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Chemical Identification of Single Ultrafine Particles Using Surface-Enhanced Infrared Absorption
摘要： In the past decade, it has been demonstrated that surface-enhanced infrared absorption (SEIRA) is a powerful method to enhance vibrational signals of thin molecular layers. Much less attention has so far been given to the possibility of using SEIRA for the detection and characterization of nanometer-sized particles, such as ultrafine dust particles. Here, we report on SEIRA measurements demonstrating that even one single particle with a deeply subwavelength dimension of less than 100 nm can be detected and chemically characterized with standard infrared microspectroscopy. Our approach is based on plasmonic resonances of bowtie-shaped Au apertures that are designed to extraordinarily enhance the material-specific phononic excitations of a nanometer-sized silica particle. We show that the bowtie geometry is especially suited for single-particle spectroscopy, as it combines the advantage of an intense electromagnetic hot spot, the size of which can be adjusted to the particle dimension, with easy positioning of ultrafine dust particles inside that hot spot. In agreement with numerical calculations, we show that a detection limit in terms of a particle diameter of less than 20 nm can be achieved, which corresponds to a ratio of the diameter to the vacuum wavelength below 0.002. Our approach offers the possibility of analyzing infrared bands from tiniest particles and thus paves the way toward SEIRA-based devices that can sense ultrafine dust.
关键词： SEIRA,chemical identification,ultrafine particles,plasmonics,bowtie nanoapertures,surface-enhanced infrared absorption
更新于2025-09-23 15:22:29
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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