| Metal selenides and tellurides nanomaterials are important semiconducting materials, and have attracted much attention due to their unique physical, chemical properties and the wide applications in optical, electronic, magnetic devices and biological medicines. The chemical composition and microstructure of the materials determine their physical and chemical properties, thus, altering their structure, dimension, morphology or composition in a controllable way is of great significance to tailor their optical, electrical and magnetic properties. Nevertheless, the research and application on the manganese or cobalt selenides and tellurides nanomaterials still lag far behind the other selenides and tellurides compounds. Therefore, it is a very urgent and challenging work to develop systematically different synthetic approaches of manganese or cobalt selenides and tellurides nanomaterials, adjust their structure, morphology, dimension, or composition, investigate the relationship between their microstructure and electromagnetic properties, and explore their new application potentials. In this dissertation, the work is maily focused on manganese or cobalt selenides and tellurides nanomaterials, and valuable researches have been carried out to the exploration of new synthetic methods and routes to synthesize micro-and nano-scale materials with controlled structures and morphologies, and the detailed studies of their microstructures, growth mechanism and electromagnetic properties. The main contents can be summarized as follows:Synthesis and microwave absorption properties of MnSe2 nanorods. High-quality and monodispersed MnSe2 nanorods were synthesized via a facile hydrothermal reaction. The aspect ratio of the MnSe2 nanorods ranging from～15 to ～70 can be tuned by simply changing the amount of polyvinylpyrrolidone and N, N-dimethylformamide in the reaction solution. The passivation effect of the capping agent and the reduction of the solvent have critical influence on the crystalline phase, morphology and composition of the rod-like products. Moreover, the microwave absorption properties of the MnSe2 nanorods were investigated. MnSe2 nanorods with large aspect ratio exhibit enhanced microwave absorption properties on both the maximum reflection loss and the effective absorption bandwidth.Preparation of hierarchical CoSe2 micro/nanoarchitectures and their structurally enhanced microwave absorption. A novel hierarchical CoSe2 microarchitecture was designed and fabricated via a facile solvethermal method. Hexadecyltrimethylammonium bromide and diethylenetriamine were employed as structure-directing templates. The as-synthesized CoSe2 microarchitecture exhibits a clew-like shape with an average diameter of around 1～2 μm, which is actually composed of many crisscrossing nanobelts and nanosheets. The effects of different synthetic conditions on the sizes, morphologies, structures and microwave absorption properties of the CoSe2 microarchitectures were investigated in detail and the possible formation mechanism was proposed accordingly on the basis of the experimental results. The 3-D hierarchical microstructures display enhanced microwave absorption properties compared with the 1-D nanobelts, with the value of maximum RL at-26.93 dB.Shape-Controlled synthesis of wurtzite MnSe nanocrystals with surface-dependent magnetic behavior. Highly crystalline, monodispersed, and shape-controlled wurtzite MnSe nanocrystals were first fabricated via colloidal approach with uniform sizes and tailored shapes including bullet-, shuttle-, tetrapod-, waterdrop- and matchstick- shapes. The selective binding strength of the different surfactants, reaction time, temperature, concentrations and other factors play a crucial role in tuning the shape of the wurtzite MnSe nanocrystals. Importantly, the advanced electron microscopy technologies (e.g., TEM tomography technology and electron energy-loss spectroscopy with atomic resolution) have been applied to investigate the structure details, planar defects and growth process of the as-prepared MnSe nanocrystals. The low-temperature surface spin-glass magnetic behavior for the as-prepared MnSe nanocrystals was observed due to their noncompensated surface spins, and the associated blocking temperatures were found to be increased with higher surface area/volume ratio of the nanocrystals.Preparation and electronic-structure analysis of MnTe2 nanoparticles. MnTe2 nanoparticles were successfully prepared for the first time. It is crucial to add strong reducing agent such as lithium triethyl borohydride in tellurium precursor for the successful synthesis of MnTe2 nanoparticles. Two kinds of MnTe2 nanocrystals (with or without planar defects) can be obtained by changing the manganese source and the capping agent in manganese precursor. The synthesis conditions of MnTe2 nanocrystals were fully explored, and Mn/Te ratio, reaction temperature and time had a significant impact on the crystal structures, morphology and size of the as-formed MnTe2 nanoparticles. The planar defects and growth mechanism of MnTe2 nanoparticles were analyzed via electron energy-loss spectroscopy with atomic resolution. Futhermore, the band structure and density of states of MnTe2 was performed in detail using the materials design codes of Wien2k and Castep. It is found that defects and size have obvious effect on the absorption properties and electronic structures of MnTe2. |
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