In scientific and technical applications, Langmuir-Blodgett films may be useful as nonlinear optical systems, insulating or patterning layers in microelectronics, model systems for two-dimensional phases and templates for protein crystallization. These applications are based on the assumption that a defect-free layered film structure of oriented amphiphilic molecules exists. We here present an atomic force microscopy study of nano scale defects in a typical Langmuir-Blodgett film of fatty acid with hydrocarbon chain length from C16 to C22, prepared under conditions often described in the literature. On the surfaces of all films, steps due to the layered structure were found and for a hydrocarbon chain length of C20 and C22 a surprising number of holes, approximately one monolayer deep, were identified. Molecular resolution showed that the different layers either had the same lattice orientation or a relative orientation close to 0° or 60°. Four observed grain boundaries had a relative orientation close to 60° and the lattice structure was preserved to within less than 1 nm of the grain boundaries. A typical domain size was about 2 μm. All these departures from two-dimensional periodicity may have an important bearing on applications that rely on perfect crystallinity.
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ACKNOWLEDGEMENTS We thank S. Chiruvoluf or the TED experimentasn d Frank Grunfeldo f NIMA Technologiefso r his assistancwe ith the trougha nds oftwareT. his work was supportebdy the Officeo f NavalR esearch Grant No. N00014-90-J-155t1h, e NationalS cienceF oundationG rantC TS90-15537a,n d the Donors of the PetroleumR esearchF oundationJ.G acknowledgessu pportfr omthe Danish TechnicRael search Council.
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