Contrast studies on organic monolayers of different molecular packing in FESEM and their correlation with SFM data

Organic monolayers of 1, 2-dipalmitoyl-sn-glycero-3-phosphothioethanol or dip almitoyl-phosphatity1-choline, transferred by the Langmuir-Blodgett technique in phase-coexistence regions onto a solid support, show domains differing in their molecular packing. Domains with dense molecular packing and quite upright orientation of the molecules are neighbored by a matrix with lower packing density and variable molecular orientation. In the scanning force microscope, these domains can be distinguished by a small difference in their layer heights. In the field emission scanning electron microscope (FESEM), these small height differences were not detectable. Coated monolayers show no topographic features of different domains in secondary electron (SE) micrographs. In opposition to that, the domains are easily recognizable in SE micrographs of the uncoated monolayer by a very strong contrast which presents almost a black/white pattern. Thus, the FESEM may serve as a sensitive tool for mapping areas of different molecular packing in chemically homogeneous organic monolayers.