Structure and morphology of Langmuir-Blodgett films of rod-like poly(phthalocyaninato germoxane)s, studied by transmission electron microscopy

Abstract

The domain structures and molecular orientation in Langmuir-Blodgett mono-, double and multilayers of rod-like poly(pthalocyaninato germoxane)s with dodecyloxycarbonyl side-chains deposited onto a carbon film substrate are directly visualized using electron diffraction (ED), as well as bright-field (BF) and dark-field (DF) imaging. The ED patterns show an oriented intramolecular spacing of 0.37 nm from the axially stacked phthalocyaninato rings, aligned along the dipping direction and an orthogonally oriented intermolecular spacing of 3.4 nm, arising from parallel packing of rod-like molecules parallel to the layer plane. In addition, arched ( hk0)-type reflections arise from about 40% of the film area of a single monolayer, indicating an end-on orientation of the rod-like molecules relative to the layer plane. In multilayer films, a two-dimensional hexagonal phase and a less ordered layer state with no registration between the molecules in adjacent layers coexist, and the portion of molecules oriented preferentially normal to the layer significantly decreases. The BF images of the monolayers and double layers show a mosaic-like structure, with darker band-like regions about 50 nm in size surrounding brighter mosaic pieces about 300 nm in size. The DF images confirm that the darker regions in the BF image mainly arise as a result of scattering from the 0.37 nm reflection, indicating that the rod-like molecules are oriented parallel to the layer plane. High resolution electron microscopy images taken from the monolayer films show patches of parallel fringes, directly visualizing the lateral 3.4 nm packing of the rods. The fringe regions exhibit a broad orientational distribution about the dipping direction.