In this study, the silk fibroin films with different numbers of layers were fabricated by the spin-coating method and their optical transmittances were observed. The process to synthesise the silk fibroin solution was explained – starting from the silk cocoon until the silk-fibroin solution, approximately 7.5% concentration wt/vol, was obtained. The solution was spin-coated onto clean glass substrates to fabricate samples. Totally 10 samples with different numbers of layers, from 1 to 5 layers, were obtained. All samples can be separated into two groups: those left dried at room temperature after spin-coating and those heated at 60°C. They were then measured for their transmittance over the visible-to-near-infrared region. All samples exhibited the high transmittance where the values were at 95% and 98%, for the samples at room temperature and those at 60°C, respectively. This was believed to be due to the heating effect that caused the silk fibroin to arrange itself after being heated, hence the higher transmittance. These high transmittances were maintained regardless of the number of layers and length of heating time. Results from this study could be used to fabricate a silk fibroin film with high optical transmittance and adjustable other properties.
In this report, effects of heat treatment conditions on the transmittance of titanium dioxide, TiO<sub>2</sub>, films were examined. The colloidal solution of TiO<sub>2</sub> in two different solvents – isopropanol, IPA, and sulfuric acid, H<sub>2</sub>SO<sub>4</sub>, were deposited via a spin-coating method onto clean glass substrates. The films were subsequently annealed and cooled down, either quickly or slowly, before being measured for their optical transmittances in the visible region. Three points were noted: Firstly, when the films were quickly cooled down after annealed, their transmittance depended on their annealing temperature. In IPA and H<sub>2</sub>SO<sub>4</sub>, the transmittance decreased and increased, respectively, when the annealing temperature increased. Secondly, when the films were slowly cooled down after annealed, their transmittance seemed to be independent from the annealing temperature, where the films had roughly equal transmittance regardless of annealing temperature. Lastly, the TiO<sub>2</sub> films with H<sub>2</sub>SO<sub>4</sub> provided higher transmittance than those with IPA. All the three stated characteristics were the same for all wavelengths in the visible region. These results were believed to result from the dispersibility of the TiO<sub>2</sub> in each solvent and the cooling-down processes. Such results could be further developed to select a suitable heat treatment process for a spin-coated TiO<sub>2</sub> film with a desired optical transmittance.
Integrating sphere is an important tool used in photometry and other optics-related fields to induce uniform scattering of a light source. An important property of an integrating sphere is its uniformity, which should be high so that the sphere provides smooth response. Necessary sphere components include a baffle and a photo-detector. However, the existence of the baffle is found to induce non-uniformity to the sphere response. Here we report an experimental study of the effects of integrating sphere components, especially the baffle, on its uniformity. In a typical condition, the response on the sphere wall opposite to the baffle was found to be lowered compared with that of the surrounding area, while that on the wall around the photo-detector behind the baffle was higher. Consequently, three baffle properties – reflectance of the baffle back surface, baffle size, and baffle position – were varied to see their effects on the sphere response, especially that at the sphere wall behind the baffle. It was found that the amplitude of the response of such area would be lowered regarding the following conditions: decrease in the reflectance of the baffle back surface, decrease in the baffle size, and increase in the distance between baffle and the detector. Adjusting these conditions yielded the lowered signals at such area and hence increasing sphere uniformity. However, the experiment showed that they also induced some adverse effects such as non-uniformity at other parts of the sphere. Thus these conditions should be optimised carefully in order to obtain the best uniformity.