Effect of Ag doping on structural, electrical and dielectric properties of TiO2 nanoparticles synthesized by a low temperature hydrothermal method

Silver (Ag) doped thermally stable TiO₂ nanoparticles in the anatase phase have been synthesized by a low temperature hydrothermal method. The formation of anatase phase has been investigated by X-ray diffraction. Thermogravimetry and differential scanning calorimetry have been used for thermal studies. Scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy have been used for the morphology and composition studies. Surface areas were studied by the Brunauer-Emmett-Teller method. Dielectric properties were studied for dopant levels of 0.25, 0.5 and 1.0?wt% at 300?K in the frequency range of 42?Hz–5?MHz. The crystallite size, alternating current (AC) conductivity and dielectric properties of undoped TiO₂ nanoparticles were greatly affected by doping with Ag. At high frequencies, the materials showed high AC Conductivity and low dielectric constant.     

Effect of annealing temperature on the structural and magnetic properties of Co-doped TiO2 nanoparticles via complex-polymer sol-gel method

Co-doped TiO2 nanoparticles were synthesized via non hydrous complex-polymer sol-gel method. A series of Co(x):Ti1-x O2 samples with x = 0.01, 0.03, 0.05, 0.08 and 0.10, were prepared and subsequently annealed at 400 degrees, 600 degrees and 800 degrees C. Structural and magnetic properties of Co(x):Ti1-x O2 have been studied by means of X-ray diffraction and DC magnetometry. All samples annealed at 400 degrees C show a paramagnetic behavior with an average grain size of 11 nm. With increasing annealing temperatures a complete crystallization is seen with growth of the cluster size up to 31 nm with clear evidence of a presence of CoTiO3. For all concentrations and annealing conditions no sign of a metallic phase, even at x = 0.10, is seen.     

Synthesis and characterization of solar photoactive TiO2 nanoparticles with enhanced structural and optical properties

The structural, morphological, and optical properties of the sol–gel derived TiO₂ nanoparticles at different pH and calcination temperature were investigated in the present study. X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM), UV–Visible(Vis) spectroscopy, energy dispersive studies (EDS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoluminescence (PL) spectroscopy, BET surface area analysis, and Barrett-Joyner-Halenda (BJH) pore size distribution and pore volume analysis were used to characterize the prepared TiO₂ photocatalyst. The range of crystallite size and band gap of the synthesized TiO₂ samples were in the range of 20–80?nm and 2.5–3.2?eV respectively. The photocatalytic performance of prepared TiO₂ photocatalysts was evaluated by photodegradation of Methylene Blue (MB) solution under simulated solar irradiation. Results illustrate that the synthesized TiO₂ exhibits visible light activity at higher calcination temperature. Crystallinity and surface area plays a vital role in the overall performance of the prepared TiO₂ photocatalyst.     

Effect of oxidation and annealing temperature on optical and structural properties of SnO2

Tin oxide thin films were deposited on glass substrate with 100 nm thickness of Sn, which was coated by magnetron sputtering followed by thermal oxidation at different temperatures. The effect of oxidation temperature on the optical and structural properties of SnO₂ films were investigated. Higher transmittance, lower absorption and lesser structural defects were obtained at higher temperatures. Optical bandgap increases with temperature, while the Urbach energy showed reduction. The X-ray diffraction studies showed that at lower temperatures (300, 350 °C), a combined phase of SnO and SnO₂ was obtained, while at higher temperatures (400, 450 °C), a nearly polycrystalline SnO₂ film with preferred orientation of (101) was produced. Annealing of the samples at 500–650 °C caused the transmittance and optical bandgap increased, while the absorption decreased. Reduction of the Urbach energy after annealing could be attributed to the reduction of the degree of thermal disorder. AFM studies showed that although the thin films were annealed under similar condition, their roughness was not similar because of different oxidation temperatures, which means that initial oxidation temperature played an important role on surface uniformity of SnO₂ thin films.     

Analysis of optical properties of TiO2 nanoparticles and PAN/TiO2 composite nanofibers

The aim of the study was the production of thin composite nanofibrous mats PAN/TiO₂ nanoparticles using the electrospinning method from solution of PAN/TiO2/DMF. TiO₂ nanoparticles were obtained using sol-gel method. To prepare sol mixture, organic alkoxides precursor of titanium isopropoxide and water solution were used. Calcination of TiO-gel and following milling were carried out to obtain nanoparticles of TiO₂ rutile phase. In order to analyze the structure of the obtained particles, we used X-ray diffraction analysis (XRD) and energy dispersive spectrometer (EDS). Analysis of the morphology and chemical composition of the resulting composite nanofibers were carried out using a scanning electron microscope (SEM) with EDS. The analysis of the optical properties and the energy band structure prepared nanoparticles and thin composite nanofibrous mats were determined by spectral analysis of the absorbance as a function of the energy of radiation obtained using a UV–Vis spectrophotometer.     

Effect of solvent-induced structural modifications on optical properties of CdS nanoparticles

We have investigated the effects of solvent used during synthesis on structural and optical properties of CdS quantum dots. Different methods of synthesis for the production of CdS quantum dots are presented. These are: (a) wet chemical co-precipitation in non-aqueous medium (i.e. methanol); (b) wet chemical co-precipitation in aqueous medium (deionized water) and (c) solid state reaction. It is demonstrated that the use of methanol as solvent leads to a strong enhancement of PL intensity of CdS quantum dots for use in optoelectronic devices. These products were characterized by X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). The change in bandgap with size-quantization was investigated by UV-VIS absorption spectroscopy. CdS nanocrystals prepared in non-aqueous medium have narrow size distribution than those prepared in aqueous medium and solid state reaction. Phase transformation of CdS nanocrystals from a cubic to hexagonal structure was observed in methanol solution. The formation of CdS/Cd(OH)₂ nanostructure was also confirmed using X-ray diffraction pattern. This suggests that the strong enhancement of the PL intensity may have originated from the remarkable reduction of non-radiative recombination process, due to surface defects of quantum dots. The red shift of the Raman peaks compared to that for bulk CdS may be attributed to optical phonon confinement.     

Influence of CTAB surfactant on structural and optical properties of CuS and CdS nanoparticles by hydrothermal route

Metal sulphide CuS and CdS nanoparticles capped with Cetyltrimethylammonium bromide (CTAB) were synthesized by hydrothermal method. Structural, morphological, chemical composition, optical and luminescent properties were evaluated by different analytical techniques. X-ray diffraction (XRD) analysis of the CTAB capped metal sulfide nanoparticles reveals the formation of hexagonal structure. High-resolution transmission electron microscopy (HRTEM) images show that the morphology of the capped copper sulphide samples consists of hexagonal structure and capped cadmium has spherical shape and also confirms the crystalline nature of the particles with distinct lattice fringes. In FTIR spectroscopy, the composition of the CTAB capped CuS and CdS nanoparticles have been confirmed. The analysis of photoluminescence (PL) and optical transition show a red shift due to the reduction of band gap energy and it is attributed to the low defects and high crystallinity. The optical studies indicate that CuS and CdS nanoparticles with CTAB can be suitable for optoelectronic devices and photovoltaic applications.     

Effect of vanadium and tungsten doping on the structural,optical, and electronic characteristics of TiO2 nanoparticles

Journal of Materials Science: Materials in Electronics - Nanoparticles of TiO2 and Ti0.97M0.03O2 (M≡V, W) samples were produced using sol–gel procedure. Utilizing synchrotron x-ray...     

Influence of calcination temperature on structural and optical properties of TiO2-SiO2 thin films prepared by sol-gel dip coating

We prepared TiO₂-SiO₂ thin films with various TiO₂/SiO₂ ratios by sol-gel dip coating method and explored the dependence of their structural and optical properties on calcination temperature. The absorption peaks relevant to Si—O, Si—O—Ti and Ti—O bonds appeared in the FTIR spectra. With increasing TiO₂ content, the intensity of Si—O bond peaks decreases and that of Ti—O bond peaks increases. The XRD results show that the temperature of transformation from amorphous to anatase phase is lowered as TiO₂ content increases. The crystallite size of anatase phase in composite thin films increases with increasing TiO₂ content and calcination temperature. At 1000°C, the mixed phase of anatase and rutile appears in the pure TiO₂ thin films. The rutile films are denser than the anatase films. The increase in refractive index of composite thin films with calcination temperature is related to the decreased thickness and increased density as a result of evaporation of water and organic matters below 400°C. On the other hand, it is related to the change in the crystal phase and crystallite size of the films over 400°C.     

Effect of doping on structural and optical properties of ZnO nanoparticles: study of antibacterial properties

Sol-gel method was successfully used for synthesis of ZnO nanoparticles doped with 10 % Mg or Cu. The structure, morphology and optical properties of the prepared nanoparticles were studied as a function of doping content. The synthesized ZnO:(Mg/Cu) samples were characterized using XRD, TEM, FTIR and UV-Vis spectroscopy techniques. The samples show hexagonal wurtzite structure, and the phase segregation takes place for Cu doping. Optical studies revealed that Mg doping increases the energy band gap while Cu incorporation results in decrease of the band gap. The antibacterial activities of the nanoparticles were tested against Escherichia coli (Gram negative bacteria) cultures. It was found that both pure and doped ZnO nanosuspensions show good antibacterial activity which increases with copper doping, and slightly decreases with adding Mg.     

Effect of transition metal elements on the structural and optical properties of ZnO nanoparticles

Undoped and transition metal (TM)-doped ZnO nanoparticles (Zn_0.98X_0.02O-NPs, X = Mn, Cr, Co and Fe) were synthesized from a metal nitrate precursor and gelatin by a sol–gel method. The compounds were synthesized at calcination temperatures of 550^°C for 6 h. The synthesized undoped/doped ZnO-NPs were characterized by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). XRD results indicated that the sample products were crystalline with a hexagonal wurtzite phase. SEM images showed the ZnO-NPs nearly spherical shapes and a non-uniform shape for doped ZnO-NPs. The crystalline development in the ZnO-NPs was investigated by X-ray peak broadening. The size–strain plot (SSP) method was used to study the individual contributions of crystallite sizes and lattice strain of the undoped and doped ZnO-NPs. The obtained results showed that strain of the NPs plays an important role in peak broadening; moreover, the mean crystalline size of the undoped and doped ZnO-NPs estimated from the SEM and the SSP method was highly inter-correlated. Finally, optical properties of the samples were studied by a UV–Vis spectrometer.     

Effect of Sn doping on the growth and optical properties of AgI nanoparticles

Controlled iodization and Sn doping of vacuum-evaporated Ag films has helped understand the initial-stage kinetics of AgI nanoparticle growth under ambient conditions. Use of XRD, optical spectroscopy, and AFM has unravelled systematic correlation between Sn-induced disorder in Ag crystal structure, nanoparticle size, and exciton growth dynamics. Sn doping of Ag leads to three specific effects: removal of UV absorption minimum in Ag, introduction of a plasmon-type absorption in the red region, and a reduction in particle size in thicker (than 10 nm) films (but an increase in particle size in 10 nm films) relative to that in undoped Ag films.     

Investigations on structural, optical and electrochemical properties of blue luminescence SnO2 nanoparticles

A simple solution approach has been developed to synthesis SnO₂ nanoparticles using polyethylene glycol as stabilizer. X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), UV–Vis absorption spectroscopy, photoluminescence (PL) emission spectroscopy, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to characterize the nanoparticles. XRD, HR-TEM and AFM indicate that the SnO₂ nanoparticles correspond to tetragonal crystal structure with size ranges below Bohr’s exciton radius. UV–Vis absorption spectrum showed band gap exhibiting a 1.3 eV shift from that of bulk SnO₂ structures. The blue emission owing to transition of an electron from conduction band to deeply trapped hole in SnO₂ nanoparticles was analyzed using PL spectroscopy. The charge transfer capability had been investigated using CV and EIS in different electrolytes. A detailed exploration on confinement effect that occurred in SnO₂ nanoparticles, mechanism behind visible emission and electron transfer mechanism in different electrolyte was discussed.     

Effect of growth temperature on structural, electrical and optical properties of dual ion beam sputtered ZnO thin films

ZnO epitaxial thin films were grown on p-type Si(100) substrates by dual ion beam sputtering deposition system. The crystalline quality, surface morphology, optical and electrical properties of as-deposited ZnO thin films at different growth temperatures were studied. Substrate temperature was varied from 100 to 600 °C at constant oxygen percentage O₂/(O₂ + Ar) % of 66.67 % in a mixed gas of Ar and O₂ with constant chamber pressure of 2.75 × 10^?4 mBar. X-Ray diffraction analyses revealed that all the films had (002) preferred orientation. The minimum value of stress was reported to be ?0.32 × 10¹⁰ dyne/cm² from ZnO film grown at 200 °C. Photoluminescence measurements demonstrated sharp near-band-edge emission (NBE) was observed at ~375 nm along with deep level emission (DLE) in the visible spectral range at room temperature. The DLE Peak was found to have decrement as ZnO growth temperature was increased from 200 to 600 °C. The minimum FWHM of the NBE peak of 16.76 nm was achieved at 600 °C growth temperature. X-Ray photoelectron spectroscopy study revealed presence of oxygen interstitials and vacancies point defects in ZnO film grown at 400 °C. The ZnO thin film was found to be highly resistive when grown at 100 °C. The ZnO films were found to be n-type conducting with decreasing resistivity on increasing substrate temperature from 200 to 500 °C and again increased for film grown at 600 °C. Based on these studies a correlation between native point defects, optical and electrical properties has been established.     

Synthesis and structural, optical and electrical properties of TiO2/SiO2 nanocomposites

Sole components of titania (TiO₂), silica (SiO₂) nanoparticles, and binary TiO₂–SiO₂ nanocomposites with various molar ratios of silica contents were prepared by modified sol–gel method. The samples were calcined at 500 °C for 5 h and characterized by X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy, Brunauett–Emmett–Teller (BET), and photoconductivity. The crystallite size for TiO₂/SiO₂ nanocomposites was calculated using Scherrer’s formula and found to be 5 nm for TiO₂ nanoparticles. The binary oxide shows the anatase type of TiO₂ at the mole ratio up to 80 mol% of TiO₂ added. The band gap for as-synthesized nanocomposites was calculated and it was found that the band gap decreases with increase of SiO₂ content and then decreases with excess SiO₂ content. FTIR confirms that both TiO₂ and SiO₂ phases have been formed. The BET surface area for TiO₂/SiO₂ nanocomposite is found to be 303 m²/g, and pore size distribution has an average pore diameter about 10 nm for 40 mol% of TiO₂ added. It also confirms the absence of macropores and the presence of micro and mesopores. The field-dependent dark and photoconductivity studies reveal that the dark and photocurrent increase linearly with applied field confirming the ohmic nature of the electric contacts. The dark and photocurrent increase slightly with increase of SiO₂ content and decrease with excess amount of SiO₂.