Morphology dependent field emission characteristics of polypyrrole thin film emitters

Polypyrrole (PPy) nanostructures have been synthesized on indium doped tin oxide (ITO) substrates by a facile electrochemical route employing cyclic voltammetry (CV) mode. The morphology of the PPy thin films was observed to be influenced by the monomer concentration and formation of rod-like, cauliflower and granular structures were obtained with monomer concentrations of 0.1, 0.3, and 0.5 M, respectively. Furthermore spectroscopic analysis (UV-visible and FTIR) revealed formation of electrically conducting state of PPy under the prevailing experimental conditions. The field emission investigations of the PPy nanostructures have been carried out at base pressure of 1 × 10^-8 mbar. The values of turn-on field, corresponding to emission current density of 1 μA/cm² were observed to be 0.6, 1.0 and 1.2 V/μm for the PPy films characterized with rod-like, cauliflower and granular morphology, respectively. Interestingly, in case of PPy nanorods maximum current density of 1.2 mA/cm² has been observed at electric field of 1 V/μm, which is higher than PPy cauliflower (0.4 mA/cm² at 2.4 V/μm) and granular (0.5 mA/cm² at 2.68 V/μm) morphology. The observed values of turn on and threshold field in case of PPy nanorods are comparative to earlier reported values for different conducting polymer nanostructures and nanocomposites. The observation of relatively lower turn-on field for rod-like morphology is attributed to the high aspect ratio of the PPy nanostructures. The emission current was found to be stable around the preset value for more than 2 hrs. The low turn on field, extraction of very high emission current density at relatively lower applied field and good emission stability propose the PPy nanorods as a promising material for field emission based devices.