ATOMIC-FORCE MICROSCOPY AND X-RAY STUDIES OF 3-DIMENSIONAL ISLANDS ONMONOLAYERS

The structure and morphology of the three-dimensional aggregates of ar achidic acid were studied by atomic force microscopy(AFM) after transf er onto a silicon wafer and by synchrotron grazing incidence X-ray dif fraction (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 crys tal structure of the plate islands was determined through molecular re solution by AFM. They have the C-crystal structure of arachidic acid a t the beginning of the relaxation. During further relaxation the B-cry stal structure becomes apparent. The islands with B-crystal structure dominate at the end of the relaxation process. Regions with a disorder ed 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 agg regates of arachidic acid were also found at the helium/water interfac e. No peaks of any crystal structure are observed until 20% of the mon olayer material is transformed into 3D aggregates. Then first the peak s of the B-crystal structure appear, which increase with the relaxatio n time. Additionally small peaks corresponding to the C-crystal struct ure are found.