Eisuke Tomita

Lateral Force Modulation Atomic Force Microscope for Selective Imaging of Friction Forces.

An approach to imaging friction force distribution on the nanometer scale is presented, where a sample is laterally vibrated and both the amplitude and the phase of resultant torsion vibration of the cantilever are employed for imaging. It has an advantage over the conventional friction force microscope (FFM) in that the contrast due to local gradient can be significantly reduced. The topographic contrast was almost completely suppressed on a gold evaporated film sample. A method for characterizing friction, the friction force curve (FFC), is proposed where the friction force amplitude and phase are recorded simultaneously with the normal force, as a function of the tip-sample distance. The usefulness of the FFC was verified in characterizing slip and deformation in the tip-sample interaction.

Lateral Force Modulation Atomic Force Microscopy of Langmuir-Blodgett Film in Water

The mechanical properties of a Langmuir-Blodgett (LB) film in water were investigated using an atomic force microscope with lateral force modulation. During the force curve measurement, the dynamic friction force is measured by observing the amplitude and phase of the cantilever torsion vibration, as the sample is deformed by a tip with gradually increasing normal force. In contrast to conventional friction force microscopy, the friction measurement is performed without x–y scanning, and therefore is in real time. This method was applied to a LB film consisting of an arachidic acid (AA) single layer on top of a single layer of partially fluorinated ether of carboxylic acid (PFECA), and interesting results were obtained. In particular, the film was found to be stable for a short period (<120 min) and the structure and ratio of the friction forces between the AA and PFECA areas are identical with those observed in air. Moreover, a friction force transition was observed at a normal force of around 14 nN on loading and an almost reversible decrease was observed on unloading. This result indicates penetration of the AA film by the tip and recovery of the penetrated hole on unloading.

Orientation control of liquid crystals by Langmuir-Blodgett films

Abstract Orientations of liquid crystals on modified surfaces with different chemical groups were investigated using Langmuir-Blodgett (LB) films, in order to clarify the alignment mechanism in liquid crystal cells. The surfaces, covered with carboxyl, hydroxyl, amine, cyano and alkyl groups, were prepared by combination of a conventional LB method and a horizontal lifting method. It has been found that the molecular alignment in liquid crystal cells depend on the dipole interaction term in the surface energy of the substrate film. LB films with polar groups, such as carboxyl and hydroxyl, at the outermost surface, used for the substrate, produced good liquid crystal cell properties, involving small pre-tilt angles, clear in-plane anisotropy of transmittance and sharp voltage response, as compared with polyimide films.