A novel Fe3O4/carbon nanotube composite film with a cratered surface structure for effective microwave absorption

With the rapid development of microwave technologies, electromagnetic pollution and stealth have become important problems to be solved. Carbon materials as a kind of lightweight and efficient microwave absorbing materials have been widely studied. However, it is still a great challenge to achieve strong and broadband absorption, especially at a thin thickness. Herein, an Fe3O4/carbon nanotube (CNT) composite film with a cratered surface structure is reported. This film is prepared by continuously shrinking and winding a cylindrical CNT assembly, and the cratered structure formed by inducing a reaction between the introduced ferric acetylacetone and the Al substrate of the film. While the pristine CNT film and the Fe3O4/CNT composite film with a smooth and flat surface show good microwave absorption only at large thicknesses (4 mm and above), the composite film with a cratered surface structure starts to show effective absorption over wide C and X radar bands at a thickness as small as 0.4 mm. Investigation of electromagnetic parameters suggests that the absorption may be due to the synergistic effects of dielectric and magnetic losses and internal multiple scattering. This study provides a cratered surface strategy for developing microwave absorbing materials with thin thickness, lightweight, and strong wideband absorption for applications in both civil and military fields.