Measurement of glass surface layers and their influence on thin-film optical properties

A new and simple method is proposed to analyze the profiles of glass surface layers based on their reflectance for p-polarized light. By measuring the angle spectrum gamma(theta(i)) (gamma equivalent to I-a/I-b), where I-a and I-b are the intensities of reflection from the front and the back surface of the glass, and fitting the results with theoretical relations, the refractive index n(s) and extinction coefficient k(s) of plane glass surfaces can easily be obtained. Experimentally, glass samples subjected to different cleaning treatments have been analyzed. The results show that n(s) and k(s) of the glass surface increase exponentially with the depth into the surface layers, and an etched glass sample has a smaller extinction coefficient on its surface. This is confirmed by atomic-force-microscope observation and by laser-damage testing. In addition, the influence of the glass surface layers on the properties of films coated on one side or both sides of the glass substrate is analyzed. Dip-coated polymethyltriethoxysilane. (PMTES) films and spin-coated PMMA films have been measured. It is found that the optical parameters of PMTES films and azo-doped PMMA films are in agreement with the experimental results only if the glass surface layers are considered. (C) 2002 Society of Photo-Optical Instrumentation Engineers