Fabrication and characterization of well-aligned plasmonic nanopillars with ultrasmall separations
© Si et al.; licensee Springer. 2014
Received: 2 May 2014
Accepted: 7 June 2014
Published: 13 June 2014
We show the fabrication of well-aligned gold and silver nanopillars with various array parameters via interference lithography followed by ion beam milling and compare the etching rates of these two metallic materials. Silver is suitable for fabricating ultrafine arrays with ultrasmall separations due to high milling rates. The optical properties of the fabricated nanopillars are specifically characterized from both normal incidence and oblique incident angles. Tunable surface plasmon resonances are achieved with varying structural parameters. Strong coupling effects are enabled when the separation between adjacent nanopillars is dramatically reduced, leading to useful applications in sensing and waveguiding.
KeywordsPlasmonic Nanopillars Dense arrays
Known as the electromagnetic waves propagating along metal-dielectric interfaces, surface plasmons (SPs) have drawn increasing attention in recent years[1–5]. Many plasmon-enabled applications have been developed due to their unique optical properties and particular ability of manipulating light at the nanometer scale. Additionally, SP-based waveguides are useful for developing devices with ultrahigh sensitivity and figure of merit because the near-field of electromagnetic waves can be significantly enhanced using different plasmonic nanostructures. Various plasmonic nanostructures, including nanopillars for waveguiding[6–8], and bio-sensing[9–11], or photonic crystals for efficient cavity coupling, have been demonstrated recently. Moreover, extensive useful applications have been triggered by plasmonics in super-resolution imaging[13–15], cloaking[16–18], energy harvesting[19–21], and color filtering[22–25]. Various applications (plasmonic absorbers, for instance) have been reported by using nanodisks[26–28] or nanopillars to modify the surface profile, allowing for tight confinement of more energy inside the functional layer of a solar cell. Such nanodisks/nanopillars that act as plasmonic absorbers (also known as plasmonic blackbodies) are extremely useful for energy harvesting. Metal nanopillars or wires excited by electromagnetic waves show resonance characteristics which are highly dependent on geometric parameters. In the optical regime, metals are dispersive materials with finite conductivity. Either surface plasmon polaritons (SPPs) or localized surface plasmon resonances (LSPRs) reveal salient resonance features, and the optical properties of metal nanopillars are mainly determined by their shape, size, and even the dielectric environment. Recently, the fascinating optical properties of small nanopillars/particles[30–34] and other different geometries[35–40] have been extensively investigated both experimentally and theoretically, providing a new pathway for manipulating light at the subwavelength scale.
Due to important advances in nanofabrication techniques, plasmonic nanostructures and related devices are presently gaining tremendous technological significance in nanophotonics and optics. Nanostructures could provide intriguing possibilities for resolving those challenges and improving device performance. Well-aligned nanopillars with perpendicular orientations to the substrate are becoming the main building blocks for new optical devices with promising potential applications. Here we explore, experimentally and theoretically, the optical properties of periodic nanopillars perpendicularly aligned on the supporting substrate. Combination of interference lithography (IL) and ion beam milling (IBM) techniques enables scalable fabrication of such nanopillars with excellent dimensional control and high uniformity. Detailed experimental results show that silver (Ag) has a much higher etching rate than gold (Au) under the same milling conditions, making Ag a perfect candidate for the construction of plasmonic ultrasmall features. In addition, nanopillar arrays with ultrasmall inter-pillar separations are fabricated and optically characterized.
Quartz substrates were first cleaned with acetone in an ultrasonic bath followed by isopropyl alcohol (IPA) and deionized water washing and finally blow-dried with a nitrogen gun. Subsequently, Au or Ag films with different thicknesses were deposited on quartz substrates with 4-nm titanium as the adhesion layer by electron beam evaporation (Auto 306, Edwards, Crawley, UK) at a base pressure of about 3 × 10-7 mbar. In order to minimize the deposition-introduced roughness, low evaporation rates were applied (less than 0.03 nm/s). Afterwards, positive resist (S1805, Dow, Midland, MI, USA) was used to define nanopillar arrays on the metal (Au or Ag) layer supported by a quartz substrate (refractive index = 1.46) with a laser holography system using a 325-nm helium-cadmium laser, serving as the IBM mask after development.
Parameters summary for the IBM process in this work
The optical properties of the fabricated nanopillars under normal incidence were measured using a commercial system (UV-VIS-NIR microspectrophotometer QDI 2010™, CRAIC Technologies, Inc., San Dimas, CA, USA). A × 36 objective lens with the numerical aperture of 0.5 was employed with a 75-W xenon lamp which provided a broadband spectrum. Using a beam splitter, the partial power of the incident light beam was focused onto the sample surface through the objective lens. The spectrum acquisition for all measurements was performed with a sampling aperture size of 7.1 × 7.1 μm2. Transmission and reflection were measured with respect to the light through a bare quartz substrate and an aluminum mirror, respectively. To characterize the optical properties from oblique angles, an ellipsometry setup (Uvisel, Horiba Jobin Yvon, Kyoto, Japan) was employed with a broadband light source.
Results and discussion
To conclude, we have demonstrated the fabrication of well-aligned plasmonic nanopillars by combining IL and IBM techniques. Using arrays with different geometric parameters, tunable plasmon resonances are simply achieved. It is found that Ag has a much higher milling rate than Au under the same experimental conditions, which makes Ag suitable for constructing fine nanostructures with ultrasmall features and high aspect ratios. The optical properties of the fabricated nanopillars are characterized both experimentally and theoretically. The approach developed in this work may trigger new applications in plasmon-assisted sensing and detecting.
atomic force microscopy
ion beam milling
localized surface plasmon resonances
scanning electron microscopy
surface plasmon polaritons.
This work was supported by the NEU internal funding (Grant Nos. XNB201302 and XNK201406), Natural Science Foundation of Hebei Province (Grant Nos. A2013501049 and F2014501127), Science and Technology Research Funds for Higher Education of Hebei Province (Grant No. ZD20132011), Fundamental Research Funds for the Central Universities (Grant No. N120323002), Specialized Research Fund for the Doctoral Program of Higher Education (Grant No. 20130042120048), Science and Technology Foundation of Liaoning Province (Grant No. 20131031), and Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry (Grant No. 47-4).
- Ebbesen TW, Lezec HJ, Ghaemi HF, Thio T, Wolff PA: Extraordinary optical transmission through sub-wavelength hole arrays. Nature 1998, 391: 667–669. 10.1038/35570View Article
- Liu YJ, Zheng YB, Liou J, Chiang IK, Khoo IC, Huang TJ: All-optical modulation of localized surface plasmon coupling in a hybrid system composed of photo-switchable gratings and Au nanodisk arrays. J Phys Chem C 2011, 115: 7717–7722. 10.1021/jp111256uView Article
- Zhao Y, Nawaz AA, Lin SS, Hao Q, Kiraly B, Huang TJ: Nanoscale super-resolution imaging via metal-dielectric metamaterial lens system. J Phys D Appl Phys 2011, 44: 41501.
- Liu YJ, Hao QZ, Smalley JST, Liou J, Khoo IC, Huang TJ: A frequency-addressed plasmonic switch based on dual-frequency liquid crystals. Appl Phys Lett 2010, 97: 091101. 10.1063/1.3483156View Article
- Zhao Y, Lin SS, Nawaz AA, Kiraly B, Hao Q, Liu Y, Huang TJ: Beam bending via plasmonic lenses. Opt Express 2010, 18: 23458–23465. 10.1364/OE.18.023458View Article
- Gao H, Liu C, Jeong HE, Yang P: Plasmon-enhanced photocatalytic activity of iron oxide on gold nanopillars. ACS Nano 2012, 6: 234–240. 10.1021/nn203457aView Article
- Zhang J, Cai L, Bai W, Song G: Hybrid waveguide-plasmon resonances in gold pillar arrays on top of a dielectric waveguide. Opt Lett 2010, 35: 3408–3410. 10.1364/OL.35.003408View Article
- Wang K, Crozier KB: Plasmonic trapping with a gold nanopillar. ChemPhysChem 2012, 13: 2639–2648. 10.1002/cphc.201200121View Article
- Cetin AE, Yanik AA, Yilmaz C, Somu S, Busnaina A, Altug H: Monopole antenna arrays for optical trapping, spectroscopy, and sensing. Appl Phys Lett 2011, 98: 111110. 10.1063/1.3559620View Article
- Kubo W, Fujikawa S: Au double nanopillars with nanogap for plasmonic sensor. Nano Lett 2011, 11: 8–15. 10.1021/nl100787bView Article
- Kabashin AV, Evans P, Pastkovsky S, Hendren W, Wurtz GA, Atkinson R, Pollard R, Podolskiy VA, Zayats AV: Plasmonic nanorod metamaterials for biosensing. Nat Mater 2009, 8: 867–871. 10.1038/nmat2546View Article
- Chigrin D, Lavrinenko A, Torres CS: Numerical characterization of nanopillar photonic crystal waveguides and directional couplers. Opt Quant Electron 2005, 37: 331–341. 10.1007/s11082-005-1189-1View Article
- Zhao Y, Gan D, Cui J, Wang C, Du C, Luo X: Super resolution imaging by compensating oblique lens with metallodielectric films. Opt Express 2008, 16: 5697–5707. 10.1364/OE.16.005697View Article
- Melville DOS, Blaikie RJ: Super-resolution imaging through a planar silver layer. Opt Express 2005, 13: 2127–2134. 10.1364/OPEX.13.002127View Article
- Casse BDF, Lu WT, Huang YJ, Gultepe E, Menon L, Sridhar S: Super-resolution imaging using a three-dimensional metamaterials nanolens. Appl Phys Lett 2010, 96: 023114. 10.1063/1.3291677View Article
- Cao T, Wang S: Topological insulator metamaterials with tunable negative refractive index in the optical region. Nanoscale Res Lett 2013, 8: 526. 10.1186/1556-276X-8-526View Article
- Cai W, Chettiar UK, Kildishev AV, Shalaev VM: Optical cloaking with metamaterials. Nat Photon 2007, 1: 224–227. 10.1038/nphoton.2007.28View Article
- Chen H, Chan CT: Acoustic cloaking in three dimensions using acoustic metamaterials. Appl Phys Lett 2007, 91: 183518. 10.1063/1.2803315View Article
- Xue J, Zhu Q, Liu J, Li Y, Zhou ZK, Lin Z, Yan J, Li J, Wang XH: Gold nanoarray deposited using alternating current for emission rate-manipulating nanoantenna. Nanoscale Res Lett 2013, 8: 295. 10.1186/1556-276X-8-295View Article
- Aubry A, Lei DY, Fernández-Domínguez AI, Sonnefraud Y, Maier SA, Pendry JB: Plasmonic light-harvesting devices over the whole visible spectrum. Nano Lett 2010, 10: 2574–2579. 10.1021/nl101235dView Article
- Cole JR, Halas NJ: Optimized plasmonic nanoparticle distributions for solar spectrum harvesting. Appl Phys Lett 2006, 89: 153120. 10.1063/1.2360918View Article
- Si G, Zhao Y, Liu H, Teo S, Zhang M, Huang TJ, Danner AJ, Teng JH: Annular aperture array based color filter. Appl Phys Lett 2011, 99: 033105. 10.1063/1.3608147View Article
- Liu YJ, Si GY, Leong ESP, Xiang N, Danner AJ, Teng JH: Light-driven plasmonic color filters by overlaying photoresponsive liquid crystals on gold annular aperture arrays. Adv Mater 2012, 24: OP131-OP135.
- Si G, Zhao Y, Lv J, Lu M, Wang F, Liu H, Xiang N, Huang TJ, Danner AJ, Teng J, Liu YJ: Reflective plasmonic color filters based on lithographically patterned silver nanorod arrays. Nanoscale 2013, 5: 6243–6248. 10.1039/c3nr01419cView Article
- Si G, Zhao Y, Leong ESP, Liu YJ: Liquid-crystal-enabled active plasmonics: a review. Materials 2014, 7: 1296–1317. 10.3390/ma7021296View Article
- Zhao Y, Hao Q, Ma Y, Lu M, Zhang B, Lapsley M, Khoo IC, Huang TJ: Light-driven tunable dual-band plasmonic absorber using liquid-crystal-coated asymmetric nanodisk array. Appl Phys Lett 2012, 100: 053119. 10.1063/1.3681808View Article
- Zhang B, Zhao Y, Hao Q, Kiraly B, Khoo IC, Chen S, Huang TJ: Polarization independent dual-band infrared perfect absorber based on a metal-dielectric-metal elliptical nanodisk array. Opt Express 2011, 19: 15221–15228. 10.1364/OE.19.015221View Article
- Liu N, Mesch M, Weiss T, Hentschel M, Giessen H: Infrared perfect absorber and its application as plasmonic sensor. Nano Lett 2010, 10: 2342–2348. 10.1021/nl9041033View Article
- Fan Z, Kapadia R, Leu PW, Zhang X, Chueh YL, Takei K, Yu K, Jamshidi A, Rathore AA, Ruebusch DJ, Wu M, Javey A: Ordered arrays of dual-diameter nanopillars for maximized optical absorption. Nano Lett 2010, 10: 3823–3827. 10.1021/nl1010788View Article
- Caldwell JD, Glembocki O, Bezares FJ, Bassim ND, Rendell RW, Feygelson M, Ukaegbu M, Kasica R, Shirey L, Hosten C: Plasmonic nanopillar arrays for large-area, high-enhancement surface-enhanced Raman scattering sensors. ACS Nano 2011, 5: 4046–4055. 10.1021/nn200636tView Article
- Senanayake P, Hung CH, Shapiro J, Scofield A, Lin A, Williams BS, Huffaker DL: 3D nanopillar optical antenna photodetectors. Opt Express 2012, 20: 25489–25496. 10.1364/OE.20.025489View Article
- Caldwell JD, Glembocki O, Bezares FJ, Kariniemi MI, Niinisto JT, Hatanpaa TT, Rendell RW, Ukaegbu M, Ritala MK, Prokes SM, Hosten CM, Leskela MA, Kasica R: Large-area plasmonic hot-spot arrays: sub-2 nm interparticle separations with plasma-enhanced atomic layer deposition of Ag on periodic arrays of Si nanopillars. Opt Express 2011, 19: 26056–26064. 10.1364/OE.19.026056View Article
- Tsai SJ, Ballarotto M, Romero DB, Herman WN, Kan HC, Phaneuf RJ: Effect of gold nanopillar arrays on the absorption spectrum of a bulk heterojunction organic solar cell. Opt Express 2010, 18: A528-A535. 10.1364/OE.18.00A528View Article
- Lin HY, Kuo Y, Liao CY, Yang CC, Kiang YW: Surface plasmon effects in the absorption enhancements of amorphous silicon solar cells with periodical metal nanowall and nanopillar structures. Opt Express 2012, 20: A104-A118. 10.1364/OE.20.00A104View Article
- Zeng B, Gao Y, Bartoli FJ: Ultrathin nanostructured metals for highly transmissive plasmonic subtractive color filters. Sci Rep 2013, 3: 2840.
- Zeng B, Yang X, Wang C, Luo X: Plasmonic interference nanolithography with a double-layer planar silver lens structure. Opt Express 2009, 17: 16783–16791. 10.1364/OE.17.016783View Article
- Zeng B, Gan Q, Kafafi ZH, Bartoli FJ: Polymeric photovoltaics with various metallic plasmonic nanostructures. J Appl Phys 2013, 113: 063109. 10.1063/1.4790504View Article
- Zeng B, Yang X, Wang C, Feng Q, Luo X: Super-resolution imaging at different wavelengths by using a one-dimensional metamaterial structure. J Opt 2010, 12: 035104. 10.1088/2040-8978/12/3/035104View Article
- Gao Y, Xin Z, Zeng B, Gan Q, Cheng X, Bartoli FJ: Plasmonic interferometric sensor arrays for high-performance label-free biomolecular detection. Lab Chip 2013, 13: 4755–4764. 10.1039/c3lc50863cView Article
- Xu T, Fang L, Zeng B, Liu Y, Wang C, Feng Q, Luo X: Subwavelength nanolithography based on unidirectional excitation of surface plasmons. J Opt A Pure Appl Opt 2009, 11: 085003. 10.1088/1464-4258/11/8/085003View Article
- Drezet A, Koller D, Hohenau A, Leitner A, Aussenegg FR, Krenn JR: Plasmonic crystal demultiplexer and multiports. Nano Lett 2007, 7: 1697–1700. 10.1021/nl070682pView Article
- Johnson PB, Christy RW: Optical constants of the noble metals. Phys Rev B 1972, 6: 4370–4379. 10.1103/PhysRevB.6.4370View Article
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.