Coordination-controlled self-assembled multilayers on gold

A new kind of multilayers based on metal-ion coordination was constructed o n gold surfaces, where molecular layers are successively added using a high ly controlled step-by-step procedure. A bifunctional ligand is used as the base layer, bearing a cyclic disulfide group to attach to the gold surface and a bishydroxamate group capable of ion binding. An 8-coordinating metal ion such as Zr4+ or Ce4+ is then coordinated to the bishydroxamate site, fo llowed by exposure to a second ligand possessing four hydroxamate groups. T he tetrahydroxamate molecule ligates to the metal ion (bound to the base la yer) using two of its four hydroxamate groups and is free to bind a second metal ion at its other end. A sequence of adsorption steps using metal ions and tetrahydroxamate ligands was carried out, resulting in an ordered meta l-organic multilayer. Multilayer structures comprising up to 10 tetrahydrox amate/metal ion layers were constructed, with full characterization at each step of multilayer formation using ellipsometry, contact angle measurement s, X-ray photoelectron spectroscopy, and Fourier transform infrared spectro scopy. The multilayer morphology and mechanical properties were studied by scanning force microscopy. It is shown that different base ligands induce d ramatic differences in the morphology and stiffness of the final multilayer . The possibility to construct segmented multilayers containing Zr4+ and Ce 4+ ions at defined locations is presented.