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.