ABSTRACT
The measurement of contact angles between a liquid and a solid surface is used extensively in both research and industry to characterize surfaces. Contact angle studies are useful because they often correlate with properties such as adhesion, surface energy, and wetting of materials. Furthermore, contact angles are usually easy to measure and a good reproducibility has been obtained in different studies with a variety of systems. The composition of the solid and the liquid phases, the roughness and the level of heterogeneity and contamination of the solid surface, as well as the ambient temperature are well-established parameters that determine the value of the contact angle. The substances used for materials treatment and cleaning also have important effects on contact angles because they usually ad sorb at or react with the solid surface [1]. Optoelectronic materials present addi-
tional parameters, which can modify the contact angle. Semiconductors present the so-called surface photovoltaic effect. It is well known that the densities of free and trapped charge carriers in crystalline silicon and amorphous hydrogenated silicon films are strongly dependent on both the wavelength and the intensity of the light with which the material is illuminated [2]. In fact, the illumination cre ates an electrical charge on semiconductor surfaces, which produces observable changes in the contact angle depending on the wavelength of illumination.
