SYNTHESIS, CHARACTERIZATIONS, AND OPTICAL-PROPERTIES OF STACKED POROUS THIN-FILMS DERIVED FROM SOL-GEL PROCESS

Stacked thin films consisting of a titania on top of a highly porous, colloidal silica layer have been dip-coated on silicon (100) substrate s starting from sol-gel processes, The structural evolution of the sta cked films during different treatments has been characterized by atomi c force microscopy (AFM), ellipsometry, glazing angle X-ray diffractio n (XRD), and Auger electron spectroscopy (AES). The as-deposited porou s silica layer has a refractive index of 1.18 correlating to porosity >50% after curing at 450 degrees C, Upon deposition of a titania thin film on its surface, the silica's index dramatically increases to 1.31 , which indicates an intermixing of titania coating into the porous si lica layer. In contrast to titania film deposited on a dense silica su rface, the presence of a constant amount of titanium can also be obser ved in the porous silica underlayer of the stacked films by AES. The h omogeneous intermixing of titania is further confirmed by comparison o f the reflectance measured spectroscopically with that computed from e llipsometric data, The stacked thin films prepared with distinct diffe rences in porosity and/or refractive index show a great potential for the design of novel asymmetric ceramic membranes and/or optical coatin gs.