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).

Role of molecular surface passivation in electrical transport properties of InAs nanowires.

The existence of large densities of surface states on InAs pins the surface Fermi level above the conduction band and also degrades the electron mobility in thin films and nanowires. Field effect transistors have been fabricated and characterized in the "as fabricated" state and after surface passivation with 1-octadecanethiol (ODT). Electrical characterization of the transistors shows that the subthreshold slope and electron mobility in devices passivated with ODT are superior to the respective values in unpassivated devices. An X-ray photoelectron spectroscopy study of ODT passivated undoped InAs nanowires indicates that sulfur from ODT is bonded to In on the InAs nanowires. Simulations using a two-dimensional device simulator (MEDICI) show that the improvements in device performance after ODT passivation can be quantified in terms of a decrease of interface trap electron donor states, shifts in fixed interfacial charge, and changes in body and surface mobilities.

Spectroscopic properties of colloidal indium phosphide quantum wires.

Colloidal InP quantum wires are grown by the solution-liquid-solid (SLS) method, and passivated with the traditional quantum dots surfactants 1-hexadecylamine and tri-n-octylphosphine oxide. The size dependence of the band gaps in the wires are determined from the absorption spectra, and compared to other experimental results for InP quantum dots and wires, and to the predictions of theory. The photoluminescence behavior of the wires is also investigated. Efforts to enhance photoluminescence efficiencies through photochemical etching in the presence of HF result only in photochemical thinning or photooxidation, without a significant influence on quantum-wire photoluminescence. However, photooxidation produces residual dot and rod domains within the wires, which are luminescent. The results establish that the quantum-wire band gaps are weakly influenced by the nature of the surface passivation and that colloidal quantum wires have intrinsically low photoluminescence efficiencies.

Assemblies of carbon nanotubes and unencapsulated sub-10-nm gold nanoparticles.

The development of assemblies consisting of unencapsulated, sub-10-nm gold particles attached to individual carbon nanotubes (CNTs) with diameters of 2 nm is described. The assemblies are formed on the surface of a porous anodic alumina (PAA) template on which the CNTs (single- or double-walled) are grown by plasma-enhanced chemical vapor deposition. The Au nanoparticles are formed through an indirect evaporation technique using a silicon nitride membrane mask, and diffuse along the PAA surface into the regions containing CNTs. The nanoparticles bind relatively strongly to the CNTs, as indicated by observations of nanoparticles that are suspended over pores or that move along with the CNTs. This approach may provide a new method to functionalize CNTs for chemical or biological sensing and fundamental studies of nanoscale contacts to CNTs.

A liftoff technique for molecular nanopatterning.

For quantum-dot cellular automata molecular electronic devices, one of the fundamental tasks is to arrange the molecules on a surface in a controlled manner. In this report, we discuss a molecular lift off technique to form nanopatterns toward the development of molecular circuits. In our molecular lift off technique, we use electron beam lithography to form nano-trenches on a polymethylmethacrylate (PMMA) film on a SiO2 wafer. This wafer is soaked in a Creutz-Taube ion [(NH3)5Ru(pyrazine)Ru(NH3)5](o-toluenesulfonate)5 (CT5) aqueous solution. After residual PMMA removal, atomic force microscopy is used to investigate the resulting surface. Thirty-five nanometer CT5 lines are demonstrated on a SiO2 surface. Compared with other molecular nanopatterning techniques, ours is both economical and capable of high-resolution.