Interface enhancement and tunable electromagnetic properties of vertically aligned N-doped carbon nanotube...

In this study, we investigated the impact of nitrogen doping of vertically-aligned carbon nanotube (VACNT) arrays on their interaction with an elastomeric polymer. Specifically, we synthesized undoped and N-doped VACNT (N-VACNT) arrays and examined the direct current (DC) conductivity, terahertz (THz) responses, and elastic properties of their polydimethylsiloxane (PDMS)-impregnated composites. Structural diagnostics confirmed that incorporating approximately 1 at% nitrogen yielded mechanically stiff N-CNTs with superior ordering within the array compared to undoped VACNT array. This structural enhancement led to significantly improved conductivity and THz shielding efficiency in N-VACNT/PDMS composites. For instance, a 70µm-thick N-VACNT array impregnated with PDMS achieved a transmittance of 10^-3, comparable with the value for an impregnated 200µm-thick undoped array. Despite exhibiting lower ultimate tensile strains (40% for N-VACNT/PDMS vs 70% for VACNT/PDMS), the N-VACNT/PDMS composites provided a broader conductivity and transmittance modulation window with less deformation. Under initial tension, undoped and N-doped PDMS-impregnated arrays showed distinct electrical and THz behaviors. While VACNT/PDMS composites suffered from permanent conductivity loss and material rearrangement upon initial stretching, N-VACNT/PDMS composites displayed fully reversible DC conductivity and a stable THz response over repeated stretch-release cycles. Density functional theory calculations revealed that graphite-like and pyridine-like nitrogen atoms in the nanotube walls enhance the adsorption of PDMS chains. Stronger interfacial bonding, combined with the superior ordering of stiff N-VACNTs, enables complete recovery of the N-VACNT/PDMS composite structure and its electromagnetic response after deformation. These results highlight the key role of nitrogen doping in tailoring both the nanoscale structure and performance of CNT-elastomer composites. The N-VACNT/PDMS system thus emerges as a leading candidate for stretchable THz components and other applications requiring stable, reversible electromechanical response, paving the way for advanced tunable sensors and functional composites.