Synthesis of vertically aligned polyaniline (PANI) nanofibers, nanotubes on APTMS monolayer and their field emission characteristics

Growth of aligned polyaniline (PANI) nanostructures on silicon modified with amino-silane self-assembled (3-aminopropyl)trimethoxysilane (APTMS) monolayer has been carried out by chemical polymerization in the presence of strong (HCl) and weak (CH3COOH) acids as dopant. Self assembly of aniline monomer leading to formation of aligned nanostructures on the APTMS monolayer is due to the amino (-NH2) moieties acting as growth centers. Interestingly, the nature of dopant acid (strong/weak) is found to determine the resultant form of the PANI nanostructures, either as nanofibers or nanotubes. The formation of PANI nanofibers and nanotubes has been revealed by scanning and transmission electron microscopy, whereas confirmation of the conducting phase of PANI is obtained from UV-visible and FTIR analysis. A plausible explanation illustrating the growth mechanism has been presented. Field emission studies of the PANI films have been carried out in a planar diode configuration at base pressure of similar to 1 x 10(-8) mbar. The turn-on field required to draw an emission current of 1 nA was found to 1.6 and 2.4 V mu m(-1) for aligned nanofibers and nanotubes, respectively. Interestingly, both the emitters exhibit good stability of the emission current over a duration of 4 h. The ease of the synthesis route and interesting field emission characteristics indicate the aligned PANI nanofibers and nanotubes as promising materials for field emission based applications.