Controllable Atomic Migration in Microstructures and Defects for Electromagnetic Wave Absorption Enhancement

Defects and microstructures have been utilized to effectively modulate electromagnetic (EM) wave absorption for mitigating electromagnetic pollution and stealth issues. However, precisely feasibly tailoring them still remains challenging. Here, by using a multilevel hollow cobalt sulfide embedded in a heteroatomic sulfur (S) ‐doped carbon aerogel, a preferential reaction strategy of modulating point defects and hollow microstructures via controllable S atoms migration is proposed to improve the EM wave absorption. S atoms contribute to the creation of hollow structures via Kirkendall effects, as well as inducing point defects in the carbon lattice through doping. More significantly, the mechanisms prioritizing the formation of hollow structures over defects have been discovered, with low‐velocity atomic migration primarily modulating the microstructure for interfacial polarization and impedance matching, and high‐velocity atom migration focused on introducing defects to achieve polarization and conductive loss. The resulting aerogel exhibits an exceptionally maximum reflection loss of −52.82 dB and an effective absorption bandwidth of 8.82 GHz, which far exceeds most of the currently reported materials. Experimental and theoretical approaches, including microwave heating, Tesla interaction, first principles, and far‐field simulation, are comprehensively employed to verify its absorption effect and mechanism. Furthermore, the combination of excellent infrared stealth and self‐cleaning properties opens up its potential applications in complex environments.