Spectroscopic ellipsometry study of In<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films

In₂O₃ films grown by helicon magnetron sputtering with different thicknesses were characterized by spectroscopic ellipsometry in the energy range from 1.5 to 5.0 eV. Aside from one amorphous sample prepared at room substrate temperature, polycrystalline In₂O₃ films with cubic crystal structure were confirmed for other four samples prepared at the substrate temperature of 450 °C. Excellent SE fittings were realized by applying 1 and/or 2 terms F&B amorphous formulations, building double layered film configuration models, and further taking account of void into the surface layer based on Bruggeman effective medium approximation for thinner films. Spectral dependent refractive indices and extinction coefficients were obtained for five samples. The curve shapes were well interpreted according to the applied dispersion formulas. Almost similar optical band gap values from 3.76 to 3.84 eV were obtained for five samples by Tauc plot calculation using extinction coefficients under the assumption of direct allowed optical transition mode.     

Fabrication of Cu<Subscript>2</Subscript>SnS<Subscript>3</Subscript> thin-film solar cells with oxide precursor by pulsed laser deposition

In this paper, Cu₂SnS₃ (CTS) thin film is fabricated through sulfurization of oxide precursor which is deposited by pulsed laser deposition with a mixed CuO/SnO₂ target. XRD and Raman analyses indicate a pure monoclinic Cu₂SnS₃ phase has been obtained by sulfurization at temperature from 500 to 600 °C. A compact and smooth film with polycrystalline structure is observed through SEM result. In addition, the CTS films show excellent absorbance with the band gap around 0.91 eV estimated by UV–Vis, which is suitable for the absorption layer of solar cells. Final devices were fabricated with a SLG/Mo/CTS/CdS/i-ZnO/AZO/Al structure. Device performance is improved with the temperature increasing. The best efficiency of CTS-based solar cells is 0.69% with an open-circuit voltage of 144 mV and a short-circuit current density of 18.30 mA/cm^?2.     

Effect of substrate temperature on structural, morphological and optical properties of crystalline titanium dioxide films prepared by DC reactive magnetron sputtering

Titanium dioxide (TiO₂) thin films have been deposited with various substrate temperatures by dc reactive magnetron sputtering method onto glass substrate. The effects of substrate temperature on the crystallization behavior and optical properties of the films have been studied. Chemical composition of the films was investigated by X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) analysis of the films revealed that they have polycrystalline tetragonal structure with strong (101) texture. The surface morphological study revealed the crystalline nature of the films at higher substrate temperatures. The TiO₂ films show the main bands in the range 400–700 cm^?1, which are attributed to Ti–O stretching and Ti–O–Ti bridging. The transmittance spectra of the TiO₂ thin film measured with various substrate temperatures ranged from 75 to 90 % in the visible light region. The optical band gap values of the films are increasing from 3.44 to 4.0 eV at growth temperature from 100 to 400 °C. The structural and optical properties of the films improved with the increase in the deposition temperature.     

Synthesis and characterization of Co-doped nano-TiO<Subscript>2</Subscript> through co-precipitation method for photocatalytic activity

The aim of this work was synthesis and investigation of various properties of Co-doped titanium dioxide nanostructures. Synthesis was conducted by the co-precipitation method using cobalt nitrate and titanium isopropoxide as a precursor, followed by thermal treatment at a temperature of 500 °C. The materials were fully characterized using several techniques (X-ray diffraction XRD, SEM, FTIR, TGA/DTA, UV–Vis diffuse reflectance DRS and photoluminescence). However, dopant has no effect on XRD pattern of the host but it can influence on the various characteristics of host such as optical and electrical properties. The scanning electron microscopy was used to detect the morphology of synthesized nanoparticles which sizes changed with the altitude in the doping concentration to 6%. FTIR spectra exhibit broad peaks where anatase phases of TiO₂ demonstrate very sharp UV–Vis band gap results showed the reduction in band gap from from 3.21 eV, for undoped TiO₂, to 2.74 eV, for Co doped 6% TiO₂. The photocatalytic activity of the samples were studied based on the degradation of methyl orange as a model compound, where the results showed that Co doped 6% TiO₂ a good photocatalytic activity.     

Spectral optoelectronic features of Cu-containing arsenic sulfide (As<Subscript>2</Subscript>S<Subscript>3</Subscript>)<Subscript>0.95</Subscript>Cu<Subscript>0.05</Subscript>

Chalcogenide amorphous thin films of the modification (As₂S₃)_0.95Cu_0.05 were prepared using a thermal evaporation technique. The optical properties of the resultant films were investigated based on the transmittance spectra in the photon energy range 1.6–2.82 eV. Thicknesses of the films under study were determined using the envelope technique based on the transmittance spectra. The optical measurements were carried out over the conditional temperature extending from 77 to 300 K. The results of the mentioned measurements are conductive tools in investigating the electronic structures of the Chalcogenide Glasses, however the analysis of the experimental results provide information about the optical gap width and elucidate the broadness of the band tail that may disturb the band gap edges. Moreover, the single-effective oscillator was implemented in calculating both the oscillation and dispersion energies of the films under investigation. The static refractive index and the static dielectric constant were also determined for these films.     

Synthesis and characterization of nanocrystalline TiO<Subscript>2</Subscript> thin films

Nanocrystalline thin films of TiO₂ have been synthesized by sol gel spin coating technique Thin films of TiO₂ annealed at 700 °C were characterized by X-ray diffraction(XRD), Atomic Force Microscopy, High resolution TEM and Scanning Electron Microscopy (SEM), The XRD shows formation of tetragonal anatase and rutile phases with lattice parameters a = 3.7837 Å and c = 9.5087 Å. The surface morphology of the TiO₂ films showed that the nanoparticles are fine with an average grain size of about 60 nm. Optical studies revealed a high absorption coefficient (10⁴ cm^?1) with a direct band gap of 3.24 eV. The films are of the n type conduction with room temperature electrical conductivity of 10^?6 (Ω cm)^?1.     

Optical and structural properties of ZnO + Zn<Subscript>2</Subscript>TiO<Subscript>4</Subscript> thin films prepared by the sol–gel method

ZnO + Zn₂TiO₄ thin films were obtained by the sol–gel method using precursor solutions with different Ti/Zn ratios in the 0.18–2.13 range. The films were deposited on glass substrates and annealed in an open atmosphere at 550 °C. The oxide was characterized by X-ray diffraction and photoacoustic (PA) spectroscopy. The films were constituted of polycrystalline ZnO for the lowest Ti/Zn ratio (0.18), polycrystalline Zn₂TiO₄ for the 0.70 and 1.0 ratios, and mixes of both oxides for the intermediate ratios (0.32 and 0.50). For the highest ratios studied (1.44 and 2.13), the films were amorphous. The energy band gap (E_g) values were determined from optical absorption spectra, measured by means of the PA technique spectra. E_g varied in the 3.15 eV (ZnO) to 3.70 eV (Zn₂TiO₄) range.     

Enhanced photovoltaic performance of quantum dot sensitized solar cells with Ag-doped TiO2 nanocrystalline thin films

Ag-doped titanium dioxide (TiO₂) nanocrystalline thin films have been prepared by the sol–gel dip coating method and used as photoanode to fabricate quantum dot sensitized solar cells. The X-ray diffraction studies reveal the formation of anatase phase without any impurity phase. The surface morphology studied using scanning electron microscope shows uniform distribution of particles. The optical band gap was found to be 3.5 and 3.4 eV for CdS quantum dot sensitized TiO₂ and CdS quantum dot sensitized Ag-doped TiO₂ thin film respectively. The Ag-doped TiO₂ based solar cell exhibited a power conversion efficiency of 1.48 % which is higher than that of TiO₂ (0.9 %).     

Effect of calcination temperature on structure and thermoelectric properties of CuAlO<Subscript>2</Subscript> powders

Copper aluminum oxide (CuAlO₂) with delafossite phase was synthesized by the Pechini method using different calcination temperatures to evaluate its influence on the structure and thermoelectric material properties. X-ray diffraction and Raman spectroscopy confirm that delafossite phase was formed at 1100 °C with the presence of 2H-CuAlO₂ and Al₂O₃ impurities, while at lower calcination temperatures (900 and 1000 °C), a mixture of CuO + CuAl₂O₄ (spinel phase) was observed. Energy-dispersive X-ray elemental maps display an even distribution of copper, aluminum and oxygen in the sample calcined at 1100 °C. Direct optical band gap, E _g = 3.6 eV, was calculated from reflectance diffuse spectra by Kubelka–Munk and Tauc methods. An absorption band at 1.7 eV accounts for defect levels, masking the characteristic indirect transition. The thermoelectric properties, such as Seebeck coefficient, and thermal and electrical conductivities of the sample calcined at 1100 °C were measured at different temperatures. Hall voltage and positive values of the Seebeck coefficient (425.8–434.4 µV K^?1) confirm the material’s p-type character. The independence of the Seebeck coefficient on the operation temperature indicates a small polaron electrical conduction mechanism. Thermal conductivity decreases exponentially with the temperature from 43.45 to 23.9 W m^?1 K^?1, where the principal contribution is due to phonons. Figure of merit ZT of sample calcined at 1100 °C between 100 and 800 °C increases from 1.42 × 10^?8 to 4.94 × 10^?4 in the order of the literature reports. From the Arrhenius plot ln(σT) versus 1000/T, an activation energy E _a = 0.32 eV for the electrical conductivity was calculated.     

Visible photocatalytic degradation of methylene blue on magnetic semiconducting La<Subscript>0.2</Subscript>Sr<Subscript>0.7</Subscript>Fe<Subscript>12</Subscript>O<Subscript>19</Subscript>

Methylene blue (MB) is a representative of a class of dyestuffs resistant to biodegradation. This paper presents a novel photocatalytic degradation of MB by La_0.2Sr_0.7Fe₁₂O₁₉ compound, which is a traditional permanent magnet and displays a large magnetic hysteresis (M–H) loop. The remnant magnetic moment and coercive field are determined to be 52 emu/g and 5876 Oe, respectively. UV–Visible optical spectroscopy reveals that La_0.2Sr_0.7Fe₁₂O₁₉ is simultaneously a semiconductor, whose direct and indirect band gap energies are determined to be 1.47 and 0.88 eV, respectively. The near infrared band gap makes it a good candidate to harvest sunlight for photocatalytic reaction or solar cell devices. This magnetic compound demonstrates excellent photocatalytic activity on degradation of MB under visible illumination. The colour of MB dispersion solution changes from deep blue to pale white and the absorbance decreases rapidly from 1.8 down to zero when the illumination duration extends to 6 h. Five absorption bands did not make any blue shifts along with the reaction time, suggesting a one-stepwise degradation process of MB, which makes La_0.2Sr_0.7Fe₁₂O₁₉ a unique magnetic catalyst and differs from TiO₂ and other conventional catalysts.     

Variation of structural,optical, dielectric and magnetic properties of SnO<Subscript>2</Subscript> nanoparticles

We report effect of oxygen vacancies on band gap narrowing, enhancement in electrical conductivity and room temperature ferromagnetism of SnO₂ nanoparticles synthesized by simple chemical precipitation approach. As the calcination temperature is elevated from 400 to 800 °C, the average particle size increases from 12.26 to 34.43 nm, with enhanced grain growth and crystalline quality. At low temperatures, these nanoparticles are in a rather oxygen-poor state revealing the presence of many O vacancies and Sn interstitials in SnO₂ nanoparticles as in this case Sn⁺² is not oxidized completely to Sn⁺⁴ and small sized nano particles have more specific surface area, hence defects are more prominent. The oxygen content increases steadily with increasing temperature, with the Sn:O atomic ratio very near to the stoichiometric value of 1:2 at high temperatures suggesting the low density of defects. The optical band gap energies of all SnO₂ nanoparticles are in the visible light region, decreasing from 2.89 to 1.35 eV, while room temperature ferromagnetism and electrical conductivity are enhanced with reduced temperatures. The dielectric constant (ε_r) exhibited dispersion behaviour and the Debye’s relaxation peaks were observed in tanδ. The variation of dielectric properties and ac conductivity revealed that the dispersion is due to Maxwell–Wagner interfacial polarization and hopping of charge carriers between Sn⁺²/Sn⁺⁴. The narrowed band gap energies and enhanced ferromagnetism are mainly attributed to the increase of defects density (e.g., oxygen vacancies). The presence of oxygen vacancies is confirmed by EDX, Raman, PL, XPS, and UV–Vis spectra. The band gap of 1.35 eV is the smallest value for SnO₂ reported so far. This rather small band gap, enhanced conductivity and room temperature ferromagnetism demonstrate that SnO₂ nanoparticles are very promising in the visible light photo catalysis and optoelectronic devices.     

Structural,morphological and optical properties of SnS<Subscript>2</Subscript> thin films by nebulized spray pyrolysis technique

The thin films of Nano crystalline tin disulfide (SnS₂) have been prepared by nebulized spray pyrolysis technique (NSP) with different molar concentrations (0.3, 0.4 and 0.5 M). Cleaned glass substrates were used and the substrate temperature was maintained at 300?°C. The films were deposited using tin tetrachloride monohydrate (SnCl₄·H₂O) and thiourea in de-ionized water and Isopropyl alcohol (1:3 ratio). The prepared films structural, morphological and optical properties were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), UV–Vis spectrophotometer. The structure of the films were found to be face centered cubic with preferential orientation along (002) plane. X-ray line profile analysis was used to evaluate the micro structural parameters such as crystallite size, micro strain, dislocation density and texture coefficient. The average crystallite size values are 60 nm. Morphological results of the SnS₂ thin films are small needle shaped particles and the average grain size was 400 nm. The optical studies revealed that the band gap between 2.65 and 2.72 eV and high optical transmittance 98%. EDAX spectrum of tin disulfide result showed some amount of excess tin was present in the sample. This is the method with very low cost of producing tin disulfide (SnS₂) thin films, which is very important for many applications in industry.     

Properties of AgInSe<Subscript>2</Subscript> films grown by magnetron sputtering

n-Type AgInSe₂ films 0.5 to 0.9 μm thick were grown by dc magnetron sputtering. As targets, we used AgInSe₂ crystals grown by a modified Bridgman process using high-purity precursors. The crystal structure, morphology, electrical conductivity, and Hall coefficient of the films were studied at various temperatures. We determined the optimal growth and annealing temperatures of the films (500 and 250°C, respectively). Using structures based on the films, we obtained the spectral dependences of their photoresponse, established the nature of interband transitions in the films, and evaluated their band gap. The ability to vary electrical and optical properties with no changes in stoichiometry is of interest for concentrated solar power applications.     

Effect of annealing temperature on structural,optical and humidity sensing properties of indium tin oxide (ITO) thin films

Tin doped indium oxide (ITO) thin films were prepared by sol–gel spin coating method with In (NO₃)·3H₂O and SnCl₄·5H₂O as indium and tin sources, respectively. The as deposited samples were annealed at various temperature such as, 300, 400, 500 and 600?°C for 2 h in ambient atmosphere. The grown ITO thin films are polycrystalline in nature with cubic structure of In₂O₃ with the space group La3 and the results are in good agreement with the standard JCPDS data (card no#06-0416). In addition crystalline size increases with increasing annealing temperature from 25 to 55 nm. Polycrystalline with uniform smooth surface was observed by SEM micrographs. The optical band gap energy was found to be decreased from 3.85 to 3.23 eV as the annealing temperature is increased from 300 to 600?°C. The humidity sensing performance (high sensitivity and fast response time) was significantly improved for 600?°C thin films samples, which is probably due to smaller energy band gap and physisorption between the water molecules and the surface of the thin films. The films were further characterized by PL and EDS analysis. The effect of temperature on humidity sensing mechanism of ITO thin films is also discussed.     

Characterization of titania thin films grown by dip-coating technique

A dip-coating technique was employed to prepare anatase phase of titania thin films. Fluorine doped tin oxide substrates were used to prepare titania thin films. The samples were annealed at 550 °C for 18 h. X-ray diffraction results revealed the amorphous and anatase phases of TiO₂ for as-synthesized and annealed samples, respectively. The crystallite size of anatase TiO₂ thin films was almost 25 nm for annealed samples. UV–visible confirmed the energy band gap 3.86 and 3.64 eV for as-prepared and calcinated titania thin films. The reduction in the energy band gap could be due to the change in crystallization and agglomeration of small grains after calcination. The morphology of the prepared films was investigated by field emission scanning electron microscopy which demonstrated the agglomeration of spherical particles of TiO₂ with average particle size of about 30 nm. The molecular properties (chemical bonding) of the samples were investigated by means of Fourier Transform Infrared (FTIR) spectroscopy. FTIR analysis exhibited the formation of titania, functional group OH, hydroxyl stretching vibrations of the C–OH groups, bending vibration mode of H–O–H, alkyl C–H stretch, stretching band of Ti–OH, CN asymmetric band stretching, and C=O saturated aldehyde.     

Optical properties of nanostructured ruthenium dioxide thin films via sol–gel approach

High purity ruthenium dioxide (RuO₂) nanoparticles with the average size is about 9 nm in diameter are readily synthesized through a low cost sol–gel method. RuO₂ thin films have been deposited on SiO₂ substrates by sol–gel spin coating techniques at room temperature, followed by annealing at 500 °C for 2 h. The result of X-ray diffraction indicates that the RuO₂ nanoparticles are well crystallized with a rutile tetragonal structure. Morphological of RuO₂ films were characterized using atomic force microscopy (AFM), transmission electron microscopy and high resolution transmission electron microscopy. The AFM images confirmed a spherical-shape nanoparticles with diameter of 9 nm and surface roughness of 12 nm of the films. The optical absorption studies showed the presence of direct band transition with band gap equal to 1.87 eV. Refractive index and dielectric properties of the films were estimated from optical measurements. Room temperature photoluminescence of RuO₂ film showed an emission band at 432 nm.     

Optimization of Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> thin film absorber layer growth without sulphurization using triethanolamine as complexing agent for thin film solar cells applications

Quaternary kesterite Cu₂ZnSnS₄ (CZTS) thin films have been prepared via a simple spin-coating technique based on a sol–gel precursor of 2-methoxyethanol solution with metal salts and thiourea. Solution processed CZTS thin film growth parameters using complexing agent triethanolamine (TEA) have been investigated. Effects of complexing agent TEA on structural, morphological, optical, electrical and photovoltaic properties of CZTS thin films were systematically investigated. X-ray diffraction and Raman spectroscopy studies reveal that amorphous nature of CZTS thin film changes into polycrystalline with kesterite crystal structure with optimized TEA concentartion. Surface morphology of CZTS films were analyzed by field emission scanning electron microscope and atomic force microscope, which revealed the smooth, uniform, homogeneous and densely packed grains and systematic grain growth formation with varying TEA concentrations. UV–Vis spectra revealed a direct energy band gap ranging from 1.78 to 1.50 eV, which was found to depend upon the TEA concentration. X-ray photoelectron spectroscopy demonstrated stoichiometric atomic ratios of multicationic quaternary CZTS thin film grown without sulphurization. p-type conductivity was confirmed using Hall measurements and the effect of varying concentartion of TEA on electrical and photovoltaic properties are studied. The SLG/FTO/ZnO/CZTS/Al thin film solar cell is fabricated with the CZTS absorber layer grown at optimized TAE concentration of 0.06 M. It shows a power conversion efficiency of 0.87% for a 0.16 cm² area with V_oc = 0.257 mV, J_sc = 8.95 mA/cm² and FF?=?38%.     

Brush plated copper indium sulphide films and their properties

Copper indium sulphide films were deposited for the first time by the brush plating technique at different electrolyte temperatures in the range of 30–80 °C and at a constant deposition current density of 5.0 mA cm^?2. The Films exhibited single phase copper indium sulphide. The grain size increased with increase of electrolyte temperature. Optical band gap of the films varied in the range of 1.30–1.42 eV. Atomic force microscopy studies indicated that the grain size vary from 600 to 1,000 nm, with increase of substrate temperature. Solar cells fabricated with the films exhibited V_oc of 650 mV, J_sc of 19.5 mA cm^?2, ff of 0.73 and efficiency of 9.50 %.     

Structural,morphological, optical and gas sensing properties of pure and Ce doped SnO<Subscript>2</Subscript> thin films prepared by jet nebulizer spray pyrolysis (JNSP) technique

Pure and cerium (Ce) doped tin oxide (SnO₂) thin films are prepared on glass substrates by jet nebulizer spray pyrolysis technique at 450 °C. The synthesized films are characterized by X-ray diffraction (XRD), scanning electron microscopy, energy dispersive analysis X-ray, ultra violet visible spectrometer (UV–Vis) and stylus profilometer. Crystalline structure, crystallite size, lattice parameters, texture coefficient and stacking fault of the SnO₂ thin films have been determined using X-ray diffractometer. The XRD results indicate that the films are grown with (110) plane preferred orientation. The surface morphology, elemental analysis and film thickness of the SnO₂ films are analyzed and discussed. Optical band gap energy are calculated with transmittance data obtained from UV–Visible spectra. Optical characterization reveals that the band gap energy is found decreased from 3.49 to 2.68 eV. Pure and Ce doped SnO₂ thin film gas sensors are fabricated and their gas sensing properties are tested for various gases maintained at different temperature between 150 and 250 °C. The 10 wt% Ce doped SnO₂ sensor shows good selectivity towards ethanol (at operating temperature 250 °C). The influence of Ce concentration and operating temperature on the sensor performance is discussed. The better sensing ability for ethanol is observed compared with methanol, acetone, ammonia, and 2-methoxy ethanol gases.     

Formation and properties of cadmium sulfide buffer layer for CIGS solar cells grown using hot plate bath deposition

In the present study, cadmium sulfide (CdS) thin films were deposited on different substrates [soda glass, fluoride doped tin oxide, and tin doped indium oxide (ITO) coated glass] by a hot plate method. To control the thickness and the reproducibility of the sample production, the thin films were coated at different temperatures and deposition times. The CdS thin films were heated at 400 °C in air and forming gas (FG) atmosphere to investigate the effect of the annealing temperatures. The thickness of the samples, measured by ellipsometry, could be controlled by the deposition time and temperature of the hot plate. The phase formation and structural properties of CdS thin films were studied by X-ray diffraction and scanning electron microscopy, whereas the optical properties were obtained by UV–vis spectroscopy. A hexagonal crystal structure was observed for CdS thin films and the crystallinity improved upon annealing. The structural and optical properties of CdS thin films were also enhanced by annealing at 400 °C in FG atmosphere (95 % N₂, 5 % H₂). The optical band gap was changed from 2.25 to 2.40 eV at different annealing temperatures and gas atmospheres. A higher electrical conductivity, for the sample annealed at FG, was noticed. The samples deposited on ITO and annealed in FG atmosphere showed the best structural and electrical properties compared to the other samples. CdS thin films can be widely used for application as a buffer layer for copper–indium–gallium–selenide solar cells.