The two-dimensional hexatic-B phase of single Langmuir-Blodgett monolayers observed by atomic force microscopy

Molecular resolution with the atomic force microscope has been achieved, on single Langmuir-Blodgett monolayers, using films of cadmium arachidate on mica (see also T. Kajiyama et al., Langmuir, 10 (1994) 1297). The images clearly show the molecular organization that has been postulated for the two-dimensional hexatic-B phase; the molecular chains are packed hexagonally with their long axes normal to the substrate surface and in small domains with their hexagonal patterns oriented in the same direction (known as bond orientational order) separated by regions of relative disorder. For the domains, the dimensions of the unit cell are in excellent agreement with data reported from X-ray and electron diffraction. There is some variation in film thickness, with the highly ordered hexagonal domains being slightly thicker than the regions showing dislocations and disorder. The monolayer films show a mismatch of about 10% with the mica lattice, indicating that the substrate structure does not determine the structure of the deposited monolayer