Facile synthesis of cadmium sulphide-polyaniline (CdS-PANI) nanocomposite and its field emission investigations

A simple two step chemical route has been employed to synthesize cadmium sulphide - polyaniline (CdS-PANI) nanocomposite. In the first step PANI nanotubes are synthesized by oxidative polymerization followed by deposition of CdS nanoparticles on them. In order to investigate the structural, chemical and optical properties of the CdS-PANI nanocomposite, various characterization techniques have been used. The microscopic analysis reveals that the PANI nanotubes having length in several microns with cavity diameter of ~ 10 to 20 nm are decorated with CdS nanoparticles of 5 to 10 nm. The XRD spectrum indicates formation of crystalline hexagonal phase of CdS, supported by the SAED pattern obtained during TEM analysis. The FTIR and UV-visible spectra confirm formation of the conducting phase of PANI. The field emission studies of the CdS-PANI nanocomposite indicate low turn on field of 1.4 V/μm, corresponding to emission current density ~ 1 μA/cm2, and emission current density of ~ 5.5 mA/cm2 has been drawn at an applied field of 3.8 V/μm. Furthermore the emission current is observed to be fairly stable at the preset values over long term duration. The enhanced field emission properties, exhibited in terms of low turn on field, and delivery of very high emission current density at relatively lower applied field, are attributed to the nanometric dimensions of the PANI nanotubes and CdS nanoparticles, and modulation of electronic properties due to formation of heterojunction. The overall field emission results propose the CdS-PANI nanocomposite as a promising material for field emission based devices.