Internal reflection infrared spectroscopy was used to examine the effect of potassium ions on the interaction of water with silicon dioxide at low temperature, relevant to chemical mechanical planarization (CMP) of silicon dioxide. Silanol (SiOH) formation was enhanced in silicon dioxide samples exposed to aqueous solutions of potassium chloride and potassium nitrate as compared to those exposed to water, due to a reduction in the thermodynamic activity of the water in potassium salt solutions. However, molecular water was the predominant hydrous species observed in the silicon dioxide. The presence of potassium ions had no significant effect on the effective diffusion coefficient of water in silicon dioxide. Results presented here indicate that the potassium ion concentration, and more specifically the water activity, is a critical factor in the chemical component of the silicon dioxide CMP mechanism. (C) 2004 The Electrochemical Society.