Narrow Results

Ballistic electron transport through a finite chain of quantum circular rings is studied in the presence of the Rashba coupling, of strength α, and of a perpendicular magnetic field B. The transmission and reflection coefficients for a single ring, obtained analytically, help obtain the conductance through a chain of rings as a function of the strength α, the field B, and of the wave vector k of the incident electron. Due to destructive spin interferences caused by the Rashba coupling the chain can be totally opaque for certain ranges of k the width of which depends on values of α and B. Outside these ranges the conductance oscillates with high values between e²/h and 2e²/h. The effect of a periodic modulation of α or B on the conductance gaps is investigated. A periodic, square-wave conductance pattern, pertinent to the development of the spin transistor, results within wide stripes in the parameter space spanned by k, α, and B. Finite temperatures smoothen the square-wave profile of the conductance but do not alter its periodic character.

In this paper, we systemically and numerically investigate the effects of three types of Nanoparticles on the efficiency of solar cells. Finite Difference Time Domain method has been implemented to compute the absorption spectra in such proposed solar cell structure. High efficiency has been achieved by optimizing the nanoparticles layer by tuning the fraction of nanoparticles on the host layer.

We investigate transmission and reflection properties of a broadband pulse with normal incidence on silicon-metal-silicon (SMS) for the first time, to the best of our knowledge. The results show that in lower frequency range, the transmission is close to zero, and the reflection and loss are in the range 0.50–0.90, 0.10 to 0.50, respectively. In higher frequency range, the transmission spectrum has two peaks, with transmittance 0.69, 0.90, and at same frequencies as the transmission peaks, the reflection spectrum has two troughs with reflectance 0.00, 0.02 and corresponding losses are 0.10, 0.29, respectively. This simple waveguide structure may have potential applications in silicon photonics, such as filters and laser oscillation cavities.

In this paper, we explore the application of nonlocal theory to analyze the phenomenon of coupled thermoelastic wave reflection in a semiconducting diffusive medium, considering its temperature rate dependence. The governing equations are deconstructed using the Helmholtz vector rule, allowing us to delve into the behavior of the system. By calculating the dispersion relation in terms of propagation speed, we investigate four coupled longitudinal waves alongside an independent nondispersive transverse wave within the local medium. The cut-off frequencies for each wave are discussed, shedding light on their characteristics. Furthermore, we delve into the phenomenon of coupled longitudinal displacement waves at the medium’s boundary. Analytical derivations of amplitude ratios are presented, accompanied by graphical representations of their behavior, focusing on a semiconductor material such as copper. We examine the effects of physical parameters, including the nonlocal and diffusive parameters, on the obtained results. It is important to note that the existing literature primarily lacks consideration of diffusivity and plasma transportation. Lastly, we validate our findings by investigating the conservation of energy within the system.

Oblique light propagation through a chiral photonic crystal (PC) layer with gradient parameters of modulation is considered. The problem is solved by Ambartsumian's layer addition modified method. It is shown that suppressing of diffraction oscillations near the photonic band gap (PBG) is possible at certain conditions. Thus, at certain conditions, the spectra for the finite PC layer is the same as that for the half space.

We propose a reflective acoustic metasurface by taking advantage of the synergetic coupling of two kinds of widely used elements, the resonant cavity and the labyrinthine beam. A full 2$\pi$ phase shift range can be obtained by varying the neck width. The structure manipulates the reflective waves on a very deep subwavelength scale with the thickness being only 1/50 of the wavelength, which eliminates the enormous obstacle in low frequency applications. The synergetic coupling of the resonant cavity and the inner labyrinthine beams provide a useful guide for the design of acoustic metasurfaces.

We report a graphene-based tunable ultra-narrowband mid-infrared filter which can be tuned from 4.45122 $\mu$m to 4.44675 $\mu$m by tuning the Fermi level from 0.2 eV to 0.6 eV. Furthermore, the reflection bandwidth is less than 0.2 nm and the reflection rate is more than 0.55. The ultra-narrowband filter is designed based on the guided-mode resonance (GMR) effect. The shift of reflection peak is mainly caused by the change of the real part of the graphene’s permittivity. This tunable ultra-narrowband mid-infrared filter can be applied in the mid-infrared microscopy.

In this paper, photovoltaics (PV)- or solar cells based on two types of nanoparticles have been investigated. The suggested four-layer solar cell model consists of metallic nanoparticle (Ag–Au) layers that are Si-based and covered by SiN. The transmission and reflection of the incident light on the structure model have been computed for different physical parameters of the structure. Higher transmission and lower reflections have been obtained leading to higher efficiency of the solar cells. The matrix model is used, and the numerical results obtained by MAPLE Software Program. The obtained results confirm that the nanoparticle solar cell structure can effectively enhance the efficiency of such structure model.

A complete and fully developed theory of all optical phenomena (refraction, reflection, absorption, and transparency) and the corresponding optical properties of ultrathin crystalline films (optical indices) are presented in this paper, especially along the direction in which the structure is spatially limited (perpendicular to surfaces). While these indices depend on the position of the crystallographic plane (where the mentioned optical phenomena occur) with respect to the two interfaces, these values can be measured/ determined in experiments only for the film as a whole. For these reasons, it is important to answer the question of how to define these optical indices precisely.

In this paper, we discussed the longitudinal harmonic waves reflection from a solid elastic half-space with electromagnetic and gravity fields influence, considering a fractional order via fractional exponential function method. The clarifications are required for the reflection amplitudes ratios (i.e. the ratios between the reflected waves amplitude and the incident waves amplitude). The results obtained were calculated analytically and displayed by graphs to show the physical meaning of the phenomenon. A comparison has been made between the fractional and integer derivatives. The results of this paper demonstrate the rigor and effectiveness of the considered fractional technique.

The aim of this study is the formation of porous silicon (PS) and the heat treatment effect on the optical properties of the PS layer. An optimized HF:HNO₃ chemical solution is used at ambient temperature on the n + p silicon surface. Scanning electron microscopy (SEM) pictures show the form of the nanopores. We studied the effect of the heating on the morphology and the reflection of the PS layer. A chemical analysis of the surface is also carried out. The measurements show that the pore shape and the oxygen content on the surface are changing with temperature. Specular reflection spectra under variable incidence angles are measured on each treated surface. Curves of weighted reflection R_w are drawn to illustrate the evolution with temperature. The modification of oxygen content of the porous surface is correlated with the sheet resistance of the emitter. Results show the lower the oxygen percent the lower the resistivity. The layout of R_w according to the temperature of annealing indicates that the shape of the curve is the same for the angles of incidences 20°, 30°, 40°, and 50°. At a low temperature R_w is minimal indicating the presence of an oxide coating on the porous layer an indication of optical adaptation between the air and the substrate of silicon.

A method is presented that enables the determination of transient absorption in Langmuir films made from a monolayer of spiropyran on water. This is achievable even though the optical pathlength of such a monolayer is < 10^-9 m. The approach is to monitor reflectivity changes close to the Brewster angle, where the background of reflected light is minimized. This is the key to the sensitivity of the method. Relatively speaking the small changes in reflectivity due to changes in both real and imaginary parts of the refractive index are easier to observe with the intrinsically low backgrounds at the Brewster angle. Notably using Fresnel equations we can show that the real and imaginary parts of the refractive index can be independently assessed for ultrathin films and monolayers using the approach presented.

Recent designs of dielectric-metamaterial composites have some advantages in improving the coupling effect of light in the visible region. The refractive index of the designed metal mesh or fishnet metamaterial structure consists of metals such as Ag, Cu and Al with MgF₂ dielectric material as the substrate which is calculated theoretically using Bruggeman equation. It has been established recently that the dielectric-metamaterial reflector coating (DMMRC) produces outstanding results. It drastically increases the internal reflection and enhances absorption in the visible region. DMMRC is designed by two slabs with exclusive thickness and contrary refractive indices. One is dielectric material and the other is negative refractive index material (NIM). This theoretical model can be treated as a photonic crystal and hence novel light trapping mechanism can be revealed. The transmission spectrum is analyzed using the transverse matrix method (TMM). This system may also be analyzed for various incident angles and for various substrates which are used to improve the efficiency of the solar cell.