Uniform Fe₃O₄ coating on flower-like ZnO nanostructures by atomic layer deposition for electromagnetic wave absorption

An elegant atomic layer deposition (ALD) method has been employed for controllable preparation of a uniform Fe₃O₄-coated ZnO (ZnO@Fe₃O₄) core-shell flower-like nanostructure. The Fe₃O₄ coating thickness of the ZnO@Fe₃O₄ nanostructure can be tuned by varying the cycle number of ALD Fe₂O₃. When serving as additives for microwave absorption, the ZnO@Fe₃O₄-paraffin composites exhibit a higher absorption capacity than the ZnO-paraffin composites. For ZnO@500-Fe₃O₄, the effective absorption bandwidth below -10 dB can reach 5.2 GHz and the RL values below -20 dB also cover a wide frequency range of 11.6-14.2 GHz when the coating thickness is 2.3 mm, suggesting its potential application in the treatment of the electromagnetic pollution problem. On the basis of experimental observations, a mechanism has been proposed to understand the enhanced microwave absorption properties of the ZnO@Fe₃O₄ composites.