Water adsorption at ionic crystal surfaces

点击翻译按钮获取中文摘要

1. We have investigated the behavior of water adsorption on alkali halide surfaces in air and at room temperature observed with the non-contact monitoring mode of a scanning force microscope (SFM). We have found a formation of water droplet pattern on LiF(001) surface and thereafter the formation of a uniform film, in the similarway as observed on the BaF2(111) surface. However, there appears to be no water droplet pattern on the NaC(001) surface. The SFM image from the NaF(001) surface has revealed complicated features with water droplet pattern resulting in films formed with different thickness. These results indicate that in those cases where a water-water interaction is stronger than a water-substrate interaction, water droplets would grow easily on the surfaces, but in the opposite case, the uniform film with a monolayer or submonolayer would be formed.2. We have researched water adsorption on an electron irradiated NaF(001) surface. Although water adsortion on the non- electron i … More rradiated surface continues a complicated feature with water islands over several hours, water adsorption on the electron irradiated surface has a fast formation in lh from a water island pattern to a uniform film. This is because the surface irradiated by electrons has surface OH-centers. It is possible, by the electron irradiation technique, to control the wettability of the NaF(001) surface.3. We have discovered the stepwise frictional forces with increasing load and the anisotropy of the frictional forces via a scanning direction. This indicates the discreteness of the effective interaction area between a tip and surface. These experimental results also clarify the influence on the friction due to a surface deformation and/or damage with increasing loads.4. We have studied the nanotribological behavior of C_<60> films formed on a KCl(001) surface at an extremely low load in dry air, using scanning force microscopy (SFM). it has been observed that the SFM tip undergoes molecularly resolved stick-slip motions depending on its scanning direction. The frictional force at 0.024nN load is about one-sixth that at 2nN load, which indicates rolling and/or translation of a C_<60> molecule due to a single-molecule tip-sample contact. Less