Coordinate covalent cobalt-diisocyanide multilayer thin films grown one molecular layer at a time

Multilayer thin films consisting of alternating layers of cobalt and 1,4-diisocyano-benzene (DiCNB) synthesized layer by layer on an amine functionalized silicon substrate were first reported in 1996. This paper describes further work in characterizing these films using X-ray photoelectron spectroscopy (XPS), ellipsometry, attenuated total reflectance-infrared spectroscopy (ATR--IR), and reflection-absorption infrared spectroscopy (RAIRS). Ellipsometry shows the films grow uniformly, suggesting sequential binding of metal and diisocyanide components. Control experiments confirm that both components are necessary for film growth and that 1-isocyano-2-phenylethane, a mono-functional isocyanide, caps the film and terminates further growth. Although the ellipsometry data suggests uniform film growth consistent with DiCNB molecules oriented perpendicular to the plane of the substrate, in accord with a simple model of these films, a more complex picture of the resulting film constituents is seen with further analysis. FTIR and XPS results indicate the presence of significant amounts of oligomeric isocyanide species in the films. We also report the growth of uniform multilayers of cobalt and 1,6-diisocyanohexane.