| Metal tellurides have attracted substantial research interests for their superior optical and thermal properties during the past years. Metal telluride Bi2Te3 is well-known for its utility in thermoelectrical applications and more recently as topological insulator. The topological insulator heterojunction possess many novel interface effects, such as magnetic and superconducting proximity effect etc. The composites have been the important topic for the understanding of interface effect. Nevertheless, the research on metal telluride composites lags far behind the nanomaterials. This paper mainly focused on the fabrication and study of metal telluride NiTe2 bulk single crystals and Bi2Te3/NiTe2 polycrystal composites.The main works of the thesis are summarized as follows:Firstly, the NiTe2 bulk single crystals about 6mm length and 5mm width were successfully prepared by solid state reaction method, which was the largest one to our knowledge. The structure of the sample was refined on the basis of X-ray powder diffraction data using the Rietveld method over a wide range of angles. The system crystallizes in the space group R3ml (164), lattice parameters a=b=3.871A, c=5.308A, α=β=90°, γ=120°. The layer properties and lattice parameters were further characterized by SEM and HRTEM, of which the results were consistent with XRD measurements. The EDS quantitative analysis showed that the sample’s composition in line with the expected value of the chemical formula. All the results above fully illustrated the samples as-grown were high-quality single crystals without impurity.Secondly, we studied the fluorescence and Raman spectroscopy of the NiTe2 small bulk single crystal samples. Room-temperature photoluminescence was excited by the 280nm light waves. NiTe2 small single crystal samples had an emission peak at 327nm (3.8eV), which was different from the nano-samples. We speculate that the fluorescence effect of samples here primarily caused by the surface states. Raman results show the NiTe2 single crystal samples have three Raman peaks:1121.27cm-1,2101.86cm-1 and 2164.98cm-1. Gaussian fitting data demonstrate the half peak width of NiTe2 single crystal sample was narrow and the crystallinity was good.Thirdly, we developed a novel two-step method route to synthesize the Bi2Te3/NiTe2 composites. The samples were characterized by XRD, SEM and EDS. The results show that the composition of samples as-prepared is uniform. The experimental exploration illustrate that the optimal sintering conditions of composites were:500℃,24h, and high vacuum degree. The phase composition of samples prepared by two-step method can be effectively controlled, which pave a way to the research of interface phase and the fabrication of bulk composite materials.Finally, Bi2Te3/NiTe2 composites were studied by the fluorescence and Raman spectroscopy. The fluorescence spectrum show that under the excitation of 280nm light waves, Bi2Te3/NiTe2 composite existed two emission peaks at about 306nm (4.1eV) and 330nm (3.8eV), wherein the 330nm emission peak was caused by the fluorescent effect of NiTe2 samples. Due to the interface effect the fluorescence intensity of Bi2Te3/NiTe2 composite is higher than NiTe2. Raman measurements show that Bi2Te3/NiTe2 composite samples containing seven Raman peaks:52.15cm-1,90.75cm-1,108.18cm-1,125.64cm-1, 1115.33cm-1,2096.57cm’1 and 2159.74cm-1, of which the first four peaks corresponding to Bi2Te3 samples, the latter three corresponding to NiTe2 samples. In addition, due to the influence of the interface effect of Bi2Te3/NiTe2 composite, there existed different levels of red shift (range within 5～10cm-1) between the Raman spectra of composite and raw materials. |
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