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Strongly coupled, high-quality plasmonic dimer antennas fabricated using a sketch-and-peel technique
摘要： A combination of helium- and gallium-ion beam milling together with a fast and reliable sketch-and-peel technique is used to fabricate gold nanorod dimer antennas with an excellent quality factor and with gap distances of less than 6 nm. The high fabrication quality of the sketch-and-peel technique compared to a conventional ion beam milling technique is proven by polarisation-resolved linear dark-field spectromicroscopy of isolated dimer antennas. We demonstrate a strong coupling of the two antenna arms for both fabrication techniques, with a quality factor of more than 14, close to the theoretical limit, for the sketch-and-peel–produced antennas compared to only 6 for the conventional fabrication process. The obtained results on the strong coupling of the plasmonic dimer antennas are supported by finite-difference time-domain simulations of the light-dimer antenna interaction. The presented fabrication technique enables the rapid fabrication of large-scale plasmonic or dielectric nanostructures arrays and metasurfaces with single-digit nanometer scale milling accuracy.
关键词： helium-ion beam lithography,near-field enhancement,strong coupling,plasmonic nanostructures,sketch and peel,quality factor,single-particle dark-field spectroscopy
更新于2025-09-16 10:30:52
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Remarkable surface-enhanced Raman scattering on self-assembled {201} anatase
摘要： Semiconductors exhibit great potential as a surface-enhanced Raman scattering (SERS) substrate due to their low cost, stability, and biocompatibility. However, their application has been essentially restricted by their intrinsically low SERS sensitivity (10–102). Herein, sea urchin-like TiO2 was obtained by a self-assembled growth of crystals enclosed with the {201} facet. The high-symmetric spiny spheres exhibited appreciable Raman enhancement factors (EFs) of 1.6 (cid:2) 106, three orders of magnitude higher than those asymmetric TiO2 with exposed {101}, {001}, and {100} facets. The greatest charge transfer upon dopamine adsorption occurred on {201} TiO2 due to its high density of unoccupied t2g orbitals, partly contributing to the excellent SERS performance. More importantly, the sea urchin-like spheres created high-density hotspots evenly distributed in the vicinity of sharp tips and at narrow gaps between the spines, enabling a strong electromagnetic field enhancement (1.4 (cid:2) 104). Benefiting from the specific electronic and morphologic properties, the self-assembled {201} TiO2 exhibited superior SERS performance in terms of both intensity and reproducibility. The insights gained from this study open a new avenue to improve the SERS performance of semiconductors for applications in biomedical analysis, food detection, and toxicity tests.
关键词： SERS,{201} facet,self-assembled,surface-enhanced Raman scattering,electromagnetic field enhancement,TiO2,charge transfer
更新于2025-09-16 10:30:52
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Collective multipole oscillations direct the plasmonic coupling at the nanojunction interfaces
摘要： We present a systematic study of the effect of higher-multipolar order plasmon modes on the spectral response and plasmonic coupling of silver nanoparticle dimers at nanojunction separation and introduce a coupling mechanism. The most prominent plasmonic band within the extinction spectra of coupled resonators is the dipolar coupling band. A detailed calculation of the plasmonic coupling between equivalent particles suggests that the coupling is not limited to the overlap between the main bands of individual particles but can also be affected by the contribution of the higher-order modes in the multipolar region. This requires an appropriate description of the mechanism that goes beyond the general coupling phenomenon introduced as the plasmonic ruler equation in 2007. In the present work, we found that the plasmonic coupling of nearby Ag nanocubes does not only depend on the plasmonic properties of the main band. The results suggest the decay length of the higher-order plasmon mode is more sensitive to changes in the magnitude of the interparticle axis and is a function of the gap size. For cubic particles, the contribution of the higher-order modes becomes significant due to the high density of oscillating dipoles localized on the corners. This gives rise to changes in the decay length of the plasmonic ruler equation. For spherical particles, as the size of the particle increases (i.e., ≥80 nm), the number of dipoles increases, which results in higher dipole–multipole interactions. This exhibits a strong impact on the plasmonic coupling, even at long separation distances (20 nm).
关键词： plasmonic coupling equation,silver nanoparticle pairs,localized surface plasmon resonance,field enhancement,dipole–multipole interaction
更新于2025-09-16 10:30:52
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Simulations of the Near-Field Enhancement on AFM Tip Irradiated by Annular Laser Beam
摘要： The near-field enhancement underneath the AFM tip irradiated by a laser beam is widely utilized in various nanofabrication techniques, such as nano-welding, nano-manipulation, nano-etching and so on. In this paper, a numerical model of near-field enhancement on AFM tip irradiated by annular laser beam is established using COMSOL Multiphysics. The results show that when the AFM tip is irradiated by annular laser beam, strong near-field enhancement is induced at the apex of the tip. The field distribution curve with the substrate presents a saddle shape, which demonstrates that the annular beam irradiated the AFM tip produce an extremely high near-field enhancement between the particle and the tip. In addition, the results indicate that when the AFM tip is irradiated by the annular laser with higher frequency, the near-field enhancement underneath the apex of the tip increases correspondingly. Moreover, when the irradiation angle is 60 Deg and the irradiation distance is 65 nm, the near-field enhancement reaches the peak. Based on the numerical simulation of the near-field enhancement, the system of the AFM tip irradiated by annular laser beam can be anticipated for further application in the field of nanofabrication.
关键词： Near-field enhancement,nanofabrication,COMSOL Multiphysics simulation,annular laser beam
更新于2025-09-16 10:30:52
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Plasmonic Metamaterials for Nanochemistry and Sensing
摘要： Plasmonic nanostructures were initially developed for sensing and nanophotonic applications but, recently, have shown great promise in chemistry, optoelectronics, and nonlinear optics. While smooth plasmonic films, supporting surface plasmon polaritons, and individual nanostructures, featuring localized surface plasmons, are easy to fabricate and use, the assemblies of nanostructures in optical antennas and metamaterials provide many additional advantages related to the engineering of the mode structure (and thus, optical resonances in the given spectral range), field enhancement, and local density of optical states required to control electronic and photonic interactions. Focusing on two of the many applications of plasmonic metamaterials, in this Account, we review our work on the sensing and nanochemistry applications of metamaterials based on the assemblies of plasmonic nanorods under optical, as well as electronic interrogation.
关键词： field enhancement,sensing,localized surface plasmons,optical antennas,nanochemistry,optical resonances,electronic interrogation,surface plasmon polaritons,metamaterials,Plasmonic nanostructures
更新于2025-09-12 10:27:22
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Near-Field-Induced Femtosecond Breakdown of Plasmonic Nanoparticles
摘要： We studied the evolution of femtosecond breakdown in lithographically produced plasmonic nanoparticles with increasing laser intensity. Localized plasmons were generated with 40-fs laser pulses with up to 1.4 × 1012 W/cm2 peak intensity. The damage morphology shows substantial variation with intensity, starting with the detachment of hot spots and stochastic nanoparticle removal. For higher intensities, we observe precise nanolithographic mapping of near-field distributions via ablation. The common feature of these phenomena is the central role played by the single plasmonic hot spot of the triangular nanoparticles used. We also derive a damage threshold value from stochastic damage trends on the arrays fostering the optimization of novel nanoarchitectures for nonlinear plasmonics.
关键词： Laser-induced damage threshold,Plasmonic nanoparticles,Plasmonics,Field enhancement mapping
更新于2025-09-12 10:27:22
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Theoretical Investigation of Plasmonic Properties of Quantum-Sized Silver Nanoparticles
摘要： Plasmonic nanoparticles (NPs) like silver (Ag) strongly absorb the incident light and produce enhanced localized electric field at the localized surface plasmon resonance (LSPR) frequency. Enormous theoretical and experimental research has focused on the plasmonic properties of the metallic nanoparticles with sizes greater than 10 nm. However, such studies on smaller sized NPs in the size range of 3 to 10 nm (quantum-sized regime) are sparse. In this size regime, the conduction band of the metal particles discretizes, thus altering plasmon properties of the NPs from classical to the quantum regime. In this study, plasmonic properties of the spherical Ag NPs in size range of 3 to 20 nm were investigated using both quantum and classical modeling to understand the importance of invoking quantum regime to accurately describing their properties in this size regime. Theoretical calculations using standard Mie theory were carried out to monitor the LSPR peak shift and electric field enhancement as a function of the size of the bare plasmonic nanoparticle and the refractive index (RI) of the surrounding medium. Comparisons were made with and without invoking quantum regime. Also, the optical properties of metallic NPs conjugated with a chemical ligand using multi-layered Mie theory were studied, and interesting trends were observed.
关键词： Absorption,Ligand,Multi-layered Mie theory,Field enhancement,Quantum regime,LSPR
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Plasmon-Plasmon Coupling Probed by Ultrafast, Strong-Field Photoemission with <7 ? Sensitivity
摘要： The coupling of propagating surface plasmon waves and localized plasmon oscillations in nanostructures is an essential phenomenon determining electromagnetic field enhancement on the nanoscale. With our recently developed experimental method [1], we can measure the maximum plasmonic field enhancement at any nanostructured metal surface. Here we use our method to investigate the fundamental question of plasmon-plasmon coupling and its effect on large field enhancement factors. Coupling is studied on different nanostructured Ag thin films supporting not only propagating plasmons, but also localized plasmon oscillations due to the different surface nanostructures. Ultrashort laser pulses excite propagating plasmons in Kretschmann geometry (Fig. 1 (a)), while localized plasmons are excited on the surface nanostructures via the coupling of propagating and localized surface plasmons. Photoelectron spectra of the electrons photoemitted due to the plasmonic near fields are measured by a time-of-flight spectrometer [1,2]. The analysis of the cutoffs (highest electron energies, Fig. 1 (b)) of the electron spectra yields maximum plasmonic field enhancement values ×21, ×23 and ×31 for surfaces exhibiting 0.8, 1.6 and 4.5 nm average roughness values, respectively. The finite-difference time-domain (FDTD) simulation of the individual rough surfaces not only support the measured field enhancement values, but also reveal the contributions from propagating and localized plasmons (Fig. 1. (c) and (d)). The dependence of the field localization, i. e. the resulting field enhancement values on the grain size is also demonstrated. It is shown, that when resonance conditions are met, a significant portion of the field enhancement can be attributed to the generation of localized plasmons on the grainy surface nanostructures, acting as dipole sources resonantly driven by the propagating plasmon field [3].
关键词： plasmon-plasmon coupling,ultrafast photoemission,field enhancement,nanostructured Ag thin films
更新于2025-09-12 10:27:22
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[IEEE 2019 IEEE 31st International Conference on Microelectronics (MIEL) - Nis, Serbia (2019.9.16-2019.9.18)] 2019 IEEE 31st International Conference on Microelectronics (MIEL) - Arrays of Bowtie Plasmonic Nanoantennas for Field Enhancement in MOEMS
摘要： Many micro(nano)optoelectromechanical systems (MOEMS, NOEMS) require optical (generally, electromagnetic) field localization and concentration. These include for instance photocatalytic microreactors and labs on a chip, where it is necessary to localize optical energy into a fluidic channel. Other examples are chemical and biological sensors. Plasmonics on the other hand ensures field localization down to subwavelength volumes where evanescent fields can be tailored to the shape of minuscule channels in MOEMS and NOEMS. In this work we present a possible approach to the enhancement of optical fields in MOEMS and NOEMS systems where a linear array of plasmonic bowtie structures is used to concentrate the optical field into a dielectric channel. We perform our numerical simulations using the finite element method to analyze field distributions that can be achieved by the use of the bowtie antenna and the possibility to tailor these fields. We also analyze the influence of the shape of the coupled tips of bowties to the field distribution and frequency dispersion. We conclude that arrays of plasmonic bowties could be a promising candidate for optically assisted micro and nanofluidics.
关键词： field enhancement,bowtie nanoantennas,MOEMS,NOEMS,plasmonics,finite element method
更新于2025-09-12 10:27:22
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Coherent Vibrational Spectroscopy of Electrochemical Interfaces with Plasmonic Nano-gratings
摘要： The fundamental understanding of electrochemistry urges accurate knowledge of all interfacial properties at the molecular-level, but the retrieval of such information is a real challenge. Optical spectroscopies facilitated by surface plasmon enhancement can shed light on this field, yet past studies relied on either highly inhomogeneous “hot spots”, or planar plasmon modes with limited enhancement. Here we report an in situ sum-frequency vibrational spectroscopy scheme using plasmonic nano-gratings, which enable strong, coherent surface plasmon excitation even on planar electrodes. With two classical reactions, the gold oxidation and pyridine adsorption in water, we demonstrate the realization of coherent vibrational spectroscopy in the strong absorption region, revealing the polar orientation and ordering of interfacial species that are crucial toward the mechanistic understanding of electrochemical phenomena.
关键词： field enhancement,surface plasmon resonance,molecular-level information,in situ spectroelectrochemistry,electrode/electrolyte interfaces
更新于2025-09-12 10:27:22