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Self-doped polyaniline (SPANI) ultrathin films were prepared by using a self-assembly process consisting of a self-doping monomer (o-aminobenzenesulfonic acid, SAN) and aniline (AN). SAN-AN copolymerization and film formation were simultaneously performed in aqueous solution. An immersing self-assembly method was developed to build up a SPANI nanofilm on an ITO glass, providing a hole injection layer in a doublelayer electroluminescence (EL) device ITO/SPANI nanofilm//MEH-PV//Ca/Al. This device produces an orange EL as compared with a single-layer EL device of ITO//MEH-PV//Ca/Al. A double-layer device demonstrates that a SPANI film is capable of transporting holes in a polymer light-emitting diode (PLED).

Self-doped polyaniline ͑SPANI͒ nanostructures were synthesized using a self-assembly process consisting of an active self-doping monomer ͑o-aminobenzenesulfonic acid, SAN͒ and aniline ͑AN͒. SAN plays the key roles of a self-doping monomer and a surfactant in the process of forming nanostructures. SAN-AN copolymerizations were carried out using the oxidant ammonium persulfate ͑APS͒ dissolved in the aqueous solution. The self-doped polyaniline demonstrates nanotube and nanofibril structures corresponding to the AN/SAN mole ratio of 4 and 1, respectively, through the examination of transmission electron microscopy. Reduction of ionic silver along the nanotubes resulted in the production of nanorod about 140 nm in diam. Nanotubular materials have attracted much attention since the discovery of carbon nanotubes. 1 These materials possess diverse potential applications such as nanoelectronics and biomedical devices. 2 Junctions often exist in the nanotube demonstrating a dendritic morphology. 3 Nanotube junctions play an important role in nanoelectronic devices. [4][5][6] Polyaniline ͑PANI͒ is the simplest linear conjugated macromolecule and a representative of conducting polymers. 7 Pristine polyaniline is a typical semiconductor, but its electrical conductivity can be varied by several orders of magnitude through doping. Recently, conducting polymer nanotube has proven to be a promising material for applications in molecular electronics, molecular wires, and devices. 8,9 Several methods have been used for the preparation of polymer nanostructures, for example, template synthesis, 10-14 charily reaction, 15 and self-assembly. 16 The template method is a common route for preparing micro/nanotubes and nanofibrils of conducting polymers. The advantage of this method is that the length and diameter of the resulting tubes can be controlled by the selected porous membrane. Thus, a regular micro/nanotube can be obtained. In contrast, disadvantages of this method include that a soluble porous membrane as template must be used and then the membrane must be dissolved after preparation and that it is difficult to produce nanostructures in large scale by a template method for practical applications.More recently, micro/nanotubes of polyaniline 17 have been synthesized using ammonium persulfate as an oxidant in the presence of protonic acid as an external dopant. This self-assembly method is an essential process that the external dopant is used as a template ͑or a surfactant͒ in forming a nanotube. 18 Although micro-and nanotubes of conducting polymers have been prepared by template synthesis and self-assembly, the external dopants are not easily controlled in these nanotube materials, especially during the de-doping process with the addition of a base. Here, we report on self-doped polyaniline nanotubes, which have been synthesized using a self-doping monomer as a template without an external dopant ͑or surfactant͒ in the process of forming nanotubes. In addition, we show that silver nanoparticles assemble along the nanotubes res...