Structural,optical and microscopic properties of chemically deposited In<Subscript>2</Subscript>Se<Subscript>3</Subscript> thin films

Solar cell technologically important binary indium selenide thin film has been developed by relatively simple chemical method. The reaction between indium chloride, tartaric acid, hydrazine hydrate and sodium selenosulphate in an aqueous alkaline medium at room temperature gives deposits In₂Se₃ thin film. Various preparative parameters are discussed. The as grown films were found to be transparent, uniform, well adherent, red in color. The prepared films were studied using X-ray diffraction, scanning electron microscopy, atomic absorption spectroscopy, Energy dispersive atomic X-ray diffraction, optical absorption and electrical conductivity properties. The direct optical band gap value E_g for the films was found to be as the order of 2.35 eV at room temperature and having specific electrical conductivity of the order of 10⁻² (Ω cm)⁻¹ showing n-type conduction mechanism. The utility of the adapted technique is discussed from the point of view of applications considering the optoelectric and structural data obtained.     

Structural,optical and microscopic properties of chemically deposited Mo<Subscript>0.5</Subscript>W<Subscript>0.5</Subscript>Se<Subscript>2</Subscript> thin films

Mo_0.5W_0.5Se₂ thin films were obtained by using relative simple chemical route at room temperature. Various preparative conditions of the thin films are outlined. The films were characterized by X-ray diffraction, scanning electron microscope, optical and electrical properties. The grown films were found to be uniform, well adherent to substrate and brown in color. The X-ray diffraction pattern shows that thin films have a hexagonal phase. Optical properties show a direct band gap nature with band gap energy 1.44 eV and having specific electrical conductivity in the order of 10⁻⁵ (Ωcm)⁻¹.     

Particle size dependence of optical and defect parameters in mechanically milled Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Fe₂O₃ of particle sizes ranging from 120 to 20 nm has been prepared by the ball-milling process using different milling hour. X-ray diffraction technique and transmission electron microscopy have been used for determining the average particle sizes of the prepared samples. Direct optical band gap for the unmilled and the ball-milled samples has been calculated from the optical absorption data. A red shift in the band gap due to the reduction of particle size has been observed. The coincidence Doppler broadening of the electron positron annihilation γ-radiation spectroscopy has been employed to identify the nature of defects generated due to the ball-milling process.     

Structural and surface morphological properties of chemically deposited Mo<Subscript>0.5</Subscript>W<Subscript>0.5</Subscript>S<Subscript>2</Subscript> thin film

Preparation of layered type semiconductor Mo_0.5W_0.5S₂ ⁻ thin films has been successfully done by using chemical bath deposition method. Objective of the studies are related to structural, optical, morphological and electrical properties of the thin films. The preparation method is based on the reaction between tartarate complex of Mo and W with thiourea in an aqueous alkaline medium at 363 K. X-Ray diffraction reveals a polycrystalline film composed of both MoS₂ and WS₂ phases. The optical study shows that the band gap of the film is 1.6 eV. Electrical conductivity is high which is in the order of 10⁻³–10⁻² (Ώ cm)⁻¹.     

Synthesis and Optical Studies of Superconducting MgB<Subscript>2</Subscript> Thin Films

Synthesis and optical transmission of MgB₂ thin films on optically transparent glass are reported. In the 400–1000 nm regime as deposited films show high metallic reflectivity and very little transmission. After deposition, the films were annealedex situ and rendered superconducting withT _c of 38 K, approaching that of the bulk material. The reaction conditions where quite soft ∼ 10 min at 550°C. The optical absorption coefficient,α and photon energy,E followed a Tauc-type behavior, (αE)^1/2=β _T(E −E _g). The band gap (E _g) was observed to peak at 2.5 eV; but, the slope parameterβ _Tbehaved monotonically with reaction temperature. Our results indicate that an intermediate semiconducting phase is produced before the formation of the superconducting phase; also optical measurements provide valuable information in monitoring the synthesis of MgB₂ from its metallic constituents. In addition these films have interesting optical properties that may be integrated into optoelectronics.     

Effect of Ba(Ti<Subscript>(0.9)</Subscript>Sn<Subscript>0.1</Subscript>)O<Subscript>3</Subscript> ceramic doping on optical,thermal and dielectric properties of polycarbonate host

Ba(Ti_(0.9)Sn_0.1)O₃ (BTS) ceramic was prepared by a conventional ceramic processing. BTS-polycarbonate (PC) composites were prepared at different BTS concentrations by weight in order to study their optical and dielectric properties. The absorption coefficient (α) was determined in the wavelength range from 250–600 nm at room temperature for all BTS-PC composites. The optical gap (E _opt) was also determined for BTS-PC composites. The variation of the absorption coefficient (α) and optical gap (E _opt) with BTS content are reported. It was found that BTS ceramic highly enhances the UV absorption of PC host at 300 nm. The optical gap decreases up to the value of 3.93 eV as BTS content increases up to 35 wt% and this was attributed to the formation of localized states in the forbidden gap. The relative dielectric permittivity, dielectric loss and loss tangent were measured at temperature range from room temperature up to 150°C and at frequency values 1 kHz, 10 kHz and 50 kHz. Addition of BTS to PC host, however, will increase relative dielectric permittivity, dielectric loss and loss tangent. Besides, increasing of temperature will also increase relative dielectric permittivity, dielectric loss and loss tangent especially above the glass transition temperature of PC host and this behaviour was attributed to the segmental motion of polymer chains. On the other hand, this study shows that there is a good agreement between SEM, DSC and dielectric results and also between optical gap and a.c. conductivity results. Moreover, SEM and DSC results reveal that addition of BTS ceramic particles to PC host will reduce the physical bond between polymer chains or may be will increase the free volume in the polymer host and consequently will enhance the segmental motion of polymer chains and this behaviour is independent of ceramic phase.     

Effect of secondary heat treatment on the spectroscopic properties of Na<Subscript>2</Subscript>O-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

We have studied the optical absorption and luminescence spectra of 45Na₂O · xNb₂O₅ · (55 − x)P₂O₅ glasses containing 5, 10, 20, 25, 30, and 35 mol % Nb₂O₅. The results indicate that the absorption band around 26000 cm⁻¹, responsible for the yellow color of the glasses, is due to the [Nb^(5+)--O⁻] center and disappears upon secondary heat treatment. Heat treatment of europium-doped glasses increases the concentration of Eu³⁺ centers in an asymmetric environment, which is accompanied by an increase in luminescence efficiency. The reason for this is that the Eu³⁺ ions are located outside the niobate subsystem of the glass matrix. The europium in the glasses studied acts as a protector ion.     

Optical properties of CeO<Subscript>2</Subscript> thin films

Cerium oxide (CeO₂) thin films have been prepared by electron beam evaporation technique onto glass substrate at a pressure of about 6 × 10⁻⁶ Torr. The thickness of CeO₂ films ranges from 140–180 nm. The optical properties of cerium oxide films are studied in the wavelength range of 200–850 nm. The film is highly transparent in the visible region. It is also observed that the film has low reflectance in the ultra-violet region. The optical band gap of the film is determined and is found to decrease with the increase of film thickness. The values of absorption coefficient, extinction coefficient, refractive index, dielectric constant, phase angle and loss angle have been calculated from the optical measurements. The X-ray diffraction of the film showed that the film is crystalline in nature. The crystallite size of CeO₂ films have been evaluated and found to be small. The experimental d-values of the film agreed closely with the standard values.     

Physicochemical properties of La<Subscript>3</Subscript>Ga<Subscript>5.5</Subscript>Ta<Subscript>0.5</Subscript>O<Subscript>14</Subscript>

We report the optical and dielectric properties and microhardness of La₃Ga_5.5Ta_0.5O₁₄ lanthanum gallium tantalate (langatate) crystals. Analysis of the optical transmission spectra of the crystals in relation to their refined compositions indicates that the bands at 34000–35000 and 27000–28000 cm⁻¹ are due to lanthanum and oxygen vacancies, respectively, and that the band at 20000–21000 cm⁻¹ is responsible for the yellow (orange) coloration of the crystals. Their resistivity and microhardness decrease with increasing oxygen vacancy concentration.     

Low-loss,high-purity (TeO<Subscript>2</Subscript>)<Subscript>0.75</Subscript>(WO<Subscript>3</Subscript>)<Subscript>0.25</Subscript> glass

By melting a mixture of high-purity oxides in a platinum crucible under flowing purified oxygen, we have prepared (TeO₂)_0.75(WO₃)_0.25 glass with a total content of 3d transition metals (Fe, Ni, Co, Cu, Mn, Cr, and V) within 0.4 ppm by weight, a concentration of scattering centers larger than 300 nm in size below 10² cm⁻³, and an absorption coefficient for OH groups (λ ∼ 3 μm) of 0.008 cm⁻¹. The absorption loss in the glass has been determined to be 115 dB/km at λ = 1.06 μm, 86 dB/km at λ = 1.56 μm, and 100 dB/km at λ = 1.97 μm. From reported specific absorptions of impurities in fluorozirconate glasses and the impurity composition of the glass studied here, the absorption loss at λ ∼ 2 μm has been estimated at ≤100 dB/km. The glass has been drawn into a glass-polymer fiber, and the optical loss spectrum of the fiber has been measured.     

Specific absorption coefficient of chromium in (TeO<Subscript>2</Subscript>)<Subscript>0.80</Subscript>(MoO<Subscript>3</Subscript>)<Subscript>0.20</Subscript> glass

We have prepared (TeO₂)_0.80(MoO₃)_0.20 glass samples containing 0.01 to 0.11 wt % chromium and determined their optical transmission in the range from 450 to 2800 nm. The glasses have been shown to have a strong absorption band centered at 660 nm. From the attenuation coefficient as a function of Cr³⁺ concentration in the glasses, we have evaluated their specific absorption coefficient, which has been shown to be 190 ± 2 cm^–1/wt % at the maximum of the absorption band.     

Effects of Al content on the properties of ZnO:Al films prepared by Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and ZnO co-sputtering

Aluminum doped zinc oxide (AZO) films were deposited on quartz substrates by radio-frequency magnetron co-sputtering method with ZnO and Al₂O₃ ceramic targets. The structural, optical and electrical properties of these films as a function of the Al content were investigated. XRD results reveal that the AZO films are wurtzite structure with (002) preferred orientation. The average transmittance of all the films is higher than 80% in a wide wavelength range from 400 to 1,500 nm. The band gap energy, calculated from their optical absorption spectra, is in the range of 3.50–3.66 eV depending on the Al content. Doping of Al³⁺ in the ZnO makes the film surface roughness decrease. The dopant Al³⁺ acts as electron donor by which the electrical conductivity and carrier concentration of the films are obviously increased until the Al³⁺ reaches its saturation content of about 4.50 at.%.     

Highly Transparent and Conductive Zn<Subscript>0.86</Subscript>Cd<Subscript>0.11</Subscript>In<Subscript>0.03</Subscript>O Thin Film Prepared by Pulsed Laser Deposition

Zn_0.86Cd_0.11In_0.03O alloy semiconductor film was deposited on quartz substrate by pulsed laser deposition technique. Cd is used to change the optical band gap and In is used to increase the carrier concentration of the ZnO film. XRD studies confirm that the structure of Zn_0.86Cd_0.11In_0.03O is hexagonal wurtzite structure without CdO phase appeared. FE-SEM shows that the grain size of Zn_0.86Cd_0.11In_0.03O film is smaller than that of ZnO. These films are highly transparent (∼85%) in visible region. Most importantly, the electrical properties of Zn_0.86Cd_0.11In_0.03O film highly improved with In doped. It has low resistivity (4.42×10⁻³ Ω cm) and high carrier concentration (5.50×10¹⁹ cm⁻³) that enable this film a promising candidate for window layer in solar cells and other possible optoelectronic applications.     

Synthesis of Er<Superscript>3+</Superscript> and Er<Superscript>3+</Superscript> : Yb<Subscript>3+</Subscript> doped sol-gel derived silica glass and studies on their optical properties

Er₃₊ and Er₃₊ : Yb₃₊ doped optical quality, crack and bubble free glasses for possible use in making laser material have been prepared successfully through sol-gel route. The thermal and optical, including UV-visible absorption, FTIR etc characterizations were undertaken on the samples. The absorption characteristics of Er₃₊ doped samples clearly revealed the absorption due to Er₃₊ ions. On the other hand Yb₃₊ : Er₃₊ doped samples showed enhanced absorption due to² F _7/2 →² F _5/2 transition. The absorption and emission cross-section for² F _7/2 ↔² F _5/2 of Yb³⁺ were estimated. FTIR absorption spectra have clearly shown the reduction of the absorption peak intensity with heat treatment in the range 3700–2900 cm⁻¹. The 960 cm^-1 band also showed progressive decrease in the absorption band peak intensity with heat treatment. The result of the investigations with essential discussions and conclusions have been reported in this paper.     

Characterization of spray deposited CoWO<Subscript>4</Subscript> thin films for photovoltaic electrochemical studies

Preparation of Cobalt tungstate (CoWO₄) thin film by spray pyrolysis with ammonical solution as a precursor is presented. The phase and surface morphology characterizations have been carried out by XRD and SEM analysis. The study of optical absorption spectrum in the wavelength range 350 – 850 nm shows direct as well as indirect optical transitions in the thin film material. The d. c. electrical conductivity measurements in the temperature range 310–500 K indicate semiconducting behavior of the thin film. The thin films deposited on fluorine doped tin oxide (FTO) coated conducting glass substrates were used as a photoanode in photovoltaic electrochemical (PVEC) cell with configuration: CoWO₄ | Ce⁴⁺, Ce³⁺ | Pt; 0.1 M in 0.1 N H₂SO₄. The PVEC characterization reveals the fill factor and power conversion efficiency to be 0.36 and 0.62%, respectively. The flat band potential is found to be −0.18 V (SCE).     

Photochemical behaviors during the photosensitization of colloidal TiO<Subscript>2</Subscript> particles by a newly synthesized multidentate squaraine

A new squaraine dye Bis(4-N,N-dicarboxymethyl-2-hydroxyphenyl)squaraine (SQ) which could be used as organic photovoltaic materials, was synthesized, and its molecular structure was fully characterized by elemental analysis, IR, ¹H NMR and MS. SQ exhibits strong absorption band over 600–700 nm. Addition of TiO₂ colloids to the ethanol solution of SQ resulted in the increase of optical density, quenching of fluorescence and shortened fluorescence lifetime. The apparent association constant between the sensitizer and semiconductor as measured from the fluorescence quenching data, was 2427 M⁻¹. Fluorescence lifetime measurements gave the rate constant for the electron injection process from the excited singlet of SQ to the conduction band of TiO₂ nanoparticles as 2.55 × 10 ⁸ s⁻¹. In addition, SQ doped SiO₂ gel glass slices were prepared and characterized by absorption and emission spectra.     

Kinetics of Pu(V) disproportionation in CH<Subscript>3</Subscript>COOH-CH<Subscript>3</Subscript>COOLi aqueous solutions

The behavior of Pu(IV–VI) in CH₃COOH-CH₃COOLi solutions was studied by spectrophotometry. The Pu(VI) absorption spectrum changes essentially with an increase in the CH₃COOLi concentration. Owing to formation of Pu(VI) acetate complexes, the maximum of the main absorption band is shifted from 830.6 (in HClO₄ solution) to 845 nm, with the band intensity decreasing by a factor of approximately 8. The Pu(V) and Pu(IV) absorption spectra at low concentrations of acetate ions vary insignificantly relative to the spectra in noncomplexing media. With an increase in the acetate concentration in the system to 1–3 mM, the effect of Pu(V) complexation on its absorption spectrum becomes noticeable (the absorption intensity considerably decreases), whereas the Pu(IV) absorption spectra remain essentially unchanged. Solutions containing 1–2 mM Pu(V) and 0.2–0.5 M CH₃COOLi remain unchanged at 18–25°C for 2 days. In solutions with [CH₃COOLi] = 1–3 M, Pu(V) disproportionates with the formation of soluble Pu(VI) complexes and a suspension of Pu(IV) hydroxide. Introduction of CH₃COOH to a concentration of 0.1–1.0 M prevents the formation of a suspension of Pu(IV) hydroxide, but only up to a temperature of 45°C. The Pu(V) loss follows a second-order rate law, with the reaction products, Pu(IV) and Pu(VI), accelerating the Pu(V) consumption. The reaction rate at a constant concentration of acetate ions is proportional to [H⁺]. The reaction order with respect to Ac⁻ ions is close to 1.6. The activation energy of the Pu(V) disproportionation in the range 19–45°C is estimated at 74.5 kJ mol⁻¹. It is assumed that the disproportionation mechanism involves the formation of dimers from Pu(V) acetate complexes and aqua ions, their protonation, and decomposition with the transformation into Pu(IV) and Pu(VI).     

Optical band gap in the system ZnO<Subscript>1 – <Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>. An experimental and quantum chemical study

The synthesis of single crystalline and polycrystalline material is reported in the system ZnO_{1 – x} S _x . Substitution of oxygen by sulphur yields hexagonal wurtzite-type mixed crystals in the range 0 ≤ x ≤ 0.05. The cubic zincblende structure is observed for oxygen incorporation into ZnS for 0.96 ≤ x ≤ 1. At intermediate compositions, the system is two-phase. For both types of anion substitution, the band gap energies, as determined from optical transmission and remission experiments, are found to decrease from the pure end members. Quantum chemical calculations at density functional level identify local structural changes as the main factor responsible for the reduction of band gap energies.     

Photocatalytic activities of hollow and hierarchical Bi<Subscript>3.15</Subscript>Nd<Subscript>0.85</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> microspheres synthesized through a hydrothermal process

Hollow and hierarchical Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT) microspheres of 0.5–1.2 μm in diameter were synthesized through a hydrothermal process. Each hollow microsphere is constructed across by many single-crystalline BNdT nanoplates with in-plane dimension of ~400 nm. The BNdT nanoplates are of layered perovskites. The UV–visible absorption characteristics demonstrated that the band gap of the BNdT microspheres is 3.33 eV. The hierarchical microspheres exhibit significant photocatalytic activity. Up to 75% methyl orange was decolorized after UV irradiation for 210 min, whereas lower than 10% methyl orange decolorized using BNdT powders prepared from single crystals as catalyst. The photocatalytic decolorization of methyl orange solution is a pseudo-first-order reaction and its kinetics can be expressed as ln(C/C ₀) = kt.     

Synthesis and luminescence properties of Eu<Superscript>2+</Superscript>-doped Li<Subscript>2</Subscript>SrSiO<Subscript>4</Subscript>

We have studied the luminescence spectra of Li₂Sr_{1 − x} Eu _x SiO₄ (x = 0.0001–0.01) solid solutions prepared by solid-state reactions and a sol-gel process in a reducing atmosphere. The spectra show a broad band in the range 500–700 nm, centered at 578 nm, which is due to the 4f ⁶5d → 4f ⁷ transition. The luminescence excitation spectrum shows, in addition to bands due to Eu²⁺ 4f ⁷ → 4f ⁶5d transitions, a strong band centered at 174 nm, attributable to absorption in the SiO₄⁴⁻ group.