Quantitative Infrared Investigation of the Acido-Basic Equilibrium at a Carboxy-Terminated Silicon Surface

摘要

Silicon surfaces grafted with mixed alkyl/carboxylic acid monolayers have been investigated by in-situ quantitative infrared spectroscopy at the contact with electrolytes of various pH. Ionization of the carboxy groups is found to start around pH 6 and to extend over a wide pH range. Ionization is not complete even at pH 11. These observations point to the importance of the interactions between surface charges. This effect may be accounted for by a simple model taking into account the change in the Helmholtz potential associated with the surface charge. However, the agreement is only qualitative, which indicates that the surface charge is screened more efficiently than expected, possibly due to ion penetration between the carboxy groups.