Surface modification of silica with ultraviolet laser radiation

A frequency-doubled copper vapour laser was used to irradiate the surface of silica with ultraviolet light at fluences of between 0.1 and 0.5 J/cm² per pulse for several hundred pulses. Analysis of the surface composition using time-of-flight secondary-ion mass spectroscopy (TOF-SIMS) shows that the relative surface-hydroxyl (OH) concentration decreases with increasing laser irradiance. This dehydroxylation results in silica surfaces with final-state hydroxyl concentrations similar to those obtained through the thermal treatment of silica at around 1000°C. The mechanism for the dehydroxylation reported here, however, is more likely to be photolytic than thermal. Laser dehydroxylation allows for the selective and rapid dehydroxylation of silica offering many practical advantages over thermal dehydroxylation. The modified surface has significantly increased hydrophobicity compared to the untreated silica surface.