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Fabrication of two-dimensional periodic nanostructures by two-beam interference of femtosecond pulses
Optics Express, Vol. 16, Issue 3, pp. 1874-1878 (2008)
http://dx.doi.org/10.1364/OE.16.001874
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– Abstract
1. Introduction
2. Experiments and discussion
3. Conclusion
– References and links
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1. Introduction
2. Experiments and discussion
3. Conclusion
– References and links
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Abstract
Two-dimensional periodic nanostructures on ZnO crystal surface were fabricated by two-beam interference of 790 nm femtosecond laser. The long period is, as usually reported, determined by the interference pattern of two laser beams. Surprisingly, there is another short periodic nanostructures with periods of 220-270 nm embedding in the long periodic structures. We studied the periods, orientation, and the evolution of the short periodic nanostructures, and found them analogous to the self-organized nanostructures induced by single fs laser beam.
© 2008 Optical Society of America
1. Introduction
Recently, there have been considerable interests in the fabrication of two- and three-dimensional (2D and 3D) photonic crystals (PCs), which consists of artificial periodic structures [1-6]. Various techniques were used to fabricate these periodic structures such as self-assembly of colloidal particles, direct laser writing, and holographic lithography (HL), etc. HL is a highly useful technique to fabricate periodic patterns in photosensitive materials by the interference of several coherent laser beams. One can fabricate various 2D and 3D periodic structures by changing the number of laser beams (usually >3) and their arrangements [1-5]. The periods were larger or nearly equal to the laser wavelength [4-5], therefore, it is still a challenge to improve the resolution of laser fabrication to obtain PCs with band-gap in visible spectrum [4].
T. Kondo, S. Matsuo, S. Juodkazis, V. Mizeikis, and H. Misawa, “Multiphoton fabrication of periodic structures by multibeam interference of femtosecond pulses,” Appl. Phys. Lett. 82, 2758–2760 (2003). [CrossRef]
T. Kondo, S. Matsuo, S. Juodkazis, V. Mizeikis, and H. Misawa, “Multiphoton fabrication of periodic structures by multibeam interference of femtosecond pulses,” Appl. Phys. Lett. 82, 2758–2760 (2003). [CrossRef]
T. Kondo, S. Juodkazis, V. Mizeikis, H. Misawa, and S. Matsuo, “Holographic lithography of periodic two-and three-dimensional microstructures in photoresist SU-8,” Opt. Express , 14, 7943–7953 (2006). [CrossRef] [PubMed]
T. Kondo, S. Juodkazis, V. Mizeikis, H. Misawa, and S. Matsuo, “Holographic lithography of periodic two-and three-dimensional microstructures in photoresist SU-8,” Opt. Express , 14, 7943–7953 (2006). [CrossRef] [PubMed]
Periodic structures induced by single laser beam have been studied intensively in the last four decades [7-8]. It was found that the periods were usually close to the laser wavelength when long pulse (ns and ps) laser or cw laser were used [7]. However, nanoripples with periods much less than the laser wavelengths have been fabricated in semiconductors and dielectrics after irradiation by femtosecond (fs) laser pulses [8-12]. Nanoripples with periods of 40-500 nm have been fabricated by using lasers at wavelengths of 267-2000 nm. We further studied the formation of regular short-periodic nanogratings on the surface of semiconductor crystals irradiated by two collinear laser beams [13], which suggested that the short-periodic nanostructures have potential applications in optical recording and photonic crystal fabrication.
J. Sipe, J. Young, J. Preston, and H. Driel, “Laser-induced periodic surface structure. I. Theory,” Phys. Rev. B 27, 1141–1154 (1983). [CrossRef]
J. Sipe, J. Young, J. Preston, and H. Driel, “Laser-induced periodic surface structure. I. Theory,” Phys. Rev. B 27, 1141–1154 (1983). [CrossRef]
Y. Shimotsuma, P. Kazansky, J. Qiu, and K. Hirao, “Self-organized nanogratings in glass irradiated by ultrashort light pulses,” Phys. Rev. Lett. 91, 247405–247408 (2003). [CrossRef] [PubMed]
T. Jia, H. Chen, M. Huang, F. Zhao, J. Qiu, R. Li, Z. Xu, X. He, J. Zhang, and H. Kuroda, Phys. Rev. B 72, 125429–125433 (2005). [CrossRef]
ZnO is an important compound semiconductor with a wide band gap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature. These properties make it a very useful material in optoelectronics. Several groups have reported the fabrication and the applications of various types of ZnO nanostructures such as nanoparticles, nanowires, nanobelts, and nanofilms [14-15].
M. Huang, S. Mao, H. Feick, H. Yan, Y. Wu, H. Kind, E. Weber, R. Russo, and P. Yang, “Room-temperature ultraviolet nanowire nanolasers,” Science , 292, 1897–1899 (2001). [CrossRef] [PubMed]
We demonstrated the fabrication of 2D periodic nanostructures formed on the surface of ZnO crystals applying a method of two-beam interference of femtosecond laser. This method is based on the two aspects discussed above: one is the long-periodic structures determined by the two-beam interference pattern [4-5], another is the short-periodic nanostructures induced by single fs laser beam [8-9]. Furthermore, the formation mechanism is discussed.
T. Kondo, S. Juodkazis, V. Mizeikis, H. Misawa, and S. Matsuo, “Holographic lithography of periodic two-and three-dimensional microstructures in photoresist SU-8,” Opt. Express , 14, 7943–7953 (2006). [CrossRef] [PubMed]
Y. Shimotsuma, P. Kazansky, J. Qiu, and K. Hirao, “Self-organized nanogratings in glass irradiated by ultrashort light pulses,” Phys. Rev. Lett. 91, 247405–247408 (2003). [CrossRef] [PubMed]
2. Experiments and discussion
Figure 1 shows the experimental set-up for fabrication of 2D periodic structures. Laser pulses at the wavelength of 790 nm with pulse duration of 120 fs were delivered from a commercial Ti:sapphire regenerative amplifier operated at 10 Hz repetition rate (Spectra Physics TSA-10F). The laser beam propagated through a half-wave plate and Glan polarizer, and then was split into two beams via a 50% beam splitter. Both of the two beams polarized along z-direction. One beam went through a delay line and reached the sample surface at the exact same time with the other one. Zero temporal point was determined by the signal of double frequency via a BBO crystal. The angle between the two laser beams was denoted as 2θ and could be easily changed by rotating of two mirrors of M1 and M2 [5].
N. Lai, W. Liang, J. Lin, C. Hsu, and C. Lin, “Fabrication of two- and three-dimensional periodic structures by multi-exposure of two-beam interference technique,” Opt. Express , 13, 9605–9611 (2005). [CrossRef] [PubMed]
Fig. 1. Experimental setup of two-beam interference used for fabrication of 2D periodic structures. HF=half-wave plate, GZ=Glan polarizer, BS=50% beam splitter, M=mirror, and L=lens.
ZnO crystal plate was 1.0 mm thick, and its surfaces were both normal to the c axis and optically polished. The samples were mounted on a XYZ-translation stage. After laser pulses irradiation, the sample was dipped in ethanol and pure water, and cleaned for 5 minutes with ultrasonic cleaner, respectively. The periodic structures formed on the sample surface were observed by using scanning electron microscope (SEM, JEOL JSM-5600).
The laser beams were focused with lenses of 250 mm focal length. The sample was transmitted to the position of 0.5 mm in front of the focal plane to enlarge the focus to 110 um in diameter. SEM images of the periodic structures are shown in Fig. 2. The pulse duration was about 120 fs, the spatial overlapping length was 36 um. Only in the central part of overlapping area, two laser beams interfered thoroughly. Therefore, the periodic structures were observed on the ablation area of 30×100 um2 (see Fig. 2(a)). If diffractive beam splitter method is adopted [1, 4], the periodic structures will be observed in the whole focus with 100 um in diameter.
T. Kondo, S. Matsuo, S. Juodkazis, V. Mizeikis, and H. Misawa, “Multiphoton fabrication of periodic structures by multibeam interference of femtosecond pulses,” Appl. Phys. Lett. 82, 2758–2760 (2003). [CrossRef]
T. Kondo, S. Juodkazis, V. Mizeikis, H. Misawa, and S. Matsuo, “Holographic lithography of periodic two-and three-dimensional microstructures in photoresist SU-8,” Opt. Express , 14, 7943–7953 (2006). [CrossRef] [PubMed]
Fig. 2. SEM images of 2D periodic nanostructures. The total pulse energy and irradiation time were 127 uJ and 6 s in (a -c), 154 uJ and 4s in (d), and 250 uJ and 10 s in (e), respectively.
Figures 2(b) and 2(c) show the SEM images in the white square marked in Figs. 2(a) and 2(b) at higher magnifications, respectively. These photos surprisingly represented 2D periodic structures. As reported update [4-5], only one dimensional periodic structure was obtained by two-beam interference method, and the period was determined by the interference pattern: Λ=λ/2sinθ. The laser wavelength λ is 790 nm, and the angle between the two laser beams is 2θ=35.2°. The period is estimated to be 1.31 um. The long period is 1.33 um (see Figs. 2(b) and 2(c)), which is in accordance with the theoretical value. Therefore, the long periodic structures are determined by the interference pattern of the two laser beams.
T. Kondo, S. Juodkazis, V. Mizeikis, H. Misawa, and S. Matsuo, “Holographic lithography of periodic two-and three-dimensional microstructures in photoresist SU-8,” Opt. Express , 14, 7943–7953 (2006). [CrossRef] [PubMed]
Besides the long periodic structures, there are short periodic nanostructures (nanogratings) embedding in the long ones. The nanograting is of 1.14 um wide, and its period is only 250 nm. If the total pulse energy increased to 154 uJ and the irradiation time decreased to 4 s, the nanograting width decreased to 1 um, and its period increased to 270 nm (shown in Fig. 2(d)). We adjusted the laser conditions, and found the width of the short periodic structure changed in the range of 0.4-1.15 um while the long period kept as 1.33 um. If the pulse energy was higher than 240 uJ, the nanogratings were ablated. However, on the interval line between each nanogratings, periodic nanospots of 0.5 um long and 0.25 um wide appeared (Fig. 2(e)). In one square centimeter in the sample surface, there was about (1/1.33)×(1/0.25)×108=3×108 cm-2 nanoripples or nanospots, and the short period was only 250 nm. Therefore, the 2D periodic nanostructures have great potential applications in ultra-high density optical record and photonic crystals in ultraviolet and visible light range.
The evolution of short periodic nanostrucutures with the increase of laser intensity was studied, and the results are shown in Fig. 3. At the edge of ablation area denoted as strip 1, the sample surface was melted slightly. Some small ripples emerged randomly on strips 2-4 with the increase of laser intensity. In strip 5, several groups of nanoripples began to emerge. There were two or three parallel nanoripples in one group, and all of these nanoripples were perpendicular to the laser polarization. With further increase of laser intensity, these groups of nanoripples extended and connected each other (see strips 6 and 7). Regular short periodic nanoripples formed in strips 8 and 9. The evolution processes with laser irradiation time were also studied. The two processes were similar to each other.
Fig. 3. The evolution of short-periodic nanoripples with the increase of laser intensity in each strip denoted as 1, 2,…9. The total pulse energy is 153 uJ, and laser irradiation time is 6s.
We have conducted experiments to study the formation of nanoripples in ZnO crystal surface induced by single beam of 790 nm fs laser, and found the periods were in the range of 200-240 nm. The results as shown in Fig. 2 were very close to this value. We rotated the laser polarization by 45°, and found that the orientation of nanogratings embedding in the long periodic structures rotated by 45°, too. The formation processes discussed in the above paragraph were also similar to the cases of single fs laser beam. These three aspects indicated that the formation mechanism of the short-periodic nanostructures in the 2D periodic patterns was similar to that induced by single fs laser beam.
Recently, the formation mechanisms of short periodic nanoripples have been studied intensively. Shimotsuma et al. studied the formation of nanogratings in silica glass, and proposed that the periodic structure was induced by the interference between the incident laser and electron density wave. V. Bhardwaj et al. proposed that local field enhancement influenced the electrons excitation, and led to the growth of nanoplanes (nanograting). Juodkazis et al. modeled the local field enhancement in plasma nanoparticles, and numerically simulated the spatial intensity distribution [16-17]. Several other different opinions, such as the interference between incident laser and its surface scattered wave, Coulomb explosion, etc., have also been proposed. However, the formation mechanism of the short periodic nanostructures is still unclear, and it needs more experimental and theoretical studies.
S. Juodkazis, H. Misawa, E. Vanagas, and M. Li, JLMN-J. Las. Micro/Nanoengineering 1, 253 (2006). [CrossRef]
The interference method of two fs laser beams is rather complicated, and it is not convenient to be used in 3D microfabrication. To overcome this problem, the laser beam was enlarged to more than 40 mm in diameter via a couple of positive and negative lenses, then a double iris was used to select two laser beams of the same profile, same polarization, and same intensity [5]. These two laser beams were exactly focused on the sample surface. Figure 4 represented the results induced by a Ti-sapphire fs laser operated at 1 kHz repetition rate. Several ablation spots were observed on the sample surface. They were distributed periodically and symmetrically, and the period was equal to that expected by λ/(2sinθ). Therefore, these periodic ablation spots were determined by the interference between two laser beams. On each spot, there were many nanoripples with periods of 230 nm. The nanoripples were in 45° direction for the laser polarization was rotated by 45°. We transmitted the sample at a speed of 0.2 mm/s, and obtained regular 2D periodic structures with periods of 3.3 um and 250 nm, respectively (see Fig. 4(c) and (d)).
N. Lai, W. Liang, J. Lin, C. Hsu, and C. Lin, “Fabrication of two- and three-dimensional periodic structures by multi-exposure of two-beam interference technique,” Opt. Express , 13, 9605–9611 (2005). [CrossRef] [PubMed]
3. Conclusion
In summary, 2D periodic nanostructures were fabricated in ZnO crystal surface induced by two-beam interference of fs laser. The long period was Λ=λ/(2sinθ), and it was determined by the interference pattern of the two laser beams. Besides the long periodic structure, there is another short periodic nanostructures embedding in the long ones. We studied the periods, orientation, and the evolution of the short periodic nanostructures, and found it was self-organized nanostructure similar to that induced by single fs laser beam.
Acknowledgments
This work was supported by Japan Society for the Promotion of Science (JSPS Fellowship No. P060405) and Grant in-Aid for Creative Scientific Research (14GS0206).
References and links
T. Kondo, S. Matsuo, S. Juodkazis, V. Mizeikis, and H. Misawa, “Multiphoton fabrication of periodic structures by multibeam interference of femtosecond pulses,” Appl. Phys. Lett. 82, 2758–2760 (2003). [CrossRef] | |
G. Liang, W. Mao, Y. Pu, H. Zou, H. Wang, and Z. Zeng, “Fabrication of two-dimensional coupled photonic crystal resonator arrays by holographic lithography,” Appl. Phys. Lett. 89, 041902–041904 (2006). [CrossRef] | |
I. Divliansky, A. Shishido, I. Khoo, T. Mayer, D. Pensa, S. Nishimura, C. Keating, and T. Mallouk, “Fabrication of two-dimensional photonic crystals using interference lithography and electrodeposition of CdSe,” Appl. Phys. Lett. 79, 3392–3394 (2001). [CrossRef] | |
T. Kondo, S. Juodkazis, V. Mizeikis, H. Misawa, and S. Matsuo, “Holographic lithography of periodic two-and three-dimensional microstructures in photoresist SU-8,” Opt. Express , 14, 7943–7953 (2006). [CrossRef] [PubMed] | |
N. Lai, W. Liang, J. Lin, C. Hsu, and C. Lin, “Fabrication of two- and three-dimensional periodic structures by multi-exposure of two-beam interference technique,” Opt. Express , 13, 9605–9611 (2005). [CrossRef] [PubMed] | |
M. Campbell, D. Sharp, M. Harrison, R. Denning, and A. Turberfield, “Fabrication of photonic crystals for the visible spectrum by holographic lithography,” Nature 404, 53–56 (2000). [CrossRef] [PubMed] | |
J. Sipe, J. Young, J. Preston, and H. Driel, “Laser-induced periodic surface structure. I. Theory,” Phys. Rev. B 27, 1141–1154 (1983). [CrossRef] | |
Y. Shimotsuma, P. Kazansky, J. Qiu, and K. Hirao, “Self-organized nanogratings in glass irradiated by ultrashort light pulses,” Phys. Rev. Lett. 91, 247405–247408 (2003). [CrossRef] [PubMed] | |
V. Bhardwaj, E. Simova, P. Rajeev, C. Hnatovsky, R. Taylor, D. Rayner, and P. Corkum, “Optically produced arrays of planar nanostructures inside fused silica,” Phys. Rev. Lett. 96, 057404–057407 (2006). [CrossRef] [PubMed] | |
A. Borowiec and H. Haugen, “Subwavelength ripple formation on the surface of compound semiconductors irradiated with femtosecond laser pulses,” Appl. Phys. Lett. 82, 4462–4464 (2003). [CrossRef] | |
N. Yasumaru, K. Miyazaki, and J. Kiuchi, “Femtoseocnd-laser-induced nanostructure formed on hard thin films of TiN and DLC,” Appl. Phys. A 76, 983–985 (2003). [CrossRef] | |
W. Kautek, P. Rudolph, G. Daminelli, and J. Krüger, Appl. Phys. A 81, 65 (2005). [CrossRef] | |
T. Jia, H. Chen, M. Huang, F. Zhao, J. Qiu, R. Li, Z. Xu, X. He, J. Zhang, and H. Kuroda, Phys. Rev. B 72, 125429–125433 (2005). [CrossRef] | |
M. Huang, S. Mao, H. Feick, H. Yan, Y. Wu, H. Kind, E. Weber, R. Russo, and P. Yang, “Room-temperature ultraviolet nanowire nanolasers,” Science , 292, 1897–1899 (2001). [CrossRef] [PubMed] | |
P. Gao, Y. Ding, W. Mai, W. Hughes, C. Lao, and Z. Wang, “Conversion of Zinc Oxide nanobelts into superlattice-structured nanohelices,” Science 309, 1700–1704 (2005). [CrossRef] [PubMed] | |
S. Juodkazis, H. Misawa, E. Vanagas, and M. Li, JLMN-J. Las. Micro/Nanoengineering 1, 253 (2006). [CrossRef] | |
S. Juodkazis, E. Vanagas, and H. Misawa, Adv. Polym. Sci. 12, 122 (2007). |
OCIS Codes
(140.3390) Lasers and laser optics : Laser materials processing
(220.4241) Optical design and fabrication : Nanostructure fabrication
(050.6624) Diffraction and gratings : Subwavelength structures
ToC Category:
Optical Design and Fabrication
History
Original Manuscript: October 12, 2007
Revised Manuscript: January 9, 2008
Manuscript Accepted: January 10, 2008
Published: January 28, 2008
Citation
Tianqing Jia, Motoyoshi Baba, Masayuki Suzuki, Radish A. Ganeev, Hiroto Kuroda, Jianrong Qiu, Xinshun Wang, Ruxin Li, and Zhizhan Xu, "Fabrication of two-dimensional periodic nanostructures by two-beam interference of femtosecond pulses," Opt. Express 16, 1874-1878 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-3-1874
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References
- T. Kondo, S. Matsuo, S. Juodkazis, V. Mizeikis, and H. Misawa, "Multiphoton fabrication of periodic structures by multibeam interference of femtosecond pulses," Appl. Phys. Lett. 82, 2758-2760 (2003). [CrossRef]
- G. Liang, W. Mao, Y. Pu, H. Zou, H. Wang, and Z. Zeng, "Fabrication of two-dimensional coupled photonic crystal resonator arrays by holographic lithography," Appl. Phys. Lett. 89, 041902-041904 (2006). [CrossRef]
- I. Divliansky, A. Shishido, I. Khoo, T. Mayer, D. Pensa, S. Nishimura, C. Keating, and T. Mallouk, "Fabrication of two-dimensional photonic crystals using interference lithography and electrodeposition of CdSe," Appl. Phys. Lett. 79, 3392-3394 (2001). [CrossRef]
- T. Kondo, S. Juodkazis, V. Mizeikis, H. Misawa, and S. Matsuo, "Holographic lithography of periodic two- and three-dimensional microstructures in photoresist SU-8," Opt. Express, 14, 7943-7953 (2006). [CrossRef] [PubMed]
- N. Lai, W. Liang, J. Lin, C. Hsu, and C. Lin, "Fabrication of two- and three-dimensional periodic structures by multi-exposure of two-beam interference technique," Opt. Express, 13, 9605-9611 (2005). [CrossRef] [PubMed]
- M. Campbell, D. Sharp, M. Harrison, R. Denning, and A. Turberfield, "Fabrication of photonic crystals for the visible spectrum by holographic lithography," Nature 404, 53-56 (2000). [CrossRef] [PubMed]
- J. Sipe, J. Young, J. Preston, and H. Driel, "Laser-induced periodic surface structure. I. Theory," Phys. Rev. B 27, 1141-1154 (1983). [CrossRef]
- Y. Shimotsuma, P. Kazansky, J. Qiu, and K. Hirao, "Self-organized nanogratings in glass irradiated by ultrashort light pulses," Phys. Rev. Lett. 91, 247405-247408 (2003). [CrossRef] [PubMed]
- V. Bhardwaj, E. Simova, P. Rajeev, C. Hnatovsky, R. Taylor, D. Rayner, and P. Corkum, "Optically produced arrays of planar nanostructures inside fused silica," Phys. Rev. Lett. 96, 057404-057407 (2006). [CrossRef] [PubMed]
- A. Borowiec and H. Haugen, "Subwavelength ripple formation on the surface of compound semiconductors irradiated with femtosecond laser pulses," Appl. Phys. Lett. 82, 4462-4464 (2003). [CrossRef]
- N. Yasumaru, K. Miyazaki, and J. Kiuchi, "Femtoseocnd-laser-induced nanostructure formed on hard thin films of TiN and DLC," Appl. Phys. A 76, 983-985 (2003). [CrossRef]
- W. Kautek, P. Rudolph, G. Daminelli, and J. Krüger, Appl. Phys. A 81, 65 (2005). [CrossRef]
- T. Jia, H. Chen, M. Huang, F. Zhao, J. Qiu, R. Li, Z. Xu, X. He, J. Zhang, and H. Kuroda, Phys. Rev. B 72, 125429-125433 (2005). [CrossRef]
- M. Huang, S. Mao, H. Feick, H. Yan, Y. Wu, H. Kind, E. Weber, R. Russo, and P. Yang, "Room-temperature ultraviolet nanowire nanolasers," Science, 292, 1897-1899 (2001). [CrossRef] [PubMed]
- P. Gao, Y. Ding, W. Mai, W. Hughes, C. Lao, and Z. Wang, "Conversion of Zinc Oxide nanobelts into superlattice-structured nanohelices," Science, 309, 1700-1704 (2005). [CrossRef] [PubMed]
- S. Juodkazis, H. Misawa, E. Vanagas, and M. Li, JLMN-J. Las. Micro/Nanoengineering 1, 253 (2006). [CrossRef]
- S. Juodkazis, E. Vanagas, and H. Misawa, Adv. Polym. Sci. 12, 122 (2007).
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