscope is used to observe
single nanowire.
150
TUNA Current (pA)
Raman spectra of nanowires synthesized at 1300℃, nanowires were
scratched from the Si wafer to avoid their Raman signals. The peaks
both belong to both Si NWs.
20pA
(b)
50
0
-50
-100
-150
-10
-5
0
5
10
Sample Bias (V)
2um
2um
-100nm
-20pA
Typical I–V characteristics curves of a single Si NW and Si
substrate at a different bias
Conductive-Atomic Force Microscope image of Si NW (a)Height image (b)TUNA CURRENT
image at DC Sample Bias of -2V
3 Conclusion
We have obtained Si nanowires by directly heating Fe-coated Si wafer. The diameter of Si nanowires range from dozens of nanometers to about 200nm.
There are synthesized by Solid-Liquid-Solid method which Fe acted as catalyst. Electrical properties have observed by Conductive-Atomic Force Microscope,
we can find that the Si nanowire is poor electric conduction, there maybe some other factors influencing our results we next have to resolve.
Reference
[1] Andrew T. Heitsh; Dayne D. Fanfair; Hsing-Yu Tuan; Brian A. Korgel , J. Am. Chem. Soc. 2008, 130, 5436–5437
[2] Nie T-X; Chen Z-G; Wu Y-Q; Wang J-L; Zhang J-Z; Fan Y-L;Yang X-J; Jiang Z-M and Zou J 2010 J. Phys. Chem. C,114,15370
[3]Wang, R. P.; Zhou, G. W.; Liu, Y. L.; Pan, S. H.; Zhang, H. Z.; Yu, D. P.; Zhang, Z. Phys. Rev. B 2000, 61, 16827.