AIR POCKETS IN THIN POROUS PLATINUM FILMS STUDIED BY SPECTROSCOPIC ELLIPSOMETRY

Optical characterization of thin porous platinum films has been carrie d out by spectroscopic ellipsometry in air, in water and in methanol. From the measurements in air, the thicknesses and porosity of the film s were determined. The measurements in water showed that air pockets a re present at the interface between water and a platinum film if the s ample surface is made hydrophobic by silanization. In methanol such pl atinum films are wetting and the air pockets vanish. In the optical an alysis it was necessary to include a thin organic layer on the hydroph obic surfaces. However, no organic layer or air pockets were found in water on as-prepared hydrophillic surfaces. Furthermore, upon storage in laboratory air, an organic layer formed spontaneously on the hydrop hillic surface. The ellipsometric results support the suggestion that, by means of the air pockets, hydrophobic thin platinum films act as g as permeable structures in electrolytes which leads to a possibility t o develop chemical sensors for molecular species in solutions.