Enhanced microwave absorption of ZnO coated with Ni nanoparticles produced by atomic layer deposition

In this work, flower-like ZnO coated by Ni nanoparticles has been synthesized by the reduction of NiO-coated ZnO produced by an atomic layer deposition (ALD) method. The structure and electromagnetic (EM) absorption properties of the as-prepared samples are investigated. By applying 800 ALD cycles of NiO deposition followed by a reduction process, the surfaces of ZnO are densely covered by Ni nanoparticles with a narrow particle size distribution and an average size of 13.1 nm. ZnO@Ni exhibits remarkably improved EM absorption properties compared to ZnO. The optimal RL calculated from the measured complex permittivity and permeability is -48.0 dB at 10.4 GHz. Moreover, the EM wave absorption less than -10 dB is found to reach 5.3 GHz for an absorber thickness of 1.5 mm. The enhanced absorption ability arises from the effective combination of multiple dielectric-magnetic loss mechanisms.