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Near-field observation of guided-mode resonances on a metasurface via dielectric nanosphere excitation
摘要： We study laser-induced guided-mode resonances on an ultra-thin anisotropic metallic metasurface using direct near-field mapping. Coupling of the incident light to the surface waves is provided by a resonant laser-printed silicon nanosphere placed on the metasurface using nano-manipulation under electron-beam supervision. To visualize the propagation of the guided modes, we employ scattering-type scanning near-field optical microscopy in the near-infrared region (850 nm). The guided-mode resonances excited by the nanosphere demonstrate vanishing anisotropy due to weak confinement at the metasurface/air interface. We also extract the wavenumber of the observed modes through Fourier transformation of the measured near-field maps and find it to be in good agreement with numerical calculations.
关键词： Metasurface,Surface waves,Anisotropy,s-SNOM,Guided-mode resonance,Nano-Optics
更新于2025-09-23 15:21:01
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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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Probing Polaritons in 2D Materials with Synchrotron Infrared Nanospectroscopy
摘要： Polaritons, which are quasiparticles composed of a photon coupled to an electric or magnetic dipole, are a major focus in nanophotonic research of van der Waals (vdW) crystals and their derived 2D materials. For the variety of existing vdW materials, polaritons can be active in a broad range of the electromagnetic spectrum (meVs to eVs) and exhibit momenta much higher than the corresponding free-space radiation. Hence, the use of high momentum broadband sources or probes is imperative to excite those quasiparticles and measure the frequency-momentum dispersion relations, which provide insights into polariton dynamics. Synchrotron infrared nanospectroscopy (SINS) is a technique that combines the nanoscale spatial resolution of scattering-type scanning near-field optical microscopy with ultrabroadband synchrotron infrared radiation, making it highly suitable to probe and characterize a variety of vdW polaritons. Here, the advances enabled by SINS on the study of key photonic attributes of far- and mid-infrared plasmon- and phonon-polaritons in vdW and 2D crystals are reviewed. In that context the SINS technique is comprehensively described and it is demonstrated how fundamental polaritonic properties are retrieved for a range of atomically thin systems including hBN, MoS2, graphene and 2D heterostructures.
关键词： s-SNOM,hexagonal boron nitride,far-infrared SINS,2D materials,polaritons,infrared synchrotron nanospectroscopy,graphene
更新于2025-09-12 10:27:22
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Nano Focus: IR vibrational crystallography visualizes molecular orientation on the nanoscale
摘要： The orientation of molecules is of central importance in determining the photophysical properties of organic materials, such as mobility of charge carriers and ions. These orientation-dependent properties of materials further control their functionalities in biological systems and electronic devices, including organic light-emitting diodes and solar cells. Until now, optical crystallography has failed to yield high-resolution images of molecular arrangement, due to the diffraction-limited response, weak photon–material interaction between x-rays and organic materials, or sample damage. A group of researchers from the University of Colorado Boulder and Lawrence Berkeley National Laboratory has developed a new mapping technique called infrared scattering-type scanning near-field optical microscopy (IR s-SNOM), which can identify the molecular arrangement of subdomains smaller than hundreds of nanometers.
关键词： IR vibrational crystallography,IR s-SNOM,organic materials,molecular orientation,nanoscale
更新于2025-09-09 09:28:46
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Numerical simulation of light propagation in metal-coated SNOM tips
摘要： Presented are the results of numerical simulations accomplished to investigate the propagation of electromagnetic excitations in certain types of metal-coated tapered tips terminating SiO2 multimode optical fibres with a subwavelength output aperture. The numerical simulations were initiated in order to enable better interpretation of previously reported experimental results concerning some features of the mesoscopic effect of spectral modulation observed for a broadband light transmitted by such tips. This effect occurs due to the interference between a small number of waveguide modes exiting a metal-coated tip, and the experimental results indicate a possible mode-selective photon-plasmon coupling in the studied tips. To match the experimental conditions, the tips were modelled for the light wavelength of 800 nm as three-layer systems (with the intermediate adhesion Cr layer and the outer layer of Al or Au). However, due to computational restrictions the end of a tip, only 18 μm long (most significant), was modelled. Numerical simulations yielded the dependences of propagation and attenuation constants on the fibre core radius for the most intensive (both photonic and plasmonic) output modes. The pairs of modes most probably contributing to the observed spectral modulation were identified. Although the simulations did not reveal any explicit mode coupling, the imperfections of real tips can cause mode transformations implying possible involvement of more than two modes. The thin (20 nm) Cr layer plays the main role for plasmonic modes generated on its SiO2 interface, which explains the small outer metal layer influence on the observed modal dispersion.
关键词： numerical simulation,multimode optical fibre,optics,spectral modulation,SNOM tip,plasmonics,photonics
更新于2025-09-04 15:30:14
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Nanoapertures without nanolithography
摘要： We propose and experimentally demonstrate the implementation of lithography-free nano-apertures on optical fibers. By sputtering metallic nanofilms onto the end face of step index fibers that contain central nano-channels, fiber-integrated nano-apertures are instantaneously implemented without the use of any kind of lithographic step. In accordance with simulations, the experiments show diffraction-limited nano-spots in the far-field at the location of the nano-aperture for sufficiently thick films. We reproducibly implement a series of devices by sputtering Al and Pt nano-films, reaching aperture diameters as small as 40 nm and showing spectrally broadband operation. Due to its simplicity, scalability and potential for large-scale production the nano-aperture enhanced fiber concept will be highly relevant for lab-on-a-fiber applications and for the development of future fiber-based nano-probes with high spatial resolutions.
关键词： lab-on-a-fiber,hybrid fibers,nanofabrication,scanning near-field optical microscopy (SNOM),nanoapertures
更新于2025-09-04 15:30:14