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Optical Properties of Bowtie-Type Nanoantennas Integrated Onto a Silicon Waveguide Platform
摘要： In this paper, we provide a detailed three-dimensional numerical analysis of the optical properties of common and modified bowtie aperture antennas integrated onto a silicon waveguide platform, to discuss the influence of geometrical parameters on the electric field enhancement factor and waveguide transmission when such antennas are excited by the evanescent field of the Si waveguide mode. We demonstrate that waveguide transmission is severely affected by the interference between Si waveguide modes and surface plasmon polariton modes excited in the antenna, while the antenna’s field enhancement factor is mainly determined by the localized surface plasmon resonance occurring in its nano-gap. These mechanisms lead to a mismatch between the wavelength at which the antenna’s field enhancement factor is maximized, and the wavelength at which transmission through the Si waveguide is minimized, suggesting that in some multi-mode cases, the optical properties of integrated nanoantennas determined through direct measurement of Si waveguide transmission may be misleading. Methods for improving the electric field enhancement (such that it has a bigger modulation depth) that have minimal impact on the resonant wavelength, and for improving the shape and location of the corresponding hot spot of the bowtie aperture antennas, are also discussed and analyzed. We believe that this analysis will be helpful in design of on-chip bowtie-type optical antennas for surface enhanced Raman spectroscopy, near-field optical microscopy, high sensitivity detection, and plasmonic optical tweezers.
关键词： Bowtie aperture antenna,Transmission,Silicon waveguide platform,Electric field enhancement
更新于2025-09-11 14:15:04
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European Microscopy Congress 2016: Proceedings || Can transverse plasmonic fields be revealed by differential phase contrast?
摘要： Surface plasmons give rise to a wide range of applications from molecular sensors [1] over novel circuit designs [2] to the design of meta-materials with highly unusual optical properties [3]. Of particular importance are localized surface plasmons (LSPs) that are confined to the surface of nanoparticles as they can give rise to a significant enhancement of electromagnetic fields in the vicinity of the nanostructure. Because LSPs typically are confined to the nanometer regime, TEM is ideally suited for mapping those charge oscillations. So far, the predominant method of studying plasmon oscillations has been EELS, which allows mapping the strength of selected resonance modes by measuring the energy loss probability of the probe beam for different LSP energies. In a non-relativistic approximation, this energy loss is brought about by the component of the electric field along the optical axis (and, in principle, the magnetic component perpendicular to the optical axis) of the excited plasmon resonance. Thus, it is impossible to gain any information about the electric field in the viewing plane (i.e., perpendicular to the optical axis). Precisely this component can, however, be studied using differential phase contrast (DPC) [4,5]. DPC exploits the fact that electrons subject to an electromagnetic field are deflected according to the Lorentz force. Any deflection along the optical axis gives rise to a change in kinetic energy and, hence, shows up in EELS. Any deflection perpendicular to the optical axis, however, changes the direction of the electron's momentum, but not its magnitude (in first order approximation). This gives rise to a shift in the electron's momentum distribution. The final momentum distribution, after passing the nanostructure, can then conveniently be measured in the TEM's diffraction plane. Compared to a reference measured without field, the displacement of the transmitted beam shows a shift that is proportional to the field integrated along the electron trajectory. Here, we used the MNPBEM toolbox [6,7] to simulate the plasmonic response of a 200x50x50 nm3 Ag nanorod to the electron beam (see fig. 1). From the data of the surface charges and currents, we then calculated the EELS maps (see fig. 1) and in-plane deflections along a line parallel to the nanorod (see fig. 2) for different plasmonic modes. The EELS maps show the typical excitation probabilities for the first two modes with two and three maxima. The in-plane electric field components show a similar behavior in general, although the local extrema are less pronounced. The DPC deflections are found to be in good agreement with the electric field with some small differences close to the center of the rod which can be attributed to the cumulative nature of the DPC deflections as well as retardation effects. The absolute magnitude of the DPC deflections in fig. 2 is of the order of 0.1 μrad at 300 keV which, albeit small, should be measurable with latest generation TEMs when using large camera lengths and/or the LACBED technique. In addition, the deflections can be increased, e.g., by using a lower acceleration voltage. This work shows that it should be feasible to determine all three components of the electromagnetic field caused by plasmons using a combination of DPC and EELS using state-of-the-art TEMs. This will open up new possibilities for understanding and designing novel plasmonic devices.
关键词： DPC,electric field,EELS,surface plasmon
更新于2025-09-11 14:15:04
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Interface-controlled band alignment transition and optical properties of Janus MoSSe/GaN vdW heterobilayers
摘要： Here, based on first-principles calculations, we construct theoretically two-dimensionally (2D) Janus MoSSe/GaN van der Waals (vdW) heterobilayers, and demonstrate that it has direct band structures and staggered type-II band alignments, and the gap values are modified. Moreover, the interlayer coupling and electronic field effects on electronic structures depend on interface characteristics in Janus MoSSe/GaN heterobilayers. The studies provide the idea to modify the electronic characteristics using interface characteristics in the 2D materials-based vdW heterostructures.
关键词： electric field,optical properties,van der Waals heterobilayers,interface characteristics
更新于2025-09-11 14:15:04
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Coupled Plasmon Oscillations in a Cluster Consisting of Three Silver Nanocylinders with Different Diameters
摘要： 2D problem of the diffraction of the TM plane electromagnetic wave by a cluster consisting of three self-similar silver nanocylinders with different sizes is considered. Rigorous numerical procedures are used to study quasi-static plasmon resonances in such a cluster. Frequency characteristics of the scattering cross section and spatial structure of the field in the vicinity of the cylinders are calculated for different angles of incidence of the plane wave, self-similarity coefficients, and diameters of cylinders. It is shown that an increase in the distance between the cylinders is accompanied by degeneration of the resonances of scattering cross section. When real loss of silver is taken into account, electric field at the exit of the cluster cannot be amplified by a factor of greater than 10.
关键词： plasmon resonances,electric field amplification,diffraction,silver nanocylinders,TM plane electromagnetic wave,scattering cross section
更新于2025-09-11 14:15:04
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Enhancement of ablation rate and production of colloidal nanoparticles by irradiation of metals with nanosecond pulsed laser in presence of external electric field
摘要： This paper presents the results of experimental study on the effect of electric field on the ablation rate during the nanosecond pulsed laser ablation of aluminum and copper in deionized water. The effect of electric field strength on the material removal rate and its mechanisms were investigated both in the electric field parallel and perpendicular to the laser beam path schemes. The ablation rate was estimated by measuring the dimensions of craters on the target induced by laser. The crater dimensions and optical properties of the produced colloidal nanoparticles were characterized by means of optical microscopy and UV–Vis absorption spectroscopy, respectively. The results indicate that pulsed laser ablation in the presence of an electric field significantly leads to higher material removal rate. The experimental results also confirm that the crater geometry extremely depends on the direction of the electric field with respect to the laser beam direction. The UV–Vis spectra show that the nanoparticles production efficiency increases with increasing the electric field strength.
关键词： Electric field,Colloidal nanoparticles,Laser ablation efficiency,Ablation rate
更新于2025-09-11 14:15:04
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Electro-optic sensor for static fields
摘要： A sensor has been developed for low frequency and DC electric fields E. The device is capable of measuring fields with ??E = 4 (1) V/cm resolution. It is based on a Y-cut Z-propagation lithium niobate electro-optic crystal. For a particular commercially available bare crystal, we achieved an in air time constant ?? c(air) =6.4(1.8) h for the decay of the electro-optic signal. This enables field monitoring for several hours. As an application, we demonstrated that a constant electric field Eext = 640 V/cm applied via external electrodes to a particular spherical glass container holding an Xe/He gas mixture decays inside this cell with a time constant ??glass E = 2.5(5) h. This is sufficient for the needs of experiments searching for a permanent electric dipole moment in Xe. An integrated electric field sensor has been constructed which is coupled to a light source and light detectors via optical fibers. The sensor head does not contain any electrically conducting material.
关键词： Electric field monitoring,Static fields,Electro-optic sensor,Lithium niobate
更新于2025-09-11 14:15:04
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Study of charge injection in Ortho-, Meta- and Para-NKX-2553 in Dye-Sensitized Solar Cells: A theoretical approach
摘要： Dye sensitizers due to their significant role in the efficiency of Dye-Sensitized Solar Cells (DSSCs) have become the focal center of interest in recent years. In this study, NKX-2553 as one of the appealing metal-free organic dyes in different configurations of Ortho, Meta, and Para has been investigated. Parameters such as geometries, electronic structures, and optical properties, along with dipole moment, polarizability and first-order hyperpolarizability were calculated using density functional theory (DFT) and time-dependent DFT (TD-DFT). Results show that the Para-NKX-2553 is the best configuration in respect of increasing the charge injection in DSSCs. Moreover, according to our study, the efficiency of DSSCs can be improved through applying an external electric field in an appropriate direction.
关键词： Electric field,Charge injection,DFT,TD-DFT,Dye-sensitized solar cells,Electronic structure
更新于2025-09-11 14:15:04
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Mode resolved heating dynamics in pulsed microwave CO<sub>2</sub> plasma from laser Raman scattering
摘要： Efficient CO2 reduction is predicted for CO2 microwave plasma by virtue of predominant excitation of the asymmetric stretch vibration. Although interpretation of ongoing research is generally based on this mechanism, direct measurement of the power partitioning to support the assumed preferential vibrational excitation in CO2 microwave plasma is currently lacking. Here, such measurements are performed on a 100 μs pulsed microwave CO2 discharge. The <1% duty cycle ensures low gas temperature conditions at the discharge onset. Raman and Rayleigh scattering are employed to reveal vibrational, rotational, and gas temperatures in a spatially and temporally resolved manner. A novelty in the approach is that asymmetric stretch excitation is determined from the bending – symmetric stretch Raman spectrum. During the first 40 μs a significant inter-vibrational non-equilibrium is observed with the symmetric stretch and bending temperature reaching 750 K and the asymmetric stretch temperature reaching 1150 K. A maximum rotational-vibrational non-equilibrium occurs after 60 μs when the rotational temperature is half of the 1150 K vibrational temperature. Rotational and translational modes are measured to be in equilibrium at all times. The power partitioning is analyzed to estimate the power consumed by vibrational excitation, which is used to estimate the reduced electric field in the discharge. This work confirms strong vibrational excitation in CO2 microwave plasma albeit less predominant than often assumed.
关键词： Raman scattering,vibrational excitation,reduced electric field,power partitioning,CO2 microwave plasma
更新于2025-09-11 14:15:04
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Electric-Field-Controllable Conductance Switching of an Overcrowded Ethylene Self-Assembled Monolayer
摘要： Molecular isomerism has been discussed from the viewpoint of tiniest switch and memory elements in electronics. Here, we report an overcrowded ethylene-based molecular conductance switch, which fulfills all the essential requirements for implementation onto electronic devices, namely, electric-field-controllable reversible conductance change with a molecular-level spatial resolution, robust conformational bistability under ambient conditions, and ordered monolayer formation on electrode surfaces. The conformational state of this overcrowded ethylene, represented by a folded or twisted conformer, is susceptible to external environments. Nanoscopic measurements using scanning tunneling microscopy techniques, together with theoretical simulations, revealed the electronic properties of each conformer adsorbed on Au(111). While the twisted conformer prevails in the molecularly dispersed state, upon self-assembly into a monolayer, a two-dimensional network structure of the folded conformer is preferentially formed due to particular intermolecular interaction. In the monolayer state, folded-to-twisted and its reverse isomerization can be controlled by the modulation of electric fields.
关键词： overcrowded ethylene,molecular conductance switch,scanning tunneling microscopy,electric-field control,self-assembled monolayer
更新于2025-09-11 14:15:04
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Elasto-electric coupling for direct electric field distribution measurement in semiconductor structures
摘要： Semiconductor materials are widely used in electronic industry, but their electrical characterization remains complex to estimate without a good model. It has already been shown that an elasto-electric coupling can be used to directly and non-destructively probe the electrical properties at the external interfaces of semi-conductor structures. In this paper, it is shown that such a coupling can also be used to probe the inner interfaces of semi-conductor structures. This capability is demonstrated by using a specific semi-conductor structure including a buried silicon p-n junction 720 lm away from the external electrodes. The signal generated by the elasto-electric coupling clearly shows separately the electric field at the electrodes and at the buried junction. The contact potential at the buried junction estimated from the measurements is in accordance with the semiconductor doping. This makes it possible to use an elasto-electric coupling for the complete characterization of semiconductor structures.
关键词： Pressure-Wave-Propagation method,elasto-electric coupling,semiconductor structures,p-n junction,electric field distribution
更新于2025-09-10 09:29:36