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Plasmonic Nanocavity Metasurface Based on Laser-Structured Silver Surface and Silver Nanoprisms for the Enhancement of Adenosine Nucleotide Photoluminescence
摘要： A reliable photoluminescence (PL) spectroscopy and imaging of biomolecules at room temperature is a challenging and important problem of biophysics, biochemistry, and molecular genetics. A unique effect of strong plasmonic enhancement of the PL by metal nanostructures is one of the most effective approaches for this purpose. The highest enhancement is provided by metal nanostructures with densely packed sharp tips, periodically arranged metal nanostructures, and plasmonic cavities. All of these features have been realized in the plasmonic cavity metasurface based on the silver (Ag) laser-induced periodic surface structure and Ag triangular nanoprisms studied in the present work. The strong plasmon-enhanced PL of 5′-deoxyadenosine monophosphate deposited on such metasurfaces has been revealed at room temperature. The observed enhancement of more than 1000-fold has been interpreted as a result of synergetic action of the generation of a high concentration of hot spots near the sharp edges of the laser-induced surface structure and nanoprisms together with excitation of the collective gap mode of the cavity due to strong near-field plasmonic coupling. Correspondingly, the plasmonic cavity metasurfaces consisting of metal laser-induced periodic surface structures and nonspherical metal nanoparticles with sharp edges have been shown to be crucial for the highly sensitive detection and imaging of biomolecules at room temperature without consuming any dye labels.
关键词： hot spots,plasmon gap mode,plasmonic metasurface,near-field coupling,nucleotide photoluminescence enhancement
更新于2025-11-19 16:46:39
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Planar plasmonic nanocavity for efficient enhancement of photoluminescence of molecular emitters
摘要： Effects of plasmonic gap mode formation due to coupling between metal nanoparticles and thin metal film separated by thin dielectric luminescent film-spacer (gap) have been studied by means of light extinction and photoluminescence in three-layer planar Au NPs monolayer/shellac-dye film/Au film nanostructure with spacer thickness varied in the range 8–47 nm. The 3-fold enhancement of light extinction and 90 nm red shift of the plasmon mode have been observed in extinction spectra. The 37-fold enhancement of dye photoluminescence and the significant (48 nm) red shift of dye photoluminescence band have been observed for Au NPs monolayer/shellac-dye film/Au film nanostructure in comparison with bare shellac-dye film for the spacer thickness of 8 nm. The decrease of the spacer thickness causes the increase of the enhancement factor of dye photoluminescence indicating the strengthening of the gap mode field. FDTD calculations of the dependence of the intensity of the field of gap mode on the gap thickness have demonstrated good quantitative agreement with experimental data that proves the key role of gap mode in the enhancement of the electromagnetic field in planar metal NPs monolayer/dielectric film/metal film plasmonic nanocavity nanostructures. The variation of the gap thickness provides the possibility to tune controllably the spectral position and enhancement factor of the light emission from the molecular emitters located in the gap that can be used in the novel nanophotonics devices and for highly sensitive detection of the single molecules.
关键词： Near field coupling,Gap thickness dependence,Molecular emitters,Gap mode,Plasmonic nanocavity,Photoluminescence enhancement
更新于2025-11-19 16:46:39
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Femtosecond Pulse Laser Near-Field Ablation of Ag Nanorods
摘要： Ag nanorods (Ag NRs) with a mean aspect ratio of 3.9 were prepared through a wet-chemical method, and the absorption spectra for various aspect ratios were obtained. The morphology transformation of Ag NRs irradiated with a femtosecond pulse laser was investigated through transmission electron microscopy (TEM). The near-field ablation was dependent on the laser polarization and wavelength. Laser-induced high electric field intensity was observed at the ends, middle, and junctions of the Ag NRs under various ablation conditions. Through simulation, the evolution mechanism was analyzed in detail. The effect of laser polarization angle on plasmonic junction welding was also investigated. By controlling the electronic field distribution, several nanostructures were obtained: bone-shaped NRs, T-shaped NRs, dimers, trimers, curved NRs, and nanodots. This study suggests a potentially useful approach for the reshaping, cutting, and welding of nanostructures.
关键词： femtosecond pulse laser,polarization,Ag nanorods,near-field ablation
更新于2025-11-14 17:04:02
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Accurate Determination of Radiation Patterns from Near-Field Measurements in Highly Reflective Environments
摘要： The radiation pattern of an antenna under test is determined from measurements in a highly reflective, fully metallic measurement environment similar to a reverberation chamber. The undesired influence of the reflecting walls is eliminated by processing the data obtained for a large number of frequencies and different probe locations in the chamber. The post-processing concept effectively combines temporal and spatial filtering of the measured signals in an innovative field synthesis concept. S-Band measurements show the effectiveness of the proposed processing concepts. The accuracy is comparable to anechoic measurements, however, for the cost of increased measurement and post-processing effort.
关键词： echo suppression,near-field far-field transformation,antenna measurement
更新于2025-09-23 15:23:52
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Reconfigurable Near-field Enhancement with Hybrid Metal-Dielectric Oligomers
摘要： Tailoring of the near-field properties of the nanostructures is a significant task for the control of radiation of nanoscale light sources as well as for sensing applications. Generally, this task is solved in plasmonic oligomers on the fabrication step by the choice of geometry or by controlling the excitation light during the experiments. Here, the pronounced modification of the near-field pattern in hybrid gold-silicon oligomers by femtosecond laser reshaping by visualizing it with aperture-type near-field optical microscope is demonstrated. This effect correlates with a moderate red-shift of the broadband magnetic dipole resonance of the structure that occurs upon reshaping the gold component of the oligomers. The proposed all-optical near-field reconfiguration approach makes hybrid oligomers a promising platform for on-demand engineering of local field enhancement in metadevices for data recording and sensing.
关键词： near-field tuning,metal-dielectric oligomers,femtosecond laser reconfiguration
更新于2025-09-23 15:23:52
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Two-Dimensional Imaging Based on Near-Field Focused Array Antenna
摘要： In this letter, a near-field focused array antenna is applied to two-dimensional (2-D) microwave imaging, which steers its focus on the designed focal plane by changing the operating frequency and by phase control in two directions, respectively. The imaging system is composed of this array and two microstrip antennas, as receiver and transmitters, respectively. Simulations and measurements have proved the feasibility of the image reconstruction approach. The proposed method has a high imaging speed due to fast electrical beam scan, and thanks to the frequency scan performance of the array in one dimension, it also shows low-cost property against the fully phased method.
关键词： near-field focused beams,Microwave imaging,phased arrays,reconstruction algorithm
更新于2025-09-23 15:23:52
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Control of plasmon dephasing time using stacked nanogap gold structures for strong near-field enhancement
摘要： The construction of metallic nanostructures with strong near-field enhancement is becoming increasingly significant for the practical use of plasmonic devices, such as plasmonic sensors and light-energy conversion systems. Importantly, the near-field enhancement effect depends on the plasmon dephasing time. Here, we propose a method for controlling plasmon dephasing time by utilizing plasmonic coupling for stronger near-field enhancement. Ordered arrays of stacked nanogap gold (Au) structures composed of a metal/insulator/metal nanostructure were fabricated by electron beam lithography and dry etching processes on a niobium-doped titanium dioxide substrate. The dark plasmon mode was excited by the near-field coupling between the upper and lower Au nanostructures separated by an alumina layer with a thickness of 15 nm. A strong near-field enhancement effect was induced by the localization of the electromagnetic field between the upper and lower Au nanostructures and the longer plasmon dephasing time based on the excitation of the dark plasmon mode. It is noteworthy that the dephasing time of the dark plasmon mode measured by time-resolved photoemission electron microscopy was extended 3-fold compared with that of the plasmon mode of the Au nanoblock, which can be controlled by the structural design of the stacked nanogap Au structures.
关键词： Dark plasmon mode,Plasmon dephasing,Near-field enhancement,Photoemission electron microscopy (PEEM),Surface plasmon resonance
更新于2025-09-23 15:23:52
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Disentangling topographic contributions to near-field scanning microwave microscopy images
摘要： We develop empirical models to predict the contribution of topographic variations in a sample to near-field scanning probe microwave microscopy (NSMM) images. In particular, we focus on |S11| images of a thin Perovskite photovoltaic material and a GaN nanowire. The difference between the measured NSMM image and this prediction is our estimate of the contribution of material property variations to the measured image. Prediction model parameters are determined from either a reference sample that is nearly free of material property variations or directly from the sample of interest. The parameters of the prediction model are determined by robust linear regression so as to minimize the effect of material property variations on results. For the case where the parameters are determined from the reference sample, the prediction is adjusted to account for instrument drift effects. Our statistical approach is fully empirical and thus complementary to current approaches based on physical models that are often overly simplistic.
关键词： Near-field scanning probe microwave microscopy,Signal extraction,GaN nanowire,Statistical methods,Perovskite materials,Atomic force microscopy
更新于2025-09-23 15:23:52
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Deeply subwavelength phonon-polaritonic crystal made of a van der Waals material
摘要： Photonic crystals (PCs) are periodically patterned dielectrics providing opportunities to shape and slow down the light for processing of optical signals, lasing and spontaneous emission control. Unit cells of conventional PCs are comparable to the wavelength of light and are not suitable for subwavelength scale applications. We engineer a nanoscale hole array in a van der Waals material (h-BN) supporting ultra-confined phonon polaritons (PhPs)—atomic lattice vibrations coupled to electromagnetic fields. Such a hole array represents a polaritonic crystal for mid-infrared frequencies having a unit cell volume of 10??λ?3 (with λ? being the free-space wavelength), where PhPs form ultra-confined Bloch modes with a remarkably flat dispersion band. The latter leads to both angle- and polarization-independent sharp Bragg resonances, as verified by far-field spectroscopy and near-field optical microscopy. Our findings could lead to novel miniaturized angle- and polarization-independent infrared narrow-band couplers, absorbers and thermal emitters based on van der Waals materials and other thin polar materials.
关键词： van der Waals material,near-field microscopy,phonon-polaritonic crystal,mid-infrared,hexagonal boron nitride,Bragg resonance
更新于2025-09-23 15:23:52
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[IEEE 2018 IEEE International Conference on RFID Technology & Application (RFID-TA) - Macau (2018.9.26-2018.9.28)] 2018 IEEE International Conference on RFID Technology & Application (RFID-TA) - Near Field Sources Localization Based on Robust Propagator Method
摘要： The problem of joint direction-of-arrival (DOA) and range estimation of near-field multiple sources under α-stable distributed impulsive noise environments is studied in this paper. The proposed algorithm constructs the MUSIC spectral spectrum based on the noise subspace which is obtained by applying the propagator method on the fractional lower order statistical matrix of the array received signal, and then estimates the multiple sources’ DOA and range parameters by the spectral peak search. Compared with the corresponding algorithms based on second-order statistics, the proposed algorithm can effectively suppress the impulse noise by using the fractional lower-order statistics. At same time, the inherent large computational complexity of the eigenvalue decomposition based methods can also be avoided. Simulation experiments prove the effectiveness of the proposed algorithm.
关键词： impulsive noise,direction of arrival,fraction lower order statistics,range estimation,near-field,propagator method
更新于2025-09-23 15:23:52