Selective Binding, Self-Assembly and Nanopatterning of the Creutz-Taube Ion on Surfaces

The surface attachment properties of the Creutz-Taube ion, i.e., [(NH(3))(5)Ru(pyrazine)Ru(NH(3))(5)](5+), on both hydrophilic and hydrophobic types of surfaces were investigated using X-ray photoelectron spectroscopy (XPS). The results indicated that the Creutz-Taube ions only bound to hydrophilic surfaces, such as SiO(2) and –OH terminated organic SAMs on gold substrates. No attachment of the ions on hydrophobic surfaces such as –CH(3) terminated organic SAMs and poly(methylmethacrylate) (PMMA) thin films covered gold or SiO(2) substrates was observed. Further ellipsometric, atomic force microscopy (AFM) and time-dependent XPS studies suggested that the attached cations could form an inorganic analog of the self-assembled monolayer on SiO(2) substrate with a “lying-down” orientation. The strong electrostatic interaction between the highly charged cations and the anionic SiO(2) surface was believed to account for these observations. Based on its selective binding property, patterning of wide (∼200 nm) and narrow (∼35 nm) lines of the Creutz-Taube ions on SiO(2) surface were demonstrated through PMMA electron resist masks written by electron beam lithography (EBL).