Electric Field Of Incident Light Research Articles

Novel nano-plasmonic sensing platform based on vertical conductive bridge

A novel nano-plasmonic sensing platform based on vertical conductive bridge was suggested as an alternative geometry for taking full advantages of unique properties of conductive junction while substantially alleviating burdens in lithographic process. The effects of various geometrical parameters on the plasmonic properties were systematically investigated. Theoretical simulation on this structure demonstrates that the presence of vertical conductive bridge with smaller diameter sandwiched between two adjacent thin nanodiscs excites a bridged mode very similar to the charge transfer plasmon and exhibits a remarkable enhancement in the extinction efficiency and the sensitivity when the electric field of incident light is parallel to the conductive bridge. Furthermore, for the electric field perpendicular to the bridge, another interesting feature is observed that two magnetic resonance modes are excited symmetrically through open-gaps on both sides of the bridge together with strongly enhanced electric field intensity, which provides a very favorable environment as a surface enhanced Raman scattering substrate for fluid analysis. These results verify a great potential and versatility of our approach for use as a nanoplasmonic sensing platform. In addition, we demonstrated the feasibility of fabrication process of vertical conductive bridge and high tunability in controlling the bridge width.

Modified Drude model for small gold nanoparticles surface plasmon resonance based on the role of classical confinement

In this paper, we study the effect of restoration force caused by the limited size of a small metallic nanoparticle (MNP) on its linear response to the electric field of incident light. In a semi-classical phenomenological Drude-like model for small MNP, we consider restoration force caused by the displacement of conduction electrons with respect to the ionic positive background taking into account a free coefficient as a function of diameter of nanoparticle (NP) in the force term obtained by the idealistic Thomson model in order to adjust the classical approach. All important mechanisms of the energy dissipation such as electron-electron, electron-phonon and electron-NP surface scatterings and radiation are included in the model. In addition a correction term added to the damping factor of mentioned mechanisms in order to rectify the deficiencies of theoretical approaches. For determining the free parameters of model, the experimental data of extinction cross section of gold NPs with different sizes doped in the glass host medium are used and a good agreement between experimental data and results of our model is observed. It is shown that by decreasing the diameter of NP, the restoration force becomes larger and classical confinement effect becomes more dominant in the interaction. According to experimental data, the best fitted parameter for the coefficient of restoration force is a third order negative powers function of diameter. The fitted function for the correction damping factor is proportional to the inverse squared wavelength and third order power series of NP diameter. Based on the model parameters, the real and imaginary parts of permittivity for different sizes of gold NPs are presented and it is seen that the imaginary part is more sensitive to the diameter variations. Increase in the NP diameter causes increase in the real part of permittivity (which is negative) and decrease in the imaginary part.

Generalized Pareto distribution function for Au colloidal systems

The Raman signal can be enhanced by the SERS (Surface-Enhanced Raman Scattering) technique that uses metallic nanoparticle (NP) colloids to intensify the electric field of incident light. In this work we explore from a theoretical point of view, through simulation, the behavior of the distribution of the intensification factor (F) on the surface of Au spherical NPs formed by different aggregates (dimers and trimeros) and mixtures thereof, which can be described by the Pareto distribution function.

Discrete dipole approximation for calculating optical properties of ZnO nanoparticles and ZnO-PVP composites

Discrete dipole approximation (DDA) is a well-known method which is generally used to simulate the interaction of nanoparticles with the electric field of incident light. In this paper, DDA has been used to simulate different optical properties (absorption efficiency factor, scattering efficiency factor, extinction efficiency factor, phase lag efficiency factor and 3D near electric field) of ZnO nanoparticles (NPs) and ZnO-PVP composite. The particle sizes are varied and size corrected complex dielectric function of ZnO and its composite have been used as inputs of the simulation. The particle sizes of ZnO NPs and ZnO-PVP composites have been varied from 22 nm to 38 nm in simulation. The peak position of absorption efficiency factor matches perfectly with the experimental absorbance when the size of ZnO NPs is taken as 26 nm. The same phenomenon happens in case of ZnO-PVP composite when the size of composite NPs is considered as 28 nm. The particle within dielectric medium acts as particle with higher effective radius as the near electric field increases due to presence of local dielectric medium. We have also calculated other optical parameters of ZnO NPs and ZnO-PVP composites. Small but not negligible changes in optical properties are observed due to incorporation of PVP with ZnO nanoparticles.

Laser-induced dewetting of silver-doped chalcogenide glasses

We report the observation of laser-induced dewetting responsible for the formation of periodic relief structures in silver-based chalcogenide thin-films. By varying the concentration of silver in the Agx(As20S80)100−x system (with x = 0, 4, 9 and 36), different surface relief structures are formed. The evolution of the surface changes as a function of laser parameters (power density, duration of exposure, and polarisation) as well as film thickness and silver concentration has been investigated. The scanning electron microscopy and atomic force microscopy images of irradiated spots show periodic ripples aligned perpendicularly to the electric field of incident light. Our results show that addition of silver into sulphur-rich chalcogenide thin-films improves the dewetting when compared to pure As20S80 thin-films. The changes in surface morphology were attributable to photo-induced chemical modifications and a laser-driven molecular rearrangement.

Enhanced Efficient Light Emission of Er(Yb/Y) Silicates at the Wavelength of 1.53μm with Au Plasmonic Arrays

In this paper, we present a novel method to increase photoluminescence (PL) efficiency at the wavelength of 1.53 $\mu$ m ( $\lambda =$ 1.53 $\mu$ m) by depositing Au plasmonic arrays on $\text{SiO}_\text{2}\text{/Er}\text{(Yb/Y)}$ silicates. Theoretical analysis reveals that the PL enhancement is caused by the resonant coupling of surface plasmon polaritons from photoemission in $\text{Er(Yb/Y)}$ and the electric field of incident light at the $\text{Au/SiO}_{2}$ interface. Numerical investigations show that by using the finite-difference-time-domain (FDTD) method, the change of the peak shape and bandwidth of transmission spectra at $\lambda =$ 1.53 $\mu$ m depends strongly on the arrays period ( ${a_0}$ ) and $\text{Au}$ film thickness ( ${t_{\text{Au}}}$ ). It is demonstrated that, by experiments, the plasmonic arrays of ${a_0} =$ 1082 nm and ${t_{\text{Au}}} =$ 50 nm can enhance the PL intensity two times, compared with a flat Au film, which can serve as an excellent guideline for designing and optimizing a highly efficient solid-state light source.

Orientation Control of Selected Organic Semiconductor Crystals Achieved by Monolayer Graphene Templates

Crystal orientation in organic thin films is one of the key parameters that determine absorption cross‐section, interfacial energetics and excitonic states, and free charge properties. In this work, monolayer graphene is used to direct the crystal orientation of selected planar organic molecules. Lying‐down orientation with π‐stacking normal to the surface is achieved with graphene templating. The absorption spectra of the graphene‐templated films are correlated to molecular orientation. The same set of absorption features with or without graphene suggests that no vibronic states are forbidden or newly introduced. However, the light absorption with graphene templating is enhanced due to the altered relative orientation between the transition dipole moment of the constituent molecules and the electric field of incident light. The energy level of the highest occupied molecular orbital (HOMO) of graphene templated p‐type films is observed at a deeper‐lying value (relative to vacuum) compared to untemplated diindenoperylene films grown on indium tin oxide. In contrast, the HOMO energy levels of graphene templated n‐type films are observed at higher‐lying energy levels (relative to vacuum) compared to the respective untemplated films due to surface dipoles. Such a change can potentially increase the theoretical V oc expected for photovoltaic devices incorporating these templated films.

DFT Based Theoretical Study about the Contributions of Fluorine to Nonlinear Optical Properties in Borate Fluoride Crystals

The introduction of fluorine (F) into the borate crystals is proven to be an effective approach in designing novel non-centrosymmetric crystals, which is a requirement for nonlinear optical (NLO) materials. In this contribution, the electronic structure and optical properties of borate fluoride crystals are determined by the first-principles method. First-principles calculations indicate that the key second-harmonic generation (SHG) factor is attributed not only to borate groups but also to the bonding of the F anions with cations where F coordinates to cations (Sr, Ba). The electron withdrawing effect of the F atom leads to the higher values for anisotropy of the polarizability around cation-centered polyhedra, ultimately making it easy for the external electric field of incident light to effect the dielectric susceptibility. The direct contribution of anion on the NLO properties is observed as fluorine-induced variation of electronic structure.

Synthesis and Characterization of a Plasmonic–Semiconductor Composite Containing Rationally Designed, Optically Tunable Gold Nanorod Dimers and Anatase TiO2

Herein we utilize on-wire lithography (OWL) to synthesize a composite plasmonic–semiconductor material composed of Au nanorod dimers embedded within anatase TiO2 sheets. We demonstrate that, despite the harsh conditions necessary to synthesize crystalline TiO2, the gapped nanostructures remain intact. Additionally, we show that the optical properties of these structures can be tailored via the geometric control afforded by the OWL process to produce structures with various gap sizes exhibiting different electric field intensities near the surface of the metal particles and that those fields penetrate into the semiconductor material. Finally, we show that this composite amplifies the electric field of incident light on it by a factor of 103, which is more that 750 times greater than the isotropic materials typically used for these systems.

Dependence of optical properties of monoclinic MnWO4 on the electric field of incident light

Considering the electric field of incident light along four particular directions [100], [110], [011], and [010], the optical properties of monoclinic MnWO 4 were investigated by the first-principle methods. The calculated electronic structures show that the O 2p states and Mn 3d states dominate the top of the valence bands, while the W 5d and Mn 3d states play a key role in the bottom of the conduction bands. The dielectric function and other optical properties, including absorption coefficient, reflectivity spectra, and energy-loss spectra, were calculated and analyzed. The results predicted the maximum static dielectric function when the electric field of incident light was along the [100] direction; meanwhile the absorption edge was calculated to be consistent with the energy band gap and the values and positions of peaks in absorption coefficient are related with the electric field of light. Otherwise, it is found that the appearance of peaks in the energy-loss spectra is also dependent on the electric field and simultaneously corresponds to the edge of absorption spectra and the peaks' position of reflectivity spectra.

Localized surface plasmon resonance: Nanostructures, bioassays and biosensing—A review

Localized surface plasmon resonance (LSPR) is an optical phenomena generated by light when it interacts with conductive nanoparticles (NPs) that are smaller than the incident wavelength. As in surface plasmon resonance, the electric field of incident light can be deposited to collectively excite electrons of a conduction band, with the result being coherent localized plasmon oscillations with a resonant frequency that strongly depends on the composition, size, geometry, dielectric environment and separation distance of NPs. This review serves to describe the physical theory of LSPR formation at the surface of nanostructures, and the potential for this optical technology to serve as a basis for the development bioassays and biosensing of high sensitivity. The benefits and challenges associated with various experimental designs of nanoparticles and detection systems, as well as creative approaches that have been developed to improve sensitivity and limits of detection are highlighted using examples from the literature.

Surface-enhanced Raman scattering on multilayered nanodot arrays obtained using anodic porous alumina mask

The fabrication of 3D multilayered nanodot arrays composed of metal (Au) and dielectric material (Al 2O 3) using ordered anodic porous alumina as a mask for vacuum evaporation was demonstrated. The obtained ordered multilayered dot arrays produced the accumulated nanogaps with controlled sizes, which can effectively enhance the electric field of incident light. The obtained structures with multilayered nanodots could be applied to the substrate for surface-enhanced Raman scattering (SERS) measurement, and larger SERS signals were obtained at larger numbers of multilayers and smaller gap seizes, corresponding to the effective enhancement of the electric field of incident light.

Surface plasmon-enhanced emission from Ag-coated Ce doped Y3Al5O12 thin films phosphor capped with a dielectric layer of SiO2

The effect of a surface plasmon (SP) on the yellow emission of Ce doped Y3Al5O12 (YAG:Ce) phosphor thin films was studied. The coating of YAG:Ce thin films with silver nanoislands on a 3-nm-thick SiO2 spacer significantly enhanced their photoluminescence (PL). The PL enhancement is caused by the resonant coupling of photoemission in YAG:Ce into SP and the electric field of incident light at the metal interfaces. Varying the mass thickness and the annealing condition of the Ag layer indicated that the PL intensity was highest at an Ag mass thickness of 20 nm. Therefore, yellow emission was enhanced by tuning the matching conditions of thin film phosphor-SP coupling by controlling the structure of silver nanoislands. The PL intensity can be further and remarkably enhanced by capping Ag islands with a 10-nm-thick SiO2 layer as a dielectric medium.

Surface Plasmon-Enhanced Emission from Metal-Island-Coated YAG:Ce Thin-Film Phosphor

This work experimentally verifies that surface plasmon (SP) coupling can enhance the yellow emission of Ce-doped (YAG:Ce) thin-film phosphors. The effect of SP on yellow emission from YAG:Ce thin-film phosphor coated with a metal layer is examined. Among Ag, Al, and Au materials, the emission intensity of YAG:Ce thin-film phosphor by coating a silver layer with a thickness of nanometers was significantly enhanced by 10-fold. The enormous enhancement on photoluminescence (PL) is attributable to the resonant coupling of emission in YAG:Ce with an SP and the electric field of incident light at the metal interfaces. The mass thickness and annealing conditions of the deposited layer can be varied to transform the Ag layer into an islandlike structure; the PL intensity is highest at a Ag thickness of 20 nm.

Multipole Plasmons in Metal Nanorods: Scaling Properties and Dependence on Particle Size, Shape, Orientation, and Dielectric Environment

T-matrix formalism was used to study the multipole resonances excited by electromagnetic plane waves in gold and silver nanorods whose shape was modeled by prolate spheroids and cylinders with flat or semispherical ends (s-cylinders). The particle diameters and aspect ratio were varied from 20 to 80 nm and from 2 to 20, respectively. By using extended precision T-matrix codes, we calculated the extinction, absorption, and scattering spectra for random and fixed orientations of the particle axis with respect to the incident transverse magnetic (TM) and transverse electric (TE) polarized light, where the reference plane is defined by the particle axis and the incident wave vector. We found that the parity of a given spectral resonance number n coincides with the parity of their multipole contributions l, where l is equal to or greater than n, and the total resonance magnitude is determined by the lowest multipole contribution. The random-orientation resonances are excited most effectively by the TM scattering configurations, except for the short-wavelength resonance, which equals the sum of the dominant dipole TE resonance and the other multipole contributions. The even multipole resonances are maximal at intermediate orientations, whereas the odd multipoles can effectively be excited at both perpendicular and intermediate orientations of the rod axis with respect to the TM incident wave. In particular, the quadrupole resonance can be excited only by the TM incident wave, and the resonance magnitude is maximal for orientation of the particle symmetry axis near 54° with respect to the incident light. Finally, we found that the multipole resonance wavelengths obey a universal linear scaling when plotted versus the particle aspect ratio divided by the resonance number. This remarkable property of multipole resonances can be understood in terms of a simple concept based on plasmon standing waves excited in metal nanowires by an electric field of incident light (Schider et al. Phys. Rev. B 2003, 68, 155427). The refractive index sensitivity of the multipole resonance wavelength to a dielectric environment also exhibits linear scaling properties. Specifically, the relative shift of the resonance wavelength is proportional to the relative refractive index increment with a universal angular slope coefficient.

Rotations of eigenvibration direction in anisotropic crystals

The electric field of incident light induces dipoles in anisotropic media, vibrating in two perpendicular directions of the principal axes. Because of the tensor property of the dielectric constant, an induced dipole is subject to a torque, tending to rotate it about the axis parallel to the propagation direction. The directions of eigenvibration of the ordinary (o-ray) and extraordinary (e-ray) waves are no longer perpendicular in this sense. We propose here the relationships to describe the rotation of the induced dipole in the perpendicular electric fields. The rotation angles are found to increase with increasing dielectric constants and electric field strength of the incident light, exhibiting large values near the resonance frequencies in the infrared range at the azimuth angle π/4 of the polarized incident light. Piezoelectric and ferroelectric crystals have a large value of the dielectric constant in the infrared frequency range. Rotations of the vibration direction of the o-ray and the e-ray waves are shown in the infrared transmission spectra recorded by incidence of the polarized light and transmission through piezoelectric and ferroelectric crystals (α-quartz, LiNbO3, and LiTaO3). Interference of the o-ray and the e-ray waves transmitted through the crystals confirms the rotations of the vibration directions, a self-modulation effect of light in piezoelectric and ferroelectric crystals induced by the electric field of the propagating light.

Electromagnetic response of an electron gas in one-dimensional quantum wires.

The theory of the electromagnetic response of an electron gas in quasi-one-dimensional (1D) quantum wires to a spatially modulated electric field of incident light is developed in the random-phase approximation. In a 1D electron gas in a weak magnetic field, the incident light polarized along the wire and modulated across the wire is absorbed by both single-particle and collective excitations. The coefficient of light absorption by single-particle excitations does not depend on B, while the coefficient of light absorption by plasmons is proportional to ${\mathit{B}}^{2}$. It is shown that, in the case of a parabolic confining potential of the wire, the spatial modulation of the incident light due to the diffraction at a mesa-etched structure allows observing higher plasmon modes that are otherwise forbidden.

Optical absorption spectra of single-crystal YBa2Cu3Oy films

Abstract Optical transmittance spectra of single-crystal YBa 2 Cu 3 O y thin films ( y =6.0, 6.4, 6.8) were measured in a wavenumber range of 1500–50000 cm −1 (0.2–6 eV) at room temperature. The electric field of incident light was parallel to the Cu-O planes. An absorption spectrum for each oxygen content was obtained from the transmittance spectra of two samples with different thicknesses. In YBa 2 Cu 3 O 6.0 , an energy gap at 1.5 eV and an absorption peak at 4.1 eV were observed. When the oxygen content increases, the absorption within the energy gap increases and the 4.1 eV absorption peak becomes smaller. We found that the dependence of the 4.1 eV peak intensity on the oxygen content correlates with that of the absorption within the 1.5 eV gap. Some discussion is given in connection with hole doping.