Characterization of SiO2 surface treatments using AFM, contact angles and a novel dewpoint technique

The properties of sensing surfaces are particularly important in chemical and biosensing since they affect the adhesion of sensing films and the sorption of analyte molecules onto the active area of the sensor. The objectives of this work were to study the effects of several surface treatments on glass and quartz using atomic force microscopy, contact angle measurements, and a novel dewpoint error technique, in order to develop a better understanding of the effects of these treatments. The dewpoint error technique was also examined as a novel method for measuring surface energy that may have advantages over contact angle measurements, Most significantly, chromic acid and oxygen/argon sputtering treatments were found to substantially decrease the contact angles of both glass and quartz. The surface roughness of glass was markedly increased by acetic acid, heated NaOH, and piranha etch while HCl and KOH caused the highest surface roughness for quartz. A reasonably good correlation was found between decreasing contact angles and increasing dewpoint error, suggesting that the dewpoint technique may provide a quantitative measure of surface energy without some of the drawbacks of contact angle measurements. There was no correlation found between surface roughness and contact angle hysteresis or dewpoint error. (C) 1999 Elsevier Science B.V. All rights reserved.