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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 21 — Oct. 21, 2013
  • pp: 24490–24496
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Nanoscale tensile stress approach for the direct writing of plasmonic nanostructures

Tianrui Zhai, Yuanhai Lin, Hongmei Liu, Shengfei Feng, and Xinping Zhang  »View Author Affiliations


Optics Express, Vol. 21, Issue 21, pp. 24490-24496 (2013)
http://dx.doi.org/10.1364/OE.21.024490


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Abstract

One- and two-dimensional plasmonic nanostructures can be fabricated using nanoscale tensile stress. A polymer layer, coated with a thin metal film, is exposed to an interference pattern produced by ultraviolet laser beams. Crosslinking is induced between the polymeric molecules located within the bright fringes. This process not only increases the refractive index but also reduces the polymer layer thickness. Corrugations occur on the continuous thin metal film due to the nanoscale stress in the polymer layer. Thus, a periodic nanostructure of area 3 × 3 mm and depth 50 nm is created both in the polymer and metal films with excellent homogeneity and reproducibility. This method enables direct writing of a large-area plasmonic nanostructure at low cost which can be used in the design of optoelectronic devices and sensors.

© 2013 Optical Society of America

1. Introduction

Plasmonic structures have been investigated extensively both theoretically and experimentally, including design [1

1. M. I. Stockman, “Nanofocusing of optical energy in tapered plasmonic waveguides,” Phys. Rev. Lett. 93(13), 137404 (2004). [CrossRef] [PubMed]

,2

2. R. F. Oulton, V. J. Sorger, D. Genov, D. Pile, and X. Zhang, “A hybrid plasmonic waveguide for subwavelength confinement and long-range propagation,” Nat. Photonics 2(8), 496–500 (2008). [CrossRef]

], fabrication [3

3. J. Henzie, M. H. Lee, and T. W. Odom, “Multiscale patterning of plasmonic metamaterials,” Nat. Nanotechnol. 2(9), 549–554 (2007). [CrossRef] [PubMed]

,4

4. W. A. Murray and W. L. Barnes, “Plasmonic materials,” Adv. Mater. 19(22), 3771–3782 (2007). [CrossRef]

], characterization [5

5. F. Tam, G. P. Goodrich, B. R. Johnson, and N. J. Halas, “Plasmonic enhancement of molecular fluorescence,” Nano Lett. 7(2), 496–501 (2007). [CrossRef] [PubMed]

,6

6. G. Veronis and S. Fan, “Guided subwavelength plasmonic mode supported by a slot in a thin metal film,” Opt. Lett. 30(24), 3359–3361 (2005). [CrossRef] [PubMed]

], and application [7

7. J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, “Biosensing with plasmonic nanosensors,” Nat. Mater. 7(6), 442–453 (2008). [CrossRef] [PubMed]

9

9. T. Zhai, X. Zhang, Z. Pang, X. Su, H. Liu, S. Feng, and L. Wang, “Random laser based on waveguided plasmonic gain channels,” Nano Lett. 11(10), 4295–4298 (2011). [CrossRef] [PubMed]

]. To date, it remains a challenge to fabricate a large-area uniform plasmonic nanostructure at low cost, and in particular implemented on organic films. Inevitably, most fabrication techniques involve either high-temperature, wet processes, or expensive processes, such as solution-processable methods [10

10. X. Zhang, B. Sun, R. H. Friend, H. Guo, D. Nau, and H. Giessen, “Metallic photonic crystals based on solution-processible gold nanoparticles,” Nano Lett. 6(4), 651–655 (2006). [CrossRef] [PubMed]

,11

11. X. Zhang, H. Liu, and S. Feng, “Solution-processible fabrication of large-area patterned and unpatterned gold nanostructures,” Nanotechnology 20(42), 425303 (2009). [CrossRef] [PubMed]

], holographic fabrication [12

12. M. Lu, B. Krishna Juluri, Y. Zhao, Y. Jun Liu, T. J. Bunning, and T. Jun Huang, “Single-step holographic fabrication of large-area periodically corrugated metal films,” J. Appl. Phys. 112(11), 113101 (2012). [CrossRef] [PubMed]

], electron beam lithography [13

13. E. M. Hicks, S. Zou, G. C. Schatz, K. G. Spears, R. P. Van Duyne, L. Gunnarsson, T. Rindzevicius, B. Kasemo, and M. Käll, “Controlling plasmon line shapes through diffractive coupling in linear arrays of cylindrical nanoparticles fabricated by electron beam lithography,” Nano Lett. 5(6), 1065–1070 (2005). [CrossRef] [PubMed]

,14

14. S. A. Maier, M. L. Brongersma, P. G. Kik, S. Meltzer, A. A. Requicha, and H. A. Atwater, “Plasmonics—a route to nanoscale optical devices,” Adv. Mater. 13(19), 1501–1505 (2001). [CrossRef]

], reactive ion-beam etching [15

15. Z. Han, A. Y. Elezzabi, and V. Van, “Experimental realization of subwavelength plasmonic slot waveguides on a silicon platform,” Opt. Lett. 35(4), 502–504 (2010). [CrossRef] [PubMed]

], and nanoimprinting [16

16. V. Malyarchuk, F. Hua, N. H. Mack, V. T. Velasquez, J. O. White, R. G. Nuzzo, and J. A. Rogers, “High performance plasmonic crystal sensor formed by soft nanoimprint lithography,” Opt. Express 13(15), 5669–5675 (2005). [CrossRef] [PubMed]

,17

17. J. Yao, A. P. Le, S. K. Gray, J. S. Moore, J. A. Rogers, and R. G. Nuzzo, “Functional nanostructured plasmonic materials,” Adv. Mater. 22(10), 1102–1110 (2010). [CrossRef] [PubMed]

]. These are not suitable in producing organic optoelectronic devices or in mass production of these devices.

Recently, we introduced a nano-patterning method using interference crosslinking to produce nanoscale periodic structures into conjugated polymers [18

18. X. Zhang, H. Liu, H. Li, and T. Zhai, “Direct nanopatterning into conjugated polymers using Iinterference crosslinking,” Macromol. Chem. Phys. 213(12), 1285–1290 (2012). [CrossRef]

]. In this work, we apply nano-patterning to thin metallic films coated on conjugated polymer substrates and demonstrate a direct writing of plasmonic nanostructures with the aid of nanoscale stress. Crosslinking is known not only to increase the refractive index but also reduce the thickness of the polymer layer [19

19. U. Jeong, D. Ryu, J. Kim, D. Kim, T. P. Russell, and C. J. Hawker, “Volume contractions induced by crosslinking: a novel route to nanoporous polymer films,” Adv. Mater. 15(15), 1247–1250 (2003). [CrossRef]

,20

20. W. Zhao, T. Cao, and J. M. White, “On the origin of green emission in polyfluorene polymers: the roles of thermal oxidation degradation and crosslinking,” Adv. Funct. Mater. 14(8), 783–790 (2004). [CrossRef]

] forming a surface-relief structure in polymer films. It will yield nanoscale stress distribution in the polymer film, stretching the adjacent metal film to form corrugation. This one-step fabrication technique potentially enables the development of new optoelectronic devices.

2. Experimental details

2.1 Materials and the interference crosslinking technique

In our experiment, a typical light-emitting conjugated polymer, poly [(9,9- dioctylfluorenyl-2,7-diyl) -alt- co- (1,4- benzo-{2,1’,3}- thiadiazole)] (F8BT from Sigma Aldrich, USA), is employed to demonstrate the direct writing method. The polymer is spin-coated onto a 180-nm-thick indium-tin-oxide (ITO)-coated glass substrate of area 20 mm × 20 mm and thickness 1 mm at a speed of 1800 rpm. The concentration of the F8BT solution in chloroform is 20 mg/ml and the thickness of the F8BT film is about 120 nm. A thin film of metal (gold or aluminum) with a thickness of 30 nm is evaporated onto the F8BT layer, as illustrated in Fig. 1(a)
Fig. 1 Schematic of the nanoscale tensile stress induced plasmonic nanostructure. (a) ITO glass substrate coated with F8BT and metal layers. (b) The sample is exposed to a two-beam interference pattern with an included angle α1, forming a pattern with period Λ1. The nanoscale tensile stress distribution in the polymer layer is marked by the red arrows. The length of the red arrows denotes the magnitude of the nanoscale stress. (c) The plasmonic nanostructure after interference crosslinking. The insets depict uncrosslinked (left) and crosslinked (right) polymer molecule networks
.

During fabrication, a He-Cd laser (Kimmon Koha Co., Ltd.; model: IK3301R-G) operating at 325 nm is used as the ultraviolet (UV) light source for interference. The sample is then exposed from the glass substrate side for 15 min to an interference pattern generated by two UV beams with a diameter of 3 mm and a total power of about 30 mW. The period Λ1 of the interference pattern can be controlled by changing the included angle α1 between the two beams in Fig. 1(b). Crosslinking is initiated between polymeric molecules located within the bright fringes, whereas almost no crosslinking occurs within the dark fringes. This process not only changes the refractive index but also decreases the thickness of the polymer film because of the higher structural density.

2.2 The nanoscale tensile stress induced plasmonic nanostructures

During interference crosslinking, a periodical surface-relief structure in the F8BT layer patterned on the interference pattern is created through selective reduction of the film thickness. Thus, a nanoscale tensile stress distribution appears near the interface edge between the polymer and the metal layers as shown in Fig. 1(b), which has the same period with the interference pattern. The metal film will be stretched by the nanoscale tensile stress, forming a periodic nanostructure with nonuniform thickness. The one-dimensional (1D)/two-dimensional (2D) structure can be fabricated flexibly by a single/multiexposure process [21

21. T. Zhai, X. Zhang, Z. Pang, and F. Dou, “Direct writing of polymer lasers using interference ablation,” Adv. Mater. 23(16), 1860–1864 (2011). [CrossRef] [PubMed]

].

3. Results and discussion

3.1 Large-area plasmonic nanostructures with homogeneity and reproducibility

Atomic force microscopic (AFM) images of the gold nanostructure in Fig. 2
Fig. 2 AFM images of the one- and two-dimensional gold nanostructure achieved using interference crosslinking. Λ1 = 350 nm. Scale bar in the insets, 100 nm.
show large-area homogeneity formed by interference crosslinking. The modulation depth of the structure reaches to 50 nm; that is, 42% of the total thickness of the F8BT layer. The period of the nanostructure is about 350 nm (α1 = 55°). The area of the plasmonic nanostructure based on interference crosslinking is roughly equal to that of the interference pattern.

3.2 Effects of the metal ductility and the adhesion of the metal/polymer interface

If metal ductility is poor or the modulation depth is too high, the thin metal film will understandably crack. For experimental comparison, a 30-nm-thick aluminium (Al) film was evaporated on the F8BT layer and the same fabrication procedure applied to the sample. The resulting structure was imaged in Fig. 3(b)
Fig. 3 Nanostructures formed by metals with different ductility. (a) Gold nanograting. (b) Al nanograting.
and shows an Al film with breaks and jagged edges that formed because of Al’s poor ductility compared with gold [22

22. H. M. Lee, M. Ge, B. Sahu, P. Tarakeshwar, and K. S. Kim, “Geometrical and electronic structures of gold, silver, and gold-silver binary clusters: Origins of ductility of gold and gold-silver alloy formation,” J. Phys. Chem. B 107(37), 9994–10005 (2003). [CrossRef]

]. Besides, it is also well known that gold can diffuse in polymers during deposition. As a consequence, adhesion properties between polymer and metal are better in the case of gold [23

23. C. A. Chang, Y. K. Kim, and A. Schrott, “Adhesion studies of metals on fluorocarbon polymer films,” J. Vac. Sci. Technol. A 8(4), 3304–3309 (1990). [CrossRef]

]. So, delamination at the Al/polymer interface can induce cracks due to a lack of adhesion. Thus, a sponge-like structure is formed in the Al film which is quite different from the gold nanostructure in Fig. 3(a). Moreover, curing also induces a change of the elastic modulus of the polymer, which has an effect on the distribution of strain in the layer. Stress profiles on different sites inside the sample can induce wrinkling (or cracks).

3.3. Spectroscopic characterization of the plasmonic nanostructure

Figure 5
Fig. 5 Angle-resolved tuning properties of the waveguide mode of the gold nanogratings based on interference crosslinking. (a) TM polarization. (b) TE polarization. The angle changes from 0 to 24° with a step of 2°. The insets show the enlarged view of the dip/peak in the spectra.
demonstrates the extinction spectra of the waveguide mode with changing the incidence angle of a white light beam from a tungsten halogen lamp (Ocean Optics; model: HL-2000). The experimental setup of the measurement has been detailed in our early work [25

25. T. Zhai and X. Zhang, “Gain-and feedback-channel matching in lasers based on radiative-waveguide gratings,” Appl. Phys. Lett. 101(14), 143507 (2012). [CrossRef]

]. The waveguide mode is observed at 558 nm and 567 nm at normal incidence for TM and TE polarization, respectively, indicating that the effective refractive index of the nanostructure for the TM wave is slightly smaller than that for the TE wave. The waveguide mode is split into two branches as incidence angle is increased. The angle-resolved tuning rate is about 4.5 and 4.3 nm/degree for TM and TE waves, respectively. The bandwidth of the waveguide mode and the plasmon resonance measures to be about 10 nm and 100 nm, respectively. These characteristics indicate the excellent quality of the nanostructure based on the direct nanofabrication technique.

It should be noted that the peaks in the extinction spectra change into dips when the incidence angle is larger than 20° for the TM polarization. In brief, the anti-crossing behavior between the waveguide mode and the plasmon resonance can be observed for large incidence angle. The anti-crossing effect due to the Fano resonance as a result of the coupling between localized surface plasmon of the gold nanostructures and waveguide modes has been discussed in detail [26

26. B. Luk’yanchuk, N. I. Zheludev, S. A. Maier, N. J. Halas, P. Nordlander, H. Giessen, and C. T. Chong, “The Fano resonance in plasmonic nanostructures and metamaterials,” Nat. Mater. 9(9), 707–715 (2010). [CrossRef] [PubMed]

, 27

27. S. Linden, J. Kuhl, and H. Giessen, “Controlling the interaction between light and gold nanoparticles: Selective suppression of extinction,” Phys. Rev. Lett. 86(20), 4688–4691 (2001). [CrossRef] [PubMed]

]. The most important feature of this kind of behaviour is a dip observed in the extinction spectrum, implying enhanced transmission. A transition is thus generally observed from an extinction peak to a dip for the emergence of the localized surface plasmon, indicating the happening of the coupling process. Therefore, the change for the waveguide-mode feature from a peak to a dip in the extinction spectra in Fig. 5(a) is a convincing verification of the excitation of the localized surface palsmon resonance in the nanostructured gold films. Furthermore, for larger incidence angle, the directly transmitted light wave becomes weaker due to reflection and plasmon resonance scattering. In this case, the directly transmitted light wave is comparable with waveguide mode. Therefore, they counteract each other completely, changing the spectra from peaks to dips [28

28. S. Feng, X. Zhang, J. Li, and P. J. Klar, “Coupling between the plasmonic and photonic resonance modes in wave-guided metallic photonic crystals,” J. Nanophotonics 6(1), 063513 (2012). [CrossRef]

].

4. Discussions

The proposed fabrication technique might be used in the design of metal electrode of electrically pumped polymer lasers, which is one of the motivations of this fabrication work. It is a challenge to fabricate metal electrodes on the nanograting without disturbing the function (or mode) of the nanograting. Inhomogeneous thickness of the metal film may induce spatial modulation of charge injection and recombination in the active layer, which might be useful for exploiting organic light-emitting devices (OLEDs), which is difficult to achieve by conventional evaporation technique. Besides, this kind of structures can be used in enhancing the output coupling efficiency, for example, when a polymer layer is coated onto the gold nano-grating structures to produce OLEDs.

5. Conclusions

We introduced a direct writing technique for fabricating plasmonic structure on conjugated polymer film using interference. Different patterns generated by interference patterns can be “recorded” conveniently on the thin metal film. This direct nanofabrication technique provides an alternative means to pattern plasmonic devices.

Acknowledgments

The authors acknowledge the 973 Program (2013CB922404), the National Natural Science Foundation of China (11104007, and 11274031), Beijing Natural Science Foundation (1132004, 4133082), the Beijing Educational Commission (KM201210005034), and Beijing Nova Program (2012009) for the financial support.

References and links

1.

M. I. Stockman, “Nanofocusing of optical energy in tapered plasmonic waveguides,” Phys. Rev. Lett. 93(13), 137404 (2004). [CrossRef] [PubMed]

2.

R. F. Oulton, V. J. Sorger, D. Genov, D. Pile, and X. Zhang, “A hybrid plasmonic waveguide for subwavelength confinement and long-range propagation,” Nat. Photonics 2(8), 496–500 (2008). [CrossRef]

3.

J. Henzie, M. H. Lee, and T. W. Odom, “Multiscale patterning of plasmonic metamaterials,” Nat. Nanotechnol. 2(9), 549–554 (2007). [CrossRef] [PubMed]

4.

W. A. Murray and W. L. Barnes, “Plasmonic materials,” Adv. Mater. 19(22), 3771–3782 (2007). [CrossRef]

5.

F. Tam, G. P. Goodrich, B. R. Johnson, and N. J. Halas, “Plasmonic enhancement of molecular fluorescence,” Nano Lett. 7(2), 496–501 (2007). [CrossRef] [PubMed]

6.

G. Veronis and S. Fan, “Guided subwavelength plasmonic mode supported by a slot in a thin metal film,” Opt. Lett. 30(24), 3359–3361 (2005). [CrossRef] [PubMed]

7.

J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, “Biosensing with plasmonic nanosensors,” Nat. Mater. 7(6), 442–453 (2008). [CrossRef] [PubMed]

8.

Y. Lin, T. Zhai, Q. Ma, H. Liu, and X. P. Zhang, “Compact bandwidth-tunable polarization filter based on a plasmonic heterograting,” Opt. Express 21(9), 11315–11321 (2013). [CrossRef] [PubMed]

9.

T. Zhai, X. Zhang, Z. Pang, X. Su, H. Liu, S. Feng, and L. Wang, “Random laser based on waveguided plasmonic gain channels,” Nano Lett. 11(10), 4295–4298 (2011). [CrossRef] [PubMed]

10.

X. Zhang, B. Sun, R. H. Friend, H. Guo, D. Nau, and H. Giessen, “Metallic photonic crystals based on solution-processible gold nanoparticles,” Nano Lett. 6(4), 651–655 (2006). [CrossRef] [PubMed]

11.

X. Zhang, H. Liu, and S. Feng, “Solution-processible fabrication of large-area patterned and unpatterned gold nanostructures,” Nanotechnology 20(42), 425303 (2009). [CrossRef] [PubMed]

12.

M. Lu, B. Krishna Juluri, Y. Zhao, Y. Jun Liu, T. J. Bunning, and T. Jun Huang, “Single-step holographic fabrication of large-area periodically corrugated metal films,” J. Appl. Phys. 112(11), 113101 (2012). [CrossRef] [PubMed]

13.

E. M. Hicks, S. Zou, G. C. Schatz, K. G. Spears, R. P. Van Duyne, L. Gunnarsson, T. Rindzevicius, B. Kasemo, and M. Käll, “Controlling plasmon line shapes through diffractive coupling in linear arrays of cylindrical nanoparticles fabricated by electron beam lithography,” Nano Lett. 5(6), 1065–1070 (2005). [CrossRef] [PubMed]

14.

S. A. Maier, M. L. Brongersma, P. G. Kik, S. Meltzer, A. A. Requicha, and H. A. Atwater, “Plasmonics—a route to nanoscale optical devices,” Adv. Mater. 13(19), 1501–1505 (2001). [CrossRef]

15.

Z. Han, A. Y. Elezzabi, and V. Van, “Experimental realization of subwavelength plasmonic slot waveguides on a silicon platform,” Opt. Lett. 35(4), 502–504 (2010). [CrossRef] [PubMed]

16.

V. Malyarchuk, F. Hua, N. H. Mack, V. T. Velasquez, J. O. White, R. G. Nuzzo, and J. A. Rogers, “High performance plasmonic crystal sensor formed by soft nanoimprint lithography,” Opt. Express 13(15), 5669–5675 (2005). [CrossRef] [PubMed]

17.

J. Yao, A. P. Le, S. K. Gray, J. S. Moore, J. A. Rogers, and R. G. Nuzzo, “Functional nanostructured plasmonic materials,” Adv. Mater. 22(10), 1102–1110 (2010). [CrossRef] [PubMed]

18.

X. Zhang, H. Liu, H. Li, and T. Zhai, “Direct nanopatterning into conjugated polymers using Iinterference crosslinking,” Macromol. Chem. Phys. 213(12), 1285–1290 (2012). [CrossRef]

19.

U. Jeong, D. Ryu, J. Kim, D. Kim, T. P. Russell, and C. J. Hawker, “Volume contractions induced by crosslinking: a novel route to nanoporous polymer films,” Adv. Mater. 15(15), 1247–1250 (2003). [CrossRef]

20.

W. Zhao, T. Cao, and J. M. White, “On the origin of green emission in polyfluorene polymers: the roles of thermal oxidation degradation and crosslinking,” Adv. Funct. Mater. 14(8), 783–790 (2004). [CrossRef]

21.

T. Zhai, X. Zhang, Z. Pang, and F. Dou, “Direct writing of polymer lasers using interference ablation,” Adv. Mater. 23(16), 1860–1864 (2011). [CrossRef] [PubMed]

22.

H. M. Lee, M. Ge, B. Sahu, P. Tarakeshwar, and K. S. Kim, “Geometrical and electronic structures of gold, silver, and gold-silver binary clusters: Origins of ductility of gold and gold-silver alloy formation,” J. Phys. Chem. B 107(37), 9994–10005 (2003). [CrossRef]

23.

C. A. Chang, Y. K. Kim, and A. Schrott, “Adhesion studies of metals on fluorocarbon polymer films,” J. Vac. Sci. Technol. A 8(4), 3304–3309 (1990). [CrossRef]

24.

B. Wenger, N. Tétreault, M. Welland, and R. Friend, “Mechanically tunable conjugated polymer distributed feedback lasers,” Appl. Phys. Lett. 97(19), 193303 (2010). [CrossRef]

25.

T. Zhai and X. Zhang, “Gain-and feedback-channel matching in lasers based on radiative-waveguide gratings,” Appl. Phys. Lett. 101(14), 143507 (2012). [CrossRef]

26.

B. Luk’yanchuk, N. I. Zheludev, S. A. Maier, N. J. Halas, P. Nordlander, H. Giessen, and C. T. Chong, “The Fano resonance in plasmonic nanostructures and metamaterials,” Nat. Mater. 9(9), 707–715 (2010). [CrossRef] [PubMed]

27.

S. Linden, J. Kuhl, and H. Giessen, “Controlling the interaction between light and gold nanoparticles: Selective suppression of extinction,” Phys. Rev. Lett. 86(20), 4688–4691 (2001). [CrossRef] [PubMed]

28.

S. Feng, X. Zhang, J. Li, and P. J. Klar, “Coupling between the plasmonic and photonic resonance modes in wave-guided metallic photonic crystals,” J. Nanophotonics 6(1), 063513 (2012). [CrossRef]

29.

X. Zhang, X. Ma, F. Dou, P. Zhao, and H. Liu, “A biosensor based on metallic photonic crystals for the detection of specific bioreactions,” Adv. Funct. Mater. 21(22), 4219–4227 (2011). [CrossRef]

OCIS Codes
(160.5470) Materials : Polymers
(220.4241) Optical design and fabrication : Nanostructure fabrication
(250.5403) Optoelectronics : Plasmonics

ToC Category:
Plasmonics

History
Original Manuscript: July 18, 2013
Revised Manuscript: September 26, 2013
Manuscript Accepted: September 26, 2013
Published: October 7, 2013

Citation
Tianrui Zhai, Yuanhai Lin, Hongmei Liu, Shengfei Feng, and Xinping Zhang, "Nanoscale tensile stress approach for the direct writing of plasmonic nanostructures," Opt. Express 21, 24490-24496 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-21-24490


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References

  1. M. I. Stockman, “Nanofocusing of optical energy in tapered plasmonic waveguides,” Phys. Rev. Lett.93(13), 137404 (2004). [CrossRef] [PubMed]
  2. R. F. Oulton, V. J. Sorger, D. Genov, D. Pile, and X. Zhang, “A hybrid plasmonic waveguide for subwavelength confinement and long-range propagation,” Nat. Photonics2(8), 496–500 (2008). [CrossRef]
  3. J. Henzie, M. H. Lee, and T. W. Odom, “Multiscale patterning of plasmonic metamaterials,” Nat. Nanotechnol.2(9), 549–554 (2007). [CrossRef] [PubMed]
  4. W. A. Murray and W. L. Barnes, “Plasmonic materials,” Adv. Mater.19(22), 3771–3782 (2007). [CrossRef]
  5. F. Tam, G. P. Goodrich, B. R. Johnson, and N. J. Halas, “Plasmonic enhancement of molecular fluorescence,” Nano Lett.7(2), 496–501 (2007). [CrossRef] [PubMed]
  6. G. Veronis and S. Fan, “Guided subwavelength plasmonic mode supported by a slot in a thin metal film,” Opt. Lett.30(24), 3359–3361 (2005). [CrossRef] [PubMed]
  7. J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao, and R. P. Van Duyne, “Biosensing with plasmonic nanosensors,” Nat. Mater.7(6), 442–453 (2008). [CrossRef] [PubMed]
  8. Y. Lin, T. Zhai, Q. Ma, H. Liu, and X. P. Zhang, “Compact bandwidth-tunable polarization filter based on a plasmonic heterograting,” Opt. Express21(9), 11315–11321 (2013). [CrossRef] [PubMed]
  9. T. Zhai, X. Zhang, Z. Pang, X. Su, H. Liu, S. Feng, and L. Wang, “Random laser based on waveguided plasmonic gain channels,” Nano Lett.11(10), 4295–4298 (2011). [CrossRef] [PubMed]
  10. X. Zhang, B. Sun, R. H. Friend, H. Guo, D. Nau, and H. Giessen, “Metallic photonic crystals based on solution-processible gold nanoparticles,” Nano Lett.6(4), 651–655 (2006). [CrossRef] [PubMed]
  11. X. Zhang, H. Liu, and S. Feng, “Solution-processible fabrication of large-area patterned and unpatterned gold nanostructures,” Nanotechnology20(42), 425303 (2009). [CrossRef] [PubMed]
  12. M. Lu, B. Krishna Juluri, Y. Zhao, Y. Jun Liu, T. J. Bunning, and T. Jun Huang, “Single-step holographic fabrication of large-area periodically corrugated metal films,” J. Appl. Phys.112(11), 113101 (2012). [CrossRef] [PubMed]
  13. E. M. Hicks, S. Zou, G. C. Schatz, K. G. Spears, R. P. Van Duyne, L. Gunnarsson, T. Rindzevicius, B. Kasemo, and M. Käll, “Controlling plasmon line shapes through diffractive coupling in linear arrays of cylindrical nanoparticles fabricated by electron beam lithography,” Nano Lett.5(6), 1065–1070 (2005). [CrossRef] [PubMed]
  14. S. A. Maier, M. L. Brongersma, P. G. Kik, S. Meltzer, A. A. Requicha, and H. A. Atwater, “Plasmonics—a route to nanoscale optical devices,” Adv. Mater.13(19), 1501–1505 (2001). [CrossRef]
  15. Z. Han, A. Y. Elezzabi, and V. Van, “Experimental realization of subwavelength plasmonic slot waveguides on a silicon platform,” Opt. Lett.35(4), 502–504 (2010). [CrossRef] [PubMed]
  16. V. Malyarchuk, F. Hua, N. H. Mack, V. T. Velasquez, J. O. White, R. G. Nuzzo, and J. A. Rogers, “High performance plasmonic crystal sensor formed by soft nanoimprint lithography,” Opt. Express13(15), 5669–5675 (2005). [CrossRef] [PubMed]
  17. J. Yao, A. P. Le, S. K. Gray, J. S. Moore, J. A. Rogers, and R. G. Nuzzo, “Functional nanostructured plasmonic materials,” Adv. Mater.22(10), 1102–1110 (2010). [CrossRef] [PubMed]
  18. X. Zhang, H. Liu, H. Li, and T. Zhai, “Direct nanopatterning into conjugated polymers using Iinterference crosslinking,” Macromol. Chem. Phys.213(12), 1285–1290 (2012). [CrossRef]
  19. U. Jeong, D. Ryu, J. Kim, D. Kim, T. P. Russell, and C. J. Hawker, “Volume contractions induced by crosslinking: a novel route to nanoporous polymer films,” Adv. Mater.15(15), 1247–1250 (2003). [CrossRef]
  20. W. Zhao, T. Cao, and J. M. White, “On the origin of green emission in polyfluorene polymers: the roles of thermal oxidation degradation and crosslinking,” Adv. Funct. Mater.14(8), 783–790 (2004). [CrossRef]
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