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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 14 — Jul. 5, 2010
  • pp: 14802–14811
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Demonstration of scattering suppression in retardation-based plasmonic nanoantennas

Michael G. Nielsen, Anders Pors, Rasmus B. Nielsen, Alexandra Boltasseva, Ole Albrektsen, and Sergey I. Bozhevolnyi  »View Author Affiliations


Optics Express, Vol. 18, Issue 14, pp. 14802-14811 (2010)
http://dx.doi.org/10.1364/OE.18.014802


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Abstract

Modifications in scattering strength of and local field enhancement by retardation-based plasmonic nanoantennas when being transformed from straight nanorods to split-ring resonators are investigated experimentally. Scattering properties are characterized with linear reflection and extinction spectroscopy of nanoantenna arrays, whereas local field enhancements are evaluated for individual nanoantennas using two-photon-excited photoluminescence (TPL) microscopy. The linear and nonlinear optical characterizations reveal that the optical response of nanoantennas is determined by the interference of counter-propagating short-range surface plasmon polaritons (SR-SPP) and that the transformation of nanorods into split-rings by bending significantly influences the scattering strength. Importantly, strong suppression of scattering for the fundamental SR-SPP resonance is observed when the bend radius is decreased, a feature that is attributed to the decrease in the nanoantenna electric-dipole response when bending the nanorods. The experimental observations are corroborated with numerical simulations using the finite-element method.

© 2010 OSA

1. Introduction

Interaction of light with functionalized metal nanostructures is one of the main topics in the research area nano-optics [1

1. S. A. Maier, Plasmonics: Fundamentals and Applications, (Springer, New York,2007).

]. This is due to the fact that excitation of plasmonic resonances in metal nanostructures leads to fascinating optical phenomena exploitable in practical applications at visible and infrared frequencies, such as guidance of electromagnetic fields beyond the diffraction limit [2

2. D. K. Gramotnev and S. I. Bozhevolnyi, “Plasmonics beyond the diffraction limit,” Nat. Photonics 4(2), 83–91 (2010). [CrossRef]

], and dramatic enhancement of local and scattered electromagnetic fields that can be advantageously used for optical sensing [3

3. K. A. Willets and R. P. Van Duyne, “Localized surface plasmon resonance spectroscopy and sensing,” Annu. Rev. Phys. Chem. 58(1), 267–297 (2007). [CrossRef]

]. Plasmonic resonances are typically distinguished as being either electrostatic or retardation-based. Electrostatic resonances occur due to localized collective electron oscillations in metal nanostructures having dimensions significantly smaller than the wavelength of the driving electromagnetic field and therefore subjected only to negligible retardation effects [4

4. M. Pelton, J. Aizpurua, and G. Bryant, “Metal-nanoparticle plasmonics,” Laser Photon. Rev. 2(3), 136–159 (2008). [CrossRef]

]. Contrary, retardation-based resonances are associated with interference of counter-propagating surface plasmon polariton (SPP) modes, i.e. electromagnetic excitations resonantly coupled to collective electron oscillations at metal/dielectric interfaces [5

5. T. Søndergaard and S. I. Bozhevolnyi, “Slow-plasmon resonant nanostructures: Scattering and field enhancements,” Phys. Rev. B 75(7), 073402 (2007). [CrossRef]

]. Recent studies have demonstrated that short-range SPP (SR-SPP) modes can be excited, propagate and interfere in sub-wavelength metal structures being reflected by the structure terminations [5

5. T. Søndergaard and S. I. Bozhevolnyi, “Slow-plasmon resonant nanostructures: Scattering and field enhancements,” Phys. Rev. B 75(7), 073402 (2007). [CrossRef]

8

8. T. Søndergaard, J. Beermann, A. Boltasseva, and S. I. Bozhevolnyi, “Slow-plasmon resonant-nanostrip antennas: Analysis and demonstration,” Phys. Rev. B 77(11), 115420 (2008). [CrossRef]

]. The main property of SR-SPP modes is that they are strongly confined to the metal featuring large effective refractive indexes (ERI) with respect to that of the surrounding dielectric medium and, as a consequence, characterized with significantly reduced wavelengths. Actually, since propagating SR-SPP modes do not experience cutoff for structures with small cross sections [9

9. E. N. Economou, “Surface plasmons in thin films,” Phys. Rev. 182(2), 539–554 (1969). [CrossRef]

], retardation-based resonances involving SR-SPP modes can indeed, similar to electrostatic resonances, exist at nanoscale [5

5. T. Søndergaard and S. I. Bozhevolnyi, “Slow-plasmon resonant nanostructures: Scattering and field enhancements,” Phys. Rev. B 75(7), 073402 (2007). [CrossRef]

8

8. T. Søndergaard, J. Beermann, A. Boltasseva, and S. I. Bozhevolnyi, “Slow-plasmon resonant-nanostrip antennas: Analysis and demonstration,” Phys. Rev. B 77(11), 115420 (2008). [CrossRef]

]. SPP-modes not exhibiting cutoff exist in e.g. insulator-metal-insulator (IMI) [7

7. S. I. Bozhevolnyi and T. Søndergaard, “General properties of slow-plasmon resonant nanostructures: nano-antennas and resonators,” Opt. Express 15(17), 10869–10877 (2007). [CrossRef] [PubMed]

], metal-insulator-metal (MIM) structures [7

7. S. I. Bozhevolnyi and T. Søndergaard, “General properties of slow-plasmon resonant nanostructures: nano-antennas and resonators,” Opt. Express 15(17), 10869–10877 (2007). [CrossRef] [PubMed]

,10

10. J. Jung, T. Søndergaard, and S. Bozhevolnyi, “Gap plasmon-polariton nanoresonators: Scattering enhancement and launching of surface plasmon polaritons,” Phys. Rev. B 79(3), 035401 (2009). [CrossRef]

,11

11. H. T. Miyazaki and Y. Kurokawa, “Squeezing visible light waves into a 3-nm-thick and 55-nm-long plasmon cavity,” Phys. Rev. Lett. 96(9), 097401 (2006). [CrossRef] [PubMed]

], and in nanowires [12

12. J. Takahara, S. Yamagishi, H. Taki, A. Morimoto, and T. Kobayashi, “Guiding of a one-dimensional optical beam with nanometer diameter,” Opt. Lett. 22(7), 475–477 (1997). [CrossRef] [PubMed]

14

14. H. Ditlbacher, A. Hohenau, D. Wagner, U. Kreibig, M. Rogers, F. Hofer, F. R. Aussenegg, and J. R. Krenn, “Silver nanowires as surface plasmon resonators,” Phys. Rev. Lett. 95(25), 257403 (2005). [CrossRef] [PubMed]

], so that various configurations can be employed to facilitate efficient excitation, propagation and interference of strongly confined SPPs and, thereby, exploited in retardation-based nanoantennas.

In this paper the optical properties, in terms of scattering, extinction and field enhancement, of three-dimensional plasmonic straight nanorods being transformed into split-ring resonators by bending, are investigated by linear spectroscopy and TPL microscopy. Furthermore, optical scattering and extinction cross sections are evaluated by numerical simulations conducted with the finite-element method (FEM). Observed changes in the scattering, extinction and field enhancement of the plasmonic nanoantennas due to structural transformations are explained by considering the SR-SPP modes forming standing-wave patterns at resonance in a way somewhat similar to that employed in recent studies of two-dimensional nano-strips being transformed into split-cylinders [15

15. G. Della Valle, T. Søndergaard, and S. I. Bozhevolnyi, “Efficient suppression of radiation damping in resonant retardation-based plasmonic structures,” Phys. Rev. B 79(11), 113410 (2009). [CrossRef]

,16

16. G. Della Valle, T. Søndergaard, and S. I. Bozhevolnyi, “High-Q plasmonic resonators based on metal split nanocylinders,” Phys. Rev. B 80(23), 235405 (2009). [CrossRef]

]. The latter observations relied, however, solely on numerical results that are rather problematic to check experimentally due to the difficulty of fabricating split-cylinders with conventional top-down fabrication techniques. Although the idea of extending this work to three dimensions increases the computational complexity required for modeling it significantly eases the fabrication process which can be conducted with electron beam lithography (EBL) and lift-off technique.

2. Design and fabrication

The plasmonic nanoantennas considered in this paper are defined by the antenna length L, width w, height h [Fig. 1(a)
Fig. 1 (a) Dimensions of the straight nanorod with length L, width w and height h. (b) Split-ring obtained by bending the nanorod with a radius of curvature R while keeping w and h fixed. (c) Table indicating the design parameters varied for fixed width and height. (d-g) Representative scanning electron micrographs of fused silica substrates with periodically arranged gold nanoantennas with a length of 300nm and a pitch of 1µm. A charge density of 310 µC/cm2 in the EBL exposure yielded antenna widths of ~50nm as desired.
] and bending radius R [Fig. 1(b)]. For lengths 300nm and 400nm the nanoantenna width and height are fixed at 50nm whereas the bending radius is varied resulting in straight nanorods being transformed into split-rings by bending [Fig. 1(c)]. Two samples fabricated by EBL and lift-off is prepared in order to realize gold plasmonic nanoantennas situated on a fused silica substrate and arranged periodically with a 1µm pitch [Fig. 1(d)1(g)] in arrays of 50x50µm2.

The fabrication procedure of the two samples with antennas of lengths 300nm and 400nm, respectively, are slightly different due to the fact that bend antennas of 300nm length are more challenging to fabricate compared to those of 400nm length. In the fabrication of 300nm long nanoantennas the sample is prepared by spin coating a 4 inch fused silica wafer with the highly sensitive E-beam resist ZEP 520A 3.7% at 500rpm for 10 seconds followed by 1500rpm for 30 seconds and subsequent prebake on a hot plate for 5 minutes at 180°C yielding a resist layer thickness of ~130nm. Before E-beam exposure a ~15nm conducting thin film of aluminum is deposited thermally on top of the ZEP resist in order to prevent distorted patterns during the EBL exposure due to charge accumulation in the resist and the underlying silica substrate. Immediately after the exposure of several 50x50µm2 arrays, carried out at 100kV acceleration voltage, 0.8nA beam current and charge densities ranging from 310 µC/cm2 to 355 µC/cm2 in steps of 15 µC/cm2, the aluminum film is dissolved in photoresist developer MF-322 and the sample rinsed with water and spin dried. Hereafter, the development of the exposed ZEP-resist is initiated by immersion into ZEP-N50 developer for 2 minutes and stopped by isopropyl alcohol (IPA) rinse followed by drying with compressed nitrogen. After E-beam deposition of ~2nm titanium at 2Å/s, in order to promote adhesion of 50nm gold deposited at 10Å/s, lift-off is carried out in an acetone bath for 10 minutes and in Remover 1165 for ~24 hours. Finally, the wafer is rinsed in acetone and IPA, dried with compressed nitrogen and cut into samples of 2x2cm2 with a wafer saw.

The second sample carrying nanoantennas with a length of 400nm is fabricated in more or less a similar way, except that the E-beam resist polymethyl methacrylate (PMMA) 950K (2% solids dissolved in anisole) is applied and the acceleration voltage is reduced to 30kV. The final nanoantennas did, however, exhibit widths and heights of ~60nm, i.e. ~10nm wider and higher than the antennas fabricated with a length of 300nm.

3. Scattering and extinction properties

As a first approach, linear reflection spectroscopy measurements are conducted on the nanoantennas in order to get an overview of the positions and strengths of the plasmonic resonances. Light from a broadband tungsten halogen source (~450-2000nm) is passed through a polarizer and focused onto an array of nanoantennas with an objective [x60, numerical aperture (N.A.) = 0.85]. The reflected light is collected with the same objective, passed through an analyzer and finally focused onto and collected by a VIS/NIR optical fiber connected to a spectrometer. The reflection spectra are recorded in two wavelength intervals (450-950nm and 1000-1900nm) with a VIS- and NIR spectrometer respectively, and immediately after obtaining the reflection spectrum from an array of nanoantennas a reference reflection spectrum from the silica substrate is recorded for the purpose of normalization. After subtraction of the spectrometer dark counts, the relative reflection spectrum of a specific nanoantenna array [Fig. 2(a)
Fig. 2 (a) Experimental relative reflection spectra. (b) Simulated scattering cross section normalized to the antenna area. Spectra to the right and left of the wavelength-axis breaks are obtained with x- and y-polarization, respectively. Solid and dotted curves correspond to spectra from nanoantennas with L = 300nm and L = 400nm, respectively. The insets in (a) and (b) indicate the orientation of the electric field component as well as the plasmonic currents of the 1st order mode (right) and 2nd order mode (left) in the nanoantennas.
] is calculated as the ratio between the reflection spectrum of the nanoantennas and the reference reflection spectrum of the substrate. In the simulations, scattering and extinction cross section spectra [Fig. 2(b) and Fig. 4(b)
Fig. 4 (a) Experimentally obtained extinction spectra. (b) Simulated extinction cross section normalized to the antenna area and the energy of the incident plane wave. Spectra to the right and left of the wavelength axis break are obtained with x- and y-polarized light, respectively. Solid lines correspond to spectra obtained from antennas with L = 300nm and dotted lines are spectra obtained from antennas with L = 400nm. The insets in (a) and (b) indicate the orientation of the electric field component as well as the plasmonic currents of the 1st order mode (right) and 2nd order mode (left) in the antennas.
respectively] of the corresponding modeled nanoantenna structures are normalized with respect to the geometrical surface area of the nanoantenna. In order to limit the complexity of the FEM model and the numerical load in the simulations, two approximations are incorporated in the model compared to the experimental conditions. The scattering and extinction cross sections are simulated assuming that the nanoantennas are embedded in a homogenous dielectric substrate with a refractive index of the surrounding dielectric approximated by neff = 1.25, which is the root mean square of the refractive indexes in air (nair = 1) and silica (nsilica = 1.45) [17

17. F. Neubrech, T. Kolb, R. Lovrincic, G. Fahsold, A. Pucci, J. Aizpurua, T. W. Cornelius, M. E. Toimil-Molares, R. Neumann, and S. Karim, “Resonances of individual metal nanowires in the infrared,” Appl. Phys. Lett. 89(25), 253104 (2006). [CrossRef]

]. Experimentally, the spectra were obtained with silica below and air above the nanoantennas. Furthermore, in the simulations a plane wave (unfocused) is used as incident light, whereas a focused beam is applied when recording the experimental reflection spectra. Both approximations may slightly influence the strength and position of the simulated resonances compared to those obtained in the experiment.

The simulated scattering resonances with x-polarized light clearly exhibit blue-shifts for antennas with moderate bending radii, whereas antennas with bending radii equal to or smaller than 64nm actually exhibit red-shifts. Also noteworthy is the resonance linewidths which appear to narrow concurrently with decreasing bending radii. The red-shifts are due to coupling of the near-fields from the split-ring terminations [15

15. G. Della Valle, T. Søndergaard, and S. I. Bozhevolnyi, “Efficient suppression of radiation damping in resonant retardation-based plasmonic structures,” Phys. Rev. B 79(11), 113410 (2009). [CrossRef]

], causing a change in the phase φ in Eq. (1), whereas the reduced linewidths are due to the suppressed electric-dipole moment and the resulting reduced radiation losses when the nanorods are bent. The experimentally recorded spectra with x-polarized light, however, only reveal blue-shifts of the scattering resonances when the bending radius is decreased, whereas red-shifts and decreased linewidths are absent. In order to explain the contradictions between the simulated and experimental spectra it is necessary to have a closer look at the fabricated nanoantennas (Fig. 3
Fig. 3 Close-up of the scanning electron micrographs from Fig. 1(f) of four split-rings with bending radius 64nm. (a) Split-ring which is very similar to the design whereas (b) shows a split-ring with less bend arms, (c) increased widths in the lower part of the split-ring due to proximity effects (seen for many of the split-rings) and (d) arms of slightly different lengths.
). The curiosity of the red-shifts not being present in the experimental spectra are most likely explained by the structural imperfections induced during the E-beam exposure and caused by proximity effects resulting in a slightly broader width of the split-ring’s bottom and more narrow width and smaller length of the arms [Fig. 3(c)]. First of all, if the proximity effects lead to slightly increased split-ring cross sections the confinement will be less effective and consequently nspp decreases [7

7. S. I. Bozhevolnyi and T. Søndergaard, “General properties of slow-plasmon resonant nanostructures: nano-antennas and resonators,” Opt. Express 15(17), 10869–10877 (2007). [CrossRef] [PubMed]

], which, according to Eq. (1) results in a blue-shift of the resonance wavelengths. Secondly, the resonance wavelengths are very sensitive to the coupling between the split-ring terminations so the imperfect arms may be responsible for diminished coupling explaining the absence of the red-shifts. The absent narrowing of the resonance linewidths in the reflection spectra can be reasoned by having in mind that the reflection spectra are obtained from arrays containing ~2500 structures, i.e. an ensemble, whereas the simulated scattering cross sections are obtained from individual modeled structures. Since EBL is a quasi-reproducible technique (Fig. 3), it is reasonable to assume that inhomogeneous broadening is the cause for the decreased linewidths not being revealed in the reflection spectra. In general, it is seen that the deviations between the experimental and simulated spectra increases when the bending radius decreases, and this is simply because the split-rings with small bending radii are comparably more difficult to fabricate than split-rings with larger bending radii.

The weak scattering peak, observed for straight nanorods at ~530nm [Fig. 2(a)], is indicating that it is possible to excite an electrostatic resonance when applying y-polarization. The strength of this electrostatic resonance is quite small compared to the observed retardation-based resonances, but this is due to a comparably smaller electric-dipole response contributing to scattering in the far field when exciting with a polarization of the electric field component along the short axis of the nanorods. Finally, another important feature is that all the resonances seen in the spectra are blue-shifted when the nanoantenna length is decreased from 400nm to 300nm, which is in complete accordance with Eq. (1), and therefore may be tailored by the same scaling principles as demonstrated for nano-strips [8

8. T. Søndergaard, J. Beermann, A. Boltasseva, and S. I. Bozhevolnyi, “Slow-plasmon resonant-nanostrip antennas: Analysis and demonstration,” Phys. Rev. B 77(11), 115420 (2008). [CrossRef]

,19

19. G. Della Valle, T. Søndergaard, and S. I. Bozhevolnyi, “Plasmon-polariton nano-strip resonators: from visible to infra-red,” Opt. Express 16(10), 6867–6876 (2008). [CrossRef] [PubMed]

]. These observations are of great importance since they strongly support our assumptions of retardation-based SR-SPP resonances being excited in nanoantennas and thereby forming standing waves due to constructively interfering counter-propagating SR-SPPs.

In an identical approach, linear transmission spectroscopy and FEM modeling is employed to obtain experimental [Fig. 4(a)] and simulated [Fig. 4(b)] extinction spectra of the nanoantennas and the spectra also reveal excitation of the 1st and 2nd order modes. The experimental extinction setup is similar to the one used for reflection except that an unfocused beam of white light is used for illumination through the sample, i.e. more similar to the modeled illumination in the simulations.

4. TPL microscopy and local field enhancement

The second approach for probing the resonant behavior of the nanoantennas is by nonlinear scanning optical TPL microscopy. TPL from metals is a well known nonlinear optical phenomenon [20

20. G. T. Boyd, Z. H. Yu, and Y. R. Shen, “Photoinduced luminescence from the noble metals and its enhancement on roughened surfaces,” Phys. Rev. B Condens. Matter 33(12), 7923–7936 (1986). [CrossRef] [PubMed]

], and spatially resolved TPL measurements have shown to be suitable for characterization of local field enhancement in plasmonic nanostructures [21

21. M. R. Beversluis, A. Bouhelier, and L. Novotny, “Continuum generation from single gold nanostructures through near-field mediated intraband transitions,” Phys. Rev. B 68(11), 115433 (2003). [CrossRef]

,22

22. P. Ghenuche, S. Cherukulappurath, T. H. Taminiau, N. F. van Hulst, and R. Quidant, “Spectroscopic mode mapping of resonant plasmon nanoantennas,” Phys. Rev. Lett. 101(11), 116805 (2008). [CrossRef] [PubMed]

]. Especially, TPL is attractive as a probe for local field enhancement since TPL is quadratically dependent on the power of the local electric field, making the technique extremely sensitive to intense electric fields [20

20. G. T. Boyd, Z. H. Yu, and Y. R. Shen, “Photoinduced luminescence from the noble metals and its enhancement on roughened surfaces,” Phys. Rev. B Condens. Matter 33(12), 7923–7936 (1986). [CrossRef] [PubMed]

].

The experimental setup [Fig. 5(a)
Fig. 5 (a) Illustration of the experimental setup for nonlinear scanning optical microscopy operated in reflection with a Ti-Sapphire laser, optical isolator (OI), half-wave plate (λ/2), polarizer (P), beam splitter (BS), filters F1 and F2, wavelength selective beam splitter (WSBS), objective (L), sample (S) placed on a XY-table, analyzer A1, and photomultiplier tubes (PMTs). (b-d) FH and (e-g) corresponding TPL images of six nanoantennas with a length of 400nm and infinite, 143nm and 81nm bending radius respectively obtained with y-polarized light at λ = 750nm and incident power ~0.15mW. The average TPL signal from the six nanoantennas is (e) ~11, (f) ~211 and (g) ~460cps.
] consists of a scanning optical microscope, operated in reflection geometry, and the scanning is computer-controlled by a translation stage which steps down to 50nm (accuracy ~4nm). Linearly polarized light from a pulsating mode locked Ti-Sapphire laser with ~200fs pulse duration and ~80MHz repetition rate is used for illumination of the sample with the fundamental harmonic (FH) wavelengths ranging from approximately 720nm to 850nm, i.e. wavelengths coinciding with the resonances of the 2nd order mode. The beam of the Ti-Sapphire laser is guided through an optical isolator (OI), half-wave plate (λ/2), polarizer (P), red colour filter (F1) and wavelength selective beam splitter (WSBS) and finally focused onto the sample (S) with a Mitutoyo infinity-corrected (x100, N.A. = 0.70) objective (L). The half-wave plate and polarizer enables precise adjustment of the FH incident light power. The generated TPL radiation and the reflected FH beam are concurrently collected with the same objective, separated by the WSBS, directed through a red- and blue (F2) color filter, respectively, and finally detected with the two photomultiplier tubes (PMTs). Furthermore, the PMT for detection of the TPL signal is connected to a photon counter giving typically ~20 dark counts per second (cps).

The FH wavelength of 750nm coincides well with the scattering resonances of the antennas with a length of 400nm [Fig. 2(a)], and the distinction between the resonances, when transforming the straight nanorods to split-rings, is appreciable. Therefore, as a first experiment, FH [Fig. 5(b)5(d)] and TPL images [Fig. 5(e)5(g)] of six nanoantennas with a length of 400nm and geometry of straight nanorods [Fig. 5(b), 5(e)] and split-rings with bending radii 143nm [Fig. (c,f)] and 81nm [Fig. (d,g)] are obtained with y-polarized light for a fixed wavelength of 750nm and incident power of ~0.15mW. The recorded images verify the efficient excitation of the 2nd order mode resonance as soon as the straight nanorods are transformed into split-rings since both the FH- and TPL intensities increase concurrently with decrease in the bending radius. Actually, it was impossible to image the straight nanorods when using only ~0.15mW of incident power, whereas the periodic bright spots from the split-rings immediately appeared in the TPL image. The average TPL signal generated from the six nanoantennas (after subtracting dark counts) increased from ~11 cps for straight nanorods to ~211 and ~460 cps for split-rings with bending radii 143nm and 81nm respectively verifying that the strength of the 2nd order resonance is very sensitive to the bending radius as signified by the linear reflection- and extinction spectra. The somewhat inhomogeneous appearance of bright spots [Fig. 5(f), 5(g)] were characteristic for all the TPL images indicating that the local enhanced fields are very sensitive to minor structural variations which, as discussed when explaining the deviations of the experimental from the simulated linear spectra, are certainly present (Fig. 3).

The TPL studies demonstrate resonant excitation of the 2nd order mode leading to enhancement factors up to ~80 when averaging the enhancement from six nanoantennas. As already discussed the TPL signal and therefore also α is very sensitive to minor structural imperfections, which is why the standard deviations increase when the bending radius decreases. Nevertheless, the distinction in the intensity enhancement for the three different nanoantennas is still appreciable when taking the standard deviations into account.

5. Conclusion

References and links

1.

S. A. Maier, Plasmonics: Fundamentals and Applications, (Springer, New York,2007).

2.

D. K. Gramotnev and S. I. Bozhevolnyi, “Plasmonics beyond the diffraction limit,” Nat. Photonics 4(2), 83–91 (2010). [CrossRef]

3.

K. A. Willets and R. P. Van Duyne, “Localized surface plasmon resonance spectroscopy and sensing,” Annu. Rev. Phys. Chem. 58(1), 267–297 (2007). [CrossRef]

4.

M. Pelton, J. Aizpurua, and G. Bryant, “Metal-nanoparticle plasmonics,” Laser Photon. Rev. 2(3), 136–159 (2008). [CrossRef]

5.

T. Søndergaard and S. I. Bozhevolnyi, “Slow-plasmon resonant nanostructures: Scattering and field enhancements,” Phys. Rev. B 75(7), 073402 (2007). [CrossRef]

6.

T. Søndergaard and S. I. Bozhevolnyi, “Metal nano-strip optical resonators,” Opt. Express 15(7), 4198–4204 (2007). [CrossRef] [PubMed]

7.

S. I. Bozhevolnyi and T. Søndergaard, “General properties of slow-plasmon resonant nanostructures: nano-antennas and resonators,” Opt. Express 15(17), 10869–10877 (2007). [CrossRef] [PubMed]

8.

T. Søndergaard, J. Beermann, A. Boltasseva, and S. I. Bozhevolnyi, “Slow-plasmon resonant-nanostrip antennas: Analysis and demonstration,” Phys. Rev. B 77(11), 115420 (2008). [CrossRef]

9.

E. N. Economou, “Surface plasmons in thin films,” Phys. Rev. 182(2), 539–554 (1969). [CrossRef]

10.

J. Jung, T. Søndergaard, and S. Bozhevolnyi, “Gap plasmon-polariton nanoresonators: Scattering enhancement and launching of surface plasmon polaritons,” Phys. Rev. B 79(3), 035401 (2009). [CrossRef]

11.

H. T. Miyazaki and Y. Kurokawa, “Squeezing visible light waves into a 3-nm-thick and 55-nm-long plasmon cavity,” Phys. Rev. Lett. 96(9), 097401 (2006). [CrossRef] [PubMed]

12.

J. Takahara, S. Yamagishi, H. Taki, A. Morimoto, and T. Kobayashi, “Guiding of a one-dimensional optical beam with nanometer diameter,” Opt. Lett. 22(7), 475–477 (1997). [CrossRef] [PubMed]

13.

L. Novotny, “Effective wavelength scaling for optical antennas,” Phys. Rev. Lett. 98(26), 266802 (2007). [CrossRef] [PubMed]

14.

H. Ditlbacher, A. Hohenau, D. Wagner, U. Kreibig, M. Rogers, F. Hofer, F. R. Aussenegg, and J. R. Krenn, “Silver nanowires as surface plasmon resonators,” Phys. Rev. Lett. 95(25), 257403 (2005). [CrossRef] [PubMed]

15.

G. Della Valle, T. Søndergaard, and S. I. Bozhevolnyi, “Efficient suppression of radiation damping in resonant retardation-based plasmonic structures,” Phys. Rev. B 79(11), 113410 (2009). [CrossRef]

16.

G. Della Valle, T. Søndergaard, and S. I. Bozhevolnyi, “High-Q plasmonic resonators based on metal split nanocylinders,” Phys. Rev. B 80(23), 235405 (2009). [CrossRef]

17.

F. Neubrech, T. Kolb, R. Lovrincic, G. Fahsold, A. Pucci, J. Aizpurua, T. W. Cornelius, M. E. Toimil-Molares, R. Neumann, and S. Karim, “Resonances of individual metal nanowires in the infrared,” Appl. Phys. Lett. 89(25), 253104 (2006). [CrossRef]

18.

C. Enkrich, M. Wegener, S. Linden, S. Burger, L. Zschiedrich, F. Schmidt, J. F. Zhou, Th. Koschny, and C. M. Soukoulis, “Magnetic metamaterials at telecommunication and visible frequencies,” Phys. Rev. Lett. 95(20), 203901 (2005). [CrossRef] [PubMed]

19.

G. Della Valle, T. Søndergaard, and S. I. Bozhevolnyi, “Plasmon-polariton nano-strip resonators: from visible to infra-red,” Opt. Express 16(10), 6867–6876 (2008). [CrossRef] [PubMed]

20.

G. T. Boyd, Z. H. Yu, and Y. R. Shen, “Photoinduced luminescence from the noble metals and its enhancement on roughened surfaces,” Phys. Rev. B Condens. Matter 33(12), 7923–7936 (1986). [CrossRef] [PubMed]

21.

M. R. Beversluis, A. Bouhelier, and L. Novotny, “Continuum generation from single gold nanostructures through near-field mediated intraband transitions,” Phys. Rev. B 68(11), 115433 (2003). [CrossRef]

22.

P. Ghenuche, S. Cherukulappurath, T. H. Taminiau, N. F. van Hulst, and R. Quidant, “Spectroscopic mode mapping of resonant plasmon nanoantennas,” Phys. Rev. Lett. 101(11), 116805 (2008). [CrossRef] [PubMed]

23.

P. J. Schuck, D. P. Fromm, A. Sundaramurthy, G. S. Kino, and W. E. Moerner, “Improving the mismatch between light and nanoscale objects with gold bowtie nanoantennas,” Phys. Rev. Lett. 94(1), 017402 (2005). [CrossRef] [PubMed]

24.

A. Hohenau, J. Krenn, F. Garcia-Vidal, S. Rodrigo, L. Martin-Moreno, J. Beermann, and S. Bozhevolnyi, “Spectroscopy and nonlinear microscopy of gold nanoparticle arrays on gold films,” Phys. Rev. B 75(8), 085104 (2007). [CrossRef]

OCIS Codes
(190.0190) Nonlinear optics : Nonlinear optics
(240.6680) Optics at surfaces : Surface plasmons
(260.3910) Physical optics : Metal optics
(290.0290) Scattering : Scattering
(220.4241) Optical design and fabrication : Nanostructure fabrication
(070.5753) Fourier optics and signal processing : Resonators

ToC Category:
Optics at Surfaces

History
Original Manuscript: June 3, 2010
Manuscript Accepted: June 20, 2010
Published: June 25, 2010

Citation
Michael G. Nielsen, Anders Pors, Rasmus B. Nielsen, Alexandra Boltasseva, Ole Albrektsen, and Sergey I. Bozhevolnyi, "Demonstration of scattering suppression in retardation-based plasmonic nanoantennas," Opt. Express 18, 14802-14811 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-14-14802


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References

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