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Smith JD, Reza MA, Smith NL, Gu J, Ibrar M, Crandall DJ, Skrabalak SE. Plasmonic Anticounterfeit Tags with High Encoding Capacity Rapidly Authenticated with Deep Machine Learning. ACS NANO 2021; 15:2901-2910. [PMID: 33559464 DOI: 10.1021/acsnano.0c08974] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Counterfeit goods create significant economic losses and product failures in many industries. Here, we report a covert anticounterfeit platform where plasmonic nanoparticles (NPs) create physically unclonable functions (PUFs) with high encoding capacity. By allowing anisotropic Au NPs of different sizes to deposit randomly, a diversity of surfaces can be facilely tagged with NP deposits that serve as PUFs and are analyzed using optical microscopy. High encoding capacity is engineered into the tags by the sizes of the Au NPs, which provide a range of color responses, while their anisotropy provides sensitivity to light polarization. An estimated encoding capacity of 270n is achieved, which is one of the highest reported to date. Authentication of the tags with deep machine learning allows for high accuracy and rapid matching of a tag to a specific product. Moreover, the tags contain descriptive metadata that is leveraged to match a tag to a specific lot number (i.e., a collection of tags created in the same manner from the same formulation of anisotropic Au NPs). Overall, integration of designer plasmonic NPs with deep machine learning methods can create a rapidly authenticated anticounterfeit platform with high encoding capacity.
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Affiliation(s)
- Joshua D Smith
- Department of Chemistry, Indiana University, 800 E. Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - Md Alimoor Reza
- Department of Computer Science, Indiana University, 700 N. Woodlawn Avenue, Bloomington, Indiana 47408, United States
| | - Nathanael L Smith
- Department of Chemistry, Indiana University, 800 E. Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - Jianxin Gu
- Department of Computer Science, Indiana University, 700 N. Woodlawn Avenue, Bloomington, Indiana 47408, United States
| | - Maha Ibrar
- Department of Chemistry, Indiana University, 800 E. Kirkwood Avenue, Bloomington, Indiana 47405, United States
| | - David J Crandall
- Department of Computer Science, Indiana University, 700 N. Woodlawn Avenue, Bloomington, Indiana 47408, United States
| | - Sara E Skrabalak
- Department of Chemistry, Indiana University, 800 E. Kirkwood Avenue, Bloomington, Indiana 47405, United States
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Tran VT, Lee DK, Kim J, Lee J, Tufa LT, Pham-Cong D, Kim CS, Lee J. Porosity-controllable magnetoplasmonic nanoparticles and their assembled arrays. NANOSCALE 2020; 12:8453-8465. [PMID: 32239078 DOI: 10.1039/d0nr01178a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Control of the chemical and physical properties of nanoscale colloids and their nanoassemblies remains a challenging issue for enhancing the performance and functionalities of nanodevices. In this study, we report a post-synthesis etching method to tailor the porosity of the Fe3O4 shells coating on Ag NPs, establishing a facile but effective approach to regulate the chemical and optical properties of the colloids and their assembled structures. As the shell porosity increases, the NPs are transformed, producing enhanced catalytic activity and the surface-enhanced Raman spectroscopy (SERS) effect, which results from enhanced chemical diffusion into the Ag core. Magnetoplasmonic (MagPlas) one- (1D) and two- (2D) dimensional arrays fabricated using these porosity-controllable NPs exhibit intriguing plasmon properties that are strongly affected by the porosity of the particle shell. Furthermore, the bright coloration of the 2D arrays is tuned by changing the shell porosity or introducing an additional metallic layer. Such 1D and 2D porous MagPlas metastructures possessing Fe3O4 shells with tunable porosities are a fulcrum for developing recyclable catalysts and tunable optical filters with optimized activity, selectivity, and sensitivity, as well as color displays and sensing platforms.
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Affiliation(s)
- Van Tan Tran
- Department of Chemistry, College of Natural Science, Chungnam National University, Daejeon, 34134, Republic of Korea.
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Svyakhovskiy SE, Ternovski VV, Tribelsky MI. Anapole: Its birth, life, and death. OPTICS EXPRESS 2019; 27:23894-23904. [PMID: 31510287 DOI: 10.1364/oe.27.023894] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Accepted: 06/26/2019] [Indexed: 06/10/2023]
Abstract
Despite the recent extensive study of the nonradiating (anapole) mode in the resonant light scattering by nanoparticles, the key questions, about the dynamics of its excitation at the leading front of the incident pulse and collapse behind the trailing edge, still remain open. We answer the questions, first, by direct numerical integration of the complete set of the Maxwell equations, describing the scattering of a rectangular laser pulse by a dielectric cylinder. The simulation shows that while the excitation and the collapse periods, both have the same characteristic time-scale, the dynamics of these processes are qualitatively different. The relaxation to the steady-state scattering at the leading front is accompanied by high-amplitude oscillatory modulations of the envelope of the basic electromagnetic oscillations, while behind the trailing edge the decay of the envelope is monotonic. Then, we present the general arguments showing that this is the case for the anapole excited in any classical system. Next, we introduce a simple, exactly integrable yet accurate, physically transparent model describing the dynamics of the anapole. The model admits generalization to a broad class of resonant phenomena and may be regarded as a compliment to the commonly used Temporal Coupled-Mode Theory.
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Fang C, Liu Y, Han G, Shao Y, Zhang J, Hao Y. Localized plasmon resonances for black phosphorus bowtie nanoantennas at terahertz frequencies. OPTICS EXPRESS 2018; 26:27683-27693. [PMID: 30469830 DOI: 10.1364/oe.26.027683] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Accepted: 10/02/2018] [Indexed: 06/09/2023]
Abstract
In this work, a periodic bowtie structure based on black phosphorus (BP) is theoretically proposed and characterized. It is demonstrated that localized surface plasmons can be excited in the BP nanoantennas at terahertz (THz) frequencies. Numerical investigations, using the numerical method finite-difference time-domain (FDTD), have been utilized to analyze the the dimensions' impact on absorption spectra. Furthermore, the electric field distribution is plotted and discussed to explain the resonance wavelength tuning by different geometrical sizes of the structure. Results reveal that the optimized BP bow-tie structure can be allowed for the realization of two-dimensional nanophotonics at terahertz frequencies.
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Cao M, Wang X, Cao W, Fang X, Wen B, Yuan J. Thermally Driven Transport and Relaxation Switching Self-Powered Electromagnetic Energy Conversion. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2018; 14:e1800987. [PMID: 29882284 DOI: 10.1002/smll.201800987] [Citation(s) in RCA: 158] [Impact Index Per Article: 26.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Revised: 04/02/2018] [Indexed: 05/19/2023]
Abstract
Electromagnetic energy radiation is becoming a "health-killer" of living bodies, especially around industrial transformer substation and electricity pylon. Harvesting, converting, and storing waste energy for recycling are considered the ideal ways to control electromagnetic radiation. However, heat-generation and temperature-rising with performance degradation remain big problems. Herein, graphene-silica xerogel is dissected hierarchically from functions to "genes," thermally driven relaxation and charge transport, experimentally and theoretically, demonstrating a competitive synergy on energy conversion. A generic approach of "material genes sequencing" is proposed, tactfully transforming the negative effects of heat energy to superiority for switching self-powered and self-circulated electromagnetic devices, beneficial for waste energy harvesting, conversion, and storage. Graphene networks with "well-sequencing genes" (w = Pc /Pp > 0.2) can serve as nanogenerators, thermally promoting electromagnetic wave absorption by 250%, with broadened bandwidth covering the whole investigated frequency. This finding of nonionic energy conversion opens up an unexpected horizon for converting, storing, and reusing waste electromagnetic energy, providing the most promising way for governing electromagnetic pollution with self-powered and self-circulated electromagnetic devices.
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Affiliation(s)
- Maosheng Cao
- School of Materials Science and Engineering, Beijing Institute of Technology, Beijing, 100081, China
| | - Xixi Wang
- School of Materials Science and Engineering, Beijing Institute of Technology, Beijing, 100081, China
| | - Wenqiang Cao
- School of Materials Science and Engineering, Beijing Institute of Technology, Beijing, 100081, China
| | - Xiaoyong Fang
- School of Science, Yanshan University, Qinhuangdao, 066004, China
| | - Bo Wen
- Research School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, ACT, 2601, Australia
| | - Jie Yuan
- School of Science, Minzu University of China, Beijing, 100081, China
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6
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Zhao F, Arnob MMP, Zenasni O, Li J, Shih WC. Far-field plasmonic coupling in 2-dimensional polycrystalline plasmonic arrays enables wide tunability with low-cost nanofabrication. NANOSCALE HORIZONS 2017; 2:267-276. [PMID: 32260682 DOI: 10.1039/c7nh00067g] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
We report the experimental observation and numerical modeling study of far-field plasmonic coupling (FFPC) in 2-dimensional polycrystalline plasmonic arrays consisting of "single crystalline" domains of a random size and orientation. Even though polycrystalline plasmonic arrays are routine products of low-cost nanosphere lithography (NSL), their FFPC behavior has not been well understood. Herein, FFPC observed from gold nanodisk (AuND) arrays fabricated using NSL appears, qualitatively, to be in keeping with that of highly regular nanoparticle arrays, where they induced cyclic modulations on the peak position and linewidth of the localized surface plasmon resonance (LSPR). Remarkable blue shifts as large as 1000 nm with nearly doubled linewidth were observed experimentally. Numerical modeling was systematically carried out and showed quantitative agreement with the experimental results. Using the modeling approach, the influences of array randomness and particle size on FFPC have been studied independently for the first time. Finally, two potential applications have been developed for FFPC-based LSPR tuning. Firstly, when AuND arrays are fabricated on flexible substrates, a novel transduction mechanism can be established between the LSPR peak position and the substrate strain. Owing to the far-field propagating nature, FFPC-based transduction can effectively extend the strain-tuning displacement range by an order of magnitude compared with those based on near-field coupling. Secondly, we show that FFPC leads to an LSPR peak within 1 μm for nanoporous gold disk arrays, which otherwise have a single particle LSPR peak beyond 1.5 μm. Such a significant FFPC-induced blue shift is critically important for compatibility with the use of silicon-based detectors.
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Affiliation(s)
- Fusheng Zhao
- Department of Electrical and Computer Engineering, University of Houston, 4800 Calhoun Road, Houston, TX 77204, USA.
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Gurbatov S, Kuchmizhak A, Vitrik O, Kulchin Y. Lens-free laser nanopatterning of large-scale metal film areas with structured light for biosensing applications. OPTICS EXPRESS 2016; 24:18898-18906. [PMID: 27557171 DOI: 10.1364/oe.24.018898] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Pulsed laser nanotexturing of metal films represents an ultra-fast, high-performance and cost-effective processing technology for fabrication of various functional surfaces widely used in plasmonics, biosensing, and photovoltaics. However, this approach usually requires high-NA lenses to focus a laser beam onto a few-micron spot as well as a micropositioning platform to move this spot along the sample surface, which increases the cost of the produced functional surfaces and limits the performance of laser-assisted nanotexturing techniques. In this paper we report on a laser-assisted technology for the fabrication of large-scale nanotextured metal substrates. In our approach, speckle-modulated patterns obtained by passing nanosecond laser pulses through the simplest diffusive object were utilized to cover a thin gold film with closely packed micron-sized structures - nanojets, nanobumps and through holes - previously reported only for single-shot nanoablation with tightly focused laser beams. The presented easy-to-implement technology, being one of the simplest of ever reported, since it requires neither focusing lenses nor micropositioning platforms, was shown to provide a way to pattern millimeter-size areas with the nano-sized jets at an average recording density of 35∙103 nanostructures per square millimeter and an average recording speed of 4.5·103 nanostructures per pulse. The fabricated nanotextured Au substrates were shown to yield spatially uniform surface-enhanced fluorescence signals from the Rhodamine 6G organic dye with an averaged 5.3-fold enhancement factor as compared with non-treated Au surface.
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8
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Geraci G, Hopkins B, Miroshnichenko AE, Erkihun B, Neshev DN, Kivshar YS, Maier SA, Rahmani M. Polarisation-independent enhanced scattering by tailoring asymmetric plasmonic systems. NANOSCALE 2016; 8:6021-7. [PMID: 26927504 DOI: 10.1039/c6nr00029k] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Polarised light provides an efficient way for dynamic control over local optical properties of nanoscale plasmonic structures. Yet many applications that utilise control over the plasmonic near-field would benefit if the plasmonic device maintained the same magnitude of optical response for all polarisations. Here we show that completely asymmetric nanostructures can be designed to exhibit a broadband polarisation-independent and enhanced optical response. We provide both analytical and experimental results on two sets of plasmonic trimer nanostructures consisting of unequal nanodisks/apertures with different gap spacing. We show that, at certain inter-particle separations, enhanced far-field cross sections are independent to the incident polarisation, while still demonstrating nontrivial near-field control.
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Affiliation(s)
- Gabriel Geraci
- The Blackett Laboratory, Department of Physics, Imperial College London, London SW7 2AZ, UK
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Mirzaei A, Miroshnichenko AE. Electric and magnetic hotspots in dielectric nanowire dimers. NANOSCALE 2015; 7:5963-5968. [PMID: 25773044 DOI: 10.1039/c5nr00882d] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We study the formation of the electric and magnetic near-field hotspots in dielectric cylindrical dimers. We compare dielectric and metallic dimers by using experimental data for all materials and consider both TM and TE polarizations of light. We demonstrate that dielectric dimers allow us to simultaneously achieve pure magnetic and electric near-field hotspots for both polarizations in contrast to plasmonic structures. This offers new approaches for near-field engineering such as sensing, control of spontaneous emission, and enhanced Raman scattering.
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Affiliation(s)
- Ali Mirzaei
- Nonlinear Physics Centre, Australian National University, Acton, ACT 2601, Australia.
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Kuznetsov AI, Miroshnichenko AE, Fu YH, Viswanathan V, Rahmani M, Valuckas V, Pan ZY, Kivshar Y, Pickard DS, Luk'yanchuk B. Split-ball resonator as a three-dimensional analogue of planar split-rings. Nat Commun 2015; 5:3104. [PMID: 24430506 DOI: 10.1038/ncomms4104] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2013] [Accepted: 12/13/2013] [Indexed: 11/09/2022] Open
Abstract
Split-ring resonators are basic elements of metamaterials, which can induce a magnetic response in metallic nanosctructures. Tunability of such response up to the visible frequency range is still a challenge. Here we introduce the concept of the split-ball resonator and demonstrate the strong magnetic response in the visible for both gold and silver spherical plasmonic nanoparticles with nanometre scale cuts. We realize this concept experimentally by employing the laser-induced transfer method to produce near-perfect metallic spheres and helium ion beam milling to make cuts with the clean straight sidewalls and nanometre resolution. The magnetic resonance is observed at 600 nm in gold and at 565 nm in silver nanoparticles. This method can be applied to the structuring of arbitrary three-dimensional features on the surface of nanoscale resonators. It provides new ways for engineering hybrid resonant modes and ultra-high near-field enhancement.
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Affiliation(s)
- Arseniy I Kuznetsov
- Data Storage Institute, A*STAR (Agency for Science, Technology and Research), 5 Engineering Drive 1, 117608 Singapore, Singapore
| | - Andrey E Miroshnichenko
- Nonlinear Physics Centre, Research School of Physics and Engineering, Australian National University, Canberra, Australian Capital Territory 0200, Australia
| | - Yuan Hsing Fu
- Data Storage Institute, A*STAR (Agency for Science, Technology and Research), 5 Engineering Drive 1, 117608 Singapore, Singapore
| | - Vignesh Viswanathan
- Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117583 Singapore, Singapore
| | - Mohsen Rahmani
- Data Storage Institute, A*STAR (Agency for Science, Technology and Research), 5 Engineering Drive 1, 117608 Singapore, Singapore
| | - Vytautas Valuckas
- 1] Data Storage Institute, A*STAR (Agency for Science, Technology and Research), 5 Engineering Drive 1, 117608 Singapore, Singapore [2] Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117583 Singapore, Singapore
| | - Zhen Ying Pan
- Data Storage Institute, A*STAR (Agency for Science, Technology and Research), 5 Engineering Drive 1, 117608 Singapore, Singapore
| | - Yuri Kivshar
- Nonlinear Physics Centre, Research School of Physics and Engineering, Australian National University, Canberra, Australian Capital Territory 0200, Australia
| | - Daniel S Pickard
- Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117583 Singapore, Singapore
| | - Boris Luk'yanchuk
- Data Storage Institute, A*STAR (Agency for Science, Technology and Research), 5 Engineering Drive 1, 117608 Singapore, Singapore
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König M, Rahmani M, Zhang L, Lei DY, Roschuk TR, Giannini V, Qiu CW, Hong M, Schlücker S, Maier SA. Unveiling the correlation between nanometer-thick molecular monolayer sensitivity and near-field enhancement and localization in coupled plasmonic oligomers. ACS NANO 2014; 8:9188-9198. [PMID: 25136980 DOI: 10.1021/nn5028714] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Metal nanoclusters, sometimes called metamolecules or plasmonic oligomers, exhibit interesting optical properties such as Fano resonances and optical chirality. These properties promise a variety of practical applications, particularly in ultrasensitive biochemical sensing. Here we investigate experimentally the sensitivities of plasmonic pentamers and quadrumers to the adsorption of self-assembled nanometer-thick alkanethiol monolayers. The monolayer sensitivity of such oligomers is found to be significantly higher than that of single plasmonic nanoparticles and depends on the nanocluster arrangement, constituent nanoparticle shape, and the plasmon resonance wavelength. Together with full-wave numerical simulation results and the electromagnetic perturbation theory, we unveil a direct correlation between the sensitivity and the near-field intensity enhancement and spatial localization in the plasmonic "hot" spots generated in each nanocluster. Our observation is beyond conventional considerations (such as optimizing nanoparticle geometry or narrowing resonance line width) for improving the sensing performance of metal nanoclusters-based biosensors and opens the possibilities of using plasmonic nanoclusters for single-molecule detection and identification.
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Affiliation(s)
- Matthias König
- Department of Physics, Imperial College London , London SW7 2AZ, United Kingdom
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12
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Yang ZJ, Hao ZH, Lin HQ, Wang QQ. Plasmonic Fano resonances in metallic nanorod complexes. NANOSCALE 2014; 6:4985-4997. [PMID: 24733287 DOI: 10.1039/c3nr06502b] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Plasmonic Fano resonances (FRs) in nanostructures have been extensively studied in recent years. Nanorod-based complexes for FRs have also attracted much attention. The basic optical properties and fabrication technology of different kinds of plasmonic nanorods have been greatly developed over the last several years. The mutipole plasmon resonances and their flexible adjustment ranges on nanorods make them promising for FR modifications and structure diversity. In this paper, we review some recently studied plasmonic nanorod based nanostructures for FRs, including single nanorods, dimers, mutipole rods and nanorod-nanoparticle hybrids. The corresponding applications of the FRs are also briefly discussed.
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Affiliation(s)
- Zhong-Jian Yang
- Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University, Wuhan 430072, China.
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Zhang Y, Stokes N, Jia B, Fan S, Gu M. Towards ultra-thin plasmonic silicon wafer solar cells with minimized efficiency loss. Sci Rep 2014; 4:4939. [PMID: 24820403 PMCID: PMC4018607 DOI: 10.1038/srep04939] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2014] [Accepted: 04/09/2014] [Indexed: 11/30/2022] Open
Abstract
The cost-effectiveness of market-dominating silicon wafer solar cells plays a key role in determining the competiveness of solar energy with other exhaustible energy sources. Reducing the silicon wafer thickness at a minimized efficiency loss represents a mainstream trend in increasing the cost-effectiveness of wafer-based solar cells. In this paper we demonstrate that, using the advanced light trapping strategy with a properly designed nanoparticle architecture, the wafer thickness can be dramatically reduced to only around 1/10 of the current thickness (180 μm) without any solar cell efficiency loss at 18.2%. Nanoparticle integrated ultra-thin solar cells with only 3% of the current wafer thickness can potentially achieve 15.3% efficiency combining the absorption enhancement with the benefit of thinner wafer induced open circuit voltage increase. This represents a 97% material saving with only 15% relative efficiency loss. These results demonstrate the feasibility and prospect of achieving high-efficiency ultra-thin silicon wafer cells with plasmonic light trapping.
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Affiliation(s)
- Yinan Zhang
- Centre for Micro-Photonics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
| | - Nicholas Stokes
- Centre for Micro-Photonics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
| | - Baohua Jia
- Centre for Micro-Photonics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
| | - Shanhui Fan
- Department of Electrical Engineering, Ginzton Laboratory, Stanford University, Stanford, California 94305, United States
| | - Min Gu
- Centre for Micro-Photonics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
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Rahmani M, Yoxall E, Hopkins B, Sonnefraud Y, Kivshar Y, Hong M, Phillips C, Maier SA, Miroshnichenko AE. Plasmonic nanoclusters with rotational symmetry: polarization-invariant far-field response vs changing near-field distribution. ACS NANO 2013; 7:11138-11146. [PMID: 24187975 DOI: 10.1021/nn404869c] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Flexible control over the near- and far-field properties of plasmonic nanostructures is important for many potential applications, such as surface-enhanced Raman scattering and biosensing. Generally, any change in the polarization of the incident light leads to a change in the nanoparticle's near-field distribution and, consequently, in its far-field properties as well. Therefore, producing polarization-invariant optical responses in the far field from a changing near field remains a challenging issue. In this paper, we probe experimentally the optical properties of cruciform pentamer structures--as an example of plasmonic oligomers--and demonstrate that they exhibit such behavior due to their symmetric geometrical arrangement. We demonstrate direct control over hot spot positions in sub-20 nm gaps, between disks of 145 nm diameter at a wavelength of 850 nm, by means of scattering scanning near-field optical microscopy. In addition, we employ the coupled dipole approximation method to define a qualitative model revealing the relationship between the near and far field in such structures. The near-field profiles depend on particular mode superpositions excited by the incident field and, thus, are expected to vary with the polarization. Consequently, we prove analytically that the far-field optical properties of pentamers have to be polarization-independent due to their rotational symmetry.
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Affiliation(s)
- Mohsen Rahmani
- Department of Physics, Imperial College London , London SW7 2AZ, U.K
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