A sol-gel dip-coating process was used to deposit almost stress-free highlyc-axis oriented zinc oxide (ZnO) thin films onto glass substrates. The effects of low silver doping concentration (Ag/Zn < 1%) on the structural, morphological, optical, and waveguide properties of such films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy, UV-Visible spectrophotometry, and M-lines spectroscopy (MLS). XRD analysis revealed that all the films were in single phase and had a hexagonal wurtzite structure. The grain size values were calculated and found to be about 24–29 nm. SEM micrographs and AFM images have shown that film morphology and surface roughness were influenced by Ag doping concentration. According to UV-Vis. measurements all the films were highly transparent with average visible transmission values ranging from 80% to 86%. It was found that the Ag contents lead to widening of the band gap. MLS measurements at 632.8 nm wavelength put into evidence that all thin film planar waveguides demonstrate a well-guided fundamental mode for both transverse electric and transverse magnetic polarized light. Moreover, the refractive index of ZnO thin films was found to increase by Ag doping levels.
TiO 2 nano-aerogels are elaborated by using acid-modified sol-gel approach from titanium tetra isopropoxide under supercritical drying conditions of ethanol. The effects of Ti-precursor concentration and annealing temperature on structural and morphological properties of TiO 2 nanoparticles are investigated by XRD, infrared spectroscopy, SEM and specific surface area measurements. It was found, from XRD analysis, that pure anatase phase is obtained for the aerogels synthesized with various precursor concentrations. The increase of sol concentration leads to a slight and uniform variation of TiO 2 cell parameters. The specific surface area of aerogels particles decreases and the pore volume increases with increasing of Ti-concentration. The presence of Ti-O and Ti-O-Ti bonds is confirmed by FTIR measurements. EDAX analysis shows that TiO 2 nano-aerogels are oxygen rich. SEM images put into evidence the almost spherical elaborated particles with an enhanced agglomeration at high precursor concentration. With the increase of annealing temperature, the mixture of the phases did not happen and the pure anatase to pure rutile transition phase temperature is found to be around 900 °C. The Ti-O-C bonds disappear with annealing temperature. The heat treatment leads not only to the changes in crystal structure but also in morphology of the elaborated aerogels grains.
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