Refractive Index Of Substrate Research Articles

Enhancing silicon solar cell efficiency with double layer antireflection coating

Antireection coating on silicon, a high refractive index substrate, was theoretically investigated. The effects of antireection coating on electrical parameters such as the short circuit current, open circuit voltage, maximum current density, maximum voltage, maximum power, power density, and conversion efficiency of the solar cell were simulated. Various previous works in which solar cell efficiencies were investigated after applying double layer antireection coating (DLARC) were reviewed. Ti 2 O 3 and MgF 2 were then applied in a DLARC design, taking into consideration the refractive index dispersion of the two materials. The results were compared with other works in the solar spectral range (400{1200 nm). As a result of simulation, the reectance on the surface was reduced from 30.2% to 2.37%. Moreover, about 22% conversion efficiency and 38.6 mA/ cm 2 short circuit current density were achieved for a silicon cell with DLARC. These results were compared with the parameters of a cell without coating, one with single layer coating, and one with zero reectance on the front surface.

Plasmonic Band Gap: Role of the Slit Width in 1D Metallic Grating on Higher Refractive Index Substrate

This paper reports the excitation of surface plasmon polaritons (SPPs) and associated plasmonic band gap (PBG) while using TM plane wave interacting with 1D metallic grating on higher refractive index GaP substrate. A simple method is introduced to estimate the PBG which is crucial for many plasmonic devices. The PBG is estimated by measuring the transmission spectra obtained through the plasmonic grating structures when slit width is varied while periodicity and the thickness of the gold (Au) film remained fixed. The PBG is observed for the grating devices whose slit width is less than one third of the periodicity which is caused by the presence of a higher plasmonic mode. The PBG is absent for the grating device whose slit width is slightly less than half and greater than one third of the periodicity. Such grating devices support only a fundamental plasmonic mode because the profile/shape of the slit in the grating device is more like a sinusoidal nature. Furthermore, such grating offers intermediate scattering to the incident light and the SPP as well which in turn couple more incident energy to the SPPs. Far-field modelling results also support the results obtained through experiment.

Role of dielectric film in metal grating for improved polarized transmittance in 0.9–1.7 µm range

It is found that the TM light transmittance and polarized extinction ratio in the near infrared range (0.9–1.7 µm) can be greatly increased by incorporating a dielectric layer between metal gratings (MGs) and high refractive index substrate (InP). The role of the dielectric layer and the physical mechanism of the polarized transmittance improvement are elucidated based on numerical simulation. Besides anti-reflection role as it is known to all, the incorporated dielectric layer is found eliminating energy losses from the Rayleigh anomalies and surface plasmon (SP)-cavity mode between adjacent metal grids. By optimizing the refractive index and thickness of the dielectric layer, it is demonstrated that the TM transmittance at the central wavelength (1.3 µm) can reach above 95% for Au MG with the period as large as 400 nm.

Propagation length of surface plasmon polaritons excited by a 1D plasmonic grating

The propagation length of surface plasmon polaritons (SPPs) is investigated experimentally using a 1D metallic grating fabricated on a higher refractive index substrate (Gallium Phosphide, GaP). The experimentally measured value propagation length of the SPP (LSPP) at 785 nm wavelength is 13.33 ± 0.13 μm, which is close to the theoretical value of the LSPP on an ideal Au-thin film. The SPP resonance observed in far-field measurements confirms the underlying process and the related effects on the LSPP measured by scanning near field optical microscope (SNOM). Far-field measurements shows that LSPP is associated with the full width at half maximum (FWHM) of the SPP resonance which in-turn associated with in-plane directional scattering of the SPP.

Quasi-guiding Modes in Microfibers on a High Refractive Index Substrate

Light confinement and amplification in micro- and nanofibers have been intensively studied, and a number of applications have been developed. However, typical micro- and nanofibers are usually free-standing or positioned on a substrate with lower refractive index to ensure the light confinement and guiding mode. Here we numerically and experimentally demonstrate the possibility of confining light within a microfiber on a high refractive index substrate. In contrast to the strong leakage to the substrate, we found that the radiation loss was dependent on the radius of the microfiber and the refractive index contrast. Consequently, quasi-guiding modes could be formed and the light could propagate and be amplified in such systems. By fabricating a tapered silica fiber and dye-doped polymer fiber and placing them on sapphire substrates, the light propagation, amplification, and consequent laser behaviors have been experimentally studied to verify the quasi-guiding modes in a microfiber on a higher index subst...

Theory of Kerr and Faraday rotations and linear dichroism in Topological Weyl Semimetals.

We consider the electromagnetic response of a topological Weyl semimetal (TWS) with a pair of Weyl nodes in the bulk and corresponding Fermi arcs in the surface Brillouin zone. We compute the frequency-dependent complex conductivities σαβ(ω) and also take into account the modification of Maxwell equations by the topological θ-term to obtain the Kerr and Faraday rotations in a variety of geometries. For TWS films thinner than the wavelength, the Kerr and Faraday rotations, determined by the separation between Weyl nodes, are significantly larger than in topological insulators. In thicker films, the Kerr and Faraday angles can be enhanced by choice of film thickness and substrate refractive index. We show that, for radiation incident on a surface with Fermi arcs, there is no Kerr or Faraday rotation but the electric field develops a longitudinal component inside the TWS, and there is linear dichroism signal. Our results have implications for probing the TWS phase in various experimental systems.

Plasmonic Spectroscopy: The Electromagnetic Field Strength and its Distribution Determine the Sensitivity Factor of Face-to-Face Ag Nanocube Dimers in Solution and on a Substrate

Using the DDA method, the spectral sensitivity of a 42 nm Ag nanocube dimer oriented face-to-face in solution and placed on a substrate was investigated. The sensitivity factor was calculated as a function of both the plasmonic band that was analyzed and the refractive index of the substrate. We found that the maximum value of the electromagnetic field intensity of a given plasmonic band is not directly proportional to its extinction intensity. Also, the sensitivity factor of a plasmonic band does not depend on its extinction intensity, but rather, it is a function of the maximum value of the plasmonic electromagnetic field intensity distribution. The presence of a high refractive index substrate drastically affects the extinction intensity of a given band and selectively enhances specific plasmonic bands on the basis of their electromagnetic field distribution. The distribution of the electromagnetic field intensity on the surface of the Ag nanocube dimer is also affected by the presence of a substrate w...

Substrate-free layer-number identification of two-dimensional materials: A case of Mo0.5W0.5S2 alloy

Any of two or more two-dimensional (2D) materials with similar properties can be alloyed into a new layered material, namely, 2D alloy. Individual monolayer in 2D alloys is kept together by van der Waals interactions. The property of multilayer alloys is a function of their layer number. Here, we studied the shear (C) and layer-breathing (LB) modes of Mo0.5W0.5S2 alloy flakes and their link to the layer number. The study reveals that the disorder effect is absent in the C and LB modes of 2D alloys, and the monatomic chain model can be used to estimate the frequencies of the C and LB modes. We demonstrated how to use the frequencies of C and LB modes to identify the layer number of alloy flakes deposited on different substrates. This technique is independent of the substrate, stoichiometry, monolayer thickness, and complex refractive index of 2D materials, offering a robust and substrate-free approach for layer-number identification of ultrathin flakes of 2D materials, such as 2D crystals and 2D alloys.

Scanning Resonator Microscopy: Integrating Whispering Gallery Mode Sensing with Atomic Force Microscopy

Scanning resonator microscopy (SRM) is developed to integrate whispering gallery mode (WGM) sensing with atomic force microscopy (AFM). The hybrid technique combines the exquisite refractive index sensing of whispering gallery mode resonators with the topography mapping capabilities of AFM. A 45 μm diameter barium titanate microsphere is attached to the end of a conventional AFM cantilever and acts as both a WGM resonator and stylus for mapping surface topography. Calibration plots, taken in contact-mode feedback, show that the WGM spectrum responds to changes in both solution and substrate refractive index. SRM imaging of a glass substrate reveals changes in surface refractive index that correspond to a small, 36 nm high feature measured simultaneously in the contact-mode topography image. Spectral measurements confirm that the contrast arises from refractive index changes and not coupling with sample topography, thus validating the approach. Additional measurements on thin polymer films and protein-coated surfaces are presented and discussed in terms of possible areas of application for SRM.

Effect of Refractive Index of Substrate on Fabrication and Optical Properties of Hybrid Au-Ag Triangular Nanoparticle Arrays

In this study, the nanosphere lithography (NSL) method was used to fabricate hybrid Au-Ag triangular periodic nanoparticle arrays. The Au-Ag triangular periodic arrays were grown on different substrates, and the effect of the refractive index of substrates on fabrication and optical properties was systematically investigated. At first, the optical spectrum was simulated by the discrete dipole approximation (DDA) numerical method as a function of refractive indexes of substrates and mediums. Simulation results showed that as the substrates had the refractive indexes of 1.43 (quartz) and 1.68 (SF5 glass), the nanoparticle arrays would have better refractive index sensitivity (RIS) and figure of merit (FOM). Simulation results also showed that the peak wavelength of the extinction spectra had a red shift when the medium’s refractive index n increased. The experimental results also demonstrated that when refractive indexes of substrates were 1.43 and 1.68, the nanoparticle arrays and substrate had better adhesive ability. Meanwhile, we found the nanoparticles formed a large-scale monolayer array with the hexagonally close-packed structure. Finally, the hybrid Au-Ag triangular nanoparticle arrays were fabricated on quartz and SF5 glass substrates and their experiment extinction spectra were compared with the simulated results.

Composite dielectric metasurfaces for phase control of vector field.

We designed, fabricated, and characterized a dielectric metamaterial lens created by varying the density of subwavelength low refractive index nanoholes in a high refractive index substrate, resulting in a locally variable effective refraction index. It is shown that a constructed graded index lens can overcome diffraction effects even when the aperture/wavelength (D/λ) ratio is smaller than 40. In addition to the conventional design of a polarization insensitive lens, we also show that a polarization diversity lens (f(o)≠f(e)) can be realized by arranging nanoholes in patterns with variable density in different transverse directions. Such a anisotropic microlens demonstrates polarization dependent focal lengths of 32 and 22 μm for linearly x- and y-polarized light, respectively, operating at a wavelength of λ=1550 nm. We also show numerically and demonstrate experimentally achromatic performance of the devices operating in the wavelength range of 1500-1900 nm with full width at half-maximum (FWHM) of the focal spots of about 4 μm.

Wave transfer matrix for a spiral phase plate.

The wave transfer matrix (WTM) is applied to calculating various characteristics of a spiral phase plate (SPP) for the first time to our knowledge. This approach provides a more convenient and systematic approach to calculating properties of a multilayered SPP device. In particular, it predicts the optical wave characteristics on the input and output plane of the device when the SPP is fabricated on a substrate of the same refractive index as the SPP as well as on a substrate of a different refractive index compared to the SPP. The dependence of the parameters on the input laser frequency is studied in detail for a low finesse SPP etalon device for both cases. The equations derived from the WTM are used to show that a variation in input laser frequency causes the optical intensity pattern on the output plane to rotate, while preserving the topology of the optical vortex, i.e., the variation in laser frequency has a minimal effect on the parameters describing the azimuthal intensity modulation and orbital angular momentum content of the beam. In addition, the equations predict the presence of longitudinal modes in the SPP device.

Plasmon resonance hybridization in self-assembled copper nanoparticle clusters: efficient and precise localization of surface plasmon resonance (LSPR) sensing based on Fano resonances.

In this work, we have investigated the hybridization of plasmon resonance modes in completely copper (Cu)-based subwavelength nanoparticle clusters from simple symmetric dimers to complex asymmetric self-assembled structures. The quality of apparent bonding and antibonding plasmon resonance modes for all of the clusters has been studied, and we examined the spectral response of each one of the proposed configurations numerically using the finite-difference time domain (FDTD) method. The effect of the geometric sizes of nanoparticles used and substrate refractive index on the cross-sectional profiles of each of the studied structures has been calculated and drawn. We proved that Fano-like resonance can be formed in Cu-based heptamer clusters as in analogous noble metallic particles (e.g., Au and Ag) by determining the coupling strength and interference between sub-radiant and super-radiant resonance modes. Employing certain Cu nanodiscs in designing an octamer structure, we measured the quality of the Fano dip formation along the scattering diagram. Accurate tuning of the geometric sizes for the Cu-based octamer yields an opportunity to observe isotropic, deep, and narrow Fano minima along the scattering profile that are in comparable condition with the response of other plasmonic metallic substances. Immersing investigated final Cu-based octamer in various liquids with different refractive indices, we determined the sensing accuracy of the cluster based on the performance of the Fano dip. Plotting a linear diagram of plasmon energy differences over the refractive index variations as a figure of merit (FoM), which we have quantified as 13.25. With this method, the precision of the completely Cu-based octamer is verified numerically using the FDTD tool. This study paves the way toward the use of Cu as an efficient, low-cost, and complementary metal-oxide semiconductor (CMOS)-compatible plasmonic material with optical properties that are similar to analogous plasmonic substances.

Solution-processed organic light-emitting diodes with a power efficacy exceeding 100 lm/W using multiple light extraction approaches

Electromagnetic simulation and multiple light extraction concepts for solution-processed organic light-emitting diodes were explored in this report. Based on the optical simulation results, the device architecture was optimized for maximization of the light out-coupling efficiency. By utilizing a high refractive index substrate, a high light scattering electrode, and an external light extraction structure, trapped photons in the wave-guided and substrate modes were extracted effectively. The best solution-processed device exhibited a maximum external quantum efficiency of 42.9%, a current efficiency as high as 150.1cd/A, and a power efficacy up to 125.1lm/W.

基底折射率对金银复合纳米阵列的制备及光学性能的影响

基底折射率对金银复合纳米阵列的制备及光学性能的影响

Nano- and microlenses as concepts for enhanced performance of solar cells

Both metallic nanoparticles exhibiting plasmonic effects and dielectric nanoparticles coupling the light into resonant modes have shown successful applications to photovoltaics. On a larger scale, microconcentrator optics promise to enhance solar cell efficiency and to reduce material consumption. Here, we want to create a link between the concentrators on the nano- and on the microscale. From metallic nanospheres, we turn to dielectric ones and then look at increasing radii to approach the microscale. The lenses are investigated with respect to their interaction with light using three-dimensional simulations with the finite-element method. Resulting maps of local electric field distributions reveal the focusing behavior of the dielectric spheres. For larger lens sizes, ray tracing calculations, which give ray distributions in agreement with electric field intensities, can be applied. Calculations of back focal lengths in geometrical optics coincide with ray tracing results and allow insight into how the focal length can be tuned as a function of particle size, substrate refractive index, and the shape of the microlens. Despite the similarities we find for the nano- and the microlenses, integration into solar cells needs to be carefully adjusted, depending on the goals of material saving, concentration level, focal distance, and lens size.

Evanescent wave scattering at off-axis incidence on multiple cylinders located near a surface

The scattering characteristics of an infinite cylinder are strongly influenced by the incidence angle relative to its axis. If the incident wave propagates in the plane normal to the axis of the cylinder, the polarization of the scattered wave remains unchanged and the scattered wave propagates in the same plan as the incident wave. At off-axis incidence such that the incident direction makes an oblique angle with the cylinder axis, the scattered wave is depolarized, and its spatial distribution becomes three-dimensional. This paper presents the scattering solution for oblique incidence on multiple parallel cylinders located near a planar interface by an evanescent wave that is generated by total internal reflection of the source wave propagating in the higher refractive index substrate. Hertz potentials are utilized to formulate the interaction of inhomogeneous waves with the cylinders, scattering at the substrate interface, and near field scattering between the cylinders. Analytic formulas are derived for the electromagnetic fields and Poynting vector of scattered radiation in the near-field and their asymptotic forms in the far-field. Numerical examples are shown to illustrate scattering of evanescent wave by multiple cylinders at off-axis incidence.

Dispersion relation of a plasmonic waveguide on substrate

Dispersion relation of the surface plasmon polariton (SPP) propagating along a subwavelength gold waveguide deposited on a substrate is studied theoretically. The eigenvalues of a 1D waveguide are calculated using the finite element method combined with the method of moments in the visible-NIR regime. The dispersion curve is obtained directly by calculating the complex wavenumber versus real frequency, rather than the complex frequency versus real wavenumber. This method particularly benefits the problem with frequency-dependent material property. The shape effect (square or rectangle) of a gold nanowire and the refractive index of substrate on the propagation length, phase velocity and group velocity are investigated. Moreover, the mode profile is analyzed to evaluate the local confinement of SPP's evanescent field. In addition, the analytical solution of a circular nanowire is provided for comparison. Our results show that a plasmonic waveguide is a lowpass filter with a cutoff frequency, which decreases as the substrate's refractive index increases.

Maximum reflectance difference for incident p- and s-polarized light at air-dielectric interfaces.

New features related to the reflection of p- and s-polarized light at optically isotropic air-dielectric interfaces are determined. The intensity reflectance difference, RD = Rs - Rp, is maximum at an angle of incidence (AOI) ϕ = ϕMD in the range between the Brewster angle and grazing incidence. Both ϕMD and (Rs - Rp)max are calculated as functions of substrate refractive index n. Explicit expressions are obtained for the two angles of incidence, one below and one above the Brewster angle, at which the condition Rs = 2Rp is satisfied. Measurement of such angles enables the determination of n of transparent materials using a simple null-seeking spectroscopic ellipsometer with a ϕ-2ϕ goniometer. Finally, the AOI at which Rp'' = 0 (point of inflection in the Rp-versus-ϕ curve) is identified, and the equation that determines such an angle is also derived analytically.

47.4: Distinguished Paper: Realization of Outstandingly High Efficacy White OLED by Controlling Evanescent Mode and Wide Angular Incident Light

AbstractOptimization of angular light distribution in organic layer and light extraction structure based on high refractive index substrate were investigated. Due to advanced optical design for decreasing waveguide and evanescent modes, white OLED device with outstandingly high efficacy of 133 lm/W at 1,000 cd/m2 was realized.