Decrease In Refractive Index Research Articles

Magnetic field effect on the linear and nonlinear refractive index and optical absorption of a donor in a GaAs quantum ring

The effects of the magnetic field (γ), the radial position of impurity and the degree of confinement on the oscillator strength (OS), refractive index and optical absorption (α) of an impurity inside a GaAs quantum ring (QR) are explored using the effective mass approximation and variational method. It is shown that the peak position of the optical absorption and the refractive index decrease and move toward the lower incident photon energy as the strength of the γ increases. In addition, it is found that the strongest α relates to the case when the impurity is positioned at the right side of QR in the presence of the magnetic field. Our examinations also show that the oscillator strength decreases as the γ increases especially for an on-center donor impurity.

Examining the impact of quantum confinement energy on the optical characteristics of zinc sulfide and gallium nitrate in the ultraviolet spectral range

The study of confined quantum systems exhibit distinct behavior compared to that in bulk solids. This enables the design of materials with tunable chemical, physical, electrical and optical properties. In this paper, the effect of quantum confinement energy on the optical properties (gap energy, refractive index) of semiconductors gallium nitrate (GaN) and zinc sulfide (ZnS) is studied. The study is done using the MATLAB computer program (20a). This software is based on the Brus model and the particle in-a-box model. The results indicate that the optical properties depend on the quantum confinement energy, with an increase in quantum confinement energy corresponding to an increase in the energy gap and a decrease in refractive index.

Ellipsometric study of the porous silicon: The impact of decoration and oxidation on porosity depth profiling

The multiple-angle-of-incidence ellipsometric studies of the decoration by isopropyl alcohol of porous silicon (PSi) have been performed. The existence of a subsurface thin film of modified PSi with 5–7 % higher porosity contrary to the initial PSi layer was established. The refractive index and thickness of the film were calculated in the single-layer reflective system model. It was found that empty pores of the film after the sample was kept in isopropyl alcohol for 24 h were filled by its molecules. Thus, the effective refractive index of the modified film decreased while its thickness slightly increased. The refractive index decrease of the film over time during several months of observation is the result of the continuation of the PSi oxidation in atmospheric conditions. The work also presents the results of the PSi samples' oxidation degree by the ellipsometric method after high-temperature annealing in dry air (T = 1000 °C).

HYDROCATALYTIC PROCESSING OF FUEL OILS WITH THE USE OF NANOCATALYSTS BASED ON NICKEL AND ZINC

The article presents the results of a study of hydrocatalytic processing of two fuel oils in the presence of nanocatalytic systems in the form of oil-soluble precursors based on nickel and zinc. The process was carried out on a pilot plant for hydroprocessing with a flow reactor at a temperature of 440 ℃, a hydrogen pressure of 6 MPa, a feed space velocity of 1.0 s-1, and a hydrogen circulation ratio of 1000 nl/l. The catalyst efficiency was evaluated by changes in the material balance, in hydrogenate desulfurization degree, in 450+ °C fraction conversion degree, and by changes in density and hydrogenate refractive index. An analysis of material balances showed that the addition of nanocatalyst precursors increases the 180–350 °C fraction yield, reduces the coke yield on the fixed layer, which is a layer of ceramic balls, and reduces the 450+ °C residual fraction yield. The gas and gasoline fraction yield is slightly reduced. The analysis of hydrogenates showed a decrease in sulfur content, a decrease in density and refractive index in hydrogenates obtained during the hydroprocessing of raw materials with the addition of nanocatalyst precursors. The optimal concentrations of catalysts were experimentally determined; for nickel, the concentration is 0.1 wt %, and for zinc is 0.15 wt %. A comparison of two methods for the synthesis of nanoscale catalytic systems in raw materials was made: directly in the reaction zone in situ and outside the reaction zone ex situ. The method for synthesizing nanoscale catalytic systems outside the reaction zone makes it possible to further increase the feedstock conversion, the hydrogenate desulfurization degree, and the hydrogenate quality.

Preparation and characterization of lanthanum-based perovskite oxides LaMO3 (M=Fe, Cr, Mn) thin films by electrophoretic deposition

In this study, we report the fabrication and characterization of perovskite thin films deposited on FTO substrates via electrophoretic deposition (EPD). The x-ray diffraction (XRD) patterns showed the formation of the orthorhombic structure for and films and the trigonal structure for the film. The field-emission scanning electron microscopy (FE-SEM) micrographs revealed nano-spherical particles with an average grain size of about 50 nm covering the surface with fewer porosities compared to the other films. Moreover, the film exhibited a higher transparency in the visible region (∼84%). The estimated bandgaps of and perovskite films were found to be 2.17, 3.18, and 2.92 eV, respectively. In addition, the refractive indices of all deposited films were calculated using five empirical models that relate the refractive index to the bandgap, which consistently revealed a decrease in refractive index with an increase of bandgap energy This study holds significant implications for the field of perovskite thin films as we contribute new insights into the fabrication of lanthanum-based perovskite thin films using the EPD technique. The comprehensive characterization of microstructural, morphological, and optical properties provides valuable information for understanding the structure-property relationship in these materials. Furthermore, the determination of bandgaps and refractive indices enhances our understanding of the optical properties of perovskite films. The findings from this study pave the way for potential applications in optoelectronic devices, where fine-tuning of material properties is critical for optimal device performance.

Thermo-physical properties and thermal energy storage performance of two vegetable oils

Sensible heat storage materials are cheaper than latent heat storage materials for small storage volumes. Vegetable oils are cheap and readily available sensible heat storage materials produced locally in most countries in Sub-Saharan Africa. In this paper, the refractive indices, sound velocities, densities, specific heat capacities, and thermal conductivities of Sunflower oil and Roki oil (a blend of Palm oil and Sunflower oil) are determined experimentally. These two vegetable oils are locally produced in Uganda. Isentropic compressibility and thermal expansion coefficient are derived from the physical properties for the first time. The results show the refractive index, sound velocity, density, and thermal conductivity decrease with the increase in temperature, whereas isentropic compressibility, thermal expansion coefficient, and specific heat capacity increase with the increase in temperature for both oils. Roki oil shows higher thermal conductivity values than Sunflower oil at various temperatures. Additionally, an experimental setup to compare the performance of Roki oil and Sunflower oil as sensible heat storage materials for domestic medium temperature applications is presented. Roki oil and Sunflower oil are experimentally compared using charging and discharging experiments. The charging/heating cycles are first simulated with electrical energy followed by experimental tests with solar energy using parabolic dish solar cookers. The thermal comparison is made in terms of the temperature profiles during charging, discharging and heat utilization processes. During charging, the results show that Roki oil attains higher maximum temperatures (170–233 °C) compared to Sunflower oil (160–210 °C). Roki oil shows higher temperatures (71–78 °C) during cooling compared to Sunflower oil (67–76 °C). Roki oil shows higher heat utilization temperatures compared to Sunflower oil. The results provide insights on the utilization of locally available materials in Uganda as sensible heat thermal energy storage which are cheaper than commercial solar heat transfer oils.

In-situ PECVD-based stoichiometric SiO2 layer for semiconductor devices

We propose an in-situ stoichiometric SiO2 layer deposition using plasma-enhanced chemical vapor deposition (PECVD) to replace typical outside SiO2 deposition for semiconductor devices, such as thermal oxidation and/or wet chemical oxidation. The SiO2 films deposited in a silane (SiH4), argon (Ar), and carbon dioxide (CO2) precursor gas mixture are compared to those deposited in a standard SiH4+CO2 plasma environment. Ar gases are introduced into the plasma environment of silane (SiH4) and carbon dioxide (CO2) to improve the optoelectronic properties and stoichiometry of SiO2. The addition of the Ar gases promotes the dissociation of SiH4 and CO2, resulting in an increase in the deposition rate and a decrease in the SiO2 refractive index. The addition reduces the dielectric constant of SiO2 by analyzing the metal-oxide-semiconductor structure. The resultant SiO2 shows excellent surface passivation of crystalline silicon wafers. The mechanism of SiO2 formation in PECVD with mixture gases is thoroughly addressed. The in-situ PECVD-based stoichiometric SiO2 layer is expected to reduce the complexity of the semiconductor device procedure.

A theoretical approach on estimating temperature-dependent optical properties of two typical molten alkali chloride salts (KCl and NaCl)

Due to high working temperature of molten salts, radiative heat transfer has great effects on the temperature field computation accuracy. Since few optical property data of alkali chlorides is available, making it difficult to take radiative heat transfer into consideration, hence hindering its further application. In this paper, a theoretical approach on estimating temperature-dependent optical property of molten salts is developed to get temperature effect involved into optical property computation. After this, temperature-dependent optical properties of KCl and NaCl are estimated as an example. Due to the similarity of K and Na, the optical properties of KCl and NaCl exhibit extremely similar patterns. In short-wavelength region, they all show very high absorption intensity. In long-wavelength region the refractive index nearly keeps unchanged along with wavelength, while the extinction coefficient subtly increases. When temperature increases, the variations of optical properties of KCl are much more obviously than that of NaCl, but the overall trends are consistent. In short-wavelength region, an increase in temperature could lead to a slight red shift of refractive index peak and a decrease of extinction coefficient peak value. In long-wavelength region, increasing temperature will make both refractive index and extinction coefficient decrease.

The tin doping effect on the physicochemical and nonlinear optical properties of the manganese oxide (Mn3O4: Sn) thin films

Undoped and tin doped manganese oxide, Mn3-xSnxO4, (x=0, 2, and 4 at %) thin films were successfully elaborated by the chemical route defined in the spray pyrolysis technique and deposited on glass substrates at a temperature of 350 °C. The physicochemical characterization of the thin films was performed using an X-ray diffractometer (XRD) that showed a polycrystalline tetragonal structure for all thin films. Raman measurement confirmed the vibrational mode, A1g, and the XRD results with the presence of no secondary phases. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy depicted the surface morphology and the elemental composition (Mn, O, and Sn) of the elaborated thin films. Finally, the optical analysis was carried out, and it showed an increase in the average transmittance of the Mn3O4: Sn (0, 2, and 4 at %) from 57.6 % to 62.2 % for 700 nm and an increase of their optical band gap from 3.27 eV to 3.61 eV. We note also a decrease of their dispersive energy parameter Ed from 5.44 eV to 4.86 eV, of their static refractive index n0 from 2.02 to 1.86, as well as for their nonlinear optical parameters presented by the nonlinear refractive index n2 from 1.14 10-11 to 0.51 10-11 and the third order susceptibility χ3 from 6.14 10-13 esu to 2.49 10-13 esu. These values can be correlated to the poor crystallinity and the tensile strain of the Mn3O4: Sn (0, 2, and 4 at %) thin films, as well as to the high order of the optical bandgap energy and the decrease of the linear refractive index of these films. Hence, these thin films can be used as material for nonlinear optical applications.

The effect of Bi2O3/PbO substitution on physical, optical, structural, and gamma shielding properties of boro-tellurite glasses

Boro-tellurite glasses with molar compositions 60TeO2–20B2O3-(20-x)Bi2O3-xPbO, where x = 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 mol% were fabricated using a standard melt quenching technique and studied in term of their physical, optical, structural and gamma shielding properties. As PbO concentration increases from 0 to 10 mol% (Bi2O3 decreases), the density and molar volume of the present samples decrease from 6.08 to 5.93 gr/cm3 and 33.37 to 30.27 cm3/mol, respectively. The optical packing density increases from 71.91 to 72.67% as PbO is added to the network to substitute Bi2O3. With the increase of PbO concentration, the refractive index, molar refractivity, and ionic polarizability decrease from 1.9137 to 1.8306, 18.531 to 16.884 cm3, and 7.3534 to 6.7000 Å3, respectively. The percentage of [TeO3] (tp) and [TeO3+1] polyhedra in the glass network increase with the rise of PbO concentration. The gamma radiation shielding features were analyzed theoretically using Phy-X PSD software with photon energies varied between 0.015 and 15 MeV. For all glasses, the highest linear attenuation coefficient (LAC) values are observed at 0.015 MeV while the lowest values are observed around 5 MeV, a turning point at which pair production starts to dominate the gamma photon-electron interaction. At all photon energies, the LAC values decrease with the increase in PbO concentration (the decrease in Bi2O3). The LAC values at 0.015 MeV vary from 413.2183 to 12.4962 cm−1. At low photon energies (0.015–0.04 MeV), this compositional dependence is high. Above 0.04 MeV, this dependence is low. This LAC result suggests that adding Bi2O3 to the glasses is favorable for gamma shielding material as compared to PbO.

An extensive XPS analysis on sensitized PBDB-T-SF thin films for photovoltaic applications

A new investigation on the elemental composition and optical properties stability of PBDB-T-SF thin films was performed before and after chemical sensitization by immersion in nitromethane ferric chloride (FeCl 3 ) solution, in order to extend its photovoltaic potential. The paper presents the effect of ferric chloride on PBDB-T-SF thin films (90 ± 5 nm thickness) deposited on glass by spin coating. The optical properties changes were identified by spectrophotometry, simulated and modeled by spectroscopic ellipsometry, remarking a decrease in absorption coefficient, refractive index and extinction coefficient of the individual polymer thin film. The X-ray photoelectron spectroscopy (XPS) analysis shows the changes in terms of elemental composition. Additionally, related to the electrical properties, the study brings clarifications on the unusual increase of resistivity once the film is exposed to light, due to the attachment of iron ions to polymeric chains and to the existence of an iron oxide thin film on the top of polymer layer. These findings contribute to the understanding of the behavior of emerging fluorinated polymers, before and after chemical treatments and exposure to light. • Elemental composition and optical properties stability of PBDB-T-SF thin films • Complementarities between optical analysis and electrical measurements • Different photoconduction behavior of sensitized polymer thin films

Effect of substrate and annealing temperature on the physical properties of the thin films of SnSe2-SnSe alloy

Thin films of SnSe2-SnSe alloy were deposited at substrate temperatures 300 and 473 K by thermal evaporation. The 473 K as-deposited layers were re-grown on annealing from 523 to 623 K. The films show mixed phases of hexagonal SnSe2 and orthorhombic SnSe and display corresponding vibrational modes. The unit cell parameters and axes strain of the layers vary and show crystallite size distributions with changes in annealing temperature (Ta). Moreover, the film smoothness increases at elevated temperatures. The films as-deposited at 300 K exhibit direct bandgaps (Eg) of 1.15 and 1.52 eV. Further, the Eg values of 473 K layers vary from 1.47 to 1.56 eV with a change in temperature from 523 to 623 K and show an absorption coefficient (α) ≥ 5 × 104 cm−1. In addition, the refractive index (n) decreases, and optical mobility (μopt) increases with an increase in Ta. The above optical response indicates the films to be optically active and suitable in photonic devices in the visible and NIR portion of the EM spectrum. The PL emission peaks were observed at 805.1 and 1064.22 nm, which confirmed the presence of direct bandgaps of the SnSe2 and SnSe phases.

Modal analysis of silicon-on-insulator based rib waveguide using fully vectorial finite-difference mode solver

In order to interface optical integrated devices with external sources, an understanding of the modal characteristics of the optical waveguide is essential. The finite difference approach is utilized in this work to analyse a rib waveguide based on a silicon-on-insulator platform. A silicon device layer with thickness of 220 nm and a buried oxide with thickness of 2000 nm are considered. It is important to study the modal field distribution and parameters of the waveguide. The simulation results on the behaviour of modal parameters show that both effective refractive index and group index decrease with wavelength. The effective refractive index of the guided mode increases with rib width and slab thickness. It is also observed that energy is more confined in a deeply etched waveguide than in a shallow etched waveguide. Additionally, it is noted that the effective mode area and full-width half maximum increase with rib width and slab thickness.

Role of deposition temperature on non-linear optical properties of spray-coated Zn0.95Nd0.05O films

The influence of deposition temperature on the structure and optical (linear and nonlinear) properties of Zn0.95Nd0.05O thin films grown on glass substrates by using the spray pyrolysis method is studied. The X-ray diffraction spectra reveal the hexagonal wurtzite structure with a reduction in peak intensity as deposition temperature increases. With increasing temperature, the prominent peak intensity changes, and the dislocation density increases. Concomitantly, the surface morphology transitions from a nanoflake to a needle-like structure. With increasing deposition temperature, the optical transmittance of the films in the visible region improves, while the energy bandgap, refractive index and extinction coefficient values decrease. The reduction of refractive index and extinction coefficient values is ascribed to decreased scattering and uniformity of the films. Further, the films exhibit saturable absorption and films deposited at 300 ℃ show a maximum for third-order nonlinear susceptibility, which is quite appealing for nonlinear optical devices and components.

High-performance Bloch surface wave biosensor based on a prism-coupled porous silicon composite structure for the detection of hemoglobin.

Biosensors have various potential applications in biomedical research and clinical diagnostic, especially in detection of biomolecules in highly diluted solutions. In this study, a high-performance Bloch surface wave biosensor was constructed for the detection of hemoglobin. The procedure consisted of designing a porous silicon-based Kretschmann configuration to ensure excitation of the Bloch surface wave. The performance of the resulting sensor was then optimized by adjusting the buffer layer parameters based on the impedance matching method. The results showed an increase in the quality factor and figure of merit of the biosensor as a function of the decrease in thickness and refractive index of the buffer layer. The combination of the two optimization methods resulted in the quality factor and figure of merit of the optimized biosensor reaching as high as Q = 6967.4 and FOM = 11050RIU-1, respectively. In sum, the designed biosensor with high performance looks promising for future detection of hemoglobin.

Combined Au/Ag nanoparticle creation in ZnO nanopillars by ion implantation for optical response modulation and photocatalysis

ZnO nanopillars were implanted with Au-400 keV and Ag-252 keV ions with ion fluences from 1 × 1015 cm−2 to 1 × 1016 cm−2. We compared ZnO nanopillars solely implanted with Au-ions and dually-implanted with Au and Ag-ions. Rutherford Back-Scattering spectrometry (RBS) confirmed Ag and Au embedded in ZnO nanopillar layers in a reasonable agreement with theoretical calculations. A decreasing thickness of the ZnO nanopillar layer was evidenced with the increasing ion implantation fluences. Spectroscopic Ellipsometry (SE) showed a decrease of refractive index in the nanopillar parts with embedded Au, Ag-ions. XRD discovered vertical domain size decreasing with the proceeding radiation damage accumulated in ZnO nanopillars which effect was preferably ascribed to Au-ions. SE and diffuse reflectance spectroscopy (DRS) showed optical activity of the created nanoparticles at wavelength range 500 – 600 nm and 430 – 700 nm for the Au-implanted and Au, Ag-implanted ZnO nanopillars, respectively. Photoluminescence (PL) features linked to ZnO deep level emission appear substantially enhanced due to plasmonic interaction with metal nanoparticles created by Ag, Au-implantation. Photocatalytic activity seems to be more influenced by the nanoparticles presented in the layer rather than the surface morphology. Dual implantation with Ag, Au-ions enhanced optical activity to a larger extent without significant morphology deterioration as compared to the solely Au-ion implanted nanopillars.

Formation of diffraction gratings in optically patternable hydrogel films

AbstractLocal light‐induced material response forms the basis for volume holographic patterning of light‐responsive materials. This enables applications as multifunctional biomedical materials capable of integrating optical functions, such as for advanced intraocular lens (IOL) implants. Therefore, hydrogel films based on 8‐arm PEG and azobenzene‐functionalized acrylates are prepared. A local change in optical properties is induced by UV exposure: a decrease in refractive index is detected by ellipsometric examination. One‐dimensional diffractive surface gratings, generated using a photomask, show optical functionality and are visualized in the atomic force microscope. The results show that a local change in optical properties can be induced in functionalized hydrogel films by photochemical crosslinking, making them suitable for volume holographic patterning.

Formation mechanism of femtosecond laser induced guiding structures in y-cut LiNbO3 crystal

In this work, we have used femtosecond laser direct writing to inscribe guiding structures in y-cut LiNbO3 crystal and explored the mechanism of laser modification. Experimental results reveal the fabrication-parameter windows for the modifications with refractive index increase and decrease. We investigate the guiding properties under different polarizations at 632.8 nm. The spectral shifts of Raman modes have also been analyzed to clarify the laser-induced modifications on the crystal lattice. This study demonstrates that the lattice expansion and compression, and the damage induced by the laser energy are the key factors affecting the structural vibration and refractive index modification types.

Hydrogen Bonding in 1‐Propanol‐Ethanol Binary Mixture: Experimental and Modeling Approaches

AbstractHydrogen bonds between the constituent molecules determine the physical properties of binary liquids. In this work, we explore the nature of hydrogen bonding in ethanol‐propanol system through experimental and computational techniques. The refractive index, dielectric spectroscopy and infrared spectroscopy along with molecular dynamic simulations of 1‐propanol‐ethanol binary system over the entire concentration range are reported here. The excess static permittivity and excess relaxation time shows the evidence of hydrogen bonded multimer structures. The deconvoluted OH peaks from IR spectra indicate the presence of trimers, tetramers and pentamers. The linear decrease in refractive index indicates the absence of caged structures. Molecular Dynamics simulations confirm the presence of the multimers and the absence of caged structures. Radial distribution function shows the binary mixtures exhibit no structural change throughout the concentration range. We also examine the H‐bonding networks present in these systems via graph theoretic analysis.

Residual stress of glass and crystalline oxide thin films responding to humidity

Here, we demonstrate that oxide thin film devices could be affected by humidity in their in-plane stress and in substrate curvature. We prepared silica glass and ceria crystalline thin films on Si(100) wafers by the sol-gel method. Both films had “tensile” in-plane residual stress. We cycled the relative humidity between ca. 20% and 80% in the square wave and monitored the substrate curvature in situ, from which in-plane stress was calculated. The increase and decrease in humidity resulted in a decrease and an increase in tensile stress, respectively. In situ ellipsometric measurements during humidity cycles showed that both thickness and refractive index increase and decrease on the increase and decrease in humidity, respectively. This guarantees that the volume expansion and shrinkage caused by water molecule adsorption/absorption and desorption, respectively, are the origins of the response of the stress to humidity. Responding to the change in humidity, thicker silica glass films with low porosities of 1%–3% showed more sluggish change in stress, suggesting absorption/desorption of water via diffusion in siloxane network in such dense films. Silica glass films with a larger porosity showed more quick response to humidity, indicating adsorption/desorption on the pore wall as the primary cause of the response. “Compressive” stress in a silica glass film with ca. 1% porosity exhibited very slight response in stress to humidity, which was attributed to the hard diffusion of water in compressed siloxane network.