Nitrogen doping as a fundamental way to enhance the EMI shielding behavior of cobalt particle-embedded carbonaceous nanostructures†
The influence of nitrogen doping in pyrolysis-derived carbonaceous nanostructures with embedded Co-nanoparticles (Co@C) for electromagnetic (EM) absorption at microwave frequencies is explored. The synthesized Co-nanoparticles were found to be encapsulated by a graphitic carbon layer forming core–shell nanostructures. Interestingly, we observed that nitrogen (N) doping helps in the formation of smaller sized Co-nanoparticles embedded in the carbonaceous matrix along with a plethora of defects in the carbon layer of the Co@C sample. These defects in the carbon layer help to enhance the scattering of microwave radiation. We demonstrate that the scattering of EM waves, due to the presence of these defects, is advantageous in electromagnetic interference shielding. On the other hand, the smaller Co-nanoparticles predominantly acquire the highly magnetic hcp-phase, which helps in enhancing the EMI shielding through absorption of microwaves. Analysis of the complex permittivity and permeability suggests the enhancement of scattering at the defects and subsequent absorption of microwaves through the dispersed metallic Co nanoparticles and by the conducting graphitic C layer. The value of the shielding effectiveness was enhanced from ∼−24 dB for the (undoped) Co@C sample to ∼−33 dB for the N-doped Co@CN sample. Moreover, the shielding effectiveness due to absorption of microwaves also was found to be enhanced drastically. Hence, our results demonstrate that the effective EM shielding can be enhanced through the enhancement of microwave absorption by creating a defect-rich carbon framework via N-doping.