The Effect of Illumination on the Contact Angles of Pure Water on Amorphous Silicon

Abstract

Contact angle determinations were made to allow us to study the effect of the wavelength of illumination on the surface of hydrogenated amorphous silicon thin films. The films were prepared by the PECVD technique from pure silane under conditions which give good quality material. Advancing and receding contact angles of water drops, on hydrofluoric acid etched and nonetched silicon surfaces, were measured as a function of drop volume. Large differences in the contact angles were observed depending on the wavelength of the incident light. The contact angles on the HF-treated silicon surface under violet light yielded the lowest values, while green light yielded the highest values. However, in the case of nontreated silicon surfaces, green light yielded the lowest contact angles and red light the highest values. These surface phenomena, related to the surface photovoltage effect, were seen to be completely reversible.