Monolayers from dipalmitoylphosphatidylethanolamine head labelled with nitrobenzoxadiazole (DPPENBD) were deposited as Langmuir-Blodgett (LB) films on silicon wafers or quartz plates at different deposition pressures at room temperature. In some cases 0.5 mM NaCl was added in the water subphase or deposition was carried out at 7 °C. Phase coexistence between the liquid and the solid phases was observed by fluorescence microscopy, atomic force microscopy, friction force microscopy and scanning surface potential microscopy. This is the first observation of fluorescence self-quenching in a monolayer on a solid substrate. It is shown that there is no sharp boundary line between the liquid and solid phases. Submicrometre-sized solid domains are resolved above the phase transition together with multilayer structures. The addition of NaCl makes the domains uniform in size, circular in shape and with a sharp boundary line from liquid to solid phase. In this case domains are composed of several regions divided by liquid-phase channels. At low temperatures the domains are much more patchy in shape. For the first time scanning surface potential microscopy on a single-component system deposited as an LB film from pure water has been performed. The technique reveals a big contrast between the liquid and solid phases. Multilayer growth on top of a liquid phase in the centre of the solid domains could be resolved.

Photo-electric conversion molecular devices, i.e. molecular photodiodes based upon the charge separation mechanism of the primary process of natural photosynthesis, have been studied in our laboratory. Amphiphilic A-S-D triad molecules can be oriented unidirectionally in monolayers at the air-water interface. The resulting oriented monolayer assemblies are fabricated into thin films on electrode surfaces by the Langmuir-Blodgett (LB) technique. The A-S-D triads for charge separation together with light harvesting antenna molecules can be assembled into sub-micron island domains by making use of phase separation of mixed monolayers of hydrocarbon (HC) and fluorocarbon (FC) amphiphiles. The structure and properties of the domains of HC-FC mixed monolayers were studied by various scanning probe microscopies (SPMs) such as atomic force microscopy, friction force microscopy, scanning surface potential microscopy (SSPM), and scanning near-field optical/atomic force microscopy. Some SPMs can be used not only to characterize the LB films, but also to drive the molecular devices. The photo-induced charge separation in unidirectionally oriented triad molecules embedded in alternate LB films was observed by SSPM.

The effect of capillary force due to surface water on friction force microscopy (FFM) was examined by comparing FFM images on oxidized Si surfaces partially covered with chemically bound hydrocarbon (HC) monolayers in vacuo and in an ambient atmosphere. It was found also from force-distance curves and FFM under various relative humidities that adhesive and friction forces observed on the hydrophobic HC covered surface were almost independent of the humidity, while those on the hydrophilic bare oxidized Si surface increased with an increase in the humidity. The higher friction observed on the oxidized Si in the higher humidity was interpreted by the higher effective normal load due to the higher capillary force which originated from a surface water film formed by adsorption of water vapor in the humid air. The results suggest a novel scanning hydrophilicity microscope under a controlled humidity which can be used to map local hydrophilicities of a sample surface in a x-y plane.

The surface forces between a Si3N4 tip and sample surfaces of various oxides, such as SiO2, SnO2, and Al2O3 were measured in electrolytes with various pH values using atomic force microscopy. The isoelectric points were estimated from the force-distance curves. A similar treatment was applied to hydrocarbon-modified quartz surfaces. Almost no effect of the surface modification was found in neutral solutions, while a small difference in the force-distance curves before and after the modification was observed in acidic and alkaline solutions. The electric double layer force due to the concentration profile of the counterions at the oxide/water interface is discussed in terms of acid-base reactions of-OH groups on the oxide surface.

The Kelvin probe force microscope (KFM) can measure both the surface potential and the topographic image simultaneously without contacting the sample surface. Furthermore, both conducting and non-conducting thin layers can be measured directly with a millivolt range potential resolution and a sub-micrometer lateral resolution. In this paper, we report two improvements on the KFM which entail a new method of controlling the tip-sample distance to obtain accurate surface potentials, and a new method for increasing the topographic lateral resolution. With these improvements, we can obtain a potential resolution that is less than 1 mV and a lateral resolution of about 10 nm. Also, we report some potential measurements on Langmuir-Blodgett thin films.