Spectral Dependence Of Refractive Index Research Articles

Anionic framework descriptors and microstructure affects on optical parameters of Ag7+x(P1-xGex)S6 single crystals

Herein we present a detailed study of single crystalline samples of Ag7+x(P1-xGex)S6 (x = 0, 0.1, 0.25, 0.33, 0.5, 0.75, 1) solid solutions. The Ag7+x(P1-xGex)S6 crystals were grown by directional crystallization from melt and characterized by techniques of XRD, Raman scattering, optical transmission measurements, spectral ellipsometry and electron microscopy. XRD and Raman scattering indicates a formation of solid solutions. The spectral dependences of refractive index are nonlinear with a maximum at the spectral range of ∼645–820 nm. It has been established, that P5+→Ge4+ cationic substitution leads to a monotonic nonlinear increase in the refractive index n from 2.58 (x = 0) to 2.75 (x = 1). The obtained values of refractive index were used to describe the optical parameters by the Wemple-DiDomenico equation. The spectral dependences of lnα at all studied temperatures (77–300 K) have an exponential shape near the absorption edge, indicating that they obey Urbach's rule. The corresponding value of the pseudo-gap Eg* and Urbach energy EU were determined. Increasing the Ge content in solid solutions causes a decrease in Eg* (1.971–1.466 eV) and EU (179.46–21.90 meV) values. Revealed Eg* values suggest that single crystalline Ag7+x(P1-xGex)S6 might be used as perspective solar harvesting materials. The practical application of these materials can be further enhanced with the results of temperature studies of variations of Eg* values. The changes in optical parameters are explained based on the structural and microstructural parameters of the studied solid solutions.

Optical properties of as-deposited, annealed and laser-treated Ge2Sb2Te5 thin films

Knowledge of the correct optical properties of phase change materials (PCM) is important in the development of many devices. Here, we report on the differences in optical properties of as-deposited, annealed, laser-reamorphized and laser-recrystallized G e 2 S b 2 T e 5 thin films. While as-deposited and laser-reamorphized G e 2 S b 2 T e 5 show a similar spectral dependences of refractive indices and extinction coefficients with a small decrease in optical band gap from 0.63 to 0.59 eV, spectral dependences of annealed and laser-recrystallized G e 2 S b 2 T e 5 differ significantly from each other in the entire measured spectral region with values of optical band gap 0.51 and 0.45 eV, respectively. We discuss the main differences in the optical functions between both crystalline phases using X-ray diffraction studies. We further present that the laser-reamorphized phase transforms to the crystalline phase at about 12 °C lower temperature in contrast to the as-deposited amorphous phase.

Design, fabrication and optical characterizations of pyrimidine fused quinolone carboxylate moiety for photodiode applications

A novel ethyl 3-amino-2-cyano-6-hydroxy-7, 12-dioxo-2, 7, 12, 12a-tetrahydro-1H-benzo[g]pyrimido[1, 2-a]quinoline-5-carboxylate(3ABPQC)was synthesized by treating ethyl 2-amino-4-hydroxy-5, 10-dioxo-1, 5, 10, 10a-tetrahydrobenzo [g]quinoline-3-carboxylate 1 with methylidene malononitrile(2). Thin films of ABPQC were prepared to utilize thermal evaporation technique at room temperature under a certain condition for obtaining a high-quality film. The molecular, structural, and morphological characterizations were employed using Fourier transform IR, X-ray diffraction, and scanning electron microscopy. The analysis proved two available band gaps of 1.51 and 3.55 eV for the onset and optical gaps, respectively. The experimental optical gap was compared with those obtained using density functional theory (DFT). The spectral dependence of refractive index was explained based on single oscillator model and the main important parameters were extracted using the formula of Wemple and DiDomenico and found to be 2.91, 4.97, 0.34 and 0.21 for the oscillator energy, E0, dispersion energy, Ed, and the rth moments, M-1 and M-3, respectively. The remarkable optical behavior with the unique optical response representations of ABPQC allows designing and manufacturing organic- photodiodes based on ABPQC nanostructured films.

Influence of the Spectral Dependence of Refractive Index on the Polarimetric Properties of Ice Particles

Water ice is widespread in the Solar System. Computer simulation of light scattering by ice particles designed to interpret the observational data should take into account the spectral dependence of the refractive index of water ice. However, in practice, a single fixed value of the refractive index is often used. In this paper, we show that poor choice of a fixed refractive index commonly leads to significant errors in estimating both the intensity and the degree of polarization of single-scattered light. We have found that a fixed value of the refractive index of ice particles m0 = 1.3078 in the spectral region from 0.4 to 0.9 μm leads to minimal differences between the calculated characteristics of the light scattered by ice particles and those that take into account the spectral behavior of the refractive index. The most suitable values of the fixed refractive index for the widely used R, V, and I filters have been found. We have also studied the effect of the fixed refractive index of ice on the spectral dependence of the main parameters of the phase dependence of the linear polarization degree of single-scattered light, such as the magnitude and position of the minimum of the negative branch, the magnitude and position of the maximum of the positive branch, the inversion angle, and the polarimetric slope. The results of the calculations can be used to interpret the polarization of various objects of the Solar System that contain ice particles.

Birefringence of SnSe single crystals in excitonic and electronic transitions region

Absorption spectra in temperature range 300–10 K were studied. The minimal band gap A1 (1.091 eV at 300 K) is formed by direct allowed in E∣∣c polarization and forbidden in E∣∣a polarizations transitions. The next interval B1 (1.316 eV) is formed by direct transitions allowed in E∣∣a polarization and forbidden in E∣∣c polarization. Angular dependences of the electron transitions in the band gap minimum were investigated. Spectral dependences of refractive index (n) were calculated from wavelength modulation transmission (ΔT/Δλ) and reflection (ΔR/Δλ) spectra in the region of direct electron transitions. The absorption edge shifts to higher energies with temperature decreasing, and temperature coefficient of edge absorption shift (β) is 3.4 × 10−3 eV K−1.

Optical properties and birefringence of ZnIn2S4 layered crystals

Interference spectra of layered ZnIn2S4 crystals were investigated for samples of different thicknesses (7.5–900 μm). Spectral dependences of refractive indices (na and nb) for light waves with different polarizations were calculated and their intersection observed at energy E0 ∼ 2.38 eV. The refractive indices difference (Δn = na− nb) was determined at energy range 0.8–3.0 eV. Features observed in reflection and absorption spectra were attributed to the band-to-band electron transitions at k = 0. Magnitudes of valence bands (V1, V2 and V3, V4) splitting due to crystal field and spin–orbital interaction were determined. Electron transitions in energy interval 2–6 eV were identified on the basis of available theoretical band structure calculations.

Optical properties of HfOx (x < 2) films grown by ion beam sputtering-deposition method

The optical properties of the HfOx films of different chemical composition (x ≤ 2) deposited by ion beam sputtering-deposition (IBSD) method were studied. Spectral dependencies of refractive index n(λ) and extinction coefficient k(λ) were determined with ellipsometry in λ = 250–1100 nm wavelength region. The x values (i.e. [O]/[Hf] ratio) for the films were derived from x-ray photoelectron spectroscopy (XPS) data. The spectral dependences of optical constants n(λ) and k(λ) were found to undergo radical changes with x = 1.78–1.82. The films with x < 1.78 demonstrated high extinction coefficient k > 1 with the metallic-like behavior of optical constants spectral dependences. The films with x > 1.82 were found to be transparent, with k = 0 and n(λ) being well approximated by a Cauchy polynomial dependence for dielectrics. Using a sample with a gradient of x, it was established that the transition from the metallic to the dielectric-like behavior of the optical constants occurs not smoothly, but is discontinuous. A sharp jump in the optical constants is observed at x ≈ 1.8. According to XPS data, the transparent films were found to consist of two components only: HfO2 and Hf4O7 suboxide. Cauchy polynomial coefficients for Hf4O7 suboxide and HfO2 were found by using the Bruggeman effective medium approximation.

Far-infrared lattice vibration spectra of copper gallium (indium) ternary selenides (tellurides): A consequence of trivalent cation and anion interrelation

Experimental spectra for copper gallium (indium) ternary selenides (tellurides) crystals, measured in the 50–500cm−1 frequency range, revealed four infrared-active modes. Spectral dependencies of refractive index and absorption coefficient were computed from reflectivity experiments. The frequencies of optical modes, damping constants and oscillator strengths were also evaluated. The bands observed in IR spectra were provisionally attributed to various vibration types (valence and valence-deformation). Crystal structure and atomic composition ratio of the constituent elements in Cu3Ga5Se9, Cu3In5Se9 and Cu3In5Te9 crystals were revealed from structural characterization techniques of X-ray diffraction and energy dispersive spectroscopy.

Optical and Electron-Beam Recording of Surface Relief’s Using Ge&lt;sub&gt;5&lt;/sub&gt;As&lt;sub&gt;37&lt;/sub&gt;S&lt;sub&gt;58&lt;/sub&gt;–Se Nanomultilayers as Registering Media

Processes of e-beam and holographic recording of surface-relief structures using Ge5As37S58–Se multilayer nanostructures as registering media were studied in this paper. Optical properties of Ge5As37S58, Se layers and Ge5As37S58–Se multilayer nanostructures were investigated. Spectral dependencies of refractive index were analyzed within the frames of single-oscillator model. Values of optical band gaps for Ge5As37S58, Se layers and Ge5As37S58–Se multilayer nanostructures were obtained from Tauc dependencies. Holographic recording process depends on the polarization of the recording beams. Using e-beam and holographic recording diffraction gratings and other elements were recorded in Ge5As37S58–Se multilayer nanostructures.

Holographic and e-Beam Image Recording in Ge5As37S58-Se Nanomultilayer Structures.

Processes of e-beam and holographic recording of surface relief structures using Ge5As37S58–Se multilayer nanostructures as registering media were studied in this paper. Optical properties of Ge5As37S58, Se layers, and Ge5As37S58–Se multilayer nanostructures were investigated. Spectral dependencies of refractive index were analyzed within the frames of single oscillator model. Values of optical band gaps for Ge5As37S58, Se layers, and Ge5As37S58–Se multilayer nanostructures were obtained from Tauc dependencies. Using e-beam and holographic recording, diffraction gratings were fabricated in Ge5As37S58–Se multilayer nanostructures. Images of Ukraine and Moldova state emblems were obtained by e-beam recording. Image size consisted of 512 × 512 pixels (size of 1 pixel was ~2 μm). Ge5As37S58–Se multilayer nanostructures are perspective for the direct recording of holographic diffraction gratings and other optical elements.

Birefringence in quantum wells of heterostructures In0.68Al0.1Ga0.13As/In0.42Al0.22Ga0.24As/InP

The polarization dependences of reflection and wavelength modulated reflection spectra of quantum wells In0.68Al0.1Ga0.13As/In0.42Al0.22Ga0.24As were investigated. Spectral dependences of refractive indices, extinction coefficients, real and imaginary parts of dielectric constants of quantum wells structures for different polarizations were calculated by the Kramers–Kronig analysis. A phenomenon of birefringence and an interference of polarized light waves in quantum wells were researched. The isotropic wavelength λ0=1.246μm was found out. Interference spectra changes the density of fringes and refractive indices (Δni, ΔnKK=nР,Р–nS,S) intersect zero axis at energy of isotropic wavelength (0.955eV).

Excitonic spectra and band structure of CdGa2Se4 birefractive crystals

We report on the intersection of spectral dependences of refractive indices no and ne at the wavelengths 546nm (λ0) and 450nm (λ01) in CdGa2Se4 single crystals. The value of difference Δn=ne−no is equal to zero at the wavelengths involved. When placed between two crossed polarizers, the crystals of CdGa2Se4 exhibit a transmission band at the wavelength of λ0=546nm (300K). The ground and excited states of three excitonic series (A, B and C) were found out at 13K in CdGa2Se4 crystals, and other parameters of excitons and bands were determined. In the Г point of Brillouin zone the effective mass of electrons mc is equal to 0.14m0, and the effective masses of holes mv2 and mv3 are equal to 0.76m0 and 0.94m0, respectively. The hole mass mv1 depends upon the direction of wave vector k: at polarization E∥c, k∥a the mass mv1=1.15m0, and at polarization E∥c, k∥b mv1=0.84m0. The values of valence bands splitting in the center of Brillouin zone by the crystal field (Δcf=49meV) and spin–orbital interaction (Δso=351meV) were determined. The optical functions n, k, ε1 and ε2 in polarizations E⊥c and E∥c for the energy diapason from 3 to 6eV were calculated from the reflectivity spectra by Kramers–Kronig analysis. The evidenced features are discussed on the basis of recent theoretical calculations of the band structure of CdGa2Se4 crystals.

Optical characteristics of ZnTe1−xOx alloys from first-principles calculations

We report the optical and dielectric properties of ZnTe1−xOx ternary alloys in the zinc-blende structure. The calculations are performed using the full potential linearized augmented plane wave (FP-LAPW) method within the density functional theory (DFT) in the generalized gradient approximation (GGA) of Engel–Vosko. Features such as optical response function, spectral dependence of refractive index and the reflectivity spectrum as well as their dependence on oxygen concentration have been studied. The agreement between our results and data available in the literature is reasonably good. The present study spans very important technological visible/ultraviolet spectral region.

DISPERSIVE OPTICAL PARAMETERS OFNi(100) CRYSTAL AND THERMALLY EVAPORATED NICKEL FILMS

Structure and optical characteristics of nickel ( Ni ) single crystal (100) surface and thin films have been evaluated by the combined use of reflection high-energy electron diffraction (RHEED) and spectroscopic ellipsometry (SE). Nickel films were fabricated by thermal evaporation at 100°C while Ni single crystal was grown by vertical Bridgman method. RHEED analysis indicates that the grown Ni films were polycrystalline. Spectral dependencies of refractive index n(λ) and extinction coefficient k(λ) determined in the spectral range λ ~ 250–1030 nm indicate the typical behavior of metals. The refractive index of Ni films is found to be slightly higher compared to that of Ni (100) crystal.

Refractive index spectral dependence, Raman spectra, and transmission spectra of high-purity Si28, Si29, Si30, and Sinat single crystals

Precise measurement of the refractive index of stable silicon isotopes $^{28}$Si, $^{29}$Si, $^{30}$Si single crystals with enrichments above 99.9 at.% and a silicon single crystal $^{nat}$Si of natural isotopic composition is performed with the Fourier-transform interference refractometry method from 1.06 to more than 80 mkm with 0.1 cm$^{-1}$ resolution and accuracy of $2 \times 10^{-5} ... 1 \times 10^{-4}$. The oxygen and carbon concentrations in all crystals are within $5 \times 10^{15}$ cm$^{-3}$ and the content of metal impurities is $10^{-5} ... 10^{-6}$ at.%. The peculiar changes of the refractive index in the phonon absorption region of all silicon single crystals are shown. The coefficients of generalized Cauchy dispersion function approximating the experimental refractive index values all over the measuring range are given. The transmission and Raman spectra are also studied.

Film's Forming Materials for THz Spectral Range Purposes

At the presented work, we report the results of research of optical properties PbTe, ZnSe, ZnS, BaF2 and PbF2 thin fllms in a wide infrared spectral range. These materials are used for manufacturing thin fllm multilayer interference systems working in the mid-infrared and probably be applied in far infrared to submillimeter. Optical properties in our understand- ing are spectral dependences of refractive index and extinction coe-cient of layers. Films with thicknesses 3{7 microns were received by thermal vacuum deposition on single-crystal silicon sub- strates. Refractive index and extinction coe-cient dispersion in 1.5{150 microns spectral range (2{200THz) were determined by method based on analysis of the transmission and re∞ection interference spectra. Films of PbTe under consideration do not possess appreciable absorption bands in the investigated spectral range. While, other investigated fllms have intensive absorp- tion bands in the 25{100 microns region. With using of the investigated materials the \solar blind fllter for 1.0{50 microns spectral range on the single-crystal silicon substrate was designed and made.

On angle resolved RF magnetron sputtering of Ge–Sb–Te thin films

Thin amorphous films of Ge–Sb–Te were deposited from Ge 2Sb 2Te 5 target by RF ( f = 13.56 MHz) magnetron sputtering in argon plasma. Composition and chemical homogeneity of target and prepared thin films were traced by Energy Dispersive X-ray Analysis coupled with Scanning Electron Microscope (SEM-EDX). SEM technique was also used for surface morphology observation. Crystallinity of target and prepared thin films was studied by X-ray Diffraction (XRD). Optical parameters of prepared thin films (spectral dependence of refractive index, optical band gap energy E g opt ) and film thicknesses were established via Variable Angle Spectroscopic Ellipsometry (VASE) supported by UV–Vis–NIR spectroscopy. Influence of deposition conditions (RF power, Ar pressure, angle divergency from normal direction) to composition, crystallinity, optical properties and deposition rate was established.

Optical properties of thin films of system (As 2Se 3) 80−x(As 2Te 3) x(SnTe) 20 prepared by PLD

Thin amorphous films from system (As 2Se 3) 80− x (As 2Te 3) x (SnTe) 20 were prepared by pulsed laser deposition (PLD) from their bulk glasses and their optical properties were studied by spectral ellipsometry. Spectral dependencies of refractive index, absorption and extinction coefficient and optical gap (1.41–1.66 eV for (As 2Se 3) 80− x (As 2Te 3) x (SnTe) 20 with x = 20 resp. x = 0) were calculated from optical tansmittance, from ellipsometric data by Tauc method. High values of refractive index n 0 (2.49–2.60) and of non-linear χ (3) coefficient of index of refraction (4.9–7.5 × 10 −12 esu for the glass (As 2Se 3) 80− x (As 2Te 3) x (SnTe) 20 with x = 0 resp. x = 20) made studied thin films of system (As 2Se 3) 80− x (As 2Te 3) x (SnTe) 20 promising candidates for application in optics and optoelectronics.

Precise measurement of refractive index spectral dependence of optical materials for laser, fiber, and integrated optics

An interferometric technique for measuring the spectral dependence of the refractive index of solid-state materials to an accuracy of 10−5 over the entire transparency region is described. The possibilities of the technique are demonstrated by the example of new phosphate glasses formulated for laser and fiber optics. It is shown that, in the presence of absorption bands in the transmission spectrum, the technique allows their associated jumps in the refractive index values to be recorded on the order of 10−4−10−5 and below. The shift in the spectral dependence of the refractive index in the region of the absorption band with intensity at 1.7 cm−1 is measured for the first time.

Effects of Pb addition and heat treatment on optical properties of thermally evaporated Ge 1−xSe 2Pb x thin films

Thin chalcogenide films of Ge 1− x Se 2Pb x ( x=0, 0.2, 0.4, 0.6 and 0.8) have been prepared by the thermal evaporation technique, from previously synthesized bulk samples. The X-ray diffraction showed the amorphous nature for the as-deposited films and the partially crystalline for the annealed films. The optical constants (the refractive index, n, and absorption index k) were determined for as-deposited and annealed Ge 1− x Se 2Pb x films of different thicknesses by using spectrophotometeric measurements of the transmittance and reflectance at normal incidence in the spectral range 200–2500 nm. The obtained values of both n and k were found to be independent of the film thickness. The optical absorption edges are described using both the Urbach rule and the indirect transition. In transparent region, the spectral dependences of refractive index were interpreted in the frame of a single oscillator model.