Determination of optical parameters of Ga0.75In0.25Se layered crystals

The optical properties of the Ga_0.75In_0.25Se crystals have been investigated by means of transmission and reflection measurements in the wavelength range of 380–1100 nm. The analysis of the results performed at room temperature revealed the presence of optical indirect transtions with band gap energy of 1.89 eV. The variation of the band gap energy as a function of temperature was also studied in the temperature range of 10–300 K. The rate of change of band gap energy (γ = –6.2 × 10^–4 eV/K) and absolute zero value of the band gap (E_gi(0) = 2.01 eV) were reported. The wavelength dependence of the refractive index was analyzed using Wemple and DiDomenico, Sellmeier and Cauchy models to find the oscillator energy, dispersion energy, oscillator strength and zero‐frequency refractive index values. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Refractive index dispersion of relaxor ferroelectric 0.9Pb(Zn1/3Nb2/3)O3‐0.1PbTiO3 single crystal

The refractive indices of 0.9Pb(Zn_1/3Nb_2/3)O₃‐0.1PbTiO₃ single crystal at different wavelengths have been measured by the minimum deviation method at room temperature, and their dispersion equations are obtained. The parameters connected to the energy band structure are obtained by fitting single‐oscillator dispersion equation. Despersion energies are found to take on covalent crystal values. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature‐tuned band gap energy and oscillator parameters of Tl2InGaSe4 semiconducting layered single crystals

The optical properties of Tl₂InGaSe₄ layered single crystals have been studied through the transmission and reflection measurements in the wavelength range of 500‐1100 nm. The analysis of room temperature absorption data revealed the presence of both optical indirect and direct transitions with band gap energies of 1.86 and 2.05 eV, respectively. Transmission measurements carried out in the temperature range of 10‐300 K revealed that the rate of change of the indirect band gap with temperature is γ = – 4.4 × 10^‐4 eV/K. The absolute zero value of the band gap energy was obtained as E_gi(0) = 1.95 eV. The dispersion of the refractive index is discussed in terms of the single oscillator model. The refractive index dispersion parameters: oscillator wavelength and strength were found to be 2.53 × 10^–7 m and 9.64 × 10¹³ m^–2, respectively. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Specific features of the optical spectra in Tl2In2S3Se layered single crystals

The optical properties of Tl₂In₂S₃Se layered single crystals have been studied by means of transmission and reflection measurements in the wavelength range of 450‐1100 nm. The analysis of the absorption data revealed the presence of both optical indirect and direct transitions with energy band gaps of 2.16 and 2.42 eV, respectively. The observed coexistence of indirect and direct energy band gaps is related to the anisotropy of the Tl‐containing layered crystals. The dispersion of the refractive index is discussed in terms of the Wemple‐DiDomenico single‐effective‐oscillator model. The refractive index dispersion parameters: oscillator energy, dispersion energy, oscillator strength and zero‐frequency refractive index were found to be 4.78 eV, 43.58 eV, 13.18 × 10¹³ m^–2 and 3.18, respectively. From X‐ray powder diffraction study, the parameters of monoclinic unit cell were determined. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of thermoannealing on crystallinity and optical properties of Sb2S3 thin films

Sb₂S₃ thin films are obtained by evaporating of Sb₂S₃ powder onto glass substrates maintained at room temperature under pressure of 2×10^‐5 torr. The composition of the thin films was determined by energy dispersive analysis of X‐ray (EDAX). The effect of thermal annealing in vacuum on the structural properties was studied using X‐ray diffraction (XRD) technique and scanning electron microscopy (SEM). The as‐deposition films were amorphous, while the annealed films have an orthorhombic polycrystalline structure. The optical constants of as‐deposited and annealed Sb₂S₃ thin films were obtained from the analysis of the experimental recorded transmission spectral data over the wavelength range 400‐1400 nm. The transmittance analysis allowed the determination of refractive index as function of wavelength. It was found that the refractive dispersion data obeyed the single oscillator model, from which the dispersion parameters (oscillator energy, E₀, dispersion energy, E_d) were determined. The static refractive index n(0), static dielectric constant, ε_∞, and optical band gap energy, E_g, were also calculated using the values of dispersion parameters. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and Optical Properties of LiNbO3: MgO Single Crystals

The technological procedure of the manufacturing of the LiNbO₃^˙ single crystals doped with 5 mol.% MgO is described in this paper. The results of the investigation of the crystal optical properties, ESR spectra and optical homogeneity are presented. The refractive index dispersion in 300–700 nm region and their temperature dependencies in 20–500 °C range are measured. The dispersion curve is approximated by the two oscillator Sellmeier formula. The data on the LiNbO₃: MgO crystal optical resistance are presented.     

Thermal conductivity and refractive indices of Nd:GdVO4 crystals

The thermal conductivities of Nd:YAG, M(Y,Gd)VO₄ crystals were measured at 298 K. The value of Nd:GdVO₄ crystal along <001> direction was 11.4 W/mK, which was higher than that of YAG crystal measured to be 10.7 W/mK. The principal refractive indices of Nd:GdVO₄ crystal in the temperature range from 20 °C to 170 °C were determined by auto‐collimation method. Based on the measured values of refractive indices, the Sellmeier equation and expression of temperature dependence of refractive indices have been obtained. The measured results show that the birefringence Δn is 0.22007 at 20 °C and temperature coefficient of birefringence is 4.33 × 10⁻⁶/°C for 1.064 μm. These results prove that the GdVO₄ crystal is a laser crystal with excellent thermal and birefringence properties. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Semiconducting TiO2SiO2 glasses (II): Optical properties

The refractive index, optical absorption coefficient α and the thermomodulated absorption dα/dT have been measured on 70% TiO₂?30% SiO₂ glasses with up to 8% Ti³⁺. The direct absorption data show intense ligand field absorption at photon energies hν = 1.9 and 3.0 eV, arising from Ti³⁺ in a distorted octahedral environment. In the bandgap region at 3.5 eV α obey αhν ～ (hν ? E_g)²; it is qualitatively different from the bandgap absorption in crystalline TiO₂. The da/dT spectra show peaks in the bandgap region and at 1.1 eV in the near IR. This last peak is attributed to absorption by small polarons, and its line shape is compared with theoretical predictions.     

Effect of isomorphic atom substitution on the refractive index and oscillator parameters of TlInS2xSe2(1‐x) (0.25 ≤ x ≤ 1) layered mixed crystals

The optical properties of TlInS_2xSe_2(1‐x)mixed crystals (0.25 ≤ x ≤ 1) have been studied at room temperature through the transmittance and reflectivity measurements in the wavelength range of 400–1100 nm. The spectral dependence of the refractive index for all compositions of studied crystals were obtained. The dispersion of the refractive index is discussed in terms of the Wemple–DiDomenico single‐effective‐oscillator model. The compositional dependencies of refractive index dispersion parameters: oscillator energy, dispersion energy and zero‐frequency refractive index were revealed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical Characterization of Irradiation plus Annealing – induced VAsZnGa Pairs in p-type GaAs (Zn) Crystals

Effect of fast electron irradiation (E =2.2 Mev, ϕ_c = 1 × 10¹⁶ el/cm²) and subsequent annealings (T = 150 to 350 °C, t = 10 to 600 min) of zinc-doped p-type GaAs crystals on the formation and dissociation of V_AsZn_Ga, pairs is studied. An analysis of the formation and dissociation kinetics of V_AsZn_Ga pairs permitted to find the diffusion coefficient of radiation-induced arsenic vacancies D(D = 1.5 × 10⁻¹⁸, 1 × 10⁻¹⁷ and 5 × 10⁻¹⁷ cm²/s at 150, 175 and 200 °C accordingly), their migration energy ϵ_m(ϵ_m = 1.1 eV), the binding energy of V_AsZn_Ga, pairs ϵ_b(ϵ_b = 0.5 eV), and also their dissociation energy ϵ_d(ϵ_d = 1.6 eV).     

Single oscillator energy and dispersion energy of uniform thin chalcogenide films from Cu–As–S–Se system

This paper presents some of the results obtained by using the modified envelope method, which takes substrate absorption into account. Samples investigated in this paper are the series of amorphous thin chalcogenide uniform films from system Cu_x[As₂(S_0.5Se_0.5)₃]_100−x. Thin films were deposited under vacuum on glass substrates by thermal evaporation technique, from previously synthesized bulk samples. The dispersion of the refractive index is discussed in terms of the single oscillator model proposed by Wemple and DiDomenico. By using this model, i.e. by plotting (n² − 1)⁻¹ against (ℏω)² and fitting a straight line, oscillator parameters, E₀ – the single oscillator energy and E_d – the dispersion energy, were directly determined.     

Optical properties of Ge–Se–Te wedge-shaped films by using only transmission spectra

Amorphous Ge₁₀Se_90?xTe_x (with x = 0, 5, 10 and 15 at.%) thin films were prepared by thermal evaporation method. The optical transmission spectra of these films were measured in the wavelength range of 500–2500 nm in order to drive the refractive index and the absorption coefficient of these films. Applying the analytical expressions proposed by Swanepoel, enabling the calculations of optical constants of thin films with non-uniform thickness with high accuracy. Furthermore, the dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model. It was found that, the mechanism of the optical absorption follows the rule of the allowed non-direct transition. The optical band gab, E_g, and the oscillator energy, E_o, decrease while the dispersion energy, E_d, increases by increasing Te content. The relationship between the obtained results and the chemical compositions of the Ge₁₀Se_90?xTe_x thin films were discussed in terms of the chemical bond approach, the excess of Se–Se homopolar bonds and the cohesive energy (CE).     

Optical constants of DC magnetron sputtered titanium dioxide thin films measured by spectroscopic ellipsometry

Optical constants of DC magnetron sputtered TiO₂ thin film have been determined by Spectroscopic Ellipsometry in the photon energy range 1.2 to 5.5 eV at room temperature. The measured dielectric‐function spectra reveal distinct structures at energies of the E1, E1 + Δ1 and E2 critical points are due to interband transitions. The root mean square roughness of the magnetron sputtered TiO₂ thin films evaluated by ex‐situ atomic force microscopy is 5.8 nm. The Dielectric constant values were found to be substantially lower than those for the bulk TiO₂. The dielectric related Optical constants, such as the refractive index, extinction coefficient, absorption coefficient and normal incidence of reflectivity determined from the spectroscopic ellipsometry data are presented and analyzed. The optical constants of the films were also determined using the optical transmittance measurements and the results were discussed. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Energetic Band Location of Rhenium-doped MoSe2 Single Crystals to Assess their Usefulness in PEC Solar Cell Fabrication

Single crystals of MoSe₂ and rhenium-doped MoSe₂ have been grown by direct vapour transport technique and characterized by optical and electrochemical studies. The transmission spectra show the crystals of MoSe₂ and rhenium-doped MoSe₂ to be direct band gap semiconductors with band gap 1.6 eV and 1.2 eV, respectively. Mott-Schottky plots have been drawn to determine the type of semiconductor and its parameters, N_d, E_C and E_V.     

Characterization of Vacuum Evaporated Polycrystalline Cd0.96Zn0.04Te Thin Films by XRD,Raman Scattering and Spectroscopic Ellipsometry

Cd_0.96Zn_0.04Te thin films are deposited onto well cleaned glass substrates (Corning 7059) kept at room temperature by vacuum evaporation and the films are annealed at 423 K. Rutherford Backscattering Spectrometry and X‐ray diffraction techniques are used to determine the thickness, composition and crystalline structure and grain size of the films respectively. The films exhibited zinc blende structure with predominant (111) orientation. The surface morphology of the films is studied by Atomic Force Microscopy. The rms roughness of the as‐deposited films is 3.7 nm and on annealing the films at 423K, the rms roughness value decreases to 3.4 nm. The Raman spectra of the Cd_0.96Zn_0.04Te films are recorded at room temperature to study lattice vibrations and their interactions with other excitations. The intensity of the peak increases and the FWHM decreases on annealing the films. The pseudodielectric‐function spectra, ε(E) = ε₁(E) + i ε₂(E), of polycrystalline Cd_0.96Zn_0.04Te thin films in the 1.3 ‐ 5.5eV photon energy range at room temperature are measured by spectroscopic ellipsometry. The measured dielectric function spectra reveal distinct structures at energies of the E₁, E₁+Δ₁ and E₂ critical points are due to interband transitions.     

Annealing temperatures induced optical constant variations of methyl violet 2B thin films manufactured by the spin coating technique

Spin coating technique has been successfully applied to deposit uniform methyl violet 2B (MV2B) thin films. X-ray diffraction and Fourier-transform infrared techniques were used to study the crystal and molecular structure of MV2B. The optical properties of the films have been studied by spectrophotometer measurements of transmittance and reflectance at normal incidence of light in the spectral range of 200–2500 nm. The absorption and refractive indices are independent of the film thickness. The absorption parameters such as molar extinction coefficient, oscillator strength and electric dipole strength have been reported before and after annealing. The type of electronic transition is indirect allowed transition with onset energy gap of 1.82 eV and optical energy gap of 3.65 eV. Annealing temperatures reduce structure disorder, remove trap level, increase values of the onset and optical energy gaps and decrease refractive index. The single oscillator model has been applied for calculating the dispersion parameters. The oscillator energy, the dispersion energy, the high frequency dielectric constant, the lattice dielectric constant and the ratio of free charge carriers' concentration to its effective mass were evaluated before and after annealing. The dielectric properties of the films were also determined.     

Optical and opto‐electronic properties of polycrystalline Cd0.96Zn0.04Te thin films

Cd_0.96Zn_0.04Te thin films are deposited onto thoroughly cleaned glass substrates (Corning 7059) kept at room temperature by vacuum evaporation. The films are found to have good stoichiometry as analyzed by Rutherford Backscattering Spectrometry. The films exhibited zinc blende structure with predominant (111) orientation. The surface morphology of the films is studied by Atomic Force Microscopy. The rms roughness of the films evaluated by AFM is 3.7 nm. The pseudodielectric‐function spectra, ε(E) = ε₁(E) + i ε₂(E) at room temperature are measured by spectroscopic ellipsometry. The measured dielectric function spectra reveal distinct structures at energies of the E₁, E₁+ Δ₁ and E₂ critical points. The band gap energy of the films measured by optical transmittance measurement is 1.523 eV. The PL spectrum of the films shows intense emission due to free and bound exciton recombination and no emission associated with crystal imperfection and deeper impurity levels. The PL line shapes give indications of the high quality of the layers.     

Optical properties of pure and metal ions doped ammonium sulfate single crystals

A study of the optical properties of pure‐and some metal ions doped ammonium sulfate crystals (AS) were made. Optical constants of AS crystals were calculated at room temperature. The optical absorption coefficient (α ) was analyzed and interpreted to be in the allowed direct transition. The introduction of Rb⁺ or Cs⁺ ions gives rise to an intense charge transfer band with a maximum at λ= 310 nm in the optical spectrum. In case of Cr³⁺ ‐doping, the absorption shows a shoulder just before the onset band to band transition. The values of the allowed direct energy gap E_g for undoped and doped crystals were calculated. It was found that E_g values were decreased with metal ions doping. The refractive index, the extinction coefficient and both the real and imaginary parts of the dielectric permittivity were calculated as a function of photon energy. The validity of Cauchy‐Sellimeier equation was checked in the wavelength range 4.9 ‐ 5.6 eV and its parameters were calculated. Applying the Single‐Effective‐Oscillator model, the moments of ε (E ) could be estimated. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of annealing on the structural,electrical and optical properties of nanostructured TiO2 thin films

Nanostructured titanium dioxide thin films were prepared using reactive pulsed laser ablation technique. Effects of annealing on the structural, morphological, electrical and optical properties are discussed. The structural, electrical and optical properties of TiO₂ films are found to be sensitive to annealing temperature and are described with GIXRD, SEM, AFM, UV‐Visible spectroscopy and electrical studies. X‐ray diffraction studies showed that the as‐deposited films were amorphous and at first changed to anatase and then to rutile phase with increase of annealing temperature. Optical constants of these films were derived from the transmission spectra and the refractive index dispersion of the films, subjected to annealing at different temperatures, is discussed in terms of the single oscillator‐Wemple and Didomenico model. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

MAEAM investigation of the structural stability and theoretical strength of Fe crystals under uniaxial loading

The structural stability and theoretical strength of BCC crystal Fe under uniaxial loading have been investigated with the modified analytic embedded‐atom method (MAEAM). Even if an orthorhombic path is applied, the deformation is spontaneous along the tetragonal path till Milstein modified Born criterion B₂₂‐B₂₃>0 is violated at λ₁=0.9064 in the compressive region. The branched orthogonal path with lower compressive stress σ₁ and energy E is preferred over the conventional tetragonal Bain path. A stress‐free FCC phase with the local maximum energy of ‐4.2186eV appearing either in compressive region (orthorhombic path) at λ₁=0.8923 or in tensile region (tetragonal path) at λ₁=1.2619 is unstable and would slip spontaneously into its near neighbor stress‐free mBCT phase with the local minimum energy of ‐4.2270eV. The initial BCC phase with the lowest energy of ‐4.280eV is the most stable in correspondence with the actual behavior of Fe. Furthermore, the stable region ranges from ‐79.7eV/nm³ to 30.6eV/nm³ in the theoretical strength or from 0.9064 to 1.1788 in the stretch λ₁ correspondingly. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)