Derivation of the optical constants of spin coated CeO2-TiO2-ZrO2 thin films prepared by sol-gel route

Ternary thin films of cerium titanium zirconium mixed oxide were prepared by the sol-gel process and deposited by a spin coating technique at different spin speeds (1000-4000 rpm). Ceric ammonium nitrate, Ce(NO₃)₆(NH₄)₂, titanium butoxide, Ti[O(CH₂)₃CH₃]₄, and zirconium propoxide, Zr(OCH₂CH₂CH₃)₄, were used as starting materials. Differential calorimetric analysis (DSC) and thermogravimetric analysis (TGA) were carried out on the CeO₂-TiO₂-ZrO₂ gel to study the decomposition and phase transition of the gel. For molecular, structural, elemental, and morphological characterization of the films, Fourier Transform Infrared (FTIR) spectral analysis, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), cross-sectional scanning electron microscopy (SEM), and atomic force microscopy (AFM) were carried out. All the ternary oxide thin films were amorphous. The optical constants (refractive index, extinction coefficient, band gap) and thickness of the films were determined in the 350-1000 nm wavelength range by using an nkd spectrophotometer. The refractive index, extinction coefficient, and thickness of the films were changed by varying the spin speed. The oscillator and dispersion energies were obtained using the Wemple-DiDomenico dispersion relationship. The optical band gap is independent of the spin speed and has a value of about E_g≈2.82±0.04 eV for indirect transition.     

Structure and optical properties of chemically synthesized titanium oxide deposited by evaporation technique

Titanium oxide inorganic ion exchange material was synthesized by hydrolysis with water and ammonia solution. Structural feature of the synthesized titanium oxide was analyzed using X-ray diffraction, X-ray fluorescence and infrared spectrometer technique. Tentative formula of titanium oxide was determined and written as TiO₂·0.58H₂O. Titanium oxide films were deposited on glass substrates by means of an electron beam evaporation technique at room temperature from bulk sample. The films were annealed at 250, 350, 450, and 550 °C temperatures. Transmittance, reflectance, optical energy gap, refractive index and extinction coefficient were investigated. The transmittance values of 85% in the visible region and 88% in the near infrared region have been obtained for titanium oxide film annealed at 550 °C. Kubelka-Munk function was used to evaluate the absorption coefficient which was used to determine the optical band gap. It was found that the optical band gap increases with increasing annealing temperature whereas the refractive index and extinction coefficient decreases.     

Evolution of structural and optical properties of rutile TiO2 thin films synthesized at room temperature by chemical bath deposition method

Nanocrystalline thin films of TiO₂ were prepared on glass substrates from an aqueous solution of TiCl₃ and NH₄OH at room temperature using the simple and cost-effective chemical bath deposition (CBD) method. The influence of deposition time on structural, morphological and optical properties was systematically investigated. TiO₂ transition from a mixed anatase–rutile phase to a pure rutile phase was revealed by low-angle XRD and Raman spectroscopy. Rutile phase formation was confirmed by FTIR spectroscopy. Scanning electron micrographs revealed that the multigrain structure of as-deposited TiO₂ thin films was completely converted into semi-spherical nanoparticles. Optical studies showed that rutile thin films had a high absorption coefficient and a direct bandgap. The optical bandgap decreased slightly (3.29–3.07 eV) with increasing deposition time. The ease of deposition of rutile thin films at low temperature is useful for the fabrication of extremely thin absorber (ETA) solar cells, dye-sensitized solar cells, and gas sensors.     

Structural and optical evaluation of WOxNy films deposited by reactive magnetron sputtering

Thin films of tungsten oxynitrides were deposited on substrates preheated at 300 °C from metallic tungsten target using reactive pulsed d.c. magnetron sputtering. The deposition was carried out at different nitrogen to total reactive gas partial pressures ratios. The energy dispersive analysis of X-ray showed that significant incorporation of nitrogen occurred only when the nitrogen partial pressure exceeded 74% of the total reactive gas pressure. X-ray diffraction analysis revealed that the formation of a specific crystalline phase is affected by the composition and the possibility of competitive growth of different phases. The increase of nitrogen content into the films increases the optical absorption and decreases the optical band gap. The refractive index was determined from the transmittance spectra using Swanepoel's method. It was found that the refractive index increases with increasing nitrogen content over the entire spectral range. The values of the tungsten effective coordination number, N_c, was estimated from the analysis of the dispersion of the refractive index, and an increase in N_c with increasing nitrogen content was observed.     

Preparation of Cu2ZnSnS4 thin films by hybrid sputtering

In order to fabricate Cu₂ZnSnS₄ thin films, hybrid sputtering system with two sputter sources and two effusion cells is used. The Cu₂ZnSnS₄ films are fabricated by the sequential deposition of metal elements and annealing in S flux, varying the substrate temperature. The Cu₂ZnSnS₄ films with stoichiometric composition are obtained at the substrate temperature up to 400 °C, whereas the film composition becomes quite Zn-pool at the substrate temperature above 450 °C. The Cu₂ZnSnS₄ film shows p-type conductivity, and the optical absorption coefficient and the band gap of the Cu₂ZnSnS₄ film prepared in this experiment are suitable for fabricating a thin film solar cell.     

Leakage current, ferroelectric and structural properties in Pb1−xBaxTiO3 thin films prepared by chemical route

Single-phase perovskite structure Pb_1−xBa_xTiO₃ thin films (x=0.30, 0.50 and 0.70) were deposited on Pt/Ti/SiO₂/Si substrates by the spin-coating technique. The dielectric study reveals that the thin films undergo a diffuse type ferroelectric phase transition, which shows a broad peak. An increase of the diffusivity degree with the increasing Barium contents was observed, and it was associated to a grain decrease in the studied composition range. The temperature dependence of the phonon frequencies was used to characterize the phase transition temperatures. Raman modes persist above tetragonal to cubic phase transition temperature, although all optical modes should be Raman inactive. The origin of these modes was interpreted in terms of breakdown of the local cubic symmetry by chemical disorder. The absence of a well-defined transition temperature and the presence of broad bands in some interval temperature above FE-PE phase transition temperature suggested a diffuse type phase transition. This result corroborates the dielectric constant versus temperature data, which showed a broad ferroelectric phase transition in these thin films. The leakage current density of the PBT thin films was studied at different temperatures and the data follow the Schottky emission model. Through this analysis the Schottky barrier height values 0.75, 0.53 and 0.34 eV were obtained to the PBT70, PBT50 and PBT30 thin films, respectively.     

Structure-related infrared optical properties of BaTiO3 thin films grown on Pt/Ti/SiO2/Si substrates

BaTiO₃ thin films with different thickness have been grown on Pt/Ti/SiO₂/Si substrates by a modified sol-gel method. X-ray diffraction analyses show that the BaTiO₃ thin films are polycrystalline. The crystalline quality of the films is improved with increasing thickness. The infrared optical properties of the BaTiO₃ thin films have been investigated using an infrared spectroscopic ellipsometry in the wave number range of 800-4000 cm⁻¹ (2.5-12.5 μm). By fitting the measured pseudodielectric functions with a three-phase model (Air/BaTiO₃/Pt), and a derived classical dispersion relation for the thin films, the optical constants and thicknesses of the thin films have been simultaneously obtained. The refractive index of the BaTiO₃ thin films increases and on the other hand, the extinction coefficient does not change with increasing thickness in the entirely measured wave number range. The dependence of the refractive index on the film thickness has been discussed in detail and was mainly due to both the crystalline quality of the films and packing density. Finally, the absorption coefficient was calculated in the infrared region for applications in the pyroelectric IR detectors.     

Growth and optical properties of Eu/Li-co-doped SrB4O7 single crystals

This paper reports the growth and optical properties of Eu²⁺/Li⁺-co-doped SrB₄O₇ single crystals. High-quality Eu,Li:SrB₄O₇ crystals without macro-defects or cracks were grown using the top-seeded solution growth (TSSG) method. The absorption and luminescent properties were measured and different spectra were observed in the as-grown crystals. As the doping amount of lithium increases, the absorption peak at 300 nm becomes stronger and the emission peak shifts to a longer wavelength. This phenomenon could be attributed to the doping lithium ions, which might affect the electric field distribution in the lattice structure.     

Structural and optical properties of In35Sb45Se20−xTex phase-change thin films

Physical properties of In₃₅Sb₄₅Se_20−xTe_x thin films with different compositions (x=2.5, 5, 7.5, 10, 12.5 and 15 at %) prepared by electron beam evaporation method are studied. X-ray diffraction results indicate that the as-evaporated films depend on the Te content and the crystallized compounds consist mainly of Sb₂Se₃ with small amount of Sb₂SeTe₂. Transmittance and reflectance of the films are found to be thickness dependent. Optical-absorption data indicate that the absorption mechanism is direct transition. Optical band gap values decrease with increase in Te content as well as with increase in film thickness.     

Optical properties of natural quantum-well compounds (C6H5-CnH2n-NH3)2PbBr4 (n=1-4)

This paper describes the synthesis and characterization of self-assembled organic-inorganic layered perovskite compounds, (C₆H₅-C_nH_2n-NH₃)₂PbBr₄ (n=1-4). the effect of the number of carbon atoms of the alkyl chain length (n) on optical properties has been studied. (C₆H₅-C_nH_2n-NH₃)₂PbBr₄ films fabricated by spin-coating are microcrystalline form, single phase and oriented with the c-axis. Crystallinity, the maximum PL intensity and the lifetime of exciton emissions varied with the number of carbon atoms. the lowest-energy exciton splits into a few fine-structure levels at low temperatures. Time-resolved photoluminescence spectra reveal that (C₆H₅-C_nH_2n-NH₃)₂PbBr₄ shows both singlet and triplet excitons. with decreasing temperature, triplet exciton emissions become dominant for (C₆H₅-C_nH_2n-NH₃)₂PbBr₄ (n=1-3), while (C₆H₅-C₄H₈-NH₃)₂PbBr₄ shows mainly singlet exciton emissions. The intersystem crossing from excited singlet state to triplet state plays an important role in the relaxation process of excitons.     

Chemical spray pyrolysis deposition and characterization of p-type CuCr1−xMgxO2 transparent oxide semiconductor thin films

A chemical spray pyrolysis technique for deposition of p-type Mg-doped CuCrO₂ transparent oxide semiconductor thin films using metaloorganic precursors is described. As-deposited films contain mixed spinel CuCr₂O₄ and delafossite CuCrO₂ structural phases. Reduction in spinel CuCr₂O₄ fraction and formation of highly crystalline films with single phase delafossite CuCrO₂ structure is realized by annealing at temperatures ?700 °C in argon. A mechanism of synthesis of CuCrO₂ films involving precursor decomposition, oxidation and reaction between constituent oxides in the spray deposition process is presented. Post-annealed CuCr_0.93Mg_0.07O₂ thin films show high (?80%) visible transmittance and sharp absorption at band gap energy with direct and indirect optical band gaps 3.11 and 2.58 eV, respectively. Lower (∼450 °C) substrate temperature formed films are amorphous and yield lower direct (2.96 eV) and indirect (2.23 eV) band gaps after crystallization. Electrical conductivity of CuCr_0.93 Mg_0.07O₂ thin films ranged 0.6-1 S cm⁻¹ and hole concentration ∼2×10¹⁹ cm⁻³ determined from Seebeck analysis. Temperature dependence of conductivity exhibit activation energies ∼0.11 eV in 300-470 K and ∼0.23 eV in ?470 K region ascribed to activated conduction and grain boundary trap assisted conduction, respectively. Heterojunction diodes of the structure Au/n-(ZnO)/p-(CuCr_0.93Mg_0.07O₂)/SnO₂ (TCO) were fabricated which show potential for transparent wide band gap junction device.     

Studies on the influence of lithium incorporation in the photoluminescence of Y2O3:Eu thin films

Nanostructured europium-doped yttrium oxide thin films with lithium as a co-dopant were prepared using pulsed laser ablation technique. X-ray diffraction studies of the films indicated amorphous nature of the as deposited films and a transformation to crystalline phase with increase of annealing temperature. In this transformation, lithium co-doped films showed early crystallization. Lithium substitution resulted not only in enhancement of photoluminescence at 612 nm, resulting from ⁵D₀-⁷F₂ transition within europium, but also found to reduce the required processing temperature for intense photoemission. The deviation observed in the value of lattice constant of films annealed at different temperatures is found to be sensitive to annealing temperature. In the light of this, the dependence of photoluminescence intensity on the magnitude of lattice imperfection is also discussed. The morphology and transmittance of the films are also found to be sensitive to annealing process and lithium doping.     

Spectroscopic properties of Pr:KY(MoO4)2 crystal as a visible laser gain medium

A Pr³⁺-doped KY(MoO₄)₂ single crystal was grown by the Czochralski method. The polarized absorption and fluorescence spectra of the Pr³⁺:KY(MoO₄)₂ crystal were measured at room temperature. The stimulated emission cross-sections for the transitions from the ³P₀ multiplet were estimated from the fluorescence spectra. The fluorescence lifetime of the ³P₀ multiplet was estimated from the fluorescence decay curve at room temperature. The analysis of spectral properties shows that the Pr³⁺:KY(MoO₄)₂ crystal is a promising gain medium for visible lasers.     

Structural, electrical and optical properties of AgInS2 thin films grown by thermal evaporation method

Structural electrical and optical properties of AgInS₂ (AIS) thin films grown by the single-source thermal evaporation method were studied. The X-ray diffraction spectra indicated that the AIS single phase was successful grown by annealing above 400 °C in air. The AIS grain sizes became large with increasing the annealing temperatures. All polycrystalline AIS thin films were sulfur-poor from the electron probe microanalysis and indicated n-type conduction by the Van der Pauw technique. It was deduced that the sulfur vacancies were dominant in the films and enhanced n-type conduction.     

Optical properties of Er:SrMoO4 single crystal

Er³⁺:SrMoO₄ crystal of high optical quality was grown by the Czochralski method. The room temperature polarized absorption and emission spectra together with the lifetime decay curve were measured. Based on the Judd-Ofelt theory, three intensity parameters, radiative transition rates, radiative lifetimes and fluorescent branching ratios, were obtained. Emission cross-section and gain cross-section around 1.54 μm were also obtained.     

Electrical conduction and optical properties of amorphous (Sb2Se3)100−xSnx thin films

The variation of DC electrical conductivity and the optical properties of thermally evaporated a- (Sb₂Se₃)_100−xSn_x thin films with temperature have been studied. It is found that the thermal activation energy decreases, while the optical gap first increases (up to x=1) and then decreases, with the increase in Sn content. These results have been explained by taking into consideration the structural modifications induced by the incorporation of Sn into the parent alloy. The variation in the conductivity prefactor (σ_o) with Sn addition indicates a change in the dominant conduction transport mechanism from extended states to localized states. An experimental correlation between the activation energy and the pre-exponential factor has been observed, indicating the validity of Meyer–Neldel rule in the studied samples.     

Sr2CeO4:Eu and Sr2CeO4:5 mol% Eu, 3 mol% Dy microphosphors: Wet chemistry synthesis from hybrid precursor and photoluminescence properties

In this article, Sr₂CeO₄:x mol% Eu³⁺ and Sr₂CeO₄:5 mol%Eu³⁺, 3 mol% Dy³⁺ phosphors were synthesized from assembling hybrid precursors by wet chemical method. As-prepared samples present uniform grain-like morphology and the particle size is about 0.2 μm. The luminescence spectra of Sr₂CeO₄:x mol% Eu³⁺ have been measured to examine the influence of the intensity of red emission lines for Eu³⁺ on the concentration of Eu³⁺, showing that the intensity of the red emission increases with an increase of the concentration from 1 to 5 mol%. Additionally, from the emission spectra of Sr₂CeO₄:5 mol%Eu³⁺, 3 mol% Dy³⁺ phosphors, the characteristic lines of Dy³⁺ have also been observed. This result indicates that there also exists an energy transfer process between Sr₂CeO₄ and Dy³⁺.     

Electrical and optical properties of GexFexSe100−2x chalcogenide thin films

Optical absorption at room temperature and electrical conductivity at temperatures between 283 and 333 K of vacuum evaporated Ge_xFe_xSe_100−2x (0≤x≤15) amorphous thin films have been studied as a function of composition and film thickness. It was found that the optical absorption is due to indirect transition and the energy gap increases with increasing both Ge and Fe content; on the other hand, the width of the band tail exhibits the opposite behavior. The optical band gap E_opt was found to be almost thickness independent. The electrical conductivity show two types of conduction, at higher temperature the conduction is due to extended states, while the conduction at low temperature is due to variable range hopping in the localized states near Fermi level. Increasing Ge and Fe contents were found to decrease the localized state density N(E_F), electrical conductivity and increase the activation energy for conduction, which is nearly thickness independent. Variation of the atomic densities ρ, molar volume V, glass transition temperature T_g cohesive energy C.E and number of constraints N_Co with average coordination number Z was investigated. The relationship between the optical gap and chemical composition is discussed in terms of the cohesive energy C.E, average heat of atomization and coordination numbers.     

Effect of Bi substitution on the magnetic and dielectric properties of epitaxially grown BaFe0.3Zr0.7O3−δ thin films on SrTiO3 substrates

The structural, dielectric and magnetic properties of single crystalline Ba_1−xBi_xFe_0.3Zr_0.7O_3−δ (x=0.0-0.29) thin films have been studied. The pseudotetragonal epitaxial thin films were obtained by pulsed laser-beam deposition (PLD) on (0 0 1) SrTiO₃ (STO) single-crystal substrates. The Bi substitution for the Ba ions up to an extent of x=0.18 caused a slight improvement in the leakage current properties, as well as an enhancement of the apparent dielectric constant. The saturation magnetization of the films was significantly decreased following Bi substitution. These changes were thought to be related to the increase in oxygen deficiencies in the films. The effect of the Bi substitution on the dielectric and magnetic properties was analyzed in conjunction with the change in valence value of the Fe ions.     

Investigation of optical properties of annealed aluminum phthalocyanine derivatives thin films

Semiconducting molecular materials based on aluminum phthalocyanine chloride (AlPcCl) and bidentate amines have been successfully used to prepare thin films by using a thermal evaporation technique. The morphology of the deposited films was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Studies of the optical properties were carried out on films deposited onto quartz and (1 0 0) monocrystalline silicon wafers and films annealed after deposition. The absorption spectra recorded in the UV–vis region for the as-deposited and annealed samples showed two absorption bands, namely the Q- and B-bands. In addition, an energy doublet in the absorption spectra of the monoclinic form at 1.81 and 1.99 eV was observed. A band-model theory was employed in order to determine the optical parameters. The fundamental energy gap (direct transitions) was determined to be within the 2.47–2.59 and 2.24–2.44 eV ranges, respectively, for the as-deposited and annealed thin films.