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 ( approximately 200 nm) and narrow ( approximately 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).