Refractive Index Spectra Research Articles

The parameter of the optical indicatrix of guanidinium aluminum-sulfate hexahydrate crystals

The absorption coefficient (220–1200 nm) and refractive index (800–450 nm) spectra of a strongly anisotropic guanidinium aluminum-sulfate hexahydrate (GASH) crystals are measured. It is shown that the optical anisotropy of GASH crystals in the visible spectral region is significant, while the crystal in the polar direction becomes isotropic. The contribution of IR oscillators to the electronic polarizability of GASH is sharply anisotropic. It is found that the constants of the Sellmeier dispersion formula qualitatively agree with the vacuum ultraviolet spectra calculated from first principles. The experimental refractive indices coincide with the calculated values with an accuracy of 0.10 (n e ) and 0.1% (n o ). It is proposed to use the GASH crystal for development of optical phase difference compensators.

Terahertz frequency optical properties of acoustic materials

An investigation of the terahertz frequency electromagnetic absorption coefficient spectra and refractive index spectra is presented for many materials employed in acoustic applications. A brief discussion on the use of these material properties for terahertz imaging applications is also included. Terahertz-frequency electromagnetic radiation has the potential to image through and inside many acoustically damping materials, unlike traditional nondestructive evaluation techniques such as ultrasound. The optical properties discussed herein are necessary to quantify potential terahertz imaging performance for these and other acoustic materials.

Structural, electronic and optical properties of the quinary Al0.50Ga0.38In0.12N0.03Sb0.97:First-principles study

Abstract: The structural, electronic and optical properties of Al0.50Ga0.38In0.12N0.03Sb0.97 have been investigated using a full potential linearized augmented plane wave (FP-LAPW) method within the local density approximation (LDA).The structural properties such as the lattice parameter, bulk modulus B, pressure derivative B’ are determined and electronic properties such as band gap and density of states have been pursued. On the other hand, the dielectric function, refraction index, reflectivity, conductivity function, and energy-loss spectra were obtained and analyzed on the basis of electronic band structures and density of states.

Ultrafast third-order optical nonlinearities of heavy metal oxide glasses containing gold nanoparticles

This work reports on the third-order nonlinear properties and the response time of GeO2–Bi2O3 glass, as well as the effect of gold nanoparticles on these properties. The nonlinear refractive index spectrum and the nonlinear absorption coefficient were determined by the Z-scan technique, and the response time was obtained through Kerr gate measurements, using femtosecond pulses. The results show that the presence of gold nanoparticles causes a saturable absorption effect that is overcome by the two-photon absorption process at higher light intensities, for wavelengths within the plasmon band. We measured a constant value for the nonlinear refractive index (n2) for the visible and infrared regions, which was not affected by the presence of gold nanoparticles in the sample. However, the n2 value is one order of magnitude higher than the one for fused silica and 1.5times better than PGO (PbO–GeO2) glasses. In addition, the response time of the induced birefringence for the samples with and without gold nanoparticles is faster than the pulse duration (220fs), indicating an ultra-fast electronic process.

Optical Characteristics of Polystyrene Based Solid Polymer Composites: Effect of Metallic Copper Powder

Solid polymer composites (SPCs) were prepared by solution cast technique. The optical properties of polystyrene doped with copper powder were performed by means of UV-Vis technique. The optical constants were calculated by using UV-Vis spectroscopy. The dispersion regions were observed in both absorption and refractive index spectra at lower wavelength. However, a plateau can be observed at high wavelengths. The small extinction coefficient compared to the refractive index reveals the transparency of the composite samples. The refractive index and optical band gap were determined from the reflectance and optical absorption coefficient data, respectively. The nature of electronic transition from valence band to conduction band was determined and the energy band gaps of the solid composite samples were estimated. It was observed that, upon the addition of Cu concentration, the refractive index increased while the energy gaps are decreased. The calculated refractive indexes (low index of refraction) of the samples reveal their availability in waveguide technology.

First-principles study of the structural, elastic, and optical properties for Sr0.5Ca0.5TiO3

A detailed theoretical study of the structural, elastic, and optical properties for Sr0.5Ca0.5TiO3 is carried out by first-principles calculations. The band structure exhibits a direct bandgap of 2.08 eV at the Γ point in the Brillouin zone. The bulk modulus, shear modulus, Young's modulus, and Poisson's ratio are derived based on the calculated elastic constants. The bulk modulus B = 153 GPa and shear modulus G = 81GPa are in good agreement with available experimental data. Poisson's ratio v = 0.275 suggests that Sr0.5Ca0.5TiO3 should be classified as being a ductile material. Using the electronic band structure and density of states, we analyze the interband contribution to the optical properties. The real and imaginary parts of the dielectric function, as well as the optical properties such as the optical absorption coefficient, refractive index, extinction coefficient, and energy-loss spectrum are calculated. The static dielectric constant ε1(0) and the refractive index n(0) are also investigated.

Investigation into inhomogeneous electrical and optical properties of indium tin oxide film using spectroscopic ellipsometry with multi-layer optical models

Indium tin oxide (ITO) films with various thicknesses are deposited on glass substrates using a DC magnetron sputtering technique. The microstructure and chemical composition of the sputtered samples are examined by scanning electron microscopy (SEM), X-Ray Diffraction (XRD) and Energy Dispersive X-Ray Spectroscopy (EDS). Two-layer and three-layer optical models of the sputtered ITO films are constructed for fitting the experimental results of the spectroscopic ellipsometry. The results obtained from the two models for the resistivity, carrier density and carrier mobility are compared with those obtained via Hall effect measurements. Finally, the three-layer optical model is used to evaluate the refractive index and extinction coefficient spectra of the various samples. In general, the present results show that the three-layer model, in which the transition layer between the ITO film and the glass substrate is included, provides a better approximation of the SE results than the two-layer model. However, both models yield a reasonable estimate of the Hall resistivity. The results obtained using the three-layer model show that the carrier density and carrier mobility in the bulk layer are lower and higher, respectively, than those in the transition layer. In addition, it is shown that the refractive index of the bulk layer is lower than that of the transition layer in the UV and visible spectrum. Moreover, the extinction coefficient of the transition layer is significantly higher than that of the bulk layer in the near IR-region.

A first-principles study on the structural, elastic, electronic, and optical properties of CdRh2O4

The structural, elastic, electronic, and optical properties of CdRh2O4 with cubic \( (Fd\overline{ 3} m) \) and orthorhombic (Pnma) structures have been investigated using a pseudopotential plane wave (PP-PW) method within the local density approximation (LDA). The calculated lattice parameters agree reasonably with the experimental values. The single-crystal elastic stiffness constants Cijs of the cubic and orthorhombic phases are investigated using the stress–strain method. In addition, the polycrystalline elastic properties including bulk modulus, shear modulus, Young’s modulus, bulk modulus–shear modulus ratio, Poisson’s ratio, and elastic anisotropy ratio are determined based on Voigt–Reuss–Hill approach. The use of the hybrid functional sX-LDA leads to considerably improved electronic properties compared to standard LDA approach. On the other hand, the dielectric function, refraction index, reflectivity, conductivity function, and energy-loss spectra were obtained and analyzed on the basis of electronic band structures and density of states.

Preparation of high refractive index La2O3–TiO2 glass by aerodynamic levitation technique and effects of Bi2O3 substitution on its thermal and optical properties

La4Ti9O24 and Bi2O3-substituted La2O3–TiO2 glasses were prepared by aerodynamic levitation technique. The effect of Bi2O3 substitution on the thermal stability, refractive index and transmittance spectrum of the as-prepared samples were investigated. After Bi2O3 substitution, the stability of La2O3–TiO2–Bi2O3 glass decreased, but the Abbe number increased with glass refractive indices above 2.2 in visible region. The high refractive index can be attributed to the large oxygen packing densities and electronic polarizabilities of oxygen ions in the glasses.

Structural, elastic, electronic, chemical bonding and optical properties of Cu-based oxides ACuO (A = Li, Na, K and Rb): An ab initio study

Ab initio total energy calculations were performed to study in details the structural, elastic, electronic, chemical bonding and optical properties of Cu-based ternary oxides ACuO (A=Li, Na, K and Rb). Optimized atomic coordinates and lattice constants agree well with the existing experimental and theoretical data. Numerical estimations of the six independent elastic constants Cij and their related properties for monocrystalline ACuO were obtained. A set of elastic moduli for polycrystalline ACuO, namely bulk modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio σ, Lamé coefficients λ and Debye temperature θD were evaluated. Band structure, total and site-projected l-decomposed densities of states, charge-carrier effective masses, charge transfers and charge density distribution maps were obtained; analyzed and compared with the available theoretical data. Complex dielectric function, refractive index, extinction coefficient, reflectivity and loss function spectra were calculated with an incident radiation polarized parallel to both [100] and [001] crystalline directions.

Analysis of Optical properties of nanocrystalline titanium dioxide films

The optical properties of materials can be characterized in terms of the complex refractive index. We developed a simple and efficient method for determining the complex refractive index of nanomaterials that uses the relationship between this parameter and the light spectrum measured for a specimen. The optical properties of nanoparticle and nanotube TiO2 films were investigated. The results show that the morphology of nano-TiO2 affects the complex refractive index spectrum and therefore influences light dispersion and absorption of the film. We also simulated the optical energy density distribution within equivalent plane films using complex refractive index data.

Retrieval of Electronic Spectra of Charge Carriers in Organic Field-Effect Transistors from Charge Modulation Reflectance Spectra Distorted by Optical Interference

Charge modulation (CM) spectroscopy is useful for detecting and characterizing the electronic structure of charge carriers accumulated in organic field-effect transistors (OFETs). However, CM spectra are distorted by optical interference due to multiple reflections in OFETs particularly when reflection configurations are used. In this study, we demonstrated a method for retrieving the spectra of complex refractive indices of carriers from the distorted CM spectra by using a 4×4 matrix algorithm with general transition matrices. We tested this method by applying it to the CM spectra of a rubrene single-crystal FET measured at several incident angles of light. In spite of the strong distortion of the CM spectra, we could retrieve the spectrum of the imaginary part of refractive indices, which is similar to that observed in the transmission configuration. This method extends the applicability of CM spectroscopy to OFETs with opaque electrodes, where transmission configurations cannot possibly be applied.

A DFT study on structural, vibrational properties, and quasiparticle band structure of solid nitromethane

We report a detailed theoretical study of the structural and vibrational properties of solid nitromethane using first principles density functional calculations. The ground state properties were calculated using a plane wave pseudopotential code with either the local density approximation, the generalized gradient approximation, or with a correction to include van der Waals interactions. Our calculated equilibrium lattice parameters and volume using a dispersion correction are found to be in reasonable agreement with the experimental results. Also, our calculations reproduce the experimental trends in the structural properties at high pressure. We found a discontinuity in the bond length, bond angles, and also a weakening of hydrogen bond strength in the pressure range from 10 to 12 GPa, picturing the structural transition from phase I to phase II. Moreover, we predict the elastic constants of solid nitromethane and find that the corresponding bulk modulus is in good agreement with experiments. The calculated elastic constants show an order of C11> C22 > C33, indicating that the material is more compressible along the c-axis. We also calculated the zone center vibrational frequencies and discuss the internal and external modes of this material under pressure. From this, we found the softening of lattice modes around 8-11 GPa. We have also attempted the quasiparticle band structure of solid nitromethane with the G0W0 approximation and found that nitromethane is an indirect band gap insulator with a value of the band gap of about 7.8 eV with G0W0 approximation. Finally, the optical properties of this material, namely the absorptive and dispersive part of the dielectric function, and the refractive index and absorption spectra are calculated and the contribution of different transition peaks of the absorption spectra are analyzed. The static dielectric constant and refractive indices along the three inequivalent crystallographic directions indicate that this material has a considerable optical anisotropy.

Thickness dependent optical properties of titanium oxide thin films

TiO2 thin films of different thickness were prepared by the Electron Beam Evaporation (EBE) method on crystal silicon. A variable angle spectroscopic ellipsometer (VASE) was used to determine the optical constants and thickness of the investigated films in the spectral range from 300 to 800 nm at incident angles of 60°, 70°, and 75°, respectively. The whole spectra have been fitted by Forouhi–Bloomer (FB) model, whose best-fit parameters reveal that both electron lifetime and band gap of TiO2 thin film have positive correlation to the film thickness. The refractive indices of TiO2 thin film increase monotonically with an increase in film thickness in the investigated spectral range. The refractive index spectra of TiO2 thin films have maxima at around 320 nm and the maxima exhibit a marginally blue-shift from 327.9 to 310.0 nm with an increase in film thickness. The evolution of structural disorder in the TiO2 thin film growth can be used to explain these phenomena.

Structural, Elastic, Electronic and Optical Properties of Zinc-Blende MTe (M=Zn/Mg)

The structural, elastic, electronic, and optical properties of zinc-blende MTe (M=Zn/Mg) compounds were studied. The ultrasoft pseudopotential plane wave (PP-PW) method, based on density functional theory (DFT) within generalized gradient approximation (GGA), was used. Hybrid density functionals were applied to correct band gaps. Cubic ZnTe and MgTe are both direct band gap semiconductors, and calculated lattice parameters, elastic constants, and bulk moduli agree with previous results. Debye temperatures deduced from elastic constants for ZnTe and MgTe are 758 and 585 K, respectively. The dielectric function, refraction index, reflectivity and energy loss spectra were obtained and analyzed based on electronic band structures and densities of states.

Preparation of broadband antireflective coating by sol-gel method

A sol-gel method for the preparation of silica coating that varied in refractive index is developed. Silicon dioxide sol is obtained by hydrolysis and co-condensation reactions occurred in acid-catalyzed system. Surface morphology, refractive index, and transmission spectrum of the samples are studied. The results of transmission spectra of single-sided coatings show that the average transmittance of the samples increases about 4% compared with the uncoated one in the spectra range from 400 to 1 200 nm in the case of vertical incidence. For the double-sided coating the maximum transmittance is 99% at the wavelength of 840 nm.

N-Type microcrystalline silicon oxide layer and its application to high-performance back reflectors in thin-film silicon solar cells

Light trapping is a key issue in improving the efficiency of thin-film Si solar cells, and using a back reflector material plays a critical role in improving a cell's light-trapping efficiency. In this study, we developed n-type microcrystalline silicon oxide (n-μc-SiOx) films that are suitable for use as back reflectors in thin-film silicon solar cells. They exhibit a lower refractive index and lower absorption spectra, especially at long wavelengths of >700 nm, than conventional ZnO:Al materials, which are beneficial for this application. The n-μc-SiOx films were prepared by the PECVD (plasma-enhanced chemical vapor deposition) method and applied to the fabrication of back reflectors in μc-Si:H solar cells. We also characterized the changes in cell performance with respect to the refractive index, conductivity, and thickness of the n-μc-SiOx back reflectors. The novel back reflector boosts the total current density by up to 3.0% with the help of the enhanced long-wavelength response. It also improves open circuit voltage (Voc) and fill factor (FF), which may be attributed to the reduced shunt current caused by the anisotropic electrical characteristics of the n-μc-SiOx layer. Finally, we could achieve a conversion efficiency for the hydrogenated microcrystalline silicon (μc-Si:H) solar cells of up to 9.3% (Voc: 0.501 V, Jsc: 27.4 mA/cm2, FF: 0.68) using the n-μc-SiOx back reflector.

Rapid, Nondestructive Estimation of Surface Polymer Layer Thickness Using Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectroscopy and Synthetic Spectra Derived from Optical Principles

We have developed a rapid, nondestructive analytical method that estimates the thickness of a surface polymer layer with high precision but unknown accuracy using a single attenuated total reflection Fourier transform infrared (ATR FT-IR) measurement. Because the method is rapid, nondestructive, and requires no sample preparation, it is ideal as a process analytical technique. Prior to implementation, the ATR FT-IR spectrum of the substrate layer pure component and the ATR FT-IR and real refractive index spectra of the surface layer pure component must be known. From these three input spectra a synthetic mid-infrared spectral matrix of surface layers 0 nm to 10,000 nm thick on substrate is created de novo. A minimum statistical distance match between a process sample's ATR FT-IR spectrum and the synthetic spectral matrix provides the thickness of that sample. We show that this method can be used to successfully estimate the thickness of polysulfobetaine surface modification, a hydrated polymeric surface layer covalently bonded onto a polyetherurethane substrate. A database of 1850 sample spectra was examined. Spectrochemical matrix-effect unknowns, such as the nonuniform and molecularly novel polysulfobetaine-polyetherurethane interface, were found to be minimal. A partial least squares regression analysis of the database spectra versus their thicknesses as calculated by the method described yielded an estimate of precision of ±52 nm.

Shock-induced deformation of Shergottites: Shock-pressures and perturbations of magmatic ages on Mars

Shergottites and Chassignites practiced major deformation effects whose nature, magnitude and relevance were controversially evaluated and disputatively debated. Our studies of many shocked shergottites present, contrary to numerous previous reports, ample evidence for pervasive shock-induced melting amounting of at least 23vol.% of the shergottite consisting of maskelynite and pyrrhotite, partial melting of pyroxene, titanomagnetite, ilmenite and finding of several high-pressure polymorphs and pressure-induced dissociation reactions. Our results cast considerable doubt on using the refractive index (RI) or cathodoluminescence (CL) spectra of maskelynite, in estimating the magnitudes of peak-shock pressure in both shergottites and ordinary chondrites. RI of maskelynite was set after quenching of the feldspar liquid before decompression to maskelynite glass followed by glass relaxation after decompression at the closure temperature of relaxation. The RI procedure widely practiced in the past 38years revealed unrealistic very high-pressure estimates discrepant with the high-pressure mineral inventory in shocked shergottites and ordinary chondrites and with results obtained by robust laboratory static experiments. Shergottites contain the silica high-pressure polymorphs: the scrutinyite-structured polymorph seifertite, a monoclinic ultra dense polymorph of silica with ZrO2-structure, stishovite, a dense liquidus assemblage consisting of stishovite+Na-hexa-aluminosilicate (Na-CAS) and both K-lingunite and Ca-lingunite. Applying individual high-pressure silica polymorphs alone like stishovite, to estimate the equilibrium shock pressure, is inadequate due to the considerable shift of their nominal upper pressure bounds intrinsically induced by spatially variable absorptions of minor oxides like Al2O3, Na2O, FeO, MgO and TiO2. This practice revealed variable pressure estimates even within the same shergottite subjected to the same peak-shock pressure. Occurrence of Na-CAS+stishovite, lack of the NaAlSiO4 Ca-ferrite structured polymorph or jadeite indicates that the peak-shock pressures barely exceeded 22GPa. We present convincing and ample evidence refuting the claim that the shock-induced high-pressure inventory in shergottites and ordinary chondrites are disequilibrium assemblages resulted from local pressure spikes in excess of 80GPa and during the decompression stage. Such scenario calls for a series of incomplete and quenched retrograde reactions starting with the crystallization of Mg–silicate perovskite+magnesiowüstite, if the claimed peak-shock pressure was in excess of 80GPa. This would be followed by replacement of this pair by majorite-pyropess+magnesiowüstite or akimotoite+magnesiowüstite below 23GPa and 2000°C, polycrystalline ringwoodite above 16GPa, respectively and finally replacement by polycrystalline olivine below 16GPa. Such incomplete retrograde reactions were never encountered in any shergottite, chassignite or shocked ordinary chondrite so far. Olivine–ringwoodite phase transformation in the L6 Y-791384 commences with the coherent mechanism producing ringwoodite lamellae with their (111) planes parallel to the (100) of olivine followed by the incoherent mechanism due to build up of strain in the parental olivine. This is in accord with the olivine–ringwoodite settings produced in static laboratory experiments in a multi-anvil device. Olivine–ringwoodite phase transitions were also encountered in comparable settings in the shergottite NWA 1068. Application of experimentally obtained kinetic parameters of the olivine–ringwoodite phase transitions reveals possible duration of the natural dynamic events up to few seconds thus unambiguously refuting the claimed disequilibrium decompression mechanism.The shock-induced pervasive melting of labradorite, pyrrhotite, titanomagnetite, ilmenite and partial melting of clinopyroxene strongly suggests shock-induced partial to complete resetting of the Ar–Ar, Rb–Sr, Sm–Nd, Re–Os, U–Pb and Lu–Hf radiometric systems. This also casts considerable doubt on the radiometric ages shorter than 575Ma reported in the past 38years to allegedly be the igneous crystallization ages. These short ages probably resulted from partial or total shock-induced age resetting.

Vibrational analysis of liquid n-butylmethylether

The complex refractive index spectrum in the NIR and MIR range of liquid n-butylmethylether (NBME) was determined. Thin film recording technique was required to obtain quantitative transmission spectra in the MIR range. The experimental part was supported by a conformer population analysis and anharmonic vibrational analysis based on the B2PLYP/N07D method. The resulting population of 11 NBME conformers was analyzed and their calculated anharmonic vibrational spectra and calculated abundances (at 298K) were used to obtain the resultant spectrum of n-butylmethylether. The band assignment procedure was based on the calculated potential energy distributions.