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Direct molecular-level near-field plasmon and temperature assessment in a single plasmonic hotspot
摘要： Tip-enhanced Raman spectroscopy (TERS) is currently widely recognized as an essential but still emergent technique for exploring the nanoscale. However, our lack of comprehension of crucial parameters still limits its potential as a user-friendly analytical tool. The tip’s surface plasmon resonance, heating due to near-field temperature rise, and spatial resolution are undoubtedly three challenging experimental parameters to unravel. However, they are also the most fundamentally relevant parameters to explore, because they ultimately influence the state of the investigated molecule and consequently the probed signal. Here we propose a straightforward and purely experimental method to access quantitative information of the plasmon resonance and near-field temperature experienced exclusively by the molecules directly contributing to the TERS signal. The detailed near-field optical response, both at the molecular level and as a function of time, is evaluated using standard TERS experimental equipment by simultaneously probing the Stokes and anti-Stokes spectral intensities. Self-assembled 16-mercaptohexadodecanoic acid monolayers covalently bond to an ultra-flat gold surface were used as a demonstrator. Observation of blinking lines in the spectra also provides crucial information on the lateral resolution and indication of atomic-scale thermally induced morphological changes of the tip during the experiment. This study provides access to unprecedented molecular-level information on physical parameters that crucially affect experiments under TERS conditions. The study thereby improves the usability of TERS in day-to-day operation. The obtained information is of central importance for any experimental plasmonic investigation and for the application of TERS in the field of nanoscale thermometry.
关键词： surface plasmon resonance,nanoscale thermometry,Tip-enhanced Raman spectroscopy (TERS),spatial resolution,near-field temperature rise
更新于2025-09-19 17:13:59
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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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Derivation and Experimental Verification of the near-field 2D and 3D optical intensities from a finite-size light emitting diode (LED)
摘要： We derive the near-field light intensity distributions of an inorganic LED on its surface and in volumetric space. Our closed-form solution for 3D intensity distribution for a finite-size LED is consistent with Lambert’s Cosine Law, which provides the 3D intensity distribution for an infinitesimal, flat light source. We also derive the formula for the 2D intensity distribution on a diode surface showing its similarity to a Gaussian function, which is typically used to approximate the surface light intensity profile for an LED and a laser diode. Our 2D intensity distribution function produces light propagation similar to the Gaussian beam propagation in space. However, unlike the Gaussian approximation, our formula invariably produces this behavior without assuming the refractive index inside the diode follows a quadratic function of the transverse spatial domains. Our 2D and 3D spatial intensity formulas in near-field for LEDs offer a unique way to calculate the peak intensity that occurs at the center of the flat LED source. We demonstrate, as expected, that the peak intensity increases with the size of the LED source as well as the brightness of each radiative electron-hole pair, which is a function of the drive current and quantum efficiency of the LED.
关键词： Near-field Photometry,Optical Waveguides,Display,Optical Wave Propagation,Closed-Form Solutions,and Lighting.,Lasers,Light Emitting Diodes,Mathematical Physics
更新于2025-09-16 10:30:52
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Terahertz Near-field Metasurfaces and Superfocusing
摘要： In this work, a near-field metasurface is designed to overcome diffraction limit and superfocus terahertz waves by elaborately arranging the proposed unit cells with super small electric sizes. The full width at half-maximum beam width reaches up to 0.067λ0 (free-space wavelength) at a distance of 0.073λ0 at 0.437 THz. The near-field metasurface is beneficial for subwavelength resolution imaging, photolithography, non-contact sensing, and other applications in the near field.
关键词： subwavelength resolution,terahertz,near-field metasurface,superfocusing
更新于2025-09-16 10:30:52
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Advanced photoconductive Terahertz near-field microprobes for 1550 nm wavelength operation based on InGaAs:Rh
摘要： Photoconductive microprobes have been widely established for surface-near THz field measurements with sub-wavelength resolution and applications such as wafer scanning or metamaterial characterization. Since the standard material for these probes is still LT-GaAs, the optical pump wavelength is usually set below 890 nm for direct bandgap excitation. Adaption to modern fiber-based THz TDS systems – operating at 1550 nm – required the use of optical frequency doubling components, so far. In this work, we investigate an alternative solution based on InGaAs:Rh for direct operation at 1550 nm wavelength.
关键词： 1550 nm wavelength operation,THz near-field measurements,InGaAs:Rh,Photoconductive microprobes
更新于2025-09-16 10:30:52
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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) - Towards Near-Field Coupling of Surface Plasmon Polaritons across Few-Nanometer Gaps between two Laterally Tapered Gold Waveguides
摘要： Nanofocusing of light in combination with an efficient energy transfer of metallic nanostructures is a key task towards ultrafast, all-optical switching on the nanoscale. A possible realization of such a device is based on two tapered plasmonic nanostructures separated by a few-nanometer gap, in which information transport is controlled via strong coupling of the electromagnetic near-field and excitonic molecules in the gap region of the waveguides. The fabrication of such mesoscopic nanostructures that can concentrate free-propagating light to few-nanometers dimensions remains challenging due to the desired nanometer precision in the gap region. Here, we report on the fabrication of a plasmonic nanostructures consisting of a pair of both striped and tapered waveguides in 200 nm thick Au films with gap sizes and radii of curvature down to 11 nm using a Focused Ion Beam-based “Sketch and Peel” lithography process. Curved focused-ion beam written gratings in the waveguides enable the in- and out-coupling and focusing of surface plasmon polaritons into the nanostructure. The propagation of these SPPs is afterwards monitored using far-field confocal microscopy. We find a relatively constant transmission of light for large gap sizes, accompanied by a drastically increase for gap sizes below 20 nm. This increase for small gap sizes can be approximated best by fitting an exponential decay with a decay length of 8 nm suggesting a significant energy transport through near-field coupling of the two waveguides. These experimental findings are in accordance to finite element method and finite difference time domain calculations that show a strong localization of the electric field in the gap region of the two waveguides. The profound electric field strength and the spatial confinement of the electric fields suggest such plasmonic waveguides as prototypical structures for probing the strong coupling between propagating surface plasmon polaritons in adjacent, however separated plasmonic waveguides on one hand and between SPP waves and single quantum emitters that are placed in the gap region of the waveguides on the other hand. The realization of such coupling could enable the ultrafast, remote switching on the nanoscale.
关键词： ultrafast switching,nanofocusing,near-field coupling,surface plasmon polaritons,plasmonic nanostructures
更新于2025-09-16 10:30:52
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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) - Scanning Resonant Nano-Antenna High Resolution Imaging and Emission Control of hBN Defect Photon Emission
摘要： Single atomic defects in hexagonal boron nitride (hBN) are particularly interesting due to their stability of emission and absence of blinking and bleaching, at ambient conditions. Furthermore, they show exceptional robustness of emission, even at high temperatures of operation. Therefore, hBN defects have emerged as promising candidates for novel robust single photon sources. Several attempts have been done to induce hBN defects in a controlled manner. Because of their ease of accessibility and, due to the nanometer scale thickness of the hBN flakes, these defects are attractive to couple to plasmonic structures in order to increase their photon emission. However efficient coupling requires a high precision of positioning (<20 nm) and so far the methods adopted lack this level of control, both in assembling and imaging. Also, they present static configurations of coupled emitter-particles and no strategy is adopted in order to discern between the photons emitted by the hBN defects and the luminescence of the metallic particles. Here we present first systematic and simultaneous coupling and imaging of hBN emission centers with resonant optical antennas, with nanometer control and optical resolution of 45 nm. We show the capability of nano-antennas to manipulate hBN defects by depleting their emission 30-70%. Our setup is a near-field microscope working in scattering configuration, where we fabricate a single dipolar nano-antenna as a near-field probe that we can independently scan over hBN defects controlling the coupling and the fluorescence emission with nanometer resolution. We employ a photon time-gating technique in order to discriminate the light emitted by the metallic antenna by the one radiated by the hBN emitters. Finally, we report on a lifetime shortening of 2x, due to coupling emitter--antenna.
关键词： nano-antennas,single photon sources,plasmonic structures,near-field microscope,hBN defects
更新于2025-09-16 10:30:52
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Quantum Dots Luminescence Collection Enhancement and Nanoscopy by Dielectric Microspheres
摘要： In recent years, dielectric microspheres have been used in conjunction with optical microscopes to beat the diffraction limit and to obtain superresolution imaging. The use of microspheres on quantum dots (QDs) is investigated, for the first time, to enhance the light coupling efficiency. The enhancement of the QD luminescence collection in terms of extraction and directionality is demonstrated, as well as the enhancement of spatial resolution. In particular, it is found that a dielectric microsphere, placed on top of an epitaxial QD, increases the collected radiant energy by about a factor of 42, when a low numerical aperture objective is used. Moreover, if two or more QDs are present below the microsphere, the modification of the far field emission pattern allows selective collection of the luminescence from a single QD by simply changing the collection angle. Dielectric microspheres present a simple and efficient tool to improve the QD spectroscopy, and potentially QD-based devices.
关键词： microspheres,photoluminescence,photonic nanojet,near field
更新于2025-09-16 10:30:52
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Near-field infrared microscopy of nanometer-sized nickel clusters inside single-walled carbon nanotubes
摘要： Nickel nanoclusters grown inside single-walled carbon nanotubes (SWCNT) were studied by infrared scattering-type scanning near-field optical microscopy (s-SNOM). The metal clusters give high local contrast enhancement in near-field phase maps caused by the excitation of free charge carriers. The experimental results are supported by calculations using the finite dipole model, approximating the clusters with elliptical nanoparticles. Compared to magnetic force microscopy, s-SNOM appears much more sensitive to detect metal clusters inside carbon nanotubes. We estimate that these clusters contain fewer than 700 Ni atoms.
关键词： s-SNOM,infrared scattering-type scanning near-field optical microscopy,magnetic force microscopy,single-walled carbon nanotubes,Nickel nanoclusters
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