Mapping of electrical double-layer force between tip and sample surfaces in water with pulsed-force-mode atomic force microscopy

Pulsed-force-mode atomic force microscopy (PFM-AFM) using a cantilever with a Si3N4 tip was applied to map charge distribution on a sample surface in water. In order to confirm the applicability of the present PFM, we prepared a patterned sample by vapor deposition of Al on a quartz plate covered with silica beads, followed by oxidation of Al with O2 and removal of the beads with ultrasonication. The two different areas of Al2O3 and SiO2 had different isoelectric points and bore positive and negative charge, respectively, at pH 8.6. The lateral resolution of the present method was found to be ca. 30 nm.