Regular stripe patterns are formed in skeletonized LB films of two arachidic acid monolayers deposited on Si wafers from Cd2+-containing aqueous subphase after monolayer transfer at pH 5.7. These stripe patterns are very different from those less regular patterns observed at lower or higher pH values of the aqueous subphase. Atomic force microscopy (AFM) and phase shift interference microscopy (PSIM) studies have shown that these stripes are grooves aligned in definite distances along the meniscus and perpendicular to the dipping direction of the monolayer transfer. There exist deep straight grooves of about 6 nm depth in a regular distance and between them less marked stripelike defect lines. These regular stripe patterns occur only in the skeletonized LB films, but they are already preformed during the monolayer transfer onto the solid substrate. The formation of the regular stripe patterns is decisively affected by the arachidic acid/cadmium arachidate ratio but also by the dipping rate. The direct correlation to the autooscillations of the meniscus suggests an electrohydrodynamic instability mechanism as cause for the nonuniform ordering and composition of the LB film.
Adhesion measurements are presented which were carried out with an atomic force microscope between polymer balls attached to a cantilever and a silicon wafer under ultra high vacuum conditions. In using a silicon surface with a defined structure a correlation between adhesion force and contact area was found. This correlation could partly be explained by the Johnson-Kendall-Roberts model, if a change of the surface energy is assumed as a result of the structuring. For a constant geometric contact area an additional structuring leads to a decrease of the adhesion force.
Atomic force microscopy (AFM) in friction mode is successfully used for probing the inner structure of condensed phase domains of 1-monostearoylglycerol (MSG) monolayers transferred from the air-water interface onto mica, glass, and silicon wafers by the Langmuir-Blodgett (LB) technique. The friction anisotropy reveals the same 7-fold domain substructure as observed at the air-water interface by Brewster angle microscopy (BAM). It is caused by differences in the tilt orientation of the molecules within the domain segments. After deposition of the monolayer, the main features of the condensed phase morphology, such as size, shape, and azimuthal tilt, are preserved independent of the solid substrate. The widths of the straight segment lines were found to be <100 nm. This result supports the idea that the segment boundaries of amphiphilic monoglycerol domains are low-energy lattice rows. Differences in the smoothness of the domain boundary at the air-water interface and on solid substrates can be caused by changes in the energetic conditions along the three-phase contact line.
The structure and morphology of the three-dimensional aggregates of arachidic acid were studied by atomic force microscopy (AFM) after transfer onto a silicon wafer and by synchrotron grazing incidence X-ray diffraction (GID) at the helium/water interface. The 3D aggregates on the wafer observed by AFM are islands of granulelike and platelike shapes. The plate islands consist of terraces of different heights. The crystal structure of the plate islands was determined through molecular resolution by AFM. They have the C-crystal structure of arachidic acid at the beginning of the relaxation. During further relaxation the B-crystal structure becomes apparent. The islands with B-crystal structure dominate at the end of the relaxation process. Regions with a disordered molecular structure are found beside the ordered crystal structures. In all ordered regions of a single island the same crystal structure is observed. Using GID, the B-and C-crystal structures of the 3D aggregates of arachidic acid were also found at the helium/water interface. No peaks of any crystal structure are observed until 20% of the monolayer material is transformed into 3D aggregates. Then first the peaks of the B-crystal structure appear, which increase with the relaxation time. Additionally small peaks corresponding to the C-crystal structure are found.
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