Takashi Ishino

Measurements of Electrostatic Double-Layer Forces Due to Charged Functional Groups on Langmuir-Blodgett Films with an Atomic Force Microscope

Using an atomic force microscope, we measured the forces between a Si3N4 tip and monolayers with different polar functional groups ( –NH2, –COOH, –CONH2, and –OH) prepared by the Langmuir-Blodgett method while varying the pH value of aqueous solutions. The obtained force vs distance curves were related to the surface charges of the tip and the dissociation of the functional groups from the pH dependency, and the charged state of functional groups could thus be discerned. In addition, the electrostatic origin of the force has been confirmed assuming constant potentials on both surfaces.

Electrical Double-Layer Forces Measured with an Atomic Force Microscope while Electrochemically Controlling Surface Potential of the Cantilever

The atomic force microscope was used to detect electrostatic forces and estimate surface potentials of samples in aqueous solution by applying voltage to a conducting tip. We controlled surface potential of a Au-coated cantilever electrochemically, and measured force vs distance curves on monolayers with different kinds of functional groups. As a result, we detected force variation with applied voltage to the tip, and the direction of force variation was found to agree with the polarity of surface charges due to the dissociation of the functional groups.

Analysis on Electrostatic Tip-Sample Interaction in Aqueous Solution under Potentiostatic Condition

Using a force microscopy, we investigated electrostatic tip-sample interaction in aqueous solutions. A force between a gold-coated microsphere tip and an oxidized silicon sample was measured with their surface potentials being controlled independently by bipotentiostat. The variations in the force characteristics were observed with the respective changes in the tip potential and the sample potential. The observed force characteristics were found to agree with the theory of electrical double layer interaction under constant potential assumption.

Imaging charged functional groups with an atomic force microscope operated in aqueous solutions

Polar functional groups were introduced selectively onto micro-fabricated hydrophobic regions covered with alkane-thiol molecules. Force images were obtained on the patterns of functional groups prepared by the Langmuir-Blodgett method. The atomic force microscope was operated in aqueous solutions to evaluate charged state and spatial distributions of functional groups on the substrate.