ATOMIC-FORCE MICROSCOPY FOR LOCAL CHARACTERIZATION OF SURFACE ACID-BASE PROPERTIES

In this work, we describe a new method for characterizing surface acid-base properties by surface force measurements using an atomic force microscope (AFM) in a liquid electrolyte. The potential of AFM is to make possible the local study of surface acid-base properties of rough and inhomogeneous substrates. We demonstrate the technique by measuring the force profile between a SiO2 substrate and the Si3N4 AFM tip over a wide range of pH in an aqueous electrolyte. These first results are satisfactorily compared to the DLVO theory; we can infer that the surface isoelectric point (IEP) of the Si3N4 AFM tip has a value of 6.0 +/- 0.4. Consequently, we propose that AFM is capable of imaging surface inhomogeneities which modify the IEP by more than 0.4.