OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 16 — Aug. 3, 2009
  • pp: 13869–13874
« Show journal navigation

Study of silicon nanofibrous structure formed by femtosecond laser irradiation in air

Sivakumar Manickam, Krishnan Venkatakrishnan, Bo Tan, and Venkat Venkataramanan  »View Author Affiliations


Optics Express, Vol. 17, Issue 16, pp. 13869-13874 (2009)
http://dx.doi.org/10.1364/OE.17.013869


View Full Text Article

Acrobat PDF (393 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

In this study, we report first time the effect of laser pulse repetition frequency and pulse width of femtosecond laser radiation on silicon nanofibrous structure formation under ambient condition. Surface nanotexture analysis revealed the changes in fibrous structure density and size in respect of laser pulse width and repetition frequency. A phonon confinement model is used to explain the Raman spectra of processed specimens in order to understand the structure details of nanofibrous structure and hence to support the surface nanotexture analysis. The present investigation leads to a conclusion that nanofibrous structure is formed due to the aggregation of silicon nanoparticles and their size is estimated using the confinement model which is in the order of few nanometers.

© 2009 Optical Society of America

1. Introduction

In this work we aim to study the effect of laser pulse width and frequency of femtosecond laser radiation on silicon nanofibrous structure formation by Scanning Electron Microscopy (SEM) and micro-Raman spectroscopy. Also a model based on confinement of phonons in nanoparticles is employed to explain the Raman spectra of laser processed specimens intend to clarify the nanofibrous structure details and to support nanotextural analysis.

2. Experiment

The experimental setup used in the present study is similar to that reported in Ref. [13

13. B. Tan and K. Venkatakrishnan, “Synthesis of fibrous nanoparticle aggregates by femtosecond laser ablation in air,” Opt. Express 17(2), 1064–1069 (2009). [CrossRef] [PubMed]

]. The laser source is a diode-pumped Yb-doped fiber oscillator/amplifier system capable of producing variable pulse energies up to 10 mJ at a pulse frequency between 200 kHz and 25 MHz. The laser radiation is circularly polarized and its average power varies between 0-20W. Arrays of microvias were drilled on a specimen of boron doped blank silicon wafer with <100> crystal orientation using 428 fs laser pulses with frequencies 4, 8, 13 and 26 MHz. In another experiment the microvias were drilled in a different location of the specimen at a constant pulse frequency of 13 MHz with pulse widths 428, 714, 1428 and 3571 fs. In both set of experiments, the average laser power is kept constant. The specimens were then characterized using micro-Raman spectroscopy followed by SEM. Back scattering micro-Raman analysis was performed at room temperature using 532 nm line of Ar ion laser source. The amorphous 490 cm-1 peak is isolated from the crystalline 518 cm-1 peak by deconvolution prior to the Fourier decomposition.

3. Results and discussion

SEM micrographs of the areas of specimen processed with a frequency of 13 MHz and 428, 714, 1428 and 3571 fs laser pulses are presented in Fig. 2. It is observed that the nanofibrous structure size increases with pulse width. However this increase is not due to the increase in number of nanoparticles which are agglomerating to form the structure but this is mainly due to an increase in the individual nanoparticles size (Fig.2). This is because the interaction time increases with pulse width. Thus as explained earlier the size of the nucleus formed increases due to coalescence of many nucleuses and as a consequence the size of the individual nanoparticle increases.

Fig. 1. SEM images of Si surface treated with frequencies a) 4, b) 8, c) 13 and d) 26 MHz.
Fig. 2. SEM images of Si surface treated at 13 MHz with pulse width a) 428, b) 714, c) 1428 and d) 3571 fs.

For laser processing parameters used in the present study nanofibrous structure size is observed to vary between 50 to 70 nm. In order to evaluate further the nanofibrous structural details in both cases, micro-Raman scattering experiments are performed on the same areas where the SEM micrographs has been taken.

Raman spectroscopy is a sensitive probe to local atomic arrangements and vibrations (phonons) in solids [16

16. A. K. Arora, M. Rajalakshmi, and T. R. Ravindran, “Phonon Confinement in Nanostructured Materials,” Encyclopedia of Nanoscience and Nanotechnology 8, 499–512 (2004).

]. This technique has been used to characterize nanostructures that provide information about the nature of crystalline structure, disorder and amorphization. In the lattice of single crystal, both optic and acoustic phonons can propagate as a wave and exhibit dispersion depending on their wavelength or equivalently their wave vector in the Brillouin zone. In nanostructured materials when a grain boundary is encountered the phonon propagation is interrupted. The phonon of an isolated grain can get reflected from the boundaries and remain confined within the grain. For nanoparticles and quantum dots the phonon confinement is 3 dimensional and the wave propagation is restricted in all three directions. Raman spectroscopy technique sample the optic phonons close to the Brillouin zone center (q = 0) and is a consequence of the periodicity of the crystal lattice. In the case of nanoparticles this crystal periodicity is interrupted, (q = 0) selection rule is relaxed and phonons away from the Brillouin zone center also contribute to the phonon line shape. Similar to the optical phonons, the acoustic phonons also get confined within the nanoparticles. In the elastic continuum limit, the confinement of long-wavelength acoustic phonons leads to the emergence of discrete modes of particle which depend on the elastic properties through the longitudinal and transverse sound velocities.

Interestingly micro-Raman spectra of regions around the laser drilled microvias of the specimens show two sharp peaks as well as a broad band (Fig. 3). At 4 MHz with 428 fs pulses, the sharp Raman peaks are centered at 518 cm-1 and 491 cm-1 while the broad band at 283 cm-1 (Fig. 3a). As frequency increases, the 518 cm-1 peak remain at same position while 491 cm-1 peak is shifted to lower wave number side and appears at 490 and 488.6 cm-1 respectively for 8 and 13 MHz. Nevertheless for 26 MHz this peak is shifted back to 490 cm-1. In Fig. 3b spectra of the specimen areas processed at a constant frequency of 13 MHz with pulse widths 428, 714, 1428 and 3571 fs are presented. As in first case, with increasing pulse width the peak at 518 cm-1 continues at the same position while the other sharp peak appears at 488.6, 488.1, 492.2 and 498 cm-1. Moreover the two sharp peaks are shifted by an amount of ~2 cm-1 and ~30 cm-1 respectively from the peak at 520 cm-1 that corresponds to bulk silicon. In all the processed regions a broad band centered at 283 cm-1 is observed. The peaks at ~490 cm-1 and 283 cm-1 are in excellent agreement with the predicted transverse optic (TO) and the 2-fold transverse acoustic (TA) modes of silicon nanoparticles [20

20. A. Kailer, K. G. Nickel, and Y. G. Gogotsi, “Raman microspectroscopy of nanocrystalline and amorphous phases in hardness indentations,” Journal of Raman Spectroscopy 30(10), 939–937 (1999). [CrossRef]

, 21

21. Y. Kanemitsu, H. Uto, Y. Masumoto, T. Matsumoto, T. Futagi, and H. Mimura, “Microstructure and optical properties of free-standing porous silicon films: Size dependence of absorption spectra in Si nanometer-sized crystallites,” Phys. Rev. B 48(4), 2827–2830 (1993). [CrossRef]

].

Fig. 3. Micro-Raman spectra of laser processed silicon surfaces a) with frequency b) with pulse width

For bulk silicon 520 cm-1 peak arises from first-order Raman scattering of transverse optical (TO) phonon modes which are degenerated at the Γ-point (phonon wave vector q = 0 near the center of the Brillouin zone). The 518 cm-1 sharp peak can be attributed to substrate silicon and the 2 cm-1 shift when compared to crystalline silicon peak at 520 cm-1, is possibly due to the strain induced by laser radiation. Therefore it is difficult to retain the crystal structure, and the sharp peak at 520 cm-1 . The stress in the irradiated silicon surface can be likely due to changes in the material resulting from crystalline variations of the resolidified material [22

22. I. De Wolf and H. E. Maes, “Mechanical stress measurements using micro-Raman spectroscopy,” Microsyst. Technol. 5(1), 13–17 (1998). [CrossRef]

]. For a uniaxial stress, there is a linear relation between the internal stress (σ) and the Raman peak shift. ∆ω (cm-1) = -2 × 10-9 σ (Pa) [22

22. I. De Wolf and H. E. Maes, “Mechanical stress measurements using micro-Raman spectroscopy,” Microsyst. Technol. 5(1), 13–17 (1998). [CrossRef]

]. A positive value of the shift indicates compressive stress, and a negative value of the shift indicates tensile stress. A shift of -2 cm-would correspond to a tensile stress of 1 GPa.

W(r,L)=exp(8π2r2L2),
(1)

C(0,q)2=exp(q2L216π2).
(2)

The Raman spectrum I(ω) due to this confined optical phonon is given by:

I(ω)=02πa0C(0,q)2dq[ωω(q)]2+(Γ0/2)2,
(3)

where a0 is lattice constant (0.543 nm) of silicon and Γ2 Raman line width of bulk silicon (4.5 cm-1). The phonon dispersion relation ω(q) is given by:

ω(q)=ω0120(qq0)2,
(4)

where ω0 is the zone-center optical phonon frequency and q0=2π/a0.

4. Conclusions

In conclusion, this study reports first time the study of silicon nanofibrous structure generated using femtosecond laser radiation in air at atmospheric pressure. SEM analysis of nanofibrous structure shows that laser pulse width and frequency has a significant effect on fibrous structure size and density. Further Micro-Raman peaks of the processed specimens are explained using the phonon confinement model and leads to the conclusion that the nanofibrous structure is a consequence of agglomeration of silicon nanoparticles. The change in nanoparticle size calculated as a function of laser pulse repetition frequency and pulse width using the confinement model agree well with the surface nanotexture analysis.

Acknowledgement

This research is funded by Natural Science and Engineering Research Council of Canada.

References

1.

F. Djurabekova and K. Nordlund, “Atomistic simulation of the interface structure of Si nanocrystals embedded in amorphous silica,” Phys. Rev. B 77(11), 115325 (2008). [CrossRef]

2.

S. Tiwari, F. Rana, H. Hanafi, A. Hartstein, E. F. Crabbé, and K. Chan, “A silicon nanocrystals based memory,” Appl. Phys. Lett. 68(10), 1377–1379 (1996). [CrossRef]

3.

S. Prezioso, S. M. Hossain, A. Anopchenko, L. Pavesi, M. Wang, G. Pucker, and P. Bellutti, “Superlinear photovoltaic effect in Si nanocrystals based metal-insulator-semiconductor devices,” Appl. Phys. Lett. 94(6), 062108 (2009). [CrossRef]

4.

T. Z. Lu, M. Alexe, R. Scholz, V. Talalaev, R. J. Zhang, and M. Zacharias, “Si nanocrystal based memories: Effect of the nanocrystal density,” J. Appl. Phys. 100(1), 014310 (2006). [CrossRef]

5.

P. Alpuim, S. A. Filonovich, C. M. Costa, P. F. Rocha, M. I. Vasilevskiy, S. Lanceros-Mendez, C. Frias, A. T. Marques, R. Soares, and C. Costa, “Fabrication of a strain sensor for bone implant failure detection based on piezoresistive doped nanocrystalline silicon,” J. Non-Cryst. Solids 354(19–25), 2585–2589 (2008). [CrossRef]

6.

I. Umezu, A. Sugimura, M. Inada, T. Makino, K. Matsumoto, and M. Takata, “Formation of nanoscale fine-structured silicon by pulsed laser ablation in hydrogen background gas,” Physical Review B 76, -(2007). [CrossRef]

7.

B. R. Tull, J. E. Carey, E. Mazur, J. P. McDonald, and S. M. Yalisove, “Silicon surface morphologies after femtosecond laser irradiation,” MRS Bull. 31, 626–633 (2006). [CrossRef]

8.

S. V. Zabotnov, L. A. Golovan’, I. A. Ostapenko, Y. V. Ryabchikov, A. V. Chervyakov, V. Y. Timoshenko, P. K. Kashkarov, and V. V. Yakovlev, “Femtosecond nanostructuring of silicon surfaces,” JETP Lett. 83(2), 69–71 (2006). [CrossRef]

9.

B. N. Chichkov, C. Momma, S. Nolte, F. vonAlvensleben, and A. Tunnermann, “Femtosecond, picosecond and nanosecond laser ablation of solids,” Applied Physics a-Materials Science & Processing 63, 109–115 (1996). [CrossRef]

10.

B. R. Tull, J. E. Carey, M. A. Sheehy, C. Friend, and E. Mazur, “Formation of silicon nanoparticles and web-like aggregates by femtosecond laser ablation in a background gas,” Applied Physics a-Materials Science & Processing 83, 341–346 (2006). [CrossRef]

11.

M. Y. Shen, C. H. Crouch, J. E. Carey, and E. Mazur, “Femtosecond laser-induced formation of submicrometer spikes on silicon in water,” Appl. Phys. Lett. 85(23), 5694–5696 (2004). [CrossRef]

12.

M. A. Sheehy, L. Winston, J. E. Carey, C. M. Friend, and E. Mazur, “Role of the background gas in the morphology and optical properties of laser-microstructured silicon,” Chem. Mater. 17(14), 3582–3586 (2005).E [CrossRef]

13.

B. Tan and K. Venkatakrishnan, “Synthesis of fibrous nanoparticle aggregates by femtosecond laser ablation in air,” Opt. Express 17(2), 1064–1069 (2009). [CrossRef] [PubMed]

14.

S. T. Li, S. J. Silvers, and M. S. ElShall, “Surface oxidation and luminescence properties of weblike agglomeration of silicon nanocrystals produced by a laser vaporization-controlled condensation technique,” J. Phys. Chem. B 101(10), 1794–1802 (1997). [CrossRef]

15.

S. Senadheera, B. Tan, and K. Venkatakrishnan, “Critical Time to Nucleation: Graphite and Silicon Nanoparticle Generation by Laser Ablation,” Journal of Nanotechnology 6(2009).

16.

A. K. Arora, M. Rajalakshmi, and T. R. Ravindran, “Phonon Confinement in Nanostructured Materials,” Encyclopedia of Nanoscience and Nanotechnology 8, 499–512 (2004).

17.

H. Richter, Z. P. Wang, and L. Ley, “The one phonon Raman spectrum in microcrystalline silicon,” Solid State Commun. 39(5), 625–629 (1981). [CrossRef]

18.

J. Bonse, K. W. Brzezinka, and A. J. Meixner, “Modifying single-crystalline silicon by femtosecond laser pulses: an analysis by micro Raman spectroscopy, scanning laser microscopy and atomic force microscopy,” Appl. Surf. Sci. 221(1–4), 215–230 (2004). [CrossRef]

19.

R. Prabakaran, R. Kesavamoorthy, S. Amirthapandian, and A. Ramanand, “Raman scattering and photoluminescence studies on O+ implanted porous silicon,” Mater. Lett. 58(29), 3745–3750 (2004). [CrossRef]

20.

A. Kailer, K. G. Nickel, and Y. G. Gogotsi, “Raman microspectroscopy of nanocrystalline and amorphous phases in hardness indentations,” Journal of Raman Spectroscopy 30(10), 939–937 (1999). [CrossRef]

21.

Y. Kanemitsu, H. Uto, Y. Masumoto, T. Matsumoto, T. Futagi, and H. Mimura, “Microstructure and optical properties of free-standing porous silicon films: Size dependence of absorption spectra in Si nanometer-sized crystallites,” Phys. Rev. B 48(4), 2827–2830 (1993). [CrossRef]

22.

I. De Wolf and H. E. Maes, “Mechanical stress measurements using micro-Raman spectroscopy,” Microsyst. Technol. 5(1), 13–17 (1998). [CrossRef]

23.

I. H. Campbell and P. M. Fauchet, “The effects of microcrystal size and shape on the one phonon Raman spectra of crystalline semiconductors,” Solid State Commun. 58(10), 739–741 (1986). [CrossRef]

24.

M. Yang, D. M. Huang, P. H. Hao, F. L. Zhang, X. Y. Hou, and Wang, “Study of the Raman Peak Shift and the Linewidth of Light-Emitting Porous Silicon,” J. Appl. Phys. 75(1), 651–653 (1994). [CrossRef]

OCIS Codes
(140.3390) Lasers and laser optics : Laser materials processing
(160.6000) Materials : Semiconductor materials
(160.4236) Materials : Nanomaterials

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: May 13, 2009
Revised Manuscript: July 8, 2009
Manuscript Accepted: July 15, 2009
Published: July 27, 2009

Citation
Sivakumar Manickam, Krishnan Venkatakrishnan, Bo Tan, and Venkat Venkataramanan, "Study of silicon nanofibrous structure formed by femtosecond laser irradiation in air," Opt. Express 17, 13869-13874 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-16-13869


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. F. Djurabekova, and K. Nordlund, "Atomistic simulation of the interface structure of Si nanocrystals embedded in amorphous silica," Phys. Rev. B 77(11), 115325 (2008). [CrossRef]
  2. S. Tiwari, F. Rana, H. Hanafi, A. Hartstein, E. F. Crabbé, and K. Chan, "A silicon nanocrystals based memory," Appl. Phys. Lett. 68(10), 1377-1379 (1996). [CrossRef]
  3. S. Prezioso, S. M. Hossain, A. Anopchenko, L. Pavesi, M. Wang, G. Pucker, and P. Bellutti, "Superlinear photovoltaic effect in Si nanocrystals based metal-insulator-semiconductor devices," Appl. Phys. Lett. 94(6), 062108 (2009). [CrossRef]
  4. T. Z. Lu, M. Alexe, R. Scholz, V. Talalaev, R. J. Zhang, and M. Zacharias, "Si nanocrystal based memories: Effect of the nanocrystal density," J. Appl. Phys. 100(1), 014310 (2006). [CrossRef]
  5. P. Alpuim, S. A. Filonovich, C. M. Costa, P. F. Rocha, M. I. Vasilevskiy, S. Lanceros-Mendez, C. Frias, A. T. Marques, R. Soares, and C. Costa, "Fabrication of a strain sensor for bone implant failure detection based on piezoresistive doped nanocrystalline silicon," J. Non-Cryst. Solids 354(19-25), 2585-2589 (2008). [CrossRef]
  6. I. Umezu, A. Sugimura, M. Inada, T. Makino, K. Matsumoto, and M. Takata, "Formation of nanoscale fine-structured silicon by pulsed laser ablation in hydrogen background gas," Physical Review B 76, - (2007). [CrossRef]
  7. B. R. Tull, J. E. Carey, E. Mazur, J. P. McDonald, and S. M. Yalisove, "Silicon surface morphologies after femtosecond laser irradiation," MRS Bull. 31, 626-633 (2006). [CrossRef]
  8. S. V. Zabotnov, L. A.  Golovan’, I. A.  Ostapenko, Y. V.  Ryabchikov, A. V.  Chervyakov, V. Y.  Timoshenko, P. K.  Kashkarov, and V. V.  Yakovlev, "Femtosecond nanostructuring of silicon surfaces," JETP Lett. 83(2), 69-71 (2006). [CrossRef]
  9. B. N. Chichkov, C. Momma, S. Nolte, F. vonAlvensleben, and A. Tunnermann, "Femtosecond, picosecond and nanosecond laser ablation of solids," Applied Physics a-Materials Science & Processing 63, 109-115 (1996). [CrossRef]
  10. B. R. Tull, J. E. Carey, M. A. Sheehy, C. Friend, and E. Mazur, "Formation of silicon nanoparticles and web-like aggregates by femtosecond laser ablation in a background gas," Applied Physics a-Materials Science & Processing  83, 341-346 (2006). [CrossRef]
  11. M. Y. Shen, C. H. Crouch, J. E. Carey, and E. Mazur, "Femtosecond laser-induced formation of submicrometer spikes on silicon in water," Appl. Phys. Lett. 85(23), 5694-5696 (2004). [CrossRef]
  12. M. A. Sheehy, L. Winston, J. E. Carey, C. M. Friend, and E. Mazur, "Role of the background gas in the morphology and optical properties of laser-microstructured silicon," Chem. Mater. 17(14), 3582-3586 (2005).E [CrossRef]
  13. B. Tan, and K. Venkatakrishnan, "Synthesis of fibrous nanoparticle aggregates by femtosecond laser ablation in air," Opt. Express 17(2), 1064-1069 (2009). [CrossRef] [PubMed]
  14. S. T. Li, S. J. Silvers, and M. S. ElShall, "Surface oxidation and luminescence properties of weblike agglomeration of silicon nanocrystals produced by a laser vaporization-controlled condensation technique," J. Phys. Chem. B 101(10), 1794-1802 (1997). [CrossRef]
  15. S. Senadheera, B. Tan, and K. Venkatakrishnan, "Critical Time to Nucleation: Graphite and Silicon Nanoparticle Generation by Laser Ablation," Journal of Nanotechnology 6(2009).
  16. K. Arora, M. Rajalakshmi, and T. R. Ravindran, "Phonon Confinement in Nanostructured Materials," Encyclopedia of Nanoscience and Nanotechnology 8, 499-512 (2004).
  17. H. Richter, Z. P. Wang, and L. Ley, "The one phonon Raman spectrum in microcrystalline silicon," Solid State Commun. 39(5), 625-629 (1981). [CrossRef]
  18. J. Bonse, K. W. Brzezinka, and A. J. Meixner, "Modifying single-crystalline silicon by femtosecond laser pulses: an analysis by micro Raman spectroscopy, scanning laser microscopy and atomic force microscopy," Appl. Surf. Sci. 221(1-4), 215-230 (2004). [CrossRef]
  19. R. Prabakaran, R. Kesavamoorthy, S. Amirthapandian, and A. Ramanand, "Raman scattering and photoluminescence studies on O+ implanted porous silicon," Mater. Lett. 58(29), 3745-3750 (2004). [CrossRef]
  20. Kailer, K. G. Nickel, and Y. G. Gogotsi, "Raman microspectroscopy of nanocrystalline and amorphous phases in hardness indentations," Journal of Raman Spectroscopy 30(10), 939-937 (1999). [CrossRef]
  21. Y. Kanemitsu, H. Uto, Y. Masumoto, T. Matsumoto, T. Futagi, and H. Mimura, "Microstructure and optical properties of free-standing porous silicon films: Size dependence of absorption spectra in Si nanometer-sized crystallites," Phys. Rev. B 48(4), 2827-2830 (1993). [CrossRef]
  22. De Wolf, and H. E. Maes, "Mechanical stress measurements using micro-Raman spectroscopy," Microsyst. Technol. 5(1), 13-17 (1998). [CrossRef]
  23. H. Campbell, and P. M. Fauchet, "The effects of microcrystal size and shape on the one phonon Raman spectra of crystalline semiconductors," Solid State Commun. 58(10), 739-741 (1986). [CrossRef]
  24. M. Yang, D. M. Huang, P. H. Hao, F. L. Zhang, X. Y. 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]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.

Figures

Fig. 1. Fig. 2. Fig. 3.
 
Fig. 4.
 

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited