Calculation of the surface potential and surface charge density by measurement of the three-phase contact angle

• Published in: Journal of colloid and interface science Vol. 385; no. 1; pp. 218 - 224
• Main Authors: Horiuchi, H., Nikolov, A., Wasan, D.T.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.11.2012; Elsevier
• Subjects: aqueous solutions; Chemistry; Contact angle; Density; Electric potential; electrical resistance; equations; Exact sciences and technology; General and physical chemistry; ionization; manufacturing; Mathematical models; Mica; physical chemistry; Semiconductors; silica; silicon; Silicon dioxide; Solid-liquid interface; Solid/liquid interfacial energy; Surface charge density; Surface physical chemistry; Surface potential; surface water; titration; Wafers; Young–Lippmann equation; Solid/liquid interfacial energy; Surface charge density; Contact angle; Surface potential; Young–Lippmann equation; Water; Binary compound; Density measurement; Physical chemistry; Young-Lippmann equation; Silica; Solid; Energy; pH; Calculation; Silicon; Wafer; Surface charge; Experimental data; Semiconductor materials; Device; Equation; Dissolution; Charge density; Liquid; Ionization; Potentiometric method; Potential surface; Models; Kinetics; Aqueous solution; Interface; Mica
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2012.06.078

[Display omitted] ► Measurement of a contact angle on silica/silicon substrate as a function of PH. ► A model based on the Young-Lippmann equation can calculate surface potential and surface charge density. ► The model is validated with experimental data using a galvanic mica cell. The silica/silicon wafer is widely used in the semiconductor industry in the manufacture of electronic devices, so it is essential to understand its physical chemistry and determine the surface potential at the silica wafer/water interface. However, it is difficult to measure the surface potential of a silica/silicon wafer directly due to its high electric resistance. In the present study, the three-phase contact angle (TPCA) on silica is measured as a function of the pH. The surface potential and surface charge density at the silica/water surface are calculated by a model based on the Young–Lippmann equation in conjunction with the Gouy–Chapman model for the electric double layer. In measurements of the TPCA on silica, two distinct regions were identified with a boundary at pH 9.5—showing a dominance of the surface ionization of silanol groups below pH 9.5 and a dominance of the dissolution of silica into the aqueous solution above pH 9.5. Since the surface chemistry changes above pH 9.5, the model is applied to solutions below pH 9.5 (ionization dominant) for the calculation of the surface potential and surface charge density at the silica/aqueous interface. In order to evaluate the model, a galvanic mica cell was made of a mica sheet and the surface potential was measured directly at the mica/water interface. The model results are also validated by experimental data from the literature, as well as the results obtained by the potentiometric titration method and the electro-kinetic measurements.