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Active control of chiral optical near fields on a single metal nanorod
摘要： Chiral optical fields (typified by circularly polarized light) localized on the nanoscale enhance the chiral light-matter interaction, which may provide novel potential applications. This property enables the development of an ultrasensitive method for characterization of chiral molecules and nanoscale magnetic control realized by an all-optical method to interconnect spintronic nano-optical devices. A local chiral light source with switchable handedness or controllable chirality is indispensable for building such applications for practical use. In the current major method used for local chiral light generation, the handedness of the light is controlled by the handedness of the nanomaterial, which is not convenient when we need to change the handedness of the light. We experimentally achieve here generation and active control of a highly chiral local optical field by using a combination of an achiral gold nanorod and achiral linearly polarized optical field. By tilting the azimuth angle for the incident linear polarization relative to the axis of the nanorod, either left- or right-handed circularly polarized local optical fields can be generated. Our work may give us a chance to pioneer analytical applications of chiral optical fields and novel spintronic nano-optical devices.
关键词： near-field optics,chiral plasmonics,scanning near-field optical microscope,nanomaterial,polarimetry
更新于2025-09-19 17:15:36
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Uniqueness and Direct Imaging Method for Inverse Scattering by Locally Rough Surfaces with Phaseless Near-Field Data
摘要： This paper is concerned with inverse scattering of plane waves by a locally perturbed infinite plane (which is called a locally rough surface) with the modulus of the total-field data (also called the phaseless near-field data) at a fixed frequency in two dimensions. We consider the case where a Dirichlet boundary condition is imposed on the locally rough surface. This problem models inverse scattering of plane acoustic waves by a one-dimensional sound-soft, locally rough surface; it also models inverse scattering of plane electromagnetic waves by a locally perturbed, perfectly reflecting, infinite plane in the transverse electric polarization case. We prove that the locally rough surface is uniquely determined by the phaseless near-field data generated by a countably infinite number of plane waves and measured on an open domain above the locally rough surface. Further, a direct imaging method is proposed to reconstruct the locally rough surface from the phaseless near-field data generated by plane waves and measured on the upper part of the circle with a sufficiently large radius. Theoretical analysis of the imaging algorithm is derived by making use of properties of the scattering solution and results from the theory of oscillatory integrals (especially the method of stationary phase). Moreover, as a by-product of the theoretical analysis, a similar direct imaging method with full far-field data is also proposed to reconstruct the locally rough surface. Finally, numerical experiments are carried out to demonstrate that the imaging algorithms with phaseless near-field data and full far-field data are fast, accurate, and very robust with respect to noise in the data.
关键词： Dirichlet boundary condition,phaseless near-field data,inverse scattering,full far-field data,locally rough surface
更新于2025-09-19 17:15:36
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Imaging Carrier Inhomogeneities in Ambipolar Tellurene Field Effect Transistors
摘要： Developing van der Waals (vdW) homojunction devices requires materials with narrow bandgaps and simultaneously high hole and electron mobilities for bipolar transport, as well as methods to image and study spatial variations in carrier type and associated conductivity with nanometer spatial resolution. Here we demonstrate the general capability of near-field scanning microwave microscopy (SMM) to image and study the local carrier type and associated conductivity in operando by studying ambipolar field effect transistors (FETs) of the 1D vdW material tellurium in 2D form. To quantitatively understand electronic variations across the device, we produce nanometer resolved maps of the local carrier equivalence backgate voltage. We show that the global device conductivity minimum determined from transport measurements does not arise from uniform carrier neutrality, but rather from the continued coexistence of p-type regions at the device edge and n-type regions in the interior of our micron-scale devices. This work both underscores and addresses the need to image and understand spatial variations in the electronic properties of nanoscale devices.
关键词： 2D Materials,Field-Effect Transistor,Microwave,Near-Field Microscopy,Atomic Force Microscope
更新于2025-09-19 17:15:36
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Effects of near-field electromagnetic coupling in dimers of nanoparticles with a silver core and a J-aggregate dye shell
摘要： We report a theoretical study of the plasmon – exciton coupling effect on the absorption spectra of pairs of closely spaced double-layer hybrid nanoparticles consisting of a metallic core and a J-aggregate dye shell. The effect of frequency conversion of plasmonic lines due to the near-field interaction between plasmons and Frenkel excitons of the organic shell is demonstrated. The effect leads to the appearance of additional spectral lines in the long-wavelength part of the spectrum of the system of hybrid particles. The shapes and the relative intensities of the additional lines exactly reproduce the specific features of the original spectrum of plasmonic absorption bands in uncoated metallic nanoparticles. The discovered phenomenon can be used to design new types of high-sensitivity nanosensors, based on plasmon – exciton effects and principles of near-field optics.
关键词： near-field electromagnetic coupling,nanophotonics,Frenkel excitons,dimers of metalorganic nanoparticles,plasmon – exciton interaction,molecular J-aggregates,localised plasmons,absorption spectra
更新于2025-09-19 17:15:36
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Near-field infrared investigations of an arm-terminated spiral structure with bow-tie probe
摘要： A detailed analysis of micro- and nanoantennas is crucial for enhancing the performance of photodetectors in the mid- and far-infrared (IR) region. In contrast to the rapid progress in IR detectors based on nanodevices, the local nanoscale properties of antennas for the purpose of near-field coupling with these detectors have not been well investigated. In this work, we fabricated and studied a logarithm-spiral (log-spiral) antenna with an arm termination, which was designed as a low-loss, wide-band antenna for highly efficient near-field interaction with nanoscale IR detectors. By using a scattering-type near-field optical microscope (s-SNOM) combined with a highly stable quantum cascade laser, we observed a nanoscale spatial distribution of amplitudes generated via IR illumination on the antenna surface. Experimental and simulated results revealed a clear dependence on IR-light polarization corresponding to the rotationally symmetric structure of the spiral antenna. Furthermore, phase mapping measurements indicated a π reversal of the out-of-plane phase between two adjacent antenna probes regardless of polarization direction, providing a possibility of efficient near-field coupling with nanoscale detectors. These results demonstrate that s-SNOM imaging offers a powerful tool for gaining useful information regarding mutual coupling between optical antennas and nanostructures.
关键词： scanning near-field optical microscopy,optical phase,infrared
更新于2025-09-19 17:15:36
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Electrical Properties of a ZTO Thin-Film Transistor Prepared with Near-Field Electrohydrodynamic Jet Spraying
摘要： Zinc-tin oxide (ZTO) thin-films were prepared by applying a near-field around the tip of electro-hydrodynamic (EHD) jet spray system and characterized. Oval shaped multi droplets were obtained by the near-field assisted EHD (NF-EHD) jet spray. The optimized condition of an approximately 2.5 to 3 volts difference between the tip and near-field enabled the oxide semiconductor solution to spray properly. The electrical properties of ZTO thin-film transistor showed a mobility of 2.96 cm2/Vs, an on-to-off ratio of 107, a threshold voltage of 4.40 V, a subthreshold slope of 0.54 V/dec, and. Improved stability under bias stress and relaxation after stress were observed after applying a near-field to the EHD jet spray system.
关键词： Oxide TFT,Electrohydrodynamic Jet,Near-field,Spray,Electrical Properties
更新于2025-09-19 17:15:36
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Anisotropic Flow Control and Gate Modulation of Hybrid Phonon-Polaritons
摘要： Light-matter interaction in two-dimensional photonic materials allows for confinement and manipulation of free-space radiation in sub-wavelength scales. Most notably, the van der Waals heterostructure comprising graphene (G) and hexagonal Boron Nitride (hBN) provides for gate-tunable hybrid hyperbolic plasmon phonon-polaritons (HP3). Here, we present anisotropic flow control and gate voltage modulation of HP3 modes in G-hBN lying on air-Au microstructured substrate. Using broadband infrared synchrotron radiation coupled to a scattering-type near-field optical microscope, we launch HP3 waves in both hBN Reststrahlen bands and observe directional propagation across in-plane heterointerfaces created at the air-Au junction. HP3 hybridization is modulated by varying the gate voltage between graphene and Au. In this case, we induce modifications to the coupling of continuum graphene plasmons with the discrete hBN hyperbolic phonon polaritons, which is interpreted as an extended Fano model. This is the first demonstration of control of polariton propagation, including a theoretical approach for a break of the reflection/transmission symmetry for HP3 modes. Our findings augment the degree of control of polaritons in G-hBN and related hyperbolic metamaterial nanostructures bringing novel insights to on-chip nano-optics communication and computing.
关键词： polaritonics,nano-photonics,graphene/boron nitride,near-field optics,hybrid polaritons,synchrotron infrared
更新于2025-09-19 17:15:36
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Metal-graphene hybrid active chiral metasurfaces for dynamic terahertz wavefront modulation and near field imaging
摘要： Chiral metasurfaces can achieve giant chiral optical responses and have been expanded from the optical band to other electromagnetic bands. Here, we propose a new method for dynamic terahertz circular dichroism (CD) manipulation in metasurfaces. By introducing a patterned and electrically doped graphene into the metamirror consists of double layer C-shaped split ring resonators (SRRs), efficient terahertz CD modulation is observed. Since the electrical doping of graphene changes the absorption loss of the metasuface cavity, the structure shows switching between a chiral metasurface and an ordinary metal mirror, which can be seen as "on" and "off" states. The calculation results show an efficient modulation of the terahertz CD in a large dynamic range. In addition, we also use the new method to design two metasurfaces for dynamic terahertz wavefront modulation and near-field digital imaging, both of which show a high-performance electrical switching. This method provides a new way for the design of active terahertz devices based on metasurfaces, and also promotes the applications of terahertz chiral metasurfaces in high-speed wireless communication and dynamic imaging.
关键词： Chiral metasurfaces,terahertz,circular dichroism,near-field imaging,graphene,wavefront modulation
更新于2025-09-19 17:13:59
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[IEEE ESSDERC 2019 - 49th European Solid-State Device Research Conference (ESSDERC) - Cracow, Poland (2019.9.23-2019.9.26)] ESSDERC 2019 - 49th European Solid-State Device Research Conference (ESSDERC) - Suspended Antenna-Coupled Nanothermocouple Array for Long-Wave Infrared Detection
摘要： Heat-assisted magnetic recording (HAMR) allows for data writing in hard disks beyond 1 Tb/in2 areal density, by temporarily heating the area of a single bit to its Curie temperature. The metallic optical antenna or near-field transducer (NFT), used to apply the nanoscale heating to the media, may self-heat by several hundreds of degrees. With the NFT reaching such extreme temperatures, demonstrations of HAMR technology experience write-head lifetimes that are orders of magnitude less than that required for a commercial product. Hence, heating of the NFT is of upmost importance. In this paper, we first derive fundamental limits on the temperature ratio NFT/Media to drive NFT design choices for low-temperature operation. Next, we employ inverse electromagnetic design software, which solves for unexpected geometries of the NFT and waveguide. We present computationally generated designs for the waveguide feeding the NFT that offer a 50% reduction in NFT self-heating (～220 °C) compared with typical industry designs.
关键词： optical antenna,Adjoint method,computational electromagnetics,heat-assisted magnetic recording,near-field transducer (NFT),management,thermal,nanophotonics,plasmonics,gradient methods,inverse problem,optimization,hard disks
更新于2025-09-19 17:13:59
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Diffractive dipolar coupling in non-Bravais plasmonic lattices
摘要： Honeycomb plasmonic lattices are paradigmatic examples of non-Bravais lattices. We experimentally measure surface lattice resonances in effectively free-standing honeycomb lattices composed of silver nanospheres. By combining numerical simulations with analytical methods, we analyze the dispersion relation and the near-field properties of these modes along high symmetry trajectories. We find that our results can be interpreted in terms of dipole-only interactions between the two non-equivalent triangular sublattices, which naturally lead to an asymmetric near-field distribution around the nanospheres. We generalize the interaction between the two sublattices to the case of variable adjacent interparticle distance within the unit cell, highlighting symmetry changes and diffraction degeneracy lifting associated to the transition between Bravais and non-Bravais lattices.
关键词： honeycomb plasmonic lattices,surface lattice resonances,non-Bravais lattices,diffraction degeneracy lifting,silver nanospheres,near-field properties,dipole-only interactions
更新于2025-09-19 17:13:59