Domain boundaries and buckling superstructures in Langmuir-Blodgett films

MANY technological and scientific applications have been proposed for Langmuir-Blodgett (LB) films₁. These ordered arrays of oriented amphiphilic molecules may be useful as nonlinear optical systems², as insulating or patterning layers in microelectronics^3,4, as model systems for studies of two-dimensional phases⁵ and as molecular templates for protein crystallization⁶. The potential of LB films for these applications is sensitive to the details of their molecular packing; in particular, they require that the layers have a defect-free, periodic structure¹. Here we present images from atomic force microscopy of domain boundaries between regions of different crystallographic orientation in LB multilayers. The regular lattice structure is preserved to within 1 nm of the grain boundaries, and the domains are oriented in a near-twinning arrangement. We also observe a periodic buckling superstructure along a particular lattice symmetry direction, with a wavelength of about 2 nm and an amplitude of ≤0.1 nm. The buckling was independent of surface pressure during deposition, dipping direction, number of layers deposited and nature of the substrate, and was stable over many hours. These departures from two-dimensional periodicity may have an important bearing on applications that rely on perfect crystallinity.