Broadband and tunable terahertz absorption based on ethanol-treated carbon nanotube sponges

To eliminate the undesired terahertz (THz) interference and echo, broadband and tunable THz absorbing devices are urgently needed. Herein, we report a simple method to obtain an active THz absorption performance by ethanol-treated carbon nanotube sponges (CNT-Sponges). Firstly, the single CNT-Sponges show a high electromagnetic interference shielding effectiveness (EMI SE >40 dB), of which >80 % electromagnetic energy can be absorbed from 0.2 THz to 1.0 THz (98 % absorptivity at 1THz). Secondly, after spraying ethanol on CNT-Sponges (ECNT-Sponges), ECNT-Sponges present high reflection and a significant decrease in absorption and then undergo a recovery process with the change of ethanol content over time. The maximum absorption modulation efficiency is ∼40 %, and its tunable absorption mechanism has been explained: 1, the sprayed ethanol forms a protective film on the surface of CNT-Sponges, and then increases the surface reflection; 2, ethanol makes CNT-Sponges shrink and denser and then blocks the transmitted THz waves. Without complex element doping or outfields manipulation, this work provides a feasible way for broadband and tunable THz absorption.