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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 2 — Jan. 17, 2011
  • pp: 597–605
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Si nanorod length dependent surface Raman scattering linewidth broadening and peak shift

Gong-Ru Lin, Yung-Hsiang Lin, Yi-Hao Pai, and Fan-Shuen Meng  »View Author Affiliations


Optics Express, Vol. 19, Issue 2, pp. 597-605 (2011)
http://dx.doi.org/10.1364/OE.19.000597


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Abstract

Enhanced Stoke Raman scattering of large-area vertically aligned Si nanorod surface etched by metal-particle-catalytic is investigated. By enlarging the surface area with lengthening Si nanorods, the linear enhancement on Stoke Raman scattering intensity at 520 cm−1 is modeled to show well correlation with increasing quantity of surface Si dangling bonds. With Si nanorod length increasing from 0.19 to 2.73 μm, the Raman peaks of the as-etched and oxidized samples gradually shift from −4 cm−1 and from −4.5 cm−1 associated with their linewidth broadening from 3 to 9 cm−1 and from 7 to 18 cm−1, respectively. The peak intensity of Raman scattering signal from Si nanorod could be enhanced with the increase of interaction area as the number of phonon mode directly corresponds to the tetrahedrally coordinated Si vibrations in the bulk crystal lattice. The asymmetric linewidth broadening and corresponding Raman peak shift is affected by the strained Si nanorod surface caused by etching and the crystal quality. Fourier transform infrared spectroscopy corroborates the dependency between nanorod length and Si-O-Si stretching mode absorption (at 1097 cm−1) on oxidized Si nanorod surface, elucidating the increased transformation of surface dangling bonds to Si-O-Si bonds for passivating Si nanorods and attenuating Stoke Raman scattering after oxidation.

© 2011 OSA

1. Introduction

In this work, the enhanced Raman scattering effect of the large-area vertically aligned Si nanorod with controlled length and diameter obtained by metal-particle-catalytic wet etching process is investigated. By controlling the etching time, the linear function of rod length can be precisely detuned to change the nanorod roughened surface area and the quantity of surface Si dangling bonds. To confirm, the FTIR is employed to detect the dependency between nanorod length and the quantity of Si-O-Si stretching mode absorption (at 1097 cm−1) on the oxidized Si nanorod surface. The effect of surface dangling bond density on the enhancement of the Stoke Raman scattering intensity at 520 cm−1 is characterized. By passivating the surface Si dangling bonds of the Si nanorods with high-temperature annealing induced oxidation, the dramatic attenuation on Stoke Raman scattering intensity is observed.

2. Experiment Setup

In experiment, a metal-particle-catalytic wet-etching in HF/AgNO3 aqueous solution at 50°C is utilized to fabricate large-area vertically aligned Si nanorod on (100)-oriented p-type Si substrate. Four chemical reactions are involved to the whole process [10

10. G.-R. Lin, F. S. Meng, Y. H. Pai, Y. C. Chang, and S. H. Hsu, “Manipulative depolarization and reflectance spectra of morphologically controlled nano-pillars and nano-rods,” Opt. Express 17(23), 20824–20832 (2009). [CrossRef] [PubMed]

]: (1) 2H+ + 2e-→H2, (2) Ag+ + e-→Ag, (3) Si + 2F-→SiF2 + 2e-, (4) Si + 2F- + 2H+→SiF2. The Si substrate is initially deposited by thin silver film and the silver atoms self-aggregate with random distribution under rapid thermal annealing process. The silver dots function as the etching pores to facilitate the Si nanorod formation during wet-etching. Afterwards, a HNO3 solution is used to clean the wrapped silver film on the rods and the Si nanorod covered Si substrate.

3. Results and Discussions

As evidence, the Raman scattering signal of Si substrate greatly enhances by etching out the nanorod structure at its surface, whereas the Raman peak intensity show a slightly saturating trend with lengthening nanorods. By setting the Raman intensity of bulk Si as unitary count, the Fig. 3
Fig. 3 Raman intensity enhancement of as-etched samples and ozidized samples.
shows that the Raman scattering intensity enhancement factor (related to that of bulk Si) of the as-etched Si nanorod samples are increased from 7.1 (40.5 counts/5.7 counts) to 41.9(238.8 counts/5.7 counts) as the Si nanorod length enlarges from 0.19 μm to 2.73 μm. In opposite, the Raman scattering signal of the Si nanorod samples after high-temperature annealing at atmosphere environment diminishes its peak intensity due to the heavily oxidized surface of the Si nanorod samples. The surface Raman scattering spectra of the oxidized Si nanorod samples are demonstrated in Fig. 2(b). After heavily oxidizing the Si nanorods by annealing these samples in atmosphere at 1050°C for 30 min, the Raman scattering signal dramatically degrades with its enhancement factor decaying from 41.9 to 3.5 due to the complete passivation of surface dangling bonds by oxygen. Similar diminishing phenomenon of Si-Si dependent Raman signal can also be obtained by using hydrogen or oxygen atoms to passivate the Si surface [20

20. B. Ren, F. M. Liu, J. Xie, B. W. Mao, Y. B. Zu, and Z. Q. Tian, “In situ monitoring of Raman scattering and photoluminescence from silicon surfaces in HF aqueous solutions,” Appl. Phys. Lett. 72(8), 933–935 (1998). [CrossRef]

,21

21. L. Z. Liu, X. L. Wu, Z. Y. Zhang, T. H. Li, and P. K. Chu, “Raman investigation of oxidation mechanism of silicon nanowires,” Appl. Phys. Lett. 95(9), 093109–093111 (2009). [CrossRef]

]. In principle, the oxidation condition used in this work is expected to convert approximately 10-60 nm thick Si nanorod surface into SiO2 (based on the online Silicon Thermal Oxide Thickness Calculator developed by the Stanford University). Therefore, a significant drop on the intensity of Raman scattered signal is expectable with the complete oxidation of Si nanorod surface. After such surface oxidation procedure, the Raman scattering enhancement factor of the Si nanorods with different lengths significantly attenuates to range between 1.3 and 3.5.

Such an enhancement on surface Raman scattering intensity of the as-etched Si nanorod sample is mainly attributed to the increment of the sample surface area after a simulation on the proportionality between the Raman peak intensity and the total surface area of the Si nanorod sample. To calculate the increment on surface area by etching Si nanorods on the smooth Si substrate (with area of A0), we assume the surface area of the as-etched Si substrate as A1, the uniform Si nanorod length and diameter of h and d, respectively. The total surface area of the as-etched sample is enlarged by increasing the side walls of Si nanorods and written as A1 = A0 + Nπdh, where N is the quantity of Si nanorods. Without passivation, a Si atom at substrate surface has two dangling bonds and the quantity of dangling bonds is proportional to the surface area. Thus, the increasing ratio of surface dangling bonds as compared to the Si substrate is linearly proportional to the increasing ratio of surface area given by A1/A0 = 1 + (Nπdh)/A0. The geometrical parameters of nanorods are employed to quantitatively fit the Raman intensity of Si nanorods (normalized to that of Si). Within an effective area A0 of 25π μm2 of the micro-Raman system with 10-μm illuminating spot, the denser nanorods with similar diameter of 50 nm but shorter length are obtained in shorter etching time due to the smaller aggregated size of Ag nanodots [20

20. B. Ren, F. M. Liu, J. Xie, B. W. Mao, Y. B. Zu, and Z. Q. Tian, “In situ monitoring of Raman scattering and photoluminescence from silicon surfaces in HF aqueous solutions,” Appl. Phys. Lett. 72(8), 933–935 (1998). [CrossRef]

]. The nanorod quantity N of Si nanorods per 100 μm2 reduces from 1.85 × 104 to 0.76 × 104 with increasing etching time (from 2 to 20 min), such that the modified factor A1/A0 = 1 + (Nπdh)/A0 can coincidently fit the experimental data of Raman intensity enhancement, the Raman scattering enhancement factor as a function of rod length for the as-etched and the oxidized Si nanorod samples with the simulation curve obtained by the aforementioned formula of total surface area increasing ratio are demonstrated in Fig. 3. Consequently, the Raman intensity linearly enhances with increasing Si nanorod length as well as enlarging effective surface area, which is linearly proportional to the number of surface dangling bonds with maximum surface area density up to 5 × 1013 cm−2 [22

22. E. Cartier, J. H. Stathis, and D. A. Buchanan, “Passivation and depassivation of silicon dangling bounds at the Si/SiO2 interface by atomic hydrogen,” Appl. Phys. Lett. 63(11), 1510–1512 (1993). [CrossRef]

].

The localized strain and imperfection near Si nanorod surface inevitably leads to an optical phonon scattering with asymmetric linewidth broadening, these characteristic parameters were correlated with each other by quantum mechanics [31

31. J. Camassel, L. A. Falkovsky, and N. Planes, “Strain effect in silicon-on-insulator materials: Investigation with optical phonons,” Phys. Rev. B 63(3), 035309 (2000). [CrossRef]

] to give a relationship between the inhomogeneous phonon scattering linewidth broadening (Δτ) and the strain as below [31

31. J. Camassel, L. A. Falkovsky, and N. Planes, “Strain effect in silicon-on-insulator materials: Investigation with optical phonons,” Phys. Rev. B 63(3), 035309 (2000). [CrossRef]

],
Δτ=ττ0=Btan1θ=cν24πw0s2tan1θ=c(gr02w02)24πw0s2tan1(s2r02w0τ)cg2r02w024πτ.
(1)
where τ denotes the optical-phonon linewidth for Si nanorod, τ0 the FWHM of Raman scattering signal for bulk Si, B the phonon-strain scattering probability, c the dislocation concentration, υ the phonon-dislocation interaction, w0 the central wavenumber of Raman scattering signal for Si (520 cm−1), s the dispersion parameter for Si, g the dimensionless constant, θ = s2/r02w0τ, and r0 the radius of dislocation core. After simplification, the broadened linewidth is found to exhibit a linear proportionality with the dislocation concentration (Δτcg2r02w02/4πτ). During simulation, the aforementioned parameters are set as w0 = 520 cm−1, r0 = 0.13 nm, g = 100. The area dislocation density calculated from the experimental data are shown in Fig. 7(a)
Fig. 7 (a) Calculated area dislocation density of Si nanorod surface with different lengths. (b) The simulated spectral linewidth increment of surface Raman scattering signal from Si nanorod surface
, which is slightly larger than 108-109 cm−2 found in the HF etched porous Si. Figure 7(b) demonstrates the experimental and simulated results of the spectral linewidth increment on surface Raman scattering intensity (related to that of bulk Si sample). It is seen that the simulated results correlate well with the experimental results and increase with lengthening Si nanorod, which confirm the direct contribution of the area dislocation density on Si nanorod surface to the linewidth broadening of the enhanced Raman scattering. A corroborative derivation was also disclosed by Camassel et al. [31

31. J. Camassel, L. A. Falkovsky, and N. Planes, “Strain effect in silicon-on-insulator materials: Investigation with optical phonons,” Phys. Rev. B 63(3), 035309 (2000). [CrossRef]

]. Note that the enlarged dislocation core could effectively release the strain, whereas the variation of the dislocation core radius represents the stress of the crystal lattice. Since there is no variation on the radius of a dislocation core at Si nanorod surface during etching procedure, this parameter is thought to be independent from Si nanorod lengthening and optical-phonon linewidth broadening. In contrast, the phonon-strain interaction probability can be linearly enhanced with lengthening Si nanorod by enlarging the dislocation concentration with increasing surface area of Si nanorod. This is attributed to be the dominant factor to cause the linewidth broadening of Raman scattering signal. Increasing the Si nanorod length by etching would concurrently enlarge the surface area as well as the dislocation concentration, which not only enhances the peak intensity but also broadens the optical-phonon linewidth of the Raman scattering at Si nanorod surface. Since the Raman scattering intensity of the lengthened Si nanorod sample is at least one order of magnitude larger than that of bulk Si due to the enhanced roughening on Si nanorod surface, the increasing efficiency is well proportional to the increment of surface area as well as the quantity of surface dangling bonds. For potential applications using the nano-roughened Si nanorod sample as a sensor of specific gas- or bio-molecules, such a phenomenon can be utilized as a tooling parameter to check the residual density of gas- or bio-molecules that passivate the Si nanorod surface. That is, the detecting sensitivity of surface Raman scattering diagnosis can also be improved by more than one order of magnitude by using the precisely controlled Si nanorod lengthening technology.

4. Conclusion

Acknowledgement

This work was financially supported by the National Science Council and National Taiwan University under grants NSC98-2221-E-002-023-MY3, NSC98-2623-E-002-002-ET, NSC97-2221-E-002-055, and NTU98R0062-07.

References and links

1.

H. J. Xu and X. J. Li, “Silicon nanoporous pillar array: a silicon hierarchical structure with high light absorption and triple-band photoluminescence,” Opt. Express 16(5), 2933–2941 (2008). [CrossRef] [PubMed]

2.

D. P. Yu, Z. G. Bai, J. J. Wang, Y. H. Zou, W. Qian, J. S. Fu, H. Z. Zhang, Y. Ding, G. C. Xiong, L. P. You, J. Xu, and S. Q. Feng, “Direct evidence of quantum confinement from the size dependence of the photoluminescence of silicon quantum wires,” Phys. Rev. B 59(4), R 2498– R 2501 (1999). [CrossRef]

3.

C. Lin and M. L. Povinelli, “Optical absorption enhancement in silicon nanowire arrays with a large lattice constant for photovoltaic applications,” Opt. Express 17(22), 19371–19381 (2009). [CrossRef] [PubMed]

4.

G.-R. Lin, C.-J. Lin, H.-C. Kuo, H.-S. Lin, and C.-C. Kao, “Anomalous microphotoluminescence of high-aspect-ratio Si nanopillars formatted by dry-etching Si substrate with self-aggregated Ni nanodot mask,” Appl. Phys. Lett. 90(14), 143102 (2007). [CrossRef]

5.

M. A. Ochsenkühn, P. R. T. Jess, H. Stoquert, K. Dholakia, and C. J. Campbell, “Nanoshells for surface-enhanced Raman spectroscopy in eukaryotic cells: cellular response and sensor development,” ACS Nano 3(11), 3613–3621 (2009). [CrossRef] [PubMed]

6.

P. Prabhathan, V. M. Murukeshan, Z. Jing, and P. V. Ramana, “Compact SOI nanowire refractive index sensor using phase shifted Bragg grating,” Opt. Express 17(17), 15330–15341 (2009). [CrossRef] [PubMed]

7.

I. Park, Z. Li, X. Li, A. P. Pisano, and R. S. Williams, “Towards the silicon nanowire-based sensor for intracellular biochemical detection,” Biosens. Bioelectron. 22(9-10), 2065–2070 (2007). [CrossRef]

8.

J. B. Driscoll, X. Liu, S. Yasseri, I. Hsieh, J. I. Dadap, and R. M. Osgood Jr., “Large longitudinal electric fields (Ez) in silicon nanowire waveguides,” Opt. Express 17(4), 2797–2804 (2009). [CrossRef] [PubMed]

9.

T. Stelzner, M. Pietsch, G. Andra, F. Falk, E. Ose, and S. Christiansen, “Silicon nanowire-based solar cells,” Nanotechnology 19(29), 295203 (2008). [CrossRef] [PubMed]

10.

G.-R. Lin, F. S. Meng, Y. H. Pai, Y. C. Chang, and S. H. Hsu, “Manipulative depolarization and reflectance spectra of morphologically controlled nano-pillars and nano-rods,” Opt. Express 17(23), 20824–20832 (2009). [CrossRef] [PubMed]

11.

L. Sirleto, V. Raghunatan, A. Rossi, and B. Jalali, “Raman emission in porous silicon at 1.54 μm,” Electron. Lett. 40(19), 1221–1222 (2004). [CrossRef]

12.

Z. Sui, P. P. Leong, I. P. Herman, G. S. Higashi, and H. Temkin, “Raman analysis of light-emitting porous silicon,” Appl. Phys. Lett. 60(17), 2086–2088 (1992). [CrossRef]

13.

L. Sirleto, M. A. Ferrara, B. Jalali, and I. Rendina, “Spontaneous Raman emission in porous silicon at 1.5 µm and prospects for a Raman amplifier,” J. Opt. A, Pure Appl. Opt. 8(7), S574–S577 (2006). [CrossRef]

14.

B. Li, D. Yu, and S. L. Zhang, “Raman spectral study of silicon nanowires,” Phys. Rev. B 59(3), 1645–1648 (1999). [CrossRef]

15.

W. S. Shi, H. Y. Peng, Y. F. Zheng, N. Wang, N. G. Shang, Z. W. Pan, C. S. Lee, and S. T. Lee, “Synthesis of large areas of highly oriented, very long silicon nanowires,” Adv. Mater. 12(18), 1343–1345 (2000). [CrossRef]

16.

K. Kitahara, K. Ohnishi, Y. Katoh, R. Yamazaki, and T. Kurosawa, “Analysis of defects in polycrystalline silicon thin films using Raman scattering spectroscopy,” Jpn. J. Appl. Phys. 42(Part 1, No. 11), 6742–6747 (2003). [CrossRef]

17.

K. Peng, H. Fang, J. Hu, Y. Wu, J. Zhu, Y. Yan, and S. T. Lee, “Metal-particle-induced, highly localized site-specific etching of Si and formation of single-crystalline Si nanowires in aqueous fluoride solution,” Chemistry 12(30), 7942–7947 (2006). [CrossRef] [PubMed]

18.

W. Wang, Z. Li, B. Gu, Z. Zhang, and H. Xu, “Ag@SiO2 core-shell nanoparticles for probing spatial distribution of electromagnetic field enhancement via surface-enhanced Raman scattering,” ACS Nano 3(11), 3493–3496 (2009). [CrossRef] [PubMed]

19.

S. M. Wells, S. D. Retterer, J. M. Oran, and M. J. Sepaniak, “Controllable nanofabrication of aggregate-like nanoparticle substrates and evaluation for surface-enhanced Raman spectroscopy,” ACS Nano 3(12), 3845–3853 (2009). [CrossRef] [PubMed]

20.

B. Ren, F. M. Liu, J. Xie, B. W. Mao, Y. B. Zu, and Z. Q. Tian, “In situ monitoring of Raman scattering and photoluminescence from silicon surfaces in HF aqueous solutions,” Appl. Phys. Lett. 72(8), 933–935 (1998). [CrossRef]

21.

L. Z. Liu, X. L. Wu, Z. Y. Zhang, T. H. Li, and P. K. Chu, “Raman investigation of oxidation mechanism of silicon nanowires,” Appl. Phys. Lett. 95(9), 093109–093111 (2009). [CrossRef]

22.

E. Cartier, J. H. Stathis, and D. A. Buchanan, “Passivation and depassivation of silicon dangling bounds at the Si/SiO2 interface by atomic hydrogen,” Appl. Phys. Lett. 63(11), 1510–1512 (1993). [CrossRef]

23.

A. Torres, A. Martín-Martín, O. Martínez, A. C. Prieto, V. Hortelano, J. Jiménez, A. Rodríguez, J. Sangrador, and T. Rodríguez, “Micro-Raman spectroscopy of Si nanowires: Influence of diameter and temperature,” Appl. Phys. Lett. 96(1), 011904–011906 (2010). [CrossRef]

24.

R. P. Wang, G. W. Zhou, Y. L. Liu, S. H. Pan, H. Z. Zhang, D. P. Yu, and Z. Zhang, “Raman spectral study of silicon nanowires: High-order scattering and phonon confinement effects,” Phys. Rev. B 61(24), 16827–16832 (2000). [CrossRef]

25.

M. Yang, D. Huang, P. Hao, F. Zhang, X. Hou, and X. Wang, “Study of the Raman peak shift and the linewidth of light-emitting porous silicon,” J. Appl. Phys. 75(1), 651–653 (1994). [CrossRef]

26.

I. M. Young, M. I. J. Beale, and J. D. Benjamin, “X-ray double crystal diffraction study of porous silicon,” Appl. Phys. Lett. 46(12), 1133–1135 (1985). [CrossRef]

27.

D. B. Mawhinney Jr, J. A. Glass, J. T. Yates, J. A. Glass Jr, and J. T. Yates, “FTIR Study of the Oxidation of Porous Silicon,” J. Phys. Chem. B 101(7), 1202–1206 (1997). [CrossRef]

28.

W. Kaiser, P. H. Keck, and C. F. Lange, “Infrared absorption and oxygen content in silicon and germanium,” Phys. Rev. 101(4), 1264–1268 (1956). [CrossRef]

29.

Q. Hu, H. Suzuki, H. Gao, H. Araki, W. Yang, and T. Noda, “High-frequency FTIR absorption of SiO2/Si nanowires,” Chem. Phys. Lett. 378(3-4), 299–304 (2003). [CrossRef]

30.

F. Ay and A. Aydinli, “Comparative investigation of hydrogen bonding in silicon based PECVD grown dielectrics for optical waveguides,” Opt. Mater. 26(1), 33–46 (2004). [CrossRef]

31.

J. Camassel, L. A. Falkovsky, and N. Planes, “Strain effect in silicon-on-insulator materials: Investigation with optical phonons,” Phys. Rev. B 63(3), 035309 (2000). [CrossRef]

OCIS Codes
(290.5860) Scattering : Scattering, Raman
(160.4236) Materials : Nanomaterials
(180.5655) Microscopy : Raman microscopy

ToC Category:
Materials

History
Original Manuscript: June 7, 2010
Revised Manuscript: August 1, 2010
Manuscript Accepted: August 10, 2010
Published: January 5, 2011

Citation
Gong-Ru Lin, Yung-Hsiang Lin, Yi-Hao Pai, and Fan-Shuen Meng, "Si nanorod length dependent surface Raman scattering linewidth broadening and peak shift," Opt. Express 19, 597-605 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-2-597


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References

  1. H. J. Xu and X. J. Li, “Silicon nanoporous pillar array: a silicon hierarchical structure with high light absorption and triple-band photoluminescence,” Opt. Express 16(5), 2933–2941 (2008). [CrossRef] [PubMed]
  2. D. P. Yu, Z. G. Bai, J. J. Wang, Y. H. Zou, W. Qian, J. S. Fu, H. Z. Zhang, Y. Ding, G. C. Xiong, L. P. You, J. Xu, and S. Q. Feng, “Direct evidence of quantum confinement from the size dependence of the photoluminescence of silicon quantum wires,” Phys. Rev. B 59(4), R 2498– R 2501 (1999). [CrossRef]
  3. C. Lin and M. L. Povinelli, “Optical absorption enhancement in silicon nanowire arrays with a large lattice constant for photovoltaic applications,” Opt. Express 17(22), 19371–19381 (2009). [CrossRef] [PubMed]
  4. G.-R. Lin, C.-J. Lin, H.-C. Kuo, H.-S. Lin, and C.-C. Kao, “Anomalous microphotoluminescence of high-aspect-ratio Si nanopillars formatted by dry-etching Si substrate with self-aggregated Ni nanodot mask,” Appl. Phys. Lett. 90(14), 143102 (2007). [CrossRef]
  5. M. A. Ochsenkühn, P. R. T. Jess, H. Stoquert, K. Dholakia, and C. J. Campbell, “Nanoshells for surface-enhanced Raman spectroscopy in eukaryotic cells: cellular response and sensor development,” ACS Nano 3(11), 3613–3621 (2009). [CrossRef] [PubMed]
  6. P. Prabhathan, V. M. Murukeshan, Z. Jing, and P. V. Ramana, “Compact SOI nanowire refractive index sensor using phase shifted Bragg grating,” Opt. Express 17(17), 15330–15341 (2009). [CrossRef] [PubMed]
  7. I. Park, Z. Li, X. Li, A. P. Pisano, and R. S. Williams, “Towards the silicon nanowire-based sensor for intracellular biochemical detection,” Biosens. Bioelectron. 22(9-10), 2065–2070 (2007). [CrossRef]
  8. J. B. Driscoll, X. Liu, S. Yasseri, I. Hsieh, J. I. Dadap, and R. M. Osgood., “Large longitudinal electric fields (Ez) in silicon nanowire waveguides,” Opt. Express 17(4), 2797–2804 (2009). [CrossRef] [PubMed]
  9. T. Stelzner, M. Pietsch, G. Andra, F. Falk, E. Ose, and S. Christiansen, “Silicon nanowire-based solar cells,” Nanotechnology 19(29), 295203 (2008). [CrossRef] [PubMed]
  10. G.-R. Lin, F. S. Meng, Y. H. Pai, Y. C. Chang, and S. H. Hsu, “Manipulative depolarization and reflectance spectra of morphologically controlled nano-pillars and nano-rods,” Opt. Express 17(23), 20824–20832 (2009). [CrossRef] [PubMed]
  11. L. Sirleto, V. Raghunatan, A. Rossi, and B. Jalali, “Raman emission in porous silicon at 1.54 μm,” Electron. Lett. 40(19), 1221–1222 (2004). [CrossRef]
  12. Z. Sui, P. P. Leong, I. P. Herman, G. S. Higashi, and H. Temkin, “Raman analysis of light-emitting porous silicon,” Appl. Phys. Lett. 60(17), 2086–2088 (1992). [CrossRef]
  13. L. Sirleto, M. A. Ferrara, B. Jalali, and I. Rendina, “Spontaneous Raman emission in porous silicon at 1.5 µm and prospects for a Raman amplifier,” J. Opt. A, Pure Appl. Opt. 8(7), S574–S577 (2006). [CrossRef]
  14. B. Li, D. Yu, and S. L. Zhang, “Raman spectral study of silicon nanowires,” Phys. Rev. B 59(3), 1645–1648 (1999). [CrossRef]
  15. W. S. Shi, H. Y. Peng, Y. F. Zheng, N. Wang, N. G. Shang, Z. W. Pan, C. S. Lee, and S. T. Lee, “Synthesis of large areas of highly oriented, very long silicon nanowires,” Adv. Mater. 12(18), 1343–1345 (2000). [CrossRef]
  16. K. Kitahara, K. Ohnishi, Y. Katoh, R. Yamazaki, and T. Kurosawa, “Analysis of defects in polycrystalline silicon thin films using Raman scattering spectroscopy,” Jpn. J. Appl. Phys. 42(Part 1, No. 11), 6742–6747 (2003). [CrossRef]
  17. K. Peng, H. Fang, J. Hu, Y. Wu, J. Zhu, Y. Yan, and S. T. Lee, “Metal-particle-induced, highly localized site-specific etching of Si and formation of single-crystalline Si nanowires in aqueous fluoride solution,” Chemistry 12(30), 7942–7947 (2006). [CrossRef] [PubMed]
  18. W. Wang, Z. Li, B. Gu, Z. Zhang, and H. Xu, “Ag@SiO2 core-shell nanoparticles for probing spatial distribution of electromagnetic field enhancement via surface-enhanced Raman scattering,” ACS Nano 3(11), 3493–3496 (2009). [CrossRef] [PubMed]
  19. S. M. Wells, S. D. Retterer, J. M. Oran, and M. J. Sepaniak, “Controllable nanofabrication of aggregate-like nanoparticle substrates and evaluation for surface-enhanced Raman spectroscopy,” ACS Nano 3(12), 3845–3853 (2009). [CrossRef] [PubMed]
  20. B. Ren, F. M. Liu, J. Xie, B. W. Mao, Y. B. Zu, and Z. Q. Tian, “In situ monitoring of Raman scattering and photoluminescence from silicon surfaces in HF aqueous solutions,” Appl. Phys. Lett. 72(8), 933–935 (1998). [CrossRef]
  21. L. Z. Liu, X. L. Wu, Z. Y. Zhang, T. H. Li, and P. K. Chu, “Raman investigation of oxidation mechanism of silicon nanowires,” Appl. Phys. Lett. 95(9), 093109–093111 (2009). [CrossRef]
  22. E. Cartier, J. H. Stathis, and D. A. Buchanan, “Passivation and depassivation of silicon dangling bounds at the Si/SiO2 interface by atomic hydrogen,” Appl. Phys. Lett. 63(11), 1510–1512 (1993). [CrossRef]
  23. A. Torres, A. Martín-Martín, O. Martínez, A. C. Prieto, V. Hortelano, J. Jiménez, A. Rodríguez, J. Sangrador, and T. Rodríguez, “Micro-Raman spectroscopy of Si nanowires: Influence of diameter and temperature,” Appl. Phys. Lett. 96(1), 011904–011906 (2010). [CrossRef]
  24. R. P. Wang, G. W. Zhou, Y. L. Liu, S. H. Pan, H. Z. Zhang, D. P. Yu, and Z. Zhang, “Raman spectral study of silicon nanowires: High-order scattering and phonon confinement effects,” Phys. Rev. B 61(24), 16827–16832 (2000). [CrossRef]
  25. M. Yang, D. Huang, P. Hao, F. Zhang, X. Hou, and X. Wang, “Study of the Raman peak shift and the linewidth of light-emitting porous silicon,” J. Appl. Phys. 75(1), 651–653 (1994). [CrossRef]
  26. I. M. Young, M. I. J. Beale, and J. D. Benjamin, “X-ray double crystal diffraction study of porous silicon,” Appl. Phys. Lett. 46(12), 1133–1135 (1985). [CrossRef]
  27. D. B. Mawhinney, J. A. Glass, J. T. Yates, J. A. Glass, and J. T. Yates, “FTIR Study of the Oxidation of Porous Silicon,” J. Phys. Chem. B 101(7), 1202–1206 (1997). [CrossRef]
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