In this work, ZnO thin films were derived by sol-gel using two different techniques; dip coating and spin coating technique. The films were deposited onto glass substrate at room temperature using sol-gel composed from zinc acetate dehydrate, monoethanolamine, isopropanole, and de-ionized water, the films were preheated at 225?C for 15 min. The crystallographic structures of ZnO films were investigated using X-ray diffraction (XRD); the result shows that the good film was prepared at dip coating technique, it was polycrystalline and highly c-orientation along (002) plane, the lattice constant ratio (c/a) was calculated at (002), it was about 1.56. The structure of thin films, prepared by spin coating technique, was amorphous with low intensity and wide peaks. The optical properties of the prepared film were studied using UV-VIS spectrophotometer with the range 190 - 850 nm, and by using the fluorescence spectrometer. The optical characterization of ZnO thin films that were prepared by the dip coating method have good transmittance of about 92% in the visible region, it can be noted from the fluorescence spectrometer two broad visible emission bands centered at 380nm and 430 nm. The optical energy gaps for the direct and indirect allowed transitions were calculated, the values were equal 3.2 eV and 3.1 eV respectively. Dip coating technique create ZnO films with potential for application as transparent electrodes in optoelectronic devices such as solar cell

We have systematically studied the relationship between synthesis pH and morphological and optical properties of silica aerogels. We have determined through SEM and BET that there is a systematic correlation between the pH of the initial silica solution and the surface area, porosity, and pore size of the resulting aerogel. We find that optical transmittance, particularly its wavelength dependence (dispersion), is strongly governed by the microstructure and, therefore, synthesis pH. We have determined that the microstructure of the aerogels fall into three broad categories: monostructural, which is characterized by repeating elongated microstructural features; fractal, which shows a distinctive structure that is emulated on multiple length scales; and isotropic, which is characterized by having no distinct features in its microstructure. Simply by controlling the pH of the synthesis environment, we can tune the optical properties of silica aerogels through pH controlled the microstructural modification. We have found that pH = 1-5 gives high dispersion, pH = 6-7 results in low transmittance and low dispersion, pH = 8 shows the highest transmittance with the lowest dispersion, and pH = 9-10 transitions back to lower transmittance and higher dispersion.

No abstract

No abstract

No abstract