MOLECULAR-LEVEL PROCESSING OF CONJUGATED POLYMERS .2. LAYER-BY-LAYER MANIPULATION OF IN-SITU POLYMERIZED P-TYPE DOPED CONDUCTING POLYMERS

A novel thin-film processing technique has been developed for the fabrication of ultrathin films of conducting polymers with angstrom-level control over thickness and multilayer architecture. As part 2 of this series, we present here the molecular self-assembly of p-doped conducting polymers (e.g., polypyrrole and polyaniline), a layer-by-layer process in which a substrate is alternately dipped into a chemically active aqueous solution of an in-situ polymerized conjugated polymer and a solution of a palyanion. In-situ oxidative polymerization produces continuously the highly conductive, underivatized form of the conjugated polymer, which is deposited in single layers of precisely controlled thickness as it is formed. The thickness of each layer, ranging from 20 to 60 Angstrom, can be fine-tuned by adjusting the dipping time and the solution chemistry. The surface chemistry of the substrate (hydrophobic, charged, etc.) is key in determining the deposition characteristics and uniformity of the film. Widely different deposition characteristics onto different surfaces make it possible to selectively deposit conducting polymers onto certain, well-defined regions of a substrate by patterning the surface with different chemistries. Typical multilayer films exhibit conductivities in the range of 20-80 S/cm; however, ultrathin films with conductivities over 300 S/cm can be made with suitable adjustments to the solution chemistry.