Layer-by-layer self-assembly strategy for template synthesis of nanoscale devices

A combined membrane replication/layer-by-layer synthetic approach to preparing nanoscale rod-shaped rectifiers is described. Alumina and polycarbonate (PC) membranes (pore diameters 200, 100 and 70 nm) were used as templates for the electrochemical preparation of free-standing Au nanowires several microns in length. Wet layer-by-layer self-assembly of nanoparticle (TiO₂ or ZnO)/polymer multilayer films was performed inside the membrane pores in two ways. (1) Growing the film between metal electrodeposition steps to give in-wire junctions; (2) first coating the membrane walls with multilayer films, and then growing nanowires inside the resulting tubules to give concentric structures. TiO₂/PSS, ZnO/PSS (PSS=polystyrenesulfonate) and ZnO/PAN (PAN= polyaniline) assembly was driven by electrostatic and covalent-coordination interactions, respectively. The current-voltage (I-V) characteristics of nanowires containing semiconductor nanoparticles show current rectifying behavior. Current rectification appears to arise at the oxide semiconductor-metal interface. Switching behavior and hysteresis, which was found in all devices, was particularly evident in junctions containing anionic PSS and cationic TiO₂ particles, and less evident in ZnO-containing devices.