Preparation And Microwave Absorbing Properties Of Chrysanthemum-like Zno Nanowire Clusters

Due to predominant magnetic, optical and electrical properties, and novel morphologies, low dimensional ZnO-based nano-materials have been one of subject of extensive study at present. Especially, the good electromagnetic loss properties of one dimensional ZnO-based wave-absorbing nano-material makes it not only involved in green living space, but also related to information and national defense security. Therefore, the study of low dimensional ZnO-based nano-materials has significant scientific and practical value.The electronic structures of bulk ZnO, ZnO nanowires, and semi-conductivity doped and magnetic doped ZnO system have been studied systematically by first-principles based on density-functional theory. The results show that the conductivity of all above is effectively enhanced by Sb doping, and the net magnetic moment of the ZnO system is also effectively increased by Mn doping. Meanwhile, owing to quantum size and surface effects, more electrons participate in shared motion in semi-conductivity doped nanowires than in the bulk. The spin polarization of magnetic elements in Mn or Co doped naonowires is enhanced, and also the coupling of intrinsic ions and magnetic elements is promoted.The technological parameters for hydrothermal preparation of chrysanthemum-like ZnO nanowire clusters are optimized by orthogonal design principle. The sample's components, microstructures, morphologies and wave-absorbing properties are analyzed and characterized by X-ray diffraction, X-ray energy dispersive spectroscopy, scanning electron microscope, transmission electron microscope and microwave vector network analyzer. An important conclusion has been reached that the wave-absorbing properties of chrysanthemum-like ZnO nanowire clusters depend on their morphologies, and the nucleation and growth mechanism have been also proposed in the paper.Based on the important conclusions of theoretic study, and combined with the optimized technological parameters for preparation of chrysanthemum-like ZnO nanowire clusters, chrysanthemum-like ZnO:Sb and ZnO:Mn nanowire clusters with good wave-absorbing properties have been prepared. The formation mechanism of hexagonal crystal face (0001) at the end of Sb-doped ZnO nanowires is explained by layered superposition model of growth units, and the new loss mechanism caused by Sb doping is also analyzed in the paper. Furthermore, based on the theoretic study of ZnO:Mn nanowires and F-center model, one theoretical interpretation of the magnetic source of chrysanthemum-like ZnO:Mn nanowire clusters in room temperature is proposed. The result shows that the extremum of reflection loss of 3% Sb doped chrysanthemum-like ZnO nanowire clusters gets to -18.48dB at 16.55GHz, and 3% Mn doping is -13.55dB at 8.05GHz when the weight ratio of ZnO to paraffin is 1/4.Chrysanthemum-like ZnO nanowire clusters with good wave-absorbing properties have been prepared by PAM-assisted hydrothermal process. When the ratio of PAM concentration to Zn²⁺ concentration is 0.00005%, and the weight ratio of Chrysanthemum-like ZnO nanowires clusters to paraffin is 1/4, the extremum of reflection loss gets to -21.82dB at 13.5GHz. The influence of different PAM concentration on the growth of ZnO nanowires is explained by PAM ionization and adsorption model, and the formation mechanism of ring stripes in the ZnO nanowires is also explained by bamboo shoot model. One conclusion that PAM induced the magnetic properties of chrysanthemum-like ZnO nanowires clusters is obtained.A kind of absorber with broadband and strong absorption has been designed and prepared, based on the analysis and study of wave-absorbing properties of chrysanthemum-like ZnO:Sb, ZnO:Mn nanowire clusters and chrysanthemum-like ZnO nanowire clusters prepared by PAM-assisted hydrothermal process. The extremum of reflection loss gets to -13.77dB at 14.65GHz, and the bandwidth covers 6.9GHz under -10dB.