Morphology-dominant microwave absorption enhancement and electron tomography characterization of CoO self-assembly 3D nano-flowers

To meet the demands of strengthening microwave absorption capability, self-assembly nanoparticles (NP) with flexible morphology and abundant interfaces are important and their synthesis remains great challenge. In this paper, cobalt monoxide (CoO) nanostructures with octahedral and 3-dimensional (3D) nano-flower morphologies were controllably synthesized by decomposition of cobalt acetylacetonate at 280 °C, chelated with dual-surfactants of oleylamine and oleic acid with various volume ratios (10 : 1–7 : 4). The basic structural units of both octahedrons and 3D nano-flowers are octahedral CoO NP, which was demonstrated by advanced 3D transmission electron microscopy tomography. Dependency of the tunable microwave absorption properties on the 3D geometric morphologies of CoO NP was well established. The absorption bandwidth with a reflection loss (RL) of less than −10 dB is larger than 6 GHz for both octahedrons and nano-flowers. Compared to the spherical CoO NP, the octahedral nano-flowers have highly enhanced microwave absorption capability. Moreover, the maximum RL peak of the nano-flower CoO NP reached as high as −37 dB at 10.5 GHz, compared to that of −17 dB at 12 GHz for the octahedral CoO NP and −6.3 dB at 7.5 GHz for the spherical CoO NP. These results indicate a remarkable dependency of the dielectric polarization absorption and magnetic coupling absorption on the geometric morphology of CoO nano-architecture. It can be supposed from our findings that various morphologies of self-assembling CoO NP might become an effective path to achieve high-performance microwave absorption for electromagnetic shielding and stealth camouflage applications.