Effect of Graphite Defect Type and Heterogeneous Atomic Doping Structure on the Electromagnetic Wave Absorption Properties of Sulfur-Doped Carbon Fibers

The introduction of sulfur atom dopingstructures in graphitecrystals of carbon fibers to achieve the synergy of multiple microwaveabsorption mechanisms is discussed. The effect of graphite defecttype on the electromagnetic wave absorption performance of sulfur-dopedcarbon fibers is investigated. The heterogeneous atom-doped structure breaks the atomic-levelsymmetry of the local microstructure, and it and the defect designare considered to be an efficient way to fabricate microwave absorberswith a wide effective bandwidth and strong absorption capability.Herein, we have successfully designed and synthesized sulfur-dopedcarbon fibers by combining a strategy of introducing heterogeneousatoms with defect engineering. The analysis of Raman spectroscopyand transmission electron microscopy data reveals the correspondencebetween the type of graphite defects in sulfur-doped carbon fibersand their microwave absorption properties. The heterostructure formedby graphite and amorphous carbon can be considered a boundary-typedefect, which is beneficial for microwave absorption. The introductionof vacancy defects and sulfur atom doping in graphite crystals breaksthe symmetry of the graphite structure and leads to changes in dipolepolarization. The ratio of the two sulfur-doped structures, C USand C-S-C, is controlled to achieve the microwave absorptionproperties of the material in the high-frequency region. The three-dimensionalstructure formed by the cross-linking of one-dimensional fibers ismore conducive to the formation of macroscopic eddy current losses.The strong absorption of microwaves at extremely thin thicknesseshas been achieved with S-doped carbon fibers due to the synergy ofmultiple loss mechanisms. When the absorber thickness is only 0.98mm, the optimized S-doped carbon fiber can reach a minimum reflectionloss (RL) of -69.232 dB, and when the thickness is 1.04 mm,the widest effective bandwidth reaches 3.9 GHz (14.1-18 GHz),demonstrating a strong electromagnetic wave absorption capability.