Papers by Keyword: Refractive Index

Abstract: A theoretical study of the effect of applying a lateral electric field on type I and type II GaAs/AlGaAs quantum ring with different Al concentration in the barrier is presented. The effect on the quantum states of the carriers was investigated using the approximation of the effective mass. It’s showed that the electric field has a great effect on the wavefunction and the energy of the carriers. The transition point of the quantum ring from type I to type II was found with increasing electric field strength. For electric fields less than 4.75 x 10^-4 V/cm, the quantum ring is of type II: the symmetry of electron ground state is X. Above this threshold, it transitions to type I : the symmetry of electron ground state is Γ. Also, the effects of electric field on the linear and non-linear optical properties of the studied structure illuminated with different incident optical intensity were studied. There is an increase in the radiative lifetime with a notable decrease in the absorption coefficient and the refractive index with the increase in the intensity of the electric field. It’s noted that the increase in the type II quantum ring lifetime (20%) is greater than that of type I quantum ring (10 %) due to the confinement of the G-electron in the quantum ring which is not the case with the X-electron. To the best of our knowledge, this article is the first theoretical study of the influence of lateral electric field on physical properties of type II GaAs/AlGaAs quantum ring structures.

Abstract: Considering solar energy is being used more and more frequently in recent years, numerous studies have been conducted in order to improve the performance of the solar cell. The application of anti-reflective coating (ARC) in the solar cell is one of the most effective techniques. It has been said that although single and double ARC layers are adequate, applying triple ARC layers would render them significantly more effective across a broad spectrum. Henceforth, in this study, different materials were recently designed to produce triple layers of ARC, which are SiO₂/Si₃N₄/TiO₂, SiO₂/ZnO/TiO₂, ZnO/Si₃N₄/TiO₂, SiO₂/Si₃N₄/ZnS, and SiO₂/ZnO/ZnS, which are then applied in silicon solar cells using PC1D simulation software. The outcomes of the simulation included the analysis of the I-V curve, efficiency (ŋ), and reflection, in addition to the results for short circuit current (I_sc), maximum power output (P_max), open circuit voltage (V_oc), and fill factor (FF), which have been compared to numerous other theoretical findings from other investigations and research projects. By that, the simulation revealed that SiO₂/ZnO/TiO₂ is the most suitable triple-layer ARC to be applied to a silicon solar cell, which exhibits the highest efficiency of 22.63% with an I_sc of 3.967A, P_max of 2.489W, a V_oc of 0.7389V, and a fill factor of 84.91 at a wavelength of 400 nm.

Abstract: The review article focuses on the growth of thin film and its characterization by UV-Vis-NIR spectroscopy. For UV-Vis-NIR spectroscopy of thin films, they are usually deposited on translucent quartz glass surfaces. The article reports the extraction of various thin film optical parameters viz., absorption coefficient (α), Urbach energy (E_u), optical band gap (E_g), refractive index (n), extinction coefficient (k), dielectric constants, dissipation factor (tanδ) and optical conductivity (σ_optical) by using optical spectra (absorption(A)/transmittance (T)/reflectance (R)). Furthermore, the effect of thin film substrate temperature (T_s) and/or thickness (d) and/or post-deposition annealing temperature (T_a) on various optical parameters is discussed in detail.

Abstract: The growing interest for the use of 4H-SiC in photonics is triggering the interest for more accurate characterizations of this semiconductor from the optical and opto-electronic point of view. In this work we report about new measurements run on an undoped 4H-SiC substrate, finalized at determining the precise dependence of its refractive index on temperature in the visible spectrum, and precisely at the wavelength of λ=632.8 nm, in a temperature range from room temperature (RT) to 400K. Measurements are performed by exploiting the properties of a Fabry-Perot cavity interrogated with a laser beam. It is known that the transmitted radiation intensity shows fringes that shift with temperature and the refractive index. By precisely monitoring the transmitted signal, the thermo-optic coefficient dn/dT can be determined with a resolution that approaches 10^-6 K^-1.

Abstract: An empirical relation that correlates the optical dielectric constant and the electronegativity difference in A^NB^8-N type binary compounds is presented. The relation uses only one numerical constant common to all I-VII, II-VI and III-V compounds. The simplicity of the relation provides a clue to understand the role of the charge transfer from one atom to another in the origin of the optical dielectric constant. It is also shown that the optical dielectric constant correlates better with the Pauling ionicity scale than with the Phillips ionicity scale. The possible physical background of the found relation is discussed based on the results obtained.

Abstract: Various filling fractions of silver silica nanocomposites (Ag-SiO₂ NC) were successfully synthesized via sol-gel technique and deposited onto indium tin oxide via electrophoretic deposition (EPD). Ag-SiO₂ NC was investigated using X-ray diffraction, FTIR spectroscopy, Uv-vis and transmission electron microscopy. The XRD and Uv-vis results revealed that Ag-SiO₂ NC is stable with a filling fraction of 0.6 in the dielectric medium with excellent absorption peak. Spectroscopy Ellipsometry shows that the effective permittivity and refractive index obtained from this filling fraction are -0.88 and 0.90, respectively. We discovered a ragged of metamaterial properties at negative permittivity.

Abstract: Bruggeman's symmetric effective-medium model of vanadium oxide is introduced, in which the transmittance was studied because of its importance in the subject of smart windows, it was studied from ( 5 nm-1000 nm) for each of the regions of the electromagnetic spectrum, the ultraviolet and visible region, and the near and medium sub-regions of the infrared and the results showed that the importance of studying the transmittance of vanadium oxide as a good candidate For this kind of industries. Our results showed that the small sizes of the material guarantee an almost constant and high transmittance to the visible region; this is due to the agreement of the direction of the dipoles in the material with the direction of the internal electric field, which leads to an increase in the value of the refractive index. The refractive index represents the gain in the permittivity of the material presented by Bruggeman's model. For the other regions where the transmittance is not desirable, it can be controlled by the film’s size of the transmittance on the one hand and the wavelength on the other hand.

Abstract: In the proceeding way of material research in the field of manganites, LCMO micro and nanoparticles are synthesized via. the solid-state reaction route, glycine-nitrate combustion method respectively. The phase confirmation is done by XRD, FT-IR technique and the surface morphology viewed by Scanning Electron Microscope (SEM). The energy band gap obtained from Diffuse Reflectance Spectroscopy clearly suggests that the band gap of nanoparticles (2.06eV) is larger than that of the microparticles (1.58eV). Both samples comprise of wide band-gap semiconductor, so the refractive index is calculated using Herve and Vandamme relation. The impedance spectroscopy and dielectric properties of the two samples are studied from room temperature to 100oC over the frequency range 10²-10⁶ Hz. The Cole-Cole plot of impedance is fitted using the RC-Circuit R(Q_gR_g)(Q_gbR_gb)(CR_in). The dielectric property is found to be enhanced in nanoparticles as compared to the microparticles. The findings suggest the nanoparticles be promising candidates in the field of high frequency devices as compared to micro.

Abstract: Polydimethylsiloxane (PDMS) with two type viscosity that commonly used as vitreous humour substitutes in vitreoretinal surgery has been successfully synthesized by ring-opening polymerization. Optimization of synthesized parameters such as ratio of monomer and chain terminator, the amount of initiator, mixing temperature and reaction time was carried out to obtain PDMS materials having similar properties with commercial product. PDMS with viscosity of 1.17 Pas that very close to viscosity of commercial PDMS of 1.08 Pas, was successfully synthesized with a ratio of 26:10 monomer and terminator chain, 0.58 M of initiator KOH, 170 ^oC of mixing temperature and 35 minutes of reaction time. By changing reaction time to 40 minutes, PDMS was successfully synthesized with viscosity of 3.42 that similar to that of commercial one.

Abstract: A glass system of composition 40P₂O₅-40ZnO-(20-x)Na₂O-xCdO (where, x = 1, 2, 3, 4, 5 and 6 mol%) was prepared using the conventional melt quenching technique. The glass formability of the prepared samples was inspected using XRD technique. Archimedes’ method was used to determine the density of the prepared glass samples then the molar volume was calculated. The optical spectroscopic investigations of the prepared glass samples were carried out over the spectral range (190-2500 nm). The proposed glass showed a successive transparency in both visible and near-IR ranges of spectrum till 2500 nm with considerably high transmission of about 78%. The refractive index of the glass samples with some other useful parameters such as dielectric constant, electric susceptibility and electronic polarizability of the prepared glass were evaluated. The results suggest the practicality of utilizing such new glass in the fabrication of optical supplies such as lenses and optical windows used for Nd:YAG lasers. The metallization criteria data of the prepared glass propose a good basis for predicting new nonlinear optical materials.