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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 22 — Oct. 26, 2009
  • pp: 20301–20306
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Direct near-field optical imaging of UV bowtie nanoantennas

Liangcheng Zhou, Qiaoqiang Gan, Filbert J. Bartoli, and Volkmar Dierolf  »View Author Affiliations


Optics Express, Vol. 17, Issue 22, pp. 20301-20306 (2009)
http://dx.doi.org/10.1364/OE.17.020301


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Abstract

We report near-field optical imaging of bowtie nanoantennas obtained using a UV near-field scanning optical microscope (NSOM). A strong and highly localized UV intensity profile was observed at the antenna gap due to the localized surface plasmon resonance. The relationship of optical field enhancement and antenna size is discussed based on numerical simulations and NSOM experiments.

© 2009 Optical Society of America

1. Introduction

There is a considerable interest in the study of nanoscale optical antennas, largely due to their ability to produce giant and highly localized electromagnetic fields [1

1. P. Muhlschlegel, H.-J. Eisler, O. J. F. Martin, B. Hecht, and D. W. Pohl, “Resonant Optical Antennas,” Science 308, 1607 (2005). [CrossRef] [PubMed]

,2

2. D. P. Fromm, A. Sundaramurthy, P. J. Schuck, G. Kino, and W. E. Moerner, “Gap-Dependent Optical Coupling of Single ‘Bowtie’Nanoantennas Resonant in the Visible,” Nano Lett. 4, 957–961 (2004). [CrossRef]

]. Important applications include near field microscopy [3

3. L. Wang and X. F. Xu, “High transmission nanoscale bowtie-shaped aperture probe for near-field optical imaging,” Appl. Phys. Lett. 90, 261105 (2007). [CrossRef]

], high resolution lithography [4

4. A. Sundaramurthy, P. James Schuck, N. R. Conley, D. P. Fromm, G. S. Kino, and W. E. Moerner, “Toward Nanometer-Scale Optical Photolithography: Utilizing the Near-Field of Bowtie Optical Nanoantennas,” Nano Lett. 6, 355 (2006). [CrossRef] [PubMed]

7

7. L. Wang, E. X. Jin, S. M. Uppuluri, and X.F. Xu, “Contact optical nanolithography using nanoscale C-shaped apertures,” Opt. Express 14, 9902–9908 (2006). http://www.opticsinfobase.org/abstract.cfm?URI=oe-14-21-9902 [CrossRef] [PubMed]

], spectroscopy [8

8. N. Felidj, J. Aubard, G. Levi, J. R. Krenn, M. Salerno, G. Schider, B. Lamprecht, A. Leitner, and F. R. Aussenegg, “Controlling the optical response of regular arrays of gold particles for surface-enhanced Raman scattering,” Phys. Rev. B 65, 075419 (2002). [CrossRef]

,9

9. K. Kneipp, H. Kneipp, I. Itzkan, R. R. Dasari, and M. S. Feld, “Surface-enhanced Raman scattering and biophysics,” J. Phys.: Condens. Matter 14, R597 (2002). [CrossRef]

], novel nanophotonic devices [10

10. E. Cubukcu, E. A. Kort, K. B. Crozier, and F. Capasso, “Plasmonic laser antenna,” Appl. Phys. Lett. 89, 93120 (2006). [CrossRef]

12

12. N. Yu, E. Cubukcu, L. Diehl, D. Bour, S. Corzine, J. Zhu, G. Höfler, K. B. Crozier, and F. Capasso, “Bowtie plasmonic quantum cascade laser antenna,” Opt. Express 15, 13272–13281 (2007). http://www.opticsinfobase.org/abstract.cfm?URI=oe-15-20-13272 [CrossRef] [PubMed]

], optical tweezers for nanoparticle trapping [13

13. A. N. Grigorenko, N. W. Roberts, M. R. Dicknson, and Y. Zhang, “Nanometric optical tweezers based on nanostructured substrates,” Nature Photonics 2, 365 (2008). [CrossRef]

] and high order harmonic generation [14

14. S. Kim, J. Jin, Y. Kim, I. Park, Y. Kim, and S. Kim, “High-harmonic generation by resonant plasmon field enhancement,” Nature 453, 757 (2008). [CrossRef] [PubMed]

], etc. Numerical simulations and experimental measurements show that a high intensity hot spot could be achieved in the gap of the metallic nanoantennas in the visible [1

1. P. Muhlschlegel, H.-J. Eisler, O. J. F. Martin, B. Hecht, and D. W. Pohl, “Resonant Optical Antennas,” Science 308, 1607 (2005). [CrossRef] [PubMed]

4

4. A. Sundaramurthy, P. James Schuck, N. R. Conley, D. P. Fromm, G. S. Kino, and W. E. Moerner, “Toward Nanometer-Scale Optical Photolithography: Utilizing the Near-Field of Bowtie Optical Nanoantennas,” Nano Lett. 6, 355 (2006). [CrossRef] [PubMed]

], infrared (IR) [11

11. L. Feng, D. V. Orden, M. Abashin, Q. Wang, Y. Chen, V. Lomakin, and Y. Fainman, “Nanoscale optical field localization by resonantly focused plasmons,” Opt. Express 17, 4824 (2009). http://www.opticsinfobase.org/abstract.cfm?URI=oe-17-6-4824 [CrossRef] [PubMed]

, 12

12. N. Yu, E. Cubukcu, L. Diehl, D. Bour, S. Corzine, J. Zhu, G. Höfler, K. B. Crozier, and F. Capasso, “Bowtie plasmonic quantum cascade laser antenna,” Opt. Express 15, 13272–13281 (2007). http://www.opticsinfobase.org/abstract.cfm?URI=oe-15-20-13272 [CrossRef] [PubMed]

] and THz domains [15

15. Y. Kawano and K. Ishibashi, “An on-chip near-field terahertz probe and detector,” Nature Photonics 2, 618 (2008). [CrossRef]

]. Such a high-intensity localized spot could be very useful for future on-chip optical applications [16

16. A. Polman, “Plasmonics Applied,” Science 322, 868 (2008). [CrossRef] [PubMed]

].

The UV region of the electromagnetic spectrum has received increased attention because of numerous civil and military industrial applications [17

17. Y. Taniyasu, M. Kasu, and T. Makimoto, “An aluminium nitride light-emitting diode with a wavelength of 210 nanometres,” Nature 441, 325 (2006). [CrossRef] [PubMed]

]. Additionally, there is a great interest in solid-state UV light sources for chemical and biological agent detection and efficient solid-state lighting. The availability of chip-scale UV light sources may also open up new applications in medical research for early disease detection [18

18. A. Sandhu, “The future of ultraviolet LEDs,” Nat. Photonics 1, 38 (2007). [CrossRef]

]. Consequently, achieving similar high intensity and strongly localized UV spots for future UV on-chip applications is an active area of research.

In recent years, some groups reported measurements or numerical modeling results employing UV light to excite UV localized surface plasmons (LSP) for near-field nanolithography [5

5. L. Wang, S. M. Uppuluri, E. X. Jin, and X. F. Xu. “Nanolithography using high transmission nanoscale bowtie apertures,” Nano Lett. 6, 361(2006). [CrossRef] [PubMed]

, 7

7. L. Wang, E. X. Jin, S. M. Uppuluri, and X.F. Xu, “Contact optical nanolithography using nanoscale C-shaped apertures,” Opt. Express 14, 9902–9908 (2006). http://www.opticsinfobase.org/abstract.cfm?URI=oe-14-21-9902 [CrossRef] [PubMed]

, 19

19. N. Murphy-DuBay, L. Wang, E. C. Kinzel, S. M. V. Uppuluri, and X. Xu, “Nanopatterning using NSOM probes integrated with high transmission nanoscale bowtie aperture,” Opt. Express 16, 2584–2589 (2008). http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-4-2584 [CrossRef] [PubMed]

, 20

20. Y. Wang, W. Srituravanich, C. Sun, and X. Zhang, “Plasmonic Nearfield Scanning Probe with High Transmission,” Nano Lett. 8, 3041 (2008). [CrossRef] [PubMed]

]. They presented lithographic results on photo-resist layers as an indirect demonstration of localized UV optical field. The near-field characteristics are intimately linked to the properties of any device in SPP circuits, especially in the subwavelength regime.[21

21. W. L. Barnes, A. Dereux, and T. W. Ebbesen, “Surface plasmon sub-wavelength optics,” Nature 424, 824 (2003) [CrossRef] [PubMed]

] It is therefore valuable to provide direct access to the near-field of the modes. In order to develop novel nano-structured components that control the distribution of the UV LSP modes, it is very important to directly image the near-field distribution of the hot spot and investigate their optical properties. In a recent publication, we have demonstrated our capability to study the optical properties of UV surface plasmon standing waves on an Al/Al2O3 film surface using a UV-compatible near-field scanning optical microscope (NSOM) system [22

22. Q. Gan, L. Zhou, V. Dierolf, and F. J. Bartoli, “Direct mapping of the UV surface plasmons,” Opt. Lett. 34, 1324 (2009). [CrossRef] [PubMed]

]. So far, no direct near-field imaging of optical nanoantennas operating in the UV domain has been reported. In this work, we employ our UV-NSOM system to study the optical field distribution on a metallic bowtie nanoantenna structure in the UV domain. We believe that direct mapping of UV LSP modes supported by the nanoantenna structure is an important step towards developing a novel optical scanning probe for high-resolution imaging, spectroscopy and lithography techniques at UV wavelengths.

2. Sample preparation and characterization

Since the experiments are designed for operation in the UV spectral range, aluminum was selected as the material. In this experiment, the Al bowtie nanoantenna was fabricated on a fused silica substrate. A 200nm-thick Al layer was deposited onto the substrate plate by a magnetically controlled sputtering process. The desired structure was then created utilizing a high-precision focused ion-beam milling technique (FEI DB-235). Figure 1(a) shows a scanning electron microscope (SEM) image of one of the nanoantennas that were fabricated. The geometric parameters of the nanoantenna are annotated in Fig. 1(b). The length (L) and width (d) of the antenna structure in Fig. 1(a) was measured to be approximately 200 nm and 185 nm, respectively. The antenna gap is about 50nm.

Fig. 1. (a) The SEM image of a bowtie nanoantenna. (b) Illustration of the bow-tie nanoantenna geometry. (c) A sketch of the UV NSOM operating in the collection mode.

A modified NSOM was employed to measure the optical field distribution on the surface of the nanostructures [Fig. 1(c)]. The optics of the NSOM system was modified for operation with UV light, permitting operation down to the Deep UV wavelength range. In the measurement, the UV NSOM is configured to operate in the collection mode. A UV laser at a wavelength of 364 nm is employed to illuminate the bowtie nanoantenna through the substrate [Fig. 1(c)]. A linear polarizer was used to control the polarization direction of the incident light. The NSOM probe, which had an aperture size of 50nm, was placed about 10 nm above the sample to pick up the optical signals. This is achieved by first bringing the NSOM tip in contact with the top surface of our bowtie nano-antenna structure, and finding the structures from the surface topography scan. Then we move the tip up to a fixed height of 10 nm. During this process we closely observe the beam deflection. It could be seen that the deflected beam shifts did not change during the measurement, indicating that the tip height was fixed. Under this condition, we observed obvious localized field distribution. The UV optical field distribution in the vicinity of the nanoantenna structure is shown in Fig. 2(a). The data clearly demonstrates that the bowtie antenna produced a hot spot in the gap area between the two triangular antenna arms that is greatly enhanced relative to areas away from the gap. We believe that this strong field enhancement arises from a combination of effects, including the LSP resonance, the sharp metallic tip with thin wedges, and electromagnetic field localization in the antenna gap nano-capacitor [11

11. L. Feng, D. V. Orden, M. Abashin, Q. Wang, Y. Chen, V. Lomakin, and Y. Fainman, “Nanoscale optical field localization by resonantly focused plasmons,” Opt. Express 17, 4824 (2009). http://www.opticsinfobase.org/abstract.cfm?URI=oe-17-6-4824 [CrossRef] [PubMed]

]. The spatial profile of the LSP mode is expected to be confined to the immediate vicinity of the 50 nm nanoantenna gap. However, the measured optical spot size along the antenna axis [the x direction in Fig. 1 (b)] was larger than the 50 nm gap. This discrepancy is mainly due to the finite-size of the NSOM probe aperture, which is comparable in size to the gap. The observed profile should be a convolution of the actual optical field and the collection function of the NSOM probe. Here we employed three-dimensional (3D) finite-difference time-domain (FDTD) modeling [23

23. Fullwave simulation with the commercial FDTD solver, Fullwave (Rsoft Inc.), is used to calculate the dispersion relations of the Al structures.

] to calculate the expected optical profile. The entire volume of the 3D simulation is treated using a grid size of 5 nm. The excitation source used in our simulation is a 364 nm UV plane wave polarized along the x-axis. The plane wave is launched normal to the bowtie antenna through the substrate. Aluminum and SiO2 are used as bowtie and substrate materials respectively. The permittivity of Al at this fixed wavelength is approximately -19.459+i3.606 [24

24. E. D. Palik, Handbook of Optical Constants of Solids (Academic, Orlando, FL, 1985), Vol. 1, p. 398.

]. In this simulation, all the geometric parameters of the nanoantenna are the same as those of the real device shown in Fig. 1(b). Figure 2(b) presents the calculated electric field distribution 10nm above the bowtie antenna in the x-y plane. These results clearly show that the electric field is strongly confined within the antenna gap. The fine structure of the electric field confinement was not totally resolved in NSOM imaging because of the aforementioned finite NSOM probe aperture. To compare our simulation data to the measured data in Fig. 2(a), we performed a convolution procedure on the FDTD simulation as shown in Fig. 2(c). The 2-D convolution was done by replacing each data point from the FDTD simulation with the average value of data points within a numerical circular aperture with a diameter of 50 nm. Since the data presented in Fig. 2(b) is a collection of discrete pixels, this 2-D convolution actually outputs a weighted average of each pixel’s neighborhood [25

25. J. C. Russ, The Image Processing Handbook(CRC Press, FL, 2007), p. 206.

]. A comparison of the optical field localization along the x direction is shown in Fig. 2(d). It can be clearly seen that after the convolution, the processed image agrees reasonably with the experimental data.

Fig. 2. (a) The optical field distribution around the nanoantenna structure measured in the near field. (b) FDTD simulation of the optical field intensity of x-y plane on the surface. (c) Convolved optical intensity distribution from (b). (d) Comparison the intensity cross-section taken from (c) with the experiment data.

3. Optimization of the bowtie nanoantenna dimensions

The field enhancement in the antenna gap can be optimized when the antenna is illuminated at the resonant wavelength, which is mainly determined by the geometric shape. This behavior was discussed by H. Fischer et. al. [26

26. H. Fischer and O. J. F. Martin, “Engineering the optical response of plasmonic nanoantennas,” Opt. Express 16, 9144–9154 (2008). http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-12-9144 [CrossRef] [PubMed]

] using Green’s tensor technique in the visible spectral range. In this report we performed FDTD simulations to find the resonance condition for bowtie nanoantennas operating at UV wavelengths. We simulated a set of bowtie antennas with a fixed gap width but various lengths L and tip angles θ. In these simulations, the antenna thickness t and the antenna gap g are fixed at 200 nm and 50 nm, respectively. The electric field amplitude 10 nm away from the bowtie antenna gap is recorded and normalized to the input electric field. As shown in Fig. 3(a), there exist several peaks of localized optical field amplitude or various values of length, L. We also plotted the length L associated with each resonance peak as a function of the order of resonance [Fig. 3 (b)]. Using a linear least square fit, the resonance periodicity was found to be 205±5 nm regardless of the value of the tip angles, indicating that the length L predominantly determines the resonances of the nanoantennas. Keeping this in mind, we simplified our experiments and only varied the length of the antenna. The results are discussed in the following.

Fig. 3. (a) Electric field amplitude vs. length L for the bowtie antenna different a function of tip angle. The field is normalized to the amplitude of incident electric field. (b) Resonance peak position as a function of the order of resonance. Dashed lines are linear least square fit of the data with different tip angle.

Fig. 4. (a) SEM image of a bowtie antenna array. (b) NSOM image of the bowtie antenna array in (a). (c) Comparison of experimental data with computed field amplitude.

4. Summary

Using a UV-NSOM operating in the collection mode, we successfully performed a direct measurement of the near-field intensity profile of UV LSP near the gap of bow-tie nanoantennas. Highly confined UV hot spots are observed in the near-field of these nanostructures. FDTD simulations show good agreement with the experiments as long as the limited NSOM resolution is taken into account. The phenomena of pronounced resonances in the LSP intensity as a function of bowtie geometry (e.g.: arm length) is discussed in the context of optimizing the nanoantennas at UV wavelengths. We find good agreement between simulation and experiment. We believe that direct mapping of the UV light enhancement from a metallic bowtie nanoantenna has potential impact on novel photonic applications in the UV domain, such as photolithography, single-molecule imaging, tip-enhanced Raman spectroscopy, and nanoparticle trapping. In addition, direct measurement of the optical field near the nanoantenna contributes to a better understanding of the underlying physics of these nanoscale optical antennas, which is crucial to the studies of sub-wavelength optics on a chip.

Acknowledgements

The authors would like to acknowledge the support of this research by NSF (Award # ECS-0901324 and DMR-0602986).

References and Links

1.

P. Muhlschlegel, H.-J. Eisler, O. J. F. Martin, B. Hecht, and D. W. Pohl, “Resonant Optical Antennas,” Science 308, 1607 (2005). [CrossRef] [PubMed]

2.

D. P. Fromm, A. Sundaramurthy, P. J. Schuck, G. Kino, and W. E. Moerner, “Gap-Dependent Optical Coupling of Single ‘Bowtie’Nanoantennas Resonant in the Visible,” Nano Lett. 4, 957–961 (2004). [CrossRef]

3.

L. Wang and X. F. Xu, “High transmission nanoscale bowtie-shaped aperture probe for near-field optical imaging,” Appl. Phys. Lett. 90, 261105 (2007). [CrossRef]

4.

A. Sundaramurthy, P. James Schuck, N. R. Conley, D. P. Fromm, G. S. Kino, and W. E. Moerner, “Toward Nanometer-Scale Optical Photolithography: Utilizing the Near-Field of Bowtie Optical Nanoantennas,” Nano Lett. 6, 355 (2006). [CrossRef] [PubMed]

5.

L. Wang, S. M. Uppuluri, E. X. Jin, and X. F. Xu. “Nanolithography using high transmission nanoscale bowtie apertures,” Nano Lett. 6, 361(2006). [CrossRef] [PubMed]

6.

E. X. Jin and X. F. Xu, “Enhanced optical near field from a bowtie aperture,” Appl. Phys. Lett. 88, 153110 (2006). [CrossRef]

7.

L. Wang, E. X. Jin, S. M. Uppuluri, and X.F. Xu, “Contact optical nanolithography using nanoscale C-shaped apertures,” Opt. Express 14, 9902–9908 (2006). http://www.opticsinfobase.org/abstract.cfm?URI=oe-14-21-9902 [CrossRef] [PubMed]

8.

N. Felidj, J. Aubard, G. Levi, J. R. Krenn, M. Salerno, G. Schider, B. Lamprecht, A. Leitner, and F. R. Aussenegg, “Controlling the optical response of regular arrays of gold particles for surface-enhanced Raman scattering,” Phys. Rev. B 65, 075419 (2002). [CrossRef]

9.

K. Kneipp, H. Kneipp, I. Itzkan, R. R. Dasari, and M. S. Feld, “Surface-enhanced Raman scattering and biophysics,” J. Phys.: Condens. Matter 14, R597 (2002). [CrossRef]

10.

E. Cubukcu, E. A. Kort, K. B. Crozier, and F. Capasso, “Plasmonic laser antenna,” Appl. Phys. Lett. 89, 93120 (2006). [CrossRef]

11.

L. Feng, D. V. Orden, M. Abashin, Q. Wang, Y. Chen, V. Lomakin, and Y. Fainman, “Nanoscale optical field localization by resonantly focused plasmons,” Opt. Express 17, 4824 (2009). http://www.opticsinfobase.org/abstract.cfm?URI=oe-17-6-4824 [CrossRef] [PubMed]

12.

N. Yu, E. Cubukcu, L. Diehl, D. Bour, S. Corzine, J. Zhu, G. Höfler, K. B. Crozier, and F. Capasso, “Bowtie plasmonic quantum cascade laser antenna,” Opt. Express 15, 13272–13281 (2007). http://www.opticsinfobase.org/abstract.cfm?URI=oe-15-20-13272 [CrossRef] [PubMed]

13.

A. N. Grigorenko, N. W. Roberts, M. R. Dicknson, and Y. Zhang, “Nanometric optical tweezers based on nanostructured substrates,” Nature Photonics 2, 365 (2008). [CrossRef]

14.

S. Kim, J. Jin, Y. Kim, I. Park, Y. Kim, and S. Kim, “High-harmonic generation by resonant plasmon field enhancement,” Nature 453, 757 (2008). [CrossRef] [PubMed]

15.

Y. Kawano and K. Ishibashi, “An on-chip near-field terahertz probe and detector,” Nature Photonics 2, 618 (2008). [CrossRef]

16.

A. Polman, “Plasmonics Applied,” Science 322, 868 (2008). [CrossRef] [PubMed]

17.

Y. Taniyasu, M. Kasu, and T. Makimoto, “An aluminium nitride light-emitting diode with a wavelength of 210 nanometres,” Nature 441, 325 (2006). [CrossRef] [PubMed]

18.

A. Sandhu, “The future of ultraviolet LEDs,” Nat. Photonics 1, 38 (2007). [CrossRef]

19.

N. Murphy-DuBay, L. Wang, E. C. Kinzel, S. M. V. Uppuluri, and X. Xu, “Nanopatterning using NSOM probes integrated with high transmission nanoscale bowtie aperture,” Opt. Express 16, 2584–2589 (2008). http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-4-2584 [CrossRef] [PubMed]

20.

Y. Wang, W. Srituravanich, C. Sun, and X. Zhang, “Plasmonic Nearfield Scanning Probe with High Transmission,” Nano Lett. 8, 3041 (2008). [CrossRef] [PubMed]

21.

W. L. Barnes, A. Dereux, and T. W. Ebbesen, “Surface plasmon sub-wavelength optics,” Nature 424, 824 (2003) [CrossRef] [PubMed]

22.

Q. Gan, L. Zhou, V. Dierolf, and F. J. Bartoli, “Direct mapping of the UV surface plasmons,” Opt. Lett. 34, 1324 (2009). [CrossRef] [PubMed]

23.

Fullwave simulation with the commercial FDTD solver, Fullwave (Rsoft Inc.), is used to calculate the dispersion relations of the Al structures.

24.

E. D. Palik, Handbook of Optical Constants of Solids (Academic, Orlando, FL, 1985), Vol. 1, p. 398.

25.

J. C. Russ, The Image Processing Handbook(CRC Press, FL, 2007), p. 206.

26.

H. Fischer and O. J. F. Martin, “Engineering the optical response of plasmonic nanoantennas,” Opt. Express 16, 9144–9154 (2008). http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-12-9144 [CrossRef] [PubMed]

OCIS Codes
(180.4243) Microscopy : Near-field microscopy
(310.6628) Thin films : Subwavelength structures, nanostructures

ToC Category:
Microscopy

History
Original Manuscript: September 8, 2009
Revised Manuscript: October 8, 2009
Manuscript Accepted: October 20, 2009
Published: October 22, 2009

Citation
Liangcheng Zhou, Qiaoqiang Gan, Filbert J. Bartoli, and Volkmar Dierolf, "Direct near-field optical imaging of UV bowtie nanoantennas," Opt. Express 17, 20301-20306 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-22-20301


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References

  1. P. Muhlschlegel, H.-J. Eisler, O. J. F. Martin, B. Hecht, and D. W. Pohl, "Resonant Optical Antennas," Science 308, 1607 (2005). [CrossRef] [PubMed]
  2. D. P. Fromm, A. Sundaramurthy, P. J. Schuck, G. Kino, and W. E. Moerner, "Gap-Dependent Optical Coupling of Single ‘Bowtie’Nanoantennas Resonant in the Visible," Nano Lett. 4, 957-961 (2004). [CrossRef]
  3. L. Wang and X. F. Xu, "High transmission nanoscale bowtie-shaped aperture probe for near-field optical imaging," Appl. Phys. Lett. 90, 261105 (2007). [CrossRef]
  4. A. Sundaramurthy, P. James Schuck, N. R. Conley, D. P. Fromm, G. S. Kino, and W. E. Moerner, "Toward Nanometer-Scale Optical Photolithography: Utilizing the Near-Field of Bowtie Optical Nanoantennas," Nano Lett. 6, 355 (2006). [CrossRef] [PubMed]
  5. L. Wang, S. M. Uppuluri, E. X. Jin, X. F. Xu. "Nanolithography using high transmission nanoscale bowtie apertures," Nano Lett. 6, 361(2006). [CrossRef] [PubMed]
  6. E. X. Jin and X. F. Xu, "Enhanced optical near field from a bowtie aperture," Appl. Phys. Lett. 88, 153110 (2006). [CrossRef]
  7. L. Wang, E. X. Jin, S. M. Uppuluri, and X. F. Xu, "Contact optical nanolithography using nanoscale C-shaped apertures," Opt. Express 14, 9902-9908 (2006). http://www.opticsinfobase.org/abstract.cfm?URI=oe-14-21-9902 [CrossRef] [PubMed]
  8. N. Felidj, J. Aubard, G. Levi, J. R. Krenn, M. Salerno, G. Schider, B. Lamprecht, A. Leitner, and F. R. Aussenegg, "Controlling the optical response of regular arrays of gold particles for surface-enhanced Raman scattering," Phys. Rev. B 65, 075419 (2002). [CrossRef]
  9. K. Kneipp, H. Kneipp, I. Itzkan, R. R. Dasari, and M. S. Feld, "Surface-enhanced Raman scattering and biophysics," J. Phys.: Condens. Matter 14, R597 (2002). [CrossRef]
  10. E. Cubukcu, E. A. Kort, K. B. Crozier, and F. Capasso, "Plasmonic laser antenna," Appl. Phys. Lett. 89, 93120 (2006). [CrossRef]
  11. L. Feng, D. V. Orden, M. Abashin, Q. Wang, Y. Chen, V. Lomakin and Y. Fainman, "Nanoscale optical field localization by resonantly focused plasmons," Opt. Express 17, 4824 (2009). http://www.opticsinfobase.org/abstract.cfm?URI=oe-17-6-4824 [CrossRef] [PubMed]
  12. N. Yu, E. Cubukcu, L. Diehl, D. Bour, S. Corzine, J. Zhu, G. Höfler, K. B. Crozier, and F. Capasso, "Bowtie plasmonic quantum cascade laser antenna," Opt. Express 15, 13272-13281 (2007). http://www.opticsinfobase.org/abstract.cfm?URI=oe-15-20-13272 [CrossRef] [PubMed]
  13. A. N. Grigorenko, N. W. Roberts, M. R. Dicknson, and Y. Zhang, "Nanometric optical tweezers based on nanostructured substrates," Nat. Photonics 2, 365 (2008). [CrossRef]
  14. S. Kim, J. Jin, Y. Kim, I. Park, Y. Kim and S. Kim, "High-harmonic generation by resonant plasmon field enhancement," Nature 453, 757 (2008). [CrossRef] [PubMed]
  15. Y. Kawano and K. Ishibashi, "An on-chip near-field terahertz probe and detector," Nat. Photonics 2, 618 (2008). [CrossRef]
  16. A. Polman, "Plasmonics Applied," Science 322, 868 (2008). [CrossRef] [PubMed]
  17. Y. Taniyasu, M. Kasu, and T. Makimoto, "An aluminium nitride light-emitting diode with a wavelength of 210 nanometres," Nature 441, 325 (2006). [CrossRef] [PubMed]
  18. A. Sandhu, "The future of ultraviolet LEDs," Nat. Photonics 1, 38 (2007). [CrossRef]
  19. N. Murphy-DuBay, L. Wang, E. C. Kinzel, S. M. V. Uppuluri, and X. Xu, "Nanopatterning using NSOM probes integrated with high transmission nanoscale bowtie aperture," Opt. Express 16, 2584-2589 (2008). http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-4-2584 [CrossRef] [PubMed]
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