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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 25 — Dec. 5, 2011
  • pp: 25773–25779
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Effect of surface plasmon cross-talk on optical properties of closely packed nano-hole arrays

Fartash Vasefi, Mohamadreza Najiminaini, Bozena Kaminska, and Jeffrey J. L. Carson  »View Author Affiliations


Optics Express, Vol. 19, Issue 25, pp. 25773-25779 (2011)
http://dx.doi.org/10.1364/OE.19.025773


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Abstract

The integration and miniaturization of nanostructure-based optical devices based on interaction with surface plasmons requires the fabrication of patterns of multiple nanostructures with tight spacing. The effect of surface plasmon energy interchange (cross-talk) across large grids of nanostructures and its effect on the optical characteristics of individual nanostructures have not been investigated. In this paper, we experimentally fabricated a large grid of individual nano-hole arrays of various hole diameter, hole spacing, and inter-array spacing. The spectral optical transmission of each nano-hole array was measured and the effect of inter-array spacing on the transmission spectra and resonance wavelength was determined.

© 2011 OSA

1. Introduction

The coupling of light to surface plasmons (SP)s in nano-hole arrays (NHA)s depends highly on the dielectric properties of the metal film and the supporting material in contact with the metal film [1

1. H. F. Ghaemi, T. Thio, D. E. Grupp, T. W. Ebbesen, and H. J. Lezec, “Surface plasmons enhance optical transmission through subwavelength holes,” Phys. Rev. B 58(11), 6779–6782 (1998). [CrossRef]

]. A change in the refractive index of the dielectric material at the surface of the metal film gives rise to a shift in the resonance wavelength and is the basis for SPR sensing [2

2. A. De Leebeeck, L. K. S. Kumar, V. de Lange, D. Sinton, R. Gordon, and A. G. Brolo, “On-chip surface-based detection with nanohole arrays,” Anal. Chem. 79(11), 4094–4100 (2007). [CrossRef] [PubMed]

]. In multiplexed SPR sensing devices based on NHAs, a grid of NHAs is fabricated on to a single substrate, where each NHA has unique geometric properties and hence distinct optical properties. The miniaturization of multiplexed NHA devices inevitably requires that NHAs be fabricated with smaller size and closer inter-array spacing. However, as a grid of NHA elements is scaled down, cross-talk between elements can affect the spectral transmission of each element [3

3. A. Lesuffleur, H. Im, N. C. Lindquist, K. S. Lim, and S.-H. Oh, “Plasmonic nanohole arrays for real-time multiplex biosensing,” Proc. SPIE 7035, 703504, 703504-10 (2008). [CrossRef]

,4

4. F. Przybilla, A. Degiron, C. Genet, T. W. Ebbesen, F. de Léon-Pérez, J. Bravo-Abad, F. J. García-Vidal, and L. Martín-Moreno, “Efficiency and finite size effects in enhanced transmission through subwavelength apertures,” Opt. Express 16(13), 9571–9579 (2008). [CrossRef] [PubMed]

]. Cross-talk between two nano-hole arrays arises due to the constructive or destructive effect between two scattered SP waves between closely-packed nano-hole arrays. In order to minimize the SP interactions between NHAs, several groups have taken advantage of the design freedoms to include various SP optical isolators such as Bragg mirrors to reduce neighbor to neighbor cross-talk and enhance light transmission [5

5. N. C. Lindquist, A. Lesuffleur, and S.-H. Oh, “Periodic modulation of extraordinary optical transmission through subwavelength hole arrays using surrounding Bragg mirrors,” Phys. Rev. B 76(15), 155109 (2007). [CrossRef]

,6

6. N. C. Lindquist, A. Lesuffleur, and S.-H. Oh, “Lateral confinement of surface plasmons and polarization-dependent optical transmission using nanohole arrays with a surrounding rectangular Bragg resonator,” Appl. Phys. Lett. 91(25), 253105 (2007). [CrossRef]

]. However, the crosstalk effect and its consequence on spectral transmission and resonance wavelength for large systems of closely packed NHAs has yet to be systematically analyzed.

Hence, the objective of this work was to experimentally investigate the effect of inter-array spacing on the EOT properties of a grid of NHAs that was representative of a multiplexed SPR sensor. The approach was to fabricate different sets of NHAs with various hole diameter (D), hole periodicity (P), and inter-array spacing (S). The NHAs were arranged on a grid of 4 × 4 blocks where each block contained 4 NHAs (distributed as a 2 × 2 grid) with four specific periodicities and hole diameters. The transmission spectrum of each nano-hole array on the grid was measured and the effect of inter-array spacing on the transmission spectra was analyzed.

2. Materials and methods

2.1 Surface plasmon propagation

We estimated the propagation length of the SP wave along the surface of the metal and dielectric material using the relation
δSP=cω(εm/+εdεm/εd)32(εm/)2εm"
(1)
where εm/ and εm" are the real and imaginary parts of the dielectric function of the metal and εd is the dielectric constant of the dielectric material [7

7. W. L. Barnes, A. Dereux, and T. W. Ebbesen, “Surface plasmon subwavelength optics,” Nature 424(6950), 824–830 (2003). [CrossRef] [PubMed]

,8

8. H. Raether, Surface Plasmons (Springer-Verlag, 1988).

]. We used dielectric functions for gold and chromium from Palik [9

9. E. D. Palik, Handbook of Optical Constants of Solids (Academic Press, 1985).

]. Due to the high absorption of chromium, the SP propagation length for Pyrex-chromium is very low (Fig. 1a
Fig. 1 (a) SP propagation length [Eq. (1)] along the surface for Pyrex-gold, air-gold, and Pyrex-chromium interfaces. (b) SEM image of a series nano-hole arrays in a gold film. In this design, all nano-hole arrays had an inter-array spacing of 2 µm. (c) Transmission spectra of (NHA1-NHA4) for boundary versus center blocks with 100 µm inter-array spacing. (d) Transmission spectra of (NHA1-NHA4) for boundary versus center blocks with 20 µm inter-array spacing. The solid lines are the NHAs at the boundary region while the dashed lines are for NHAs at the central region. The transmission spectra measured using microscope setup (described in 10])
), while the SP propagation length for Pyrex-gold can be as high as 35 µm at 1000 nm (Fig. 1a). The SP propagation length is greatest for air-gold and reaches 100 µm at a wavelength of 1000 nm (Fig. 1a).

2.2 Nano-hole array fabrication

Samples were fabricated using an Electron Beam Lithography (EBL) lift off technique to produce a 100-nm-thick gold film perforated with circular nano-scale apertures. We started with a Pyrex wafer coated with a 3-nm Cr conductive layer that enabled electron beam writing. Afterward, 500 nm photo-resist (Negative tone photo-resist ma-N 2403) was spin-coated on to the sample. The nanostructure patterns were written using EBL (LEO, 1530 e-beam lithography) leaving behind nano-scale photo-resist pillars after development. In order to improve adhesion between the gold layer and the substrate, a 4-nm Cr adhesion layer was deposited on to the sample before 100-nm thick gold deposition. Finally, the sacrificial layer of nano-pillars was lifted off resulting in a nano-hole array in the gold layer. More detail on the fabrication methodology has been presented elsewhere [10

10. M. Najiminaini, F. Vasefi, B. Kaminska, and J. J. L. Carson, “Experimental and numerical analysis on the optical resonance transmission properties of nano-hole arrays,” Opt. Express 18(21), 22255–22270 (2010). [CrossRef] [PubMed]

,11

11. M. Najiminaini, F. Vasefi, C. K. Landrock, B. Kaminska, and J. J. L. Carson, “Experimental and numerical analysis of extraordinary optical transmission through nano-hole arrays in a thick metal film,” Proc. SPIE 7577, 75770Z–75770Z-7 (2010). [CrossRef]

]. Each sample was patterned with 16 blocks on a 4 × 4 grid. Each block contained four NHAs in a 2 × 2 grid with each NHA 30 µm × 30 µm in size and with circular nano-holes on a square lattice. Each NHA in the block had a unique hole diameter and spacing, which gave rise to a distinct resonance wavelength. In each sample, all NHAs were spaced by 2 µm, 5 µm, 10 µm, or 20 µm respectively to study the effect of inter-array spacing on the transmission spectra. Figure 1b shows the scanning electron micrographs of a block of 4 NHAs with 2 µm spacing. The four nano-hole array designs named NHA1 to NHA4 had hole diameters of 215 nm, 247 nm, 273 nm, and 303 nm with periodicities of 382 nm, 433 nm, 483 nm, and 536 nm, respectively. Typical variation in the hole diameter and spacing was 4–6 nm (standard deviation).

Figure 1c and Fig. 1d show the transmission spectra of NHA1-NHA4 for samples with 100 µm and 20 µm inter-array spacing collected using a microscope setup [10

10. M. Najiminaini, F. Vasefi, B. Kaminska, and J. J. L. Carson, “Experimental and numerical analysis on the optical resonance transmission properties of nano-hole arrays,” Opt. Express 18(21), 22255–22270 (2010). [CrossRef] [PubMed]

]. Although The NHA sample with 20 µm inter-array spacing showed a slightly greater variation in resonance peaks compared to the 100 µm sample, the NHA sample with 20 µm inter-array spacing had a small crosstalk effect compared to 2 µm, 5 µm, 10 µm cases and was used for comparison.

2.3 Device characterization

3. Results and discussion

3.1 Spectral response of NHAs within a block

3.2 Variation in spectral response of NHAs across each device

Since each sample contained 64 NHAs in an 8×8 grid pattern, some NHAs were situated in closer proximity to the edge of the device than others. We hypothesized that the NHAs on the perimeter of the device would be less affected by cross-talk effects compared to NHAs near the center of the device. For example, NHAs at each corner were adjacent to only three neighboring NHAs, while a NHA at least one position in from an edge had 8 NHAs immediately adjacent.

The resonance wavelength measurements supported the hypothesis since for NHAs near the boundary (see Figs. 3a–c
Fig. 3 Resonance wavelength maps of NHAs with (a) 20 µm inter-array spacing, (b) 10 µm inter-array spacing, and (c) 2 µm inter-array spacing. Resonance wavelength difference map of NHAs with (d) 10 µm inter-array spacing compared to 20 µm inter-array spacing, and (e) 2 µm inter-array spacing compared to 20 µm inter-array spacing.
), the resonance wavelength tended to be blue shifted to a smaller degree than NHAs near the center of the device. The spatially dependent blue shift of the resonance wavelength was observed in all devices, but became progressively larger as the inter-array spacing decreased (see difference maps in Fig. 3d and Fig. 3e).

Analysis of Fig. 3a suggested that even at an inter-array spacing of 20 µm there was cross-talk between NHAs. For example, the resonance wavelength for NHA1 was blue-shifted for blocks from the left side of the device to the right side. However, the differences in resonance wavelength were typically ≤ 20 nm and much smaller for NHA2 through NHA4. These observations lead us to conclude that larger inter-array spacings or intervening structures are required to completely prevent cross-talk effects between closely packed NHAs. In the case of 2 µm inter-array spacing (Figs. 3c and 3e), cross-talk introduced blue-shifts in Pyrex-gold λ(1,0) of approximately 20 to 50 nm depending on the location and design parameters of the specific NHA being considered. For multiplexed SPR sensing applications, this systematic effect is competitive with the expected changes in resonance wavelength due to local index of refraction changes. However, if small systematic shifts in resonance wavelength are tolerable, then close packing of NHAs by reduction of the inter-array spacing may be a worthwhile approach to miniaturization of multiplexed SPR sensors.

4. Conclusion

Acknowledgments

This project was funded by grants from the Natural Sciences and Engineering Research Council of Canada to Dr. Bozena Kaminska and Dr. Jeffery J. L. Carson. Dr. Fartash Vasefi was supported by a London Regional Cancer Program Translational Breast Cancer Research Trainee Fellowship.

References and links

1.

H. F. Ghaemi, T. Thio, D. E. Grupp, T. W. Ebbesen, and H. J. Lezec, “Surface plasmons enhance optical transmission through subwavelength holes,” Phys. Rev. B 58(11), 6779–6782 (1998). [CrossRef]

2.

A. De Leebeeck, L. K. S. Kumar, V. de Lange, D. Sinton, R. Gordon, and A. G. Brolo, “On-chip surface-based detection with nanohole arrays,” Anal. Chem. 79(11), 4094–4100 (2007). [CrossRef] [PubMed]

3.

A. Lesuffleur, H. Im, N. C. Lindquist, K. S. Lim, and S.-H. Oh, “Plasmonic nanohole arrays for real-time multiplex biosensing,” Proc. SPIE 7035, 703504, 703504-10 (2008). [CrossRef]

4.

F. Przybilla, A. Degiron, C. Genet, T. W. Ebbesen, F. de Léon-Pérez, J. Bravo-Abad, F. J. García-Vidal, and L. Martín-Moreno, “Efficiency and finite size effects in enhanced transmission through subwavelength apertures,” Opt. Express 16(13), 9571–9579 (2008). [CrossRef] [PubMed]

5.

N. C. Lindquist, A. Lesuffleur, and S.-H. Oh, “Periodic modulation of extraordinary optical transmission through subwavelength hole arrays using surrounding Bragg mirrors,” Phys. Rev. B 76(15), 155109 (2007). [CrossRef]

6.

N. C. Lindquist, A. Lesuffleur, and S.-H. Oh, “Lateral confinement of surface plasmons and polarization-dependent optical transmission using nanohole arrays with a surrounding rectangular Bragg resonator,” Appl. Phys. Lett. 91(25), 253105 (2007). [CrossRef]

7.

W. L. Barnes, A. Dereux, and T. W. Ebbesen, “Surface plasmon subwavelength optics,” Nature 424(6950), 824–830 (2003). [CrossRef] [PubMed]

8.

H. Raether, Surface Plasmons (Springer-Verlag, 1988).

9.

E. D. Palik, Handbook of Optical Constants of Solids (Academic Press, 1985).

10.

M. Najiminaini, F. Vasefi, B. Kaminska, and J. J. L. Carson, “Experimental and numerical analysis on the optical resonance transmission properties of nano-hole arrays,” Opt. Express 18(21), 22255–22270 (2010). [CrossRef] [PubMed]

11.

M. Najiminaini, F. Vasefi, C. K. Landrock, B. Kaminska, and J. J. L. Carson, “Experimental and numerical analysis of extraordinary optical transmission through nano-hole arrays in a thick metal film,” Proc. SPIE 7577, 75770Z–75770Z-7 (2010). [CrossRef]

12.

R. Gordon, A. G. Brolo, D. Sinton, and K. L. Kavanagh, “Resonant optical transmission through hole-arrays in metal films: physics and applications,” Laser Photonics Rev. 4(2), 311–335 (2010). [CrossRef]

13.

F. Przybilla, A. Degiron, J. Y. Laluet, C. Genet, and T. W. Ebbesen, “Optical transmission in perforated noble and transition metal films,” J. Opt. A, Pure Appl. Opt. 8(5), 458–463 (2006). [CrossRef]

14.

A. A. Yanik, A. E. Cetin, M. Huang, A. Artar, S. H. Mousavi, A. B. Khanikaev, J. H. Connor, G. Shvets, and H. Altug, “Seeing protein monolayers with naked eye through plasmonic Fano resonances,” Proc. Natl. Acad. Sci. U.S.A. 108(29), 11784–11789 (2011). [CrossRef] [PubMed]

15.

T. W. Odom, H. Gao, J. M. McMahon, J. Henzie, and G. C. Schatz, “Plasmonic superlattices: Hierarchical subwavelength hole arrays,” Chem. Phys. Lett. 483(4–6), 187–192 (2009). [CrossRef]

OCIS Codes
(240.6680) Optics at surfaces : Surface plasmons
(250.5403) Optoelectronics : Plasmonics
(050.6624) Diffraction and gratings : Subwavelength structures

ToC Category:
Optics at Surfaces

History
Original Manuscript: October 3, 2011
Revised Manuscript: November 21, 2011
Manuscript Accepted: November 22, 2011
Published: December 2, 2011

Virtual Issues
Vol. 7, Iss. 2 Virtual Journal for Biomedical Optics

Citation
Fartash Vasefi, Mohamadreza Najiminaini, Bozena Kaminska, and Jeffrey J. L. Carson, "Effect of surface plasmon cross-talk on optical properties of closely packed nano-hole arrays," Opt. Express 19, 25773-25779 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-25-25773


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References

  1. H. F. Ghaemi, T. Thio, D. E. Grupp, T. W. Ebbesen, and H. J. Lezec, “Surface plasmons enhance optical transmission through subwavelength holes,” Phys. Rev. B58(11), 6779–6782 (1998). [CrossRef]
  2. A. De Leebeeck, L. K. S. Kumar, V. de Lange, D. Sinton, R. Gordon, and A. G. Brolo, “On-chip surface-based detection with nanohole arrays,” Anal. Chem.79(11), 4094–4100 (2007). [CrossRef] [PubMed]
  3. A. Lesuffleur, H. Im, N. C. Lindquist, K. S. Lim, and S.-H. Oh, “Plasmonic nanohole arrays for real-time multiplex biosensing,” Proc. SPIE7035, 703504, 703504-10 (2008). [CrossRef]
  4. F. Przybilla, A. Degiron, C. Genet, T. W. Ebbesen, F. de Léon-Pérez, J. Bravo-Abad, F. J. García-Vidal, and L. Martín-Moreno, “Efficiency and finite size effects in enhanced transmission through subwavelength apertures,” Opt. Express16(13), 9571–9579 (2008). [CrossRef] [PubMed]
  5. N. C. Lindquist, A. Lesuffleur, and S.-H. Oh, “Periodic modulation of extraordinary optical transmission through subwavelength hole arrays using surrounding Bragg mirrors,” Phys. Rev. B76(15), 155109 (2007). [CrossRef]
  6. N. C. Lindquist, A. Lesuffleur, and S.-H. Oh, “Lateral confinement of surface plasmons and polarization-dependent optical transmission using nanohole arrays with a surrounding rectangular Bragg resonator,” Appl. Phys. Lett.91(25), 253105 (2007). [CrossRef]
  7. W. L. Barnes, A. Dereux, and T. W. Ebbesen, “Surface plasmon subwavelength optics,” Nature424(6950), 824–830 (2003). [CrossRef] [PubMed]
  8. H. Raether, Surface Plasmons (Springer-Verlag, 1988).
  9. E. D. Palik, Handbook of Optical Constants of Solids (Academic Press, 1985).
  10. M. Najiminaini, F. Vasefi, B. Kaminska, and J. J. L. Carson, “Experimental and numerical analysis on the optical resonance transmission properties of nano-hole arrays,” Opt. Express18(21), 22255–22270 (2010). [CrossRef] [PubMed]
  11. M. Najiminaini, F. Vasefi, C. K. Landrock, B. Kaminska, and J. J. L. Carson, “Experimental and numerical analysis of extraordinary optical transmission through nano-hole arrays in a thick metal film,” Proc. SPIE7577, 75770Z–75770Z-7 (2010). [CrossRef]
  12. R. Gordon, A. G. Brolo, D. Sinton, and K. L. Kavanagh, “Resonant optical transmission through hole-arrays in metal films: physics and applications,” Laser Photonics Rev.4(2), 311–335 (2010). [CrossRef]
  13. F. Przybilla, A. Degiron, J. Y. Laluet, C. Genet, and T. W. Ebbesen, “Optical transmission in perforated noble and transition metal films,” J. Opt. A, Pure Appl. Opt.8(5), 458–463 (2006). [CrossRef]
  14. A. A. Yanik, A. E. Cetin, M. Huang, A. Artar, S. H. Mousavi, A. B. Khanikaev, J. H. Connor, G. Shvets, and H. Altug, “Seeing protein monolayers with naked eye through plasmonic Fano resonances,” Proc. Natl. Acad. Sci. U.S.A.108(29), 11784–11789 (2011). [CrossRef] [PubMed]
  15. T. W. Odom, H. Gao, J. M. McMahon, J. Henzie, and G. C. Schatz, “Plasmonic superlattices: Hierarchical subwavelength hole arrays,” Chem. Phys. Lett.483(4–6), 187–192 (2009). [CrossRef]

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