Studies on a possible growth mechanism of silver nanoparticles loaded on TiO2 thin films by photoinduced deposition method

The TiO₂ thin films loaded with silver nanoparticles were prepared on soda-lime glass substrates by a photoinduced deposition method. The TiO₂ films immersed in AgNO₃ solution were vertically irradiated by UV light with center wavelength of 365 nm for 60 h. The as-produced films were characterized by X-ray diffraction (XRD), UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The studies show that the film after UV excitation is composed of anatase phase TiO₂ and metallic silver with face centered cubic structure. A possible growth mechanism of silver nanoparticles on TiO₂ thin films under UV irradiation was proposed. The charge carriers of TiO₂ semiconductor are generated by photoexcitation. Owing to the conduction band position of TiO₂ which is above the standard potential of Ag⁺/Ag, the generated electrons could transfer from the conduction band to Ag⁺ adsorbed on the surface of the TiO₂ films. Therefore, the Ag⁺ was finally reduced into a Ag atom, which could preferentially localize in the grain boundaries of TiO₂ particles due to high surface free energy there. With the irradiation time extended, silver nanoparticles were shaped into certain morphologies on the surface of the TiO₂ films.     

Effect of annealing temperatures on properties of sol‐gel grown ZnO‐ZrO2 films

Mixed ZnO‐ZrO₂ films have been obtained by sol‐gel technology. By using spin coating method, the films were deposited on Si and glass substrates. The influence of thermal annealings (the temperatures vary from 400 °C to 750 °C) on their structural properties has been studied. The structural behavior has been investigated by the means of XRD and FTIR techniques. The results revealed no presence of mixed oxide phases, the detected crystal phases were related to the hexagonal ZnO and to crystalline ZrO₂. The sol‐gel ZnO‐ZrO₂ films showed polycrystalline structure with a certain degree of an amorphous fraction. The optical transmittance reached 91% and it diminished with increasing the annealing temperatures. The optical properties of the sol‐gel ZnO‐ZrO₂ films, deposited on glass substrates are excellent with high transparency and better then those of pure ZrO₂ films, obtained at similar technological conditions. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

WO3-based electrochromic system with hybrid organic–inorganic gel electrolytes

Thin metal oxide films for a WO₃-based symmetric electrochromic system with a nickel oxide layer as the counter electrode have been prepared by spray pyrolysis on SnO₂:F coated soda-lime float glass, at a temperature of 670–720 °C and using metal acetylacetonates as precursors. The films have been characterized for composition and morphology by scanning electron microscopy equipped with an X-ray energy dispersive analyzer (SEM/EDAX), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Electrochromic properties have been examined in the electrochemical cells of a smart window arrangement using lithium ion doped sol–gel derived organic–inorganic hybrid materials as electrolytes. Hybrids with room-temperature ionic conductivities of 10^?4–10^?3 Ω^?1 cm^?1 have been synthesized from tetraethyl orthosilicate (TEOS) with an addition of 35 mass % of organic compounds. Coloration-bleaching of WO₃ films with lithium ions from hybrid electrolytes has resulted in the desired modulating the properties in the visible and near infrared spectrum range. An XPS analysis has shown the presence of a lower oxidized tungsten oxide phase (WO_2.92) in the WO₃ film.     

Thickness and substrate orientation dependence of ferromagnetism in Mn doped ZnO thin films

The effect of film thickness and substrate orientation on ferromagnetism in Mn doped ZnO thin films have been studied. The Mn doped ZnO films of different thickness (15, 35 and 105 nm) have been grown on both Si (100) and Si (111) substrates. The structural, electrical, optical, elemental and magnetic properties of the films have been investigated by X‐ray diffraction (XRD), Hall Effect measurements, photoluminescence (PL), energy dispersive spectroscopy (EDS) and vibrating sample magnetometer (VSM), respectively. It is found that all the properties are strongly influenced by the film thickness and substrate orientation. The XRD analysis confirmed that the formation of high quality monophasic hexagonal wurtzite structure for all the grown films. The room temperature VSM measurements showed that the films of lower thickness have better ferromagnetism than that of the thicker films grown on both the substrates. Among the lower thickness films, the film grown on Si (111) substrate has higher saturation magnetization (291×10^‐5 emu cm^‐3) due to high density of the defects. The observed ferromagnetism has been well justified by XRD, Hall measurements and PL. The presence of Mn atoms in the film has been confirmed by EDS. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetic properties and X‐ray photoelectron spectroscopy of nanocrystalline Ho3Al5O12

Nanocrystalline holmium aluminium garnet (Ho₃Al₅O₁₂) has been prepared for the first time by modified Pechini's reaction after sintering the precursor gel at 1223 K. The nanomaterial has been characterized by X‐ray diffraction (XRD), selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM). The XRD pattern confirms the formation of single‐phase Ho₃Al₅O₁₂; the average size of the nanoparticles has also been determined. X‐ray photoelectron spectroscopy (XPS) has been used to study the chemical composition and bonding in the as‐prepared samples. The binding energies of core‐level electrons in Ho, Al and O in the title material have been found slightly shifted compared to the values of the respective elements. DC magnetic susceptibility has been measured in the temperature range 2 – 260 K. Low effective magnetic moment of Ho³⁺, μ_eff = 1.35 µ_B and Weiss constant have been derived from the inverse magnetic susceptibility–temperature linear plot. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermally oxidized zirconium nanostructured films grown on Si substrates

Zirconium thin films grown on Si substrates by a planar magnetron sputtering system were thermally oxidized at oxygen ambient within 523‐823 K resulting in zirconium oxide films with various stoichiometries. XRD analysis of the ex situ oxidized films revealed the phases at different oxidation temperatures. To achieve a reasonable fit between the experimental and SIMNRA simulated RBS spectra of the prepared samples; it was required to introduce a SiO₂buffer layer in the simulated target between Si substrate and ZrO₂ film. The presence of this intermediate SiO₂ layer was confirmed by observation of SiO₂ phase in the XRD patterns of all the thermally oxidized samples. Using RBS analysis data, the effect of oxidation temperature on the stoichiometry of zirconium oxide films and thickness of ZrO_xand SiO₂ films were investigated. XRD patterns of thermally oxidized Zr films also revealed that crystallization of zirconium oxide films was initiated at about 673 K and was almost completed at 823 K. Diffusion of oxygen atoms through surface layer was investigated and the effective activation energy for oxygen mass transport was estimated to be 1.75 eV using RBS data and Arrhenius relation. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and optoelectrical properties of Ga‐doped ZnO semiconductor thin films grown by magnetron sputtering

Transparent conductive gallium‐doped zinc oxide (Ga‐doped ZnO) films were prepared on glass substrate by magnetron sputtering. The influence of substrate temperature on structural, optoelectrical and surface properties of the films were investigated by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), spectrophotometer, four‐point probe and goniometry, respectively. Experimental results show that all the films are found to be oriented along the c‐axis. The grain size and optical transmittance of the films increase with increasing substrate temperature. The average transmittance in the visible wavelength range is above 83% for all the samples. It is observed that the optoelectrical property is correlated with the film structure. The Ga‐doped ZnO film grown at the substrate temperature of 400 °C has the highest figure of merit of 1.25 × 10⁻² Ω⁻¹, the lowest resistivity of 1.56 × 10⁻³ Ω·cm and the highest surface energy of 32.3 mJ/m².     

Study of the gel films of Acetobacter Xylinum cellulose and its modified samples by 1H NMR cryoporometry and small-angle X-ray scattering

Gel films of Acetobacter Xylinum cellulose and its modified samples have been investigated by 1H nuclear magnetic resonance (NMR) cryoporometry and small-angle X-ray scattering. The joint use of these two methods made it possible to characterize the sizes of aqueous pores in gel films and estimate the sizes of structural inhomogeneities before and after the sorption of polyvinylpyrrolidone and Se₀ nanoparticles (stabilized by polyvinylpyrrolidone) into the films. According to small-angle X-ray scattering data, the sizes of inhomogeneities in a gel film change only slightly upon the sorption of polyvinylpyrrolidone and nanoparticles. The impregnated material is sorbed into water-filled cavities that are present in the gel film. ¹H NMR cryoporometry allowed us to reveal the details of changes in the sizes of small aqueous pores during modifications.     

Structural investigation and electronic band transitions of nanostructured TiO2 thin films

Titanium dioxide (TiO₂) thin film was deposited on n‐Si (100) substrate by reactive DC magnetron sputtering system at 250 °C temperature. The deposited film was thermally treated for 3 h in the range of 400‐1000 °C by conventional thermal annealing (CTA) in air atmosphere. The effects of the annealing temperature on the structural and morphological properties of the films were investigated by X‐ray diffraction (XRD) and atomic force microscopy (AFM), respectively. XRD measurements show that the rutile phase is the dominant crystalline phase for the film annealed at 800 °C. According to AFM results, the increased grain sizes indicate that the annealing improves the crystalline quality of the TiO₂ film. In addition, the formation of the interfacial SiO₂ layer between TiO₂ film and Si substrate was evaluated by the transmittance spectra obtained with FTIR spectrometer. The electronic band transitions of as‐deposited and annealed films were also studied by using photoluminescence (PL) spectroscopy at room temperature. The results show that the dislocation density and microstrain in the film were decreased by increasing annealing temperature for both anatase and rutile phases. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Poole‐Frenkel electrical conduction in europium oxide films deposited on Si(100)

Thin Eu₂O₃ films were prepared on Si (P) substrates to form MOS devices. The oxide crystal structure was determined by X‐ray diffraction (XRD). The electrical transport properties of the devices with amorphous and crystalline Eu oxide were investigated. The current‐voltage and current‐temperature characteristics suggest a Poole‐Frenkel (PF) type mechanism of carrier transport through the device when the applied field is more than 105 V/cm. A deviation from PF leakage current course was found and attributed to the current carrier trapping. We have also observed that, the dielectric spectra of MOS structure are different when the insulator is an amorphous or crystalline thin film. From which we calculate the relaxation time (τ) of the interface (insulator/semiconductor) dipoles. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties and synthesis of CuInSe2 thin films by selenization of Cu/In layers

In this paper, we report the effect of annealing temperature on the properties of copper indium diselenide (CuInSe₂) thin films. The CuInSe₂ thin films were fabricated at 500 °C for 2 h by annealing Cu‐In layers (as precursors) selenized in a glass tube with pure selenium powder. The structural and morphological properties of the CuInSe₂ thin films were characterized respectively by means of x‐ray diffraction (XRD) and field‐emission scanning electron microscope (FE‐SEM). The type of CuInSe₂ thin film has been identified as direct allowed and the band gap value was determined. The study of UV/Visible/NIR absorption shows that the band gap value of CuInSe₂ thin film is about 1.07 eV, which is within an optimal range for harvesting solar radiation energy. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interaction of Se0 nanoparticles stabilized by poly(vinylpyrrolidone) with gel films of cellulose Acetobacter xylinum

The sorption and desorption of poly(vinylpyrrolidone)-Se⁰ (PVP-Se⁰) nanoparticles on gel films of cellulose Acetobacter xylinum (CAX) are investigated. It is revealed that the hydrodynamic radius R _h of PVP-Se⁰ nanoparticles decreases from 57 nm in the initial solution (without CAX gel films) to 25 nm after the sorption of nanostructures on gel films and then increases to approximately 100 nm after the desorption of nanoparticles with water from dry samples of the CAX gel film-PVP-Se⁰ nanocomposite. It is found that selenium atoms do not penetrate into crystallites of the cellulose nanofibrils and replace water molecules sorbed by the primary hydroxyl groups of their walls. Poly(vinylpyrrolidone)-Se⁰ nanoclusters differ in the number and size upon their sorption inside the cellulose gel film and on the film surface.     

Optical and magnetic properties of Nd‐doped ZnO nanoparticles

Nd‐doped ZnO nanoparticles with different concentration were synthesized by sol‐gel method. The structures, magnetic and optical properties of as‐synthesized nanorods were investigated. X‐ray diffraction (XRD) and x‐ray photoelectron spectroscopy (XPS) results demonstrated that Nd ions were incorporated into ZnO lattice; but Zn_1‐xNd_xO nanoparticles with Nd concentration of x = 0.05 showed Nd₂O₃ phase, so the saturation concentration of Nd in Zn_1‐xNd_xO is less than 5 at%. Vibrating sample magnetometer (VSM) measurements indicated that Nd doped ZnO possessed dilute ferromagnetis behaviour at room temperature. Photoluminescence spectroscopy (PL) showed that Nd ions doping induced a red slight shift and decrease in UV emission with increase of Nd concentration.     

Substitution effects on ferroelectric,leakage current and anti‐fatigue characteristic of Bi4‐xSbxTi3O12 thin films

Bi_4‐xSb_xTi₃O₁₂ (BSTO) (x = 0, 0.03, 0.04, 0.05, 0.06 and 0.07) thin films have been fabricated on Pt/Ti/SiO₂/Si substrates by sol‐gel method. The effects of various Sb³⁺ content on microstructure and ferroelectric properties of systems are investigated. XRD show that Bi_4‐xSb_xTi₃O₁₂ (x≠0) thin films prefer (117) orientation. The substitution Sb³⁺ for Bi³⁺ reduces the grain size of the film surface. Compared to the BTO (x = 0) film, Bi_4‐xSb_xTi₃O₁₂ films display exciting electric properties. Especially when x = 0.04, the film Bi_3.96Sb_0.04Ti₃O₁₂ has achieved the max 2Pr value of 87μC/cm². This film also has a better anti‐fatigue characteristic, which can be up to 10¹⁰ switching cycles without fatigue. The leakage current density improved with J = 8×10⁻⁸ A/cm².     

Structural and optical properties of TiO2:SnO2 thin films prepared by sol gel method

ABSTRACT

TiO₂:SnO₂ thin films were deposited on glass substrates, by using sol gel spin coating method with different ratio (3%, 5% and 7%) at 3200 rpm, to study their effect on different properties of TiO₂: SnO₂ thin films. The structural and optical properties of films have studied for different ratio. These deposited films have been characterized by various methods such as X-Ray Diffraction (XRD), Ultra Visible spectroscopy. The (XRD) can be used to identify crystal structure of as deposited films. The Transmission spectra have shown the transparent and opaque parts in the visible and UV wavelengths.     

Preparation and characterization of ZnO-TiO2 films obtained by sol-gel method

The sol-gel route has been applied to obtain ZnO-TiO₂ thin films. For comparison, pure TiO₂ and ZnO films are also prepared from the corresponding solutions. The films are deposited by a spin-coated method on silicon and glass substrates. Their structural and vibrational properties have been studied as a function of the annealing temperatures (400-750 °C). Pure ZnO films crystallize in a wurtzite modification at a relatively low temperature of 400 °C, whereas the mixed oxide films show predominantly amorphous structure at this temperature. XRD analysis shows that by increasing the annealing temperatures, the sol-gel Zn/Ti oxide films reveal a certain degree of crystallization and their structures are found to be mixtures of wurtzite ZnO, Zn₂TiO₄, anatase TiO₂ and amorphous fraction. The XRD analysis presumes that Zn₂TiO₄ becomes a favored phase at the highest annealing temperature of 750 °C. The obtained thin films are uniform with no visual defects. The optical properties of ZnO-TiO₂ films have been compared with those of single component films (ZnO and TiO₂). The mixed oxide films present a high transparency with a slight decrease by increasing the annealing temperature.     

Synthesis and optical properties of CuInS2 thin films prepared by sulfurization of electrodeposited Cu‐In layers

The chalcopyrite CuInS₂ thin film was fabricated at 500 °C for 2 h by sulfurization of Cu‐In layers (as precursors) that were sulfurized in a glass tube with pure sulfur powder. The structural, morphological, and optical properties of CuInS₂ thin films are characterized using X‐ray diffraction (XRD), field‐emission scanning electron microscope (FE‐SEM), and UV/Visible/NIR spectrophotometer. The study of UV/Visible/NIR absorption shows the band gap energy value of CuInS₂ thin films is 1.5 eV. The XRD pattern shows the film is pure CuInS₂; no other peaks, such as CuS or CuIn₅S₈ were observed. Furthermore, the surface of the CuInS₂ film is compact characterized by FE‐SEM, which also shows the disappearance of CuS on the surface at 500 °C.     

Structure and morphological stability of (Lu1–xEux)2O3 thin films

(Lu_1–xEu_x)₂O₃ smooth, crack‐free, transparent films were prepared by the Pechini sol–gel method and a spin‐coating technique. Thermogravimetric analysis, differential thermal analysis and FITR spectroscopy were used to study the chemical processes during annealing of the films. Film structure, morphology and optical properties were investigated. X‐ray diffraction (XRD) analysis reveals the cubic phase of (Lu_1–xEu_x)₂O₃ films annealed in the 600–1000 °C temperature range. Smooth and crack‐free films with thicknesses of 250–1000 nm were obtained in the 600–800 °C temperature range. The thickness upper limit (1000 nm) of morphological stability of films (Lu_1–xEu_x)₂O₃ on sapphire substrates has been studied.     

Effect of laser fluence on c‐axis orientation of LiNbO3 piezoelectric films on nanocrystalline diamond by pulsed laser deposition

Completely c‐axis oriented LiNbO₃ piezoelectric films have been deposited on nanocrystalline diamond (NCD)/Si substrates with SiO₂ buffer layer by pulsed laser deposition. The amorphous SiO₂ buffer layer was formed on NCD/Si substrates by sol‐gel method. The c‐axis orientation and crystallinity of LiNbO₃ films are strongly dependent on the laser fluence, and the laser fluence 3.6 J/cm² is found to be the optimal value for the growth of oriented LiNbO₃ film, which has a smooth surface with composed of a large mount of uniform grains. The average surface roughness of LiNbO₃ films is about 6.7 nm.     

Fabrication of ferric oxide/reduced graphene oxide/cadmium sulfide heterostructure photoelectrode for enhanced photoelectrochemical performance

A novel high‐efficiency photoelectrode (Fe₂O₃/reduced graphene oxide/CdS) built from heterostructure and conductive scaffold has been successfully designed and synthesized. Reduced graphene oxide works as a “bridge” which benefits for electron and hole transport. The obtained heterostructure photoelectrodes were systematically characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, and X‐ray photoelectron spectroscopy (XPS). The photoconversion efficiency (η) and photocurrent densities vs. time (I‐t) curves responding to monochromatic lights have been further investigated in‐depth, which reveals that introduction of CdS and reduced graphene oxide played an important role in the enhancement of photoelectrochemical performance.