Publications by authors named "Lujun Huang"

17 Publications

  • Page 1 of 1

Sound trapping in an open resonator.

Nat Commun 2021 Aug 10;12(1):4819. Epub 2021 Aug 10.

School of Engineering and Information Technology, University of New South Wales, Canberra, ACT, Australia.

The ability of sound energy confinement with high-quality factor resonance is of vital importance for acoustic devices requiring high intensity and hypersensitivity in biological ultrasonics, enhanced collimated sound emission (i.e. sound laser) and high-resolution sensing. However, structures reported so far have been experimentally demonstrated with a limited quality factor of acoustic resonances, up to several tens in an open resonator. The emergence of bound states in the continuum makes it possible to realize high quality factor acoustic modes. Here, we report the theoretical design and experimental demonstration of acoustic bound states in the continuum supported by a single open resonator. We predicted that such an open acoustic resonator could simultaneously support three types of bound states in the continuum, including symmetry protected bound states in the continuum, Friedrich-Wintgen bound states in the continuum induced by mode interference, as well as a new type-mirror symmetry induced bound states in the continuum. We also experimentally demonstrated their existence with quality factor up to one order of magnitude greater than the highest quality factor reported in an open resonator.
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http://dx.doi.org/10.1038/s41467-021-25130-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8355331PMC
August 2021

Geometry symmetry-free and higher-order optical bound states in the continuum.

Nat Commun 2021 Jul 19;12(1):4390. Epub 2021 Jul 19.

School of Physical Science and Technology & Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, Suzhou, China.

Geometrical symmetry plays a significant role in implementing robust, symmetry-protected, bound states in the continuum (BICs). However, this benefit is only theoretical in many cases since fabricated samples' unavoidable imperfections may easily break the stringent geometrical requirements. Here we propose an approach by introducing the concept of geometrical-symmetry-free but symmetry-protected BICs, realized using the static-like environment induced by a zero-index metamaterial (ZIM). We find that robust BICs exist and are protected from the disordered distribution of multiple objects inside the ZIM host by its physical symmetries rather than geometrical ones. The geometric-symmetry-free BICs are robust, regardless of the objects' external shapes and material parameters in the ZIM host. We further show theoretically and numerically that the existence of those higher-order BICs depends only on the number of objects. By practically designing a structural ZIM waveguide, the existence of BICs is numerically confirmed, as well as their independence on the presence of geometrical symmetry. Our findings provide a way of realizing higher-order BICs and link their properties to the disorder of photonic systems.
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http://dx.doi.org/10.1038/s41467-021-24686-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8290025PMC
July 2021

Mid-infrared polarization-controlled broadband achromatic metadevice.

Sci Adv 2020 Sep 11;6(37). Epub 2020 Sep 11.

National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 500 Yu-Tian Road, Shanghai 200083, China.

Metasurfaces provide a compact, flexible, and efficient platform to manipulate the electromagnetic waves. However, chromatic aberration imposes severe restrictions on their applications in broadband polarization control. Here, we propose a broadband achromatic methodology to implement polarization-controlled multifunctional metadevices in mid-wavelength infrared with birefringent meta-atoms. We demonstrate the generation of polarization-controlled and achromatically on-axis focused optical vortex beams with diffraction-limited focal spots and switchable topological charge ( = 0 and = 2). Besides, we further implement broadband achromatic polarization beamsplitter with high polarization isolation (extinction ratio up to 21). The adoption of all-silicon configuration not only facilitates the integration with CMOS technology but also endows the polarization multiplexing meta-atoms with broad phase dispersion coverage, ensuring the large size and high performance of the metadevices. Compared with the state-of-the-art chromatic aberration-restricted polarization-controlled metadevices, our work represents a substantial advance and a step toward practical applications.
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http://dx.doi.org/10.1126/sciadv.abc0711DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7486104PMC
September 2020

Multiscale Architecture and Superior High-Temperature Performance of Discontinuously Reinforced Titanium Matrix Composites.

Adv Mater 2021 Feb 23;33(6):e2000688. Epub 2020 Jul 23.

School of Materials Science and Engineering, Harbin Institute of Technology, Harbin, 150001, P. R. China.

Discontinuously reinforced titanium matrix composites (DRTMCs), as one of the most important metal matrix composites (MMCs), are expected to exhibit high strength, elastic modulus, high-temperature endurability, wear resistance, isotropic property, and formability. Recent innovative research shows that tailoring the reinforcement network distribution totally differently from the conventional homogeneous distribution can not only improve the strengthening effect but also resolve the dilemma of DRTMCs with poor tensile ductility. Based on the network architecture, multiscale architecture, for example, two-scale network and laminate-network microstructure can further inspire superior strength, creep, and oxidation resistance at elevated temperatures. Herein, the most recent developments, which include the design, fabrication, microstructure, high-temperature performance, strengthening mechanisms, and future research opportunities for DRTMCs with multiscale architecture, are captured. In this regard, the service temperature can be increased by 200 °C, and the creep rupture time by 59-fold compared with those of conventional titanium alloys, which can meet the urgent demands of lightweight nickel-based structural materials and potentially replace nickel base superalloys at 600-800 °C to reduce weight by 45%. In fact, multiscale architecture design strategy will also favorably open a new era in the research of extensive metallic materials for improved performances.
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http://dx.doi.org/10.1002/adma.202000688DOI Listing
February 2021

Forward and Backward Switching of Nonlinear Unidirectional Emission from GaAs Nanoantennas.

ACS Nano 2020 Feb 2;14(2):1379-1389. Epub 2020 Jan 2.

Nonlinear Physics Centre, Research School of Physics , The Australian National University , Canberra , ACT 2601 , Australia.

High-index III-V semiconductor nanoantennas have gained great attention for enhanced nonlinear light-matter interactions, in the past few years. However, the complexity of nonlinear emission profiles imposes severe constraints on practical applications, such as in optical communications and integrated optoelectronic devices. These complexities include the lack of unidirectional nonlinear emission and the severe challenges in switching between forward and backward emissions, due to the structure of the susceptibility tensor of the III-V nanoantennas. Here, we propose a solution to both issues via engineering the nonlinear tensor of the nanoantennas. The special nonlinear tensorial properties of zinc-blende material can be used to engineer the nonlinear characteristics via growing the nanoantennas along different crystalline orientations. Based on the nonlinear multipolar effect, we have designed and fabricated (110)-grown GaAs nanoantennas, with engineered tensorial properties, embedded in a transparent low-index material. Our technique provides an approach not only for unidirectional second-harmonic generation (SHG) forward or backward emission but also for switching from one to another. Importantly, switching the SHG emission directionality is obtained only by rotating the polarization of the incident light, without the need for physical variation of the antennas or the environment. This characteristic is an advantage, as compared to other nonlinear nanoantennas, including (100)- and (111)-grown III-V counterparts or silicon and germanium nanoantennas. Indeed, (110)-GaAs nanoantennas allow for engineering the nonlinear nanophotonic systems including nonlinear "Huygens metasurfaces" and offer exciting opportunities for various nonlinear nanophotonics technologies, such as nanoscale light routing and light sources, as well as multifunctional flat optical elements.
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http://dx.doi.org/10.1021/acsnano.9b07117DOI Listing
February 2020

Dynamic Nonlinear Image Tuning through Magnetic Dipole Quasi-BIC Ultrathin Resonators.

Adv Sci (Weinh) 2019 Aug 23;6(15):1802119. Epub 2019 May 23.

School of Engineering and Information Technology University of New South Wales Canberra ACT 2600 Australia.

Dynamical tuning of the nonlinear optical wavefront allows for a specific spectral response of predefined profiles, enabling various applications of nonlinear nanophotonics. This study experimentally demonstrates the dynamical switching of images generated by an ultrathin silicon nonlinear metasurface supporting a high-quality leaky mode, which is formed by partially breaking a bound-state-in-the-continuum (BIC) generated by the collective magnetic dipole (MD) resonance excited in the subdiffractive periodic systems. Such a quasi-BIC MD state can be excited directly under normal plane wave incidence and leads to a strong near-field enhancement to further boost the nonlinear process, resulting in a 500-fold enhancement of the third-harmonic emission experimentally. Due to sharp spectral features and asymmetry of the unit cell, it allows for effective tailoring of the nonlinear emissions over spectral or polarization responses. Dynamical nonlinear image tuning is experimentally demonstarted via polarization and wavelength control. The results pave the way for nanophotonics applications such as tunable displays, nonlinear holograms, tunable nanolaser, and ultrathin nonlinear nanodevices with various functionalities.
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http://dx.doi.org/10.1002/advs.201802119DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6685498PMC
August 2019

In situ synthesis of BiOCl nanosheets on three-dimensional hierarchical structures for efficient photocatalysis under visible light.

Nanoscale 2019 May;11(21):10203-10208

State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.

Assembling two-dimensional (2D) nanomaterials into three-dimensional (3D) hierarchical structures with novel functions is challenging and has attracted considerable attention. However, it is quite difficult to obtain complex 3D architectures of 2D materials with a uniform and intact structure using traditional methods, such as hydrothermal/solvothermal methods and direct precipitation methods. Here, we use butterfly wing scales as bio-templates to prepare 3D hierarchical BiOCl/Au wing scales for plasmonic photocatalysis. The as-prepared materials exhibit excellent photodegradation of rhodamine B (RhB) under visible light. The degradation rates of BiOCl microspheres and BiOCl and BiOCl/Au butterfly wing scales are 48.8%, 72.6%, and 93.8%, respectively, within 20-min illumination at the same loading capacities. This excellent performance of BiOCl/Au is attributed to the coupling of enhanced carrier separation efficiency and the effect of localized surface plasmon resonance (LSPR) aroused by 3D metallic structures. This study provides a relatively facile method to obtain complex 3D constructure of 2D materials. It also demonstrates a nature-led route to prepare highly efficient plasmonic photocatalysts.
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http://dx.doi.org/10.1039/c9nr02304fDOI Listing
May 2019

Analysis of the Substrate Effect on the Zero-Backward Scattering Condition of a Cu₂O Nanoparticle under Non-Normal Illumination.

Nanomaterials (Basel) 2019 Apr 3;9(4). Epub 2019 Apr 3.

Group of Displays and Photonic Applications (GDAF-UC3M), Carlos III University of Madrid, Leganes, 28911 Madrid, Spain.

The presence of a substrate is one of the most important limitations of the real application of the directional conditions. These conditions allow the control of the spatial distribution of light scattering of nanoparticles. While the zero-forward condition is quite sensitive to any change of the surrounding medium, like the substrate, the zero-backward scattering seems to be less sensitive and very stable under normal illumination. In this letter, the zero-backward scattering condition was investigated on a homogenous Cu₂O spherical subwavelength particle, both theoretically and experimentally. In particular, the influence of the substrate and the impinging direction on the angular distribution of light scattering under this directional condition were studied. We observed that the zero-backward scattering condition was also sensitive to the presence of a substrate beneath when a non-normal illumination was considered. We believe that our finding is quite interesting from a practical point of view and for the real implementation of directional scattering in various applications like cloaking, light-emitting devices, photovoltaic devices, bio-sensing, and many more.
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http://dx.doi.org/10.3390/nano9040536DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6523745PMC
April 2019

Engineering the optical properties of dielectric nanospheres by resonant modes.

Nanotechnology 2018 Dec 27;29(50):505204. Epub 2018 Sep 27.

School of Electronic Engineering and Optoelectronic Technology, Nanjing University of Science and Technology, Nanjing, 210094, Jiangsu, People's Republic of China.

Recent progress in nanoscale optical physics is associated with the development of a new branch of nanophotonics exploring strong Mie resonances in dielectric nanoparticles with high refractive index (HRI). The high-index resonant dielectric nanostructures form building blocks for novel photonic meta-devices with low losses and advanced functionalities. In this work, we investigate the size effect of an HRI cuprous oxide (CuO) nanosphere on the optical properties of the structure, such as, scattering and absorption spectrum. We also experimentally demonstrate that the scattering field can be significantly engineered by tuning the radius of CuO. It is found that the resonant eigenmodes supported by the nanospheres play the dominant role in the absorption and scattering characteristic of the structure. From the perspective of eigenmodes, we can immediately find the right structure parameters to realize strong absorption (scattering) at either single wavelength or broadband wavelength. Furthermore, the multipole expansion method has been applied to explore the physical nature (i.e. electric mode or magnetic mode) of the eigenmode as well as contributions from different modes.
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http://dx.doi.org/10.1088/1361-6528/aae4d2DOI Listing
December 2018

Enhancing Multifunctionalities of Transition-Metal Dichalcogenide Monolayers via Cation Intercalation.

ACS Nano 2017 09 1;11(9):9390-9396. Epub 2017 Sep 1.

Institute of High Performance Computing, A*STAR , Singapore 138632.

We have demonstrated that multiple functionalities of transition-metal dichalcogenide (TMDC) monolayers may be substantially improved by the intercalation of small cations (H or Li) between the monolayers and underlying substrates. The functionalities include photoluminescence (PL) efficiency and catalytic activity. The improvement in PL efficiency may be up to orders of magnitude and can be mainly ascribed to two effects of the intercalated cations: p-doping to the monolayers and reducing the influence of substrates, but more studies are necessary to better understand the mechanism for the improvement in the catalytic functionality. The cation intercalation may be achieved by simply immersing substrate-supported monolayers into the solution of certain acids or salts. It is more difficult to intercalate under the monolayers interacting with substrates stronger, such as as-grown monolayers or the monolayers on 2D material substrates. This result presents a versatile strategy to simultaneously optimize multiple functionalities of TMDC monolayers.
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http://dx.doi.org/10.1021/acsnano.7b04880DOI Listing
September 2017

Giant Gating Tunability of Optical Refractive Index in Transition Metal Dichalcogenide Monolayers.

Nano Lett 2017 06 22;17(6):3613-3618. Epub 2017 May 22.

Hubei Key Laboratory of Plasma Chemistry and Advanced Materials, Wuhan Institute of Technology , Wuhan, 430205, P. R. China.

We report that the refractive index of transition metal dichacolgenide (TMDC) monolayers, such as MoS, WS, and WSe, can be substantially tuned by >60% in the imaginary part and >20% in the real part around exciton resonances using complementary metal-oxide-semiconductor (CMOS) compatible electrical gating. This giant tunablility is rooted in the dominance of excitonic effects in the refractive index of the monolayers and the strong susceptibility of the excitons to the influence of injected charge carriers. The tunability mainly results from the effects of injected charge carriers to broaden the spectral width of excitonic interband transitions and to facilitate the interconversion of neutral and charged excitons. The other effects of the injected charge carriers, such as renormalizing bandgap and changing exciton binding energy, only play negligible roles. We also demonstrate that the atomically thin monolayers, when combined with photonic structures, can enable the efficiencies of optical absorption (reflection) tuned from 40% (60%) to 80% (20%) due to the giant tunability of the refractive index. This work may pave the way toward the development of field-effect photonics in which the optical functionality can be controlled with CMOS circuits.
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http://dx.doi.org/10.1021/acs.nanolett.7b00768DOI Listing
June 2017

Atomically Thin MoS2 Narrowband and Broadband Light Superabsorbers.

ACS Nano 2016 08 8;10(8):7493-9. Epub 2016 Aug 8.

Departments of †Materials Science and Engineering, ‡Physics, §Chemical Engineering, and ∥Electrical and Computer Engineering, North Carolina State University , Raleigh, North Carolina 27695, United States.

We present a combined theoretical and experimental effort to enable strong light absorption (>70%) in atomically thin MoS2 films (≤4 layers) for either narrowband incidence with arbitrarily prespecified wavelengths or broadband incidence like solar radiation. This is achieved by integrating the films with resonant photonic structures that are deterministically designed using a unique reverse design approach based on leaky mode coupling. The design starts with identifying the properties of leaky modes necessary for the targeted strong absorption, followed by searching for the geometrical features of nanostructures to support the desired modes. This process is very intuitive and only involves a minimal amount of computation, thanks to the straightforward correlations between optical functionality and leaky modes as well as between leaky modes and the geometrical feature of nanostructures. The result may provide useful guidance for the development of high-performance atomic-scale photonic devices, such as solar cells, modulators, photodetectors, and photocatalysts.
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http://dx.doi.org/10.1021/acsnano.6b02195DOI Listing
August 2016

Deterministic phase engineering for optical Fano resonances with arbitrary lineshape and frequencies.

Opt Express 2015 Jul;23(15):19154-65

We present an approach of deterministic phase engineering that can enable the rational design of optical Fano resonances with arbitrarily pre-specified lineshapes. Unlike all the approaches previously used to design optical Fano resonances, which fall short of designing the resonances with arbitrary lineshapes because of the lack of information for the optical phases involved, we develop our approach by capitalizing on unambiguous knowledge for the phase of optical modes. Optical Fano resonances arise from the interference of photons interacting with two optical modes with substantially different quality factors. We find that the phase difference of the two modes involved in optical Fano resonances is determined by the eigenfrequency difference of the modes. This allows us to deterministically engineer the phase by tuning the eigenfrequency, which may be very straightforward. We use dielectric grating structures as an example to illustrate the notion of deterministic engineering for the design of optical Fano resonances with arbitrarily pre-specified symmetry, linewidth, and wavelengths.
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http://dx.doi.org/10.1364/OE.23.019154DOI Listing
July 2015

Equally efficient interlayer exciton relaxation and improved absorption in epitaxial and nonepitaxial MoS2/WS2 heterostructures.

Nano Lett 2015 Jan 16;15(1):486-91. Epub 2014 Dec 16.

Department of Materials Science and Engineering, ‡Department of Physics, ∥Analytical Instrumentation Facility, and ⊥Department of Electrical and Computer Engineering, North Carolina State University , Raleigh, North Carolina 27695, United States.

Semiconductor heterostructures provide a powerful platform to engineer the dynamics of excitons for fundamental and applied interests. However, the functionality of conventional semiconductor heterostructures is often limited by inefficient charge transfer across interfaces due to the interfacial imperfection caused by lattice mismatch. Here we demonstrate that MoS(2)/WS(2) heterostructures consisting of monolayer MoS(2) and WS(2) stacked in the vertical direction can enable equally efficient interlayer exciton relaxation regardless the epitaxy and orientation of the stacking. This is manifested by a similar 2 orders of magnitude decrease of photoluminescence intensity in both epitaxial and nonepitaxial MoS(2)/WS(2) heterostructures. Both heterostructures also show similarly improved absorption beyond the simple superimposition of the absorptions of monolayer MoS(2) and WS(2). Our result indicates that 2D heterostructures bear significant implications for the development of photonic devices, in particular those requesting efficient exciton separation and strong light absorption, such as solar cells, photodetectors, modulators, and photocatalysts. It also suggests that the simple stacking of dissimilar 2D materials with random orientations is a viable strategy to fabricate complex functional 2D heterostructures, which would show similar optical functionality as the counterpart with perfect epitaxy.
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http://dx.doi.org/10.1021/nl5038177DOI Listing
January 2015

Semiconductor solar superabsorbers.

Sci Rep 2014 Feb 17;4:4107. Epub 2014 Feb 17.

1] Department of Materials Science and Engineering, North Carolina State University, Raleigh NC 27695 [2] Department of Physics, North Carolina State University, Raleigh NC 27695.

Understanding the maximal enhancement of solar absorption in semiconductor materials by light trapping promises the development of affordable solar cells. However, the conventional Lambertian limit is only valid for idealized material systems with weak absorption, and cannot hold for the typical semiconductor materials used in solar cells due to the substantial absorption of these materials. Herein we theoretically demonstrate the maximal solar absorption enhancement for semiconductor materials and elucidate the general design principle for light trapping structures to approach the theoretical maximum. By following the principles, we design a practical light trapping structure that can enable an ultrathin layer of semiconductor materials, for instance, 10 nm thick a-Si, absorb > 90% sunlight above the bandgap. The design has active materials with one order of magnitude less volume than any of the existing solar light trapping designs in literature. This work points towards the development of ultimate solar light trapping techniques.
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http://dx.doi.org/10.1038/srep04107DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3925943PMC
February 2014

General modal properties of optical resonances in subwavelength nonspherical dielectric structures.

Nano Lett 2013 Aug 9;13(8):3559-65. Epub 2013 Jul 9.

Department of Material Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States.

Subwavelength dielectric structures offer an attractive low-loss alternative to plasmonic materials for the development of resonant optics functionalities such as metamaterials and optical antennas. Nonspherical-like rectangular dielectric structures are of the most interest from the standpoint of device development due to fabrication convenience. However, no intuitive fundamental understanding of the optical resonance in nonspherical dielectric structures is available, which has substantially delayed the development of dielectric resonant optics devices. Here, we elucidate the general fundamentals of the optical resonance in nonspherical subwavelength dielectric structures with different shapes (rectangular or triangular) and dimensionalities (1D nanowires or 0D nanoparticles). We demonstrate that the optical properties of nonspherical dielectric structures are dictated by the eigenvalue of the structure's leaky modes. Leaky modes are defined as optical modes with propagating waves outside the structure. We also elucidate the dependence of the modal eigenvalue on physical features of the structure. The eigenvalue shows scale invariance with respect to the size of the structure, weak dependence on the refractive index, but linear dependence on the size ratio of different sides of the structure. We propose a modified Fabry-Perot model to account for the linear dependence. The knowledge of leaky modes, including the role in optical responses and the dependence on physical features, can serve as a powerful guide for the rational design of devices with desired optical resonances. It may open up a pathway to design devices with functionality that has not been explored due to the lack of intuitive understanding, for instance, imaging devices able to sense incident angle or superabsorbing photodetectors.
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http://dx.doi.org/10.1021/nl401150jDOI Listing
August 2013

Fractal H-shaped plasmonic nanocavity.

Nanotechnology 2013 May 19;24(20):205702. Epub 2013 Apr 19.

National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 200083 Shanghai, People's Republic of China.

Based on complementary fractal geometry structures, we design a novel infrared quasi-three-dimensional (3D) nanocavity with a localized enhanced field with multiband resonant frequencies. The fractals offer the nanostructure two important characteristics, multiband functionality and a subwavelength effect. The electric field, power flow, and the field intensity distributions are given to indicate the internal mechanism of the localized enhanced field in the nanocavity. Additionally, the effective medium method is established to retrieve the permittivity and impedance of the structure. It is shown that a strongly enhanced localized field is achieved in the nanocavity at two different resonant frequencies by using the finite difference time domain method. The field intensity in the nanocavity is enhanced by a factor of up to 60 times over that of the incident light because of the important contribution of the loss factor in the permittivity. The surface plasmon hybridization is thought to play an important role in the strong localized field enhancement. The multiband property and high localized intensity offer the nanocavity great potential for applications in surface enhanced Raman scattering and other nanoscale novel devices.
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http://dx.doi.org/10.1088/0957-4484/24/20/205702DOI Listing
May 2013
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