Self-terminated fabrication of electrochemically-gated conducting polymer nanojunctions

In this work, we describe a method of controlling the size of a conducting polymer (CP) junction between one ultramicroelectrode (UME) and a substrate electrode using a scanning electrochemical microscopy (SECM) configuration with a variable resistor connected to the UME tip. The CP is grown by electro-polymerization from the UME tip to the substrate until contact occurs. Because of the resistor, the effective potential applied to the UME tip decreases dramatically as soon as contact is established between the electrodes. Consequently, polymer growth self-terminates, since the potential is too low to continue monomer oxidation and electropolymerization. In this way, by changing the external resistance it is possible to control the size of the CP junction, as polymer growth stops once the desired junction is established. Nanowire junctions whose conductance is controlled by a few hundred polymer strands can thus be generated in a reproducible way.