Optical characterization of tin containing novel chalcogen rich glassy semiconductors

Amorphous thin film materials with different compositions of Se_80?xTe₂₀Sn_x (0 ≤ x ≤ 10) system have been deposited on glass substrates by a well known thermal evaporation technique. Structural characterization of different compositions of aforementioned system has been done by Raman spectroscopy. The optical properties of thin films have been studied in the wavelength range 200–1100 nm by the utilization of the optical absorbance spectra of deposited thin films. To calculate the optical band gap from the optical absorption spectra, we have used Tauc model that follows the mechanism of allowed ‘non-direct electronic transition’. Subsequently, we have determined the energy band gap, metallization criterion and refractive index of thin films of aforesaid system. The variation in optical properties with composition has been interpreted in terms of density of defect states.     

Structural and optical properties of lithium borobismuthate glasses

Glasses with compositions 25Li₂O-(75−x)Bi₂O₃-x B₂O₃, with 0?x?30 mol%, have been prepared using the melt quenching technique. The density and the molar volume have been determined. IR spectroscopy is used as a structural probe of the nearest neighbor environment in the glass network. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range 400-1100 nm. The values of the optical band gap E_g^opt for indirect transition and refractive index have been determined for 0?x?30 mol%. The average electronic polarizability of the oxide ion α_o²⁻ and the optical basicity have been estimated from the calculated values of the refractive indices. Variations in the different physical parameters such as the density, molar volume, optical band gap, refractive index, average electronic polarizability of the oxide ion and optical basicity with B₂O₃ content have been analyzed and discussed in terms of the changes in the glass structure.     

Effect of change in structural and magnetic states of Pt<Subscript>74.1</Subscript>Fe<Subscript>25.9</Subscript> alloy on its optical properties

The effect of atomic disordering on the optical properties of Pt_74.1Fe_25.9 alloy, whose stoichiometry is close to that of Pt₃Fe, has been investigated. The optical constants of ordered and plastically deformed alloys, which are, respectively, in the paramagnetic and ferromagnetic states, have been measured by the polarimetric method. The frequency dispersions of the permittivity, optical conductivity, and reflectivity, as well as the microscopic characteristics of conduction electrons (plasma and relaxation frequencies), have been calculated. The energy dependences of the optical conductivity are compared to the calculated energy-band structure of atomically ordered and disordered Pt₃Fe compounds.     

Physical,optical and electrical properties of calcium bismuth borate glasses

The variation in physical, optical and electrical properties has been investigated as a function of Bi₂O₃ content in 20CaO?·?xBi₂O₃?·?(80???x)B₂O₃ (0?≤?x?≤?60, in mol%) glasses. The samples were prepared by normal melt-quenching process, and the optical absorption and reflection spectra were recorded in the wavelength range of 400–950 nm. The fundamental absorption edge has been identified from the optical absorption spectra. The optical band gap, E _g, for indirect allowed and indirect forbidden transitions has been determined from the available theories and its value lies between 1.80–2.37 eV and 1.08–2.19 eV, respectively. The theoretical fitting of the optical absorption indicates that the present glass system behaves as an indirect gap semiconductor. The origin of the Urbach energy, ΔE, has been associated with the phonon-assisted indirect transitions. The refractive index and optical dielectric constant have been evaluated from the reflection spectra. The density and molar volume are found to depend on the molar concentration of Bi₂O₃. The values of DC electrical conductivity have been measured from 373 to 623 K and the activation energy has been calculated. Theoretical optical basicity has been reported as a function of the Bi₂O₃ content. The variations have been discussed in terms of structural changes.     

Optical and acoustic properties of TeO2/WO3 glasses with small amount of additive ZrO2

The optical and acoustic properties of tellurite glasses in the system TeO₂/ZrO₂/WO₃ have been investigated. The refractive index at different wavelengths and the optical spectra of the glasses have been measured. From the refractive index and absorption edge studies for prepared glasses, the optical parameter viz; optical band gap (E_opt), Urbach energy, (ΔE), dispersion energy, E_d, and the average oscillator energy, E₀, have been calculated. Sound velocities were measured by pulse echo technique. From these velocities and densities values, various elastic moduli were calculated. The variations in the refractive index, optical energy gap and elastic moduli with WO₃ content have been discussed in terms of the glass structure. Quantitatively, we used the bond compression model for analyzing the room temperature elastic moduli data. By calculating the number of bonds per unit volume, the average stretching force constant, and the average ring size we can extract valuable information about the structure of the present glasses.     

Effect of C doping on the structural and optical properties of sol–gel TiO2 thin films

Undoped and C-doped TiO₂ thin films have been prepared by sol–gel process. Their structure and optical properties have been investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–vis spectroscopy. It has been observed that C dopants retard the transformation from anatase-to-rutile phase. Namely, C doping effect is attributed to the anatase phase stabilization. The optical analyses show that the optical band gap of anatase C-doped TiO₂ decreases with increasing amount of C. Also, it is founded that C dopants have been shown to make TiO₂ have a visible light photoresponse.     

Thin ferroelectric films: Preparation and prospects of integration

The properties of (Ba,Sr)TiO₃ and BiFeO₃ thin films and related nanostructures have been considered. The films have been prepared by rf sputtering in an oxygen atmosphere at an elevated pressure, and the nanostructures have been produced using focused ion-beam etching. The electric field has been applied across a planar interdigital structure of electrodes. The structure, dielectric, electro-optical, and nonlinear optical properties of the prepared samples have been investigated over wide ranges of thicknesses and electric field frequencies. The high efficiency of the planar switching and its influence on the optical properties of the produced structures have been demonstrated. The nanostructuring makes it possible to change the dielectric and optical properties of the materials under investigation, thus increasing the range of switching of functional parameters.     

FTIR-spectroscopy of (GaAS)n/(AlAs)m superlattices

The optical properties of (GaAs)_n/(AlAs)_m superlattices in the infra-red spectral region have been studied. The confinement of optical phonons has been observed in both GaAs and AlAs layers of superlattices under investigation. The superlattice modes caused by the coupling between LO phonons and collective intersubband excitations have been found in doped superlattices. Macroscopic and microscopic calculations have been used for the analysis of experimental results. Good agreement with experiment has been obtained.     

Optical properties in binary Si: H alloy from disilane

Binary Si: H alloy films having a wide optical band gap have been prepared by r.f. glow discharge of disilane. The optical band gap and the infrared absorption spectrum have been measured for those binary alloy films. The infrared absorption strength for 850 cm^-1 peak and the vibrational freqcencies for all absorption peaks are increased with an increase in the optical band gap. This sugests the (SiH₂)_n group formation in a wide optical gap film.     

Optical spectroscopy and electronic structure of the Er5Ge3 compound

The results of the study of the optical properties and electronic structure of the Er₅Ge₃ compound have been presented. In the wavelength range of 0.22–15 μm (0.083–5.64 eV), the optical constants have been measured, and the spectral and electronic characteristics have been determined. The spin-polarization calculations of the band spectrum have been performed in the local electron spin density approximation (LSDA) with a correction for strong correlations in the 4f shell of the rare-earth atom (LSDA + U method). The main features of the experimental dispersion dependence of the optical conductivity in the region of quantum light absorption have been interpreted based on the results of calculations of the electron density of states.     

Thickness-dependent electrical and optical properties of Ge8Sb2Te11 thin films

The amorphous Ge₈Sb₂Te₁₁thin films with varying thickness are thermally deposited on well-cleaned glass substrate from its polycrystalline bulk. Absence of any sharp peak confirms the amorphous nature of deposited films. Thickness-dependent electrical and optical properties including dc-activation energy, sheet resistivity, optical band gap, band tailing parameter, etc. of Ge₈Sb₂Te₁₁thin films have been studied. The optical parameters have been calculated from transmission, reflection and absorbance data in the spectral range of 200–1100 nm. It has been found that optical band gap and band tailing parameter decreases with the increase in Ge₈Sb₂Te₁₁thin films thickness. The dc-activation energy and sheet resistivity decreases while the crystallization temperature of the amorphous Ge₈Sb₂Te₁₁ films increases with the increase in thickness of the films. The decrease of the sheet resistivity has been substantiated quantitatively using the classical size-effect theory. These results have been explained on the basis of rearrangements of defects and disorders in the amorphous chalcogenide system.     

Electronic structure of the TbMn<Subscript>0.33</Subscript>Ge<Subscript>2</Subscript> compound: Band calculation and optical experiment

The results of the investigation of the electronic structure and optical properties of the TbMn_0.33Ge₂ compound have been presented. The spin-polarized calculations of the band spectrum have been performed within the framework of the local spin density approximation (LSDA) with a correction for strong correlations in the 4f shell of the rare-earth ion (the LSDA + U method). The optical constants have been measured using the ellipsometric method and a number of spectral and electronic characteristics of the compound under investigation have been determined over a wide range of wavelengths. The interband part of the experimental dependence of the optical conductivity has been interpreted using the results of the calculation of the electron density of states.     

Effect of Bi2O3 content on physical and optical properties of 15Li2O-15K2O-xBi2O3-(65−x) B2O3: 5V2O5 glass system

Multi-component bismuth borate glasses doped with vanadium ions 15Li₂O-15K₂O-xBi₂O₃-(65−x) B₂O₃: 5V₂O_5, (x=3, 5, 7, 10, 12 and 15) have been prepared using conventional melt quench technique. Characterization of the prepared glasses has been done using X-ray diffraction, differential scanning calorimetry and density measurements. The effect of Bi₂O₃ content on the optical properties of the present glass system is studied from the optical absorption spectra recorded in the wavelength range 200-800 nm. The fundamental absorption edge has been identified from the optical absorption spectra. The values of optical band gap for indirect allowed transitions have been determined using available theories. The origin of the Urbach energy is associated with the phonon-assisted indirect transitions. The density and molar volume studies indicate that Bi₂O₃ in these glasses is acting partly as network modifier and partly as network former. The variations in the optical band gap energies, density and molar volume with Bi₂O₃ content have been discussed in terms of changes in the glass structure. Values of the theoretical optical basicity, average crosslink density and the average electronic polarizability are also reported.     

EPR and optical spectroscopy of the Tm2+ ion in the KMgF3 single crystal

Paramagnetic Tm²⁺ ion centers in the KMgF₃ single crystal have been studied by electron paramagnetic resonance and optical spectroscopy. The Stark level energies of the cubic Tm²⁺ multiplets have been established from the luminescence spectra and the crystal field parameters have been calculated. Information about the phonon spectra of KMgF₃ crystals has been obtained from the electron-vibrational structure of the optical luminescence spectra.     

Energy and optical absorption spectra of endohedral metallofullerenes with Gd or Ho as strongly correlated π-electron systems

Isomerically pure endohedral metallofullerenes Gd@C82(C2v), Ho@C₈₂(C_2v), and their monoanions have been synthesized and separated. The optical absorption spectra of solutions of obtained compounds in o-dichlorobenzene have been studied. Within the Hubbard model, the energy spectrum of isomer of C_2v symmetry (no. 9) of fullerene С₈₂ has been calculated. Based on the obtained spectrum, optical absorption spectra of endohedral metallofullerenes Gd@C₈₂ and Ho@C₈₂ and their monoanions have been simulated. The calculated optical absorption spectra have been compared with experimental ones; it has been found that qualitative agreement between them is observed.     

Energy spectrum and optical transitions in C80 fullerene isomers

The energy spectra of all isomers of the C₈₀ fullerene have been calculated in terms of the Schubin-Wonsowskii-Hubbard model. On this basis, their optical absorption spectra have also been calculated. The optical absorption spectra calculated for the endohedral Ca@C₈₀, Ba@C₈₀, and Sr@C₈₀ fullerenes with the I _h symmetry agree well with the experimental data. This circumstance allows us to conclude that the optical absorption spectra of other isomers (for which experimental data are unavailable) obtained in this work can be used for their identification.     

Electrical and optical properties of chalcopyrite compounds

Optical and electrical properties of Zn- and Cd-modified Cu₂SnSe₄ amorphous films have been studied. The results show that Zn and Cd incorporation decreases the thermal activation energy, the pre-exponential factor and the optical gap. Variation in the refractive index and extinction coefficient with the wavelength has been also reported. The relations between the optical gap and the chemical composition in the investigated films have been discussed in terms of the average heat of atomization. The effect of γ-radiation up to 71.25 Mrad dose on the optical gap was also studied.     

Variations of the band gap of Hg1 ? x Cd x Te solid solutions in response to a magnetic field

The optical transmission spectra of Hg_{1 ? x} Cd _x Te epitaxial layers with a magnetization gradient have been investigated experimentally. The magnetization gradient has been artificially created by the opposite arrangement of the poles of the magnets. The possibility of transforming the shape of the spectral dependences of the optical transmission of the HgCdTe films after their exposure to a magnetic field has been demonstrated. Assumptions about the mechanism underlying this phenomenon have been made.     

Optical transitions of InAs/In0.36Ga0.64As/GaAs(311B) surface quantum dots clearly identified by the piezoreflectance technique

The bilayer InAs/In_0.36Ga_0.64As/GaAs(311B) quantum dots (QDs), including one InAs buried quantum dot (BQD) layer and the other InAs surface quantum dot (SQD) layer, have been grown by molecular beam epitaxy (MBE). The optical properties of these three samples have been studied by the piezoreflectance (PzR) spectroscopy. The PzR spectra do not exhibit only the optical transitions originated from the InAs BQDs, but the features originated from the InAs SQDs. After the InAs SQDs have been removed chemically, those optical transitions from InAs SQDs have been demonstrated clearly by investigating the PzR spectra of the residual InAs BQDs in these samples. The great redshift of these interband transitions of InAs SQDs has been well discussed. Due to the suitable InAs SQD sizes and the thickness of In_0.36Ga_0.64As layer, the interband transition of InAs SQDs has been shifted to ∼1.55 μm at 77 K.     

Deposition of MgF2 thin films for antireflection coating by using thermionic vacuum arc (TVA)

In this study, optical and surface properties of MgF₂ thin films produced by thermionic vacuum arc (TVA) technique have been investigated. By means of this technique the MgF₂ thin film produced by condensing the plasma of anode material generated by using TVA under high vacuum conditions on the glass. The optical properties have been investigated by using Filmetrics F20 and UV/VIS spectrometer. For surface properties of produced thin films EDS, SEM and AFM have been used. Our analysis shows that MgF₂ thin films produced by using TVA are proper single and multi layer anti-reflective (AR) coating and TVA technique brings very important advantages for ophthalmic glass coating and industrial applications' optical purposes.