Tellurium Based Nanostructures:Synthesis,Evolution And Characterization

Research into metal chalcogenides nanomaterials has become more and more popular because of their size dependent properties and potential use in various devices as compared to the bulk materials. Different synthesis methodologies of binary phase metal chalcogenides nanomaterials are well studied, but the investigation of more simple synthesis processes is very much important. A solution phase method particularly solvothermal/hydrothermal method is very effective process to prepare various delicate nanostructures of metal chalcogenides. In this dissertation new morphologies based on tellurium especially silver telluride have been synthesized via hydrothermal and hydrothermal reduction-carbonization process. Further the linear and nonlinear optical properties of these nanostructures were studied. Motivated by these findings, the main purpose of this research is to explore scientifically the role of starting materials, duration of reaction and the dependence on the capping agent or stabilizer.The growth mechanism during the hydrothermal process responsible for the formation of silver telluride zigzag morphology was monitored. The zigzag morphology was obtained by the hydrothermal reaction between silver nitrate and sodium tellurite by controlling the reaction conditions and surfactants. Cation Ag+and anions TeO3-2were formed in the solution and further reduced of TeO3-2to Te rapidly as the temperature increased and consequently nucleation of t-Te nanowires took place. Further it proceeded in the formation of zigzag nanowires by the contribution of Ag+by reacting with t-Te nanowires. This zigzag morphology was the result of nonstop anisotropic growth due to the attachment of week surfactant molecules on the surface of nanowires. Temperature variation also concluded that the oriented attachment through the dipole-dipole interaction attachment had its role in this oriented attachment mechanism which is the base of this whole anisotropic growth mechanism. The PVP shown the substantial effect on the growth and resulted in the smooth nanowires with the increase in the PVP concentration. The small concentration of polymer (PVP) provided higher surface energy and lower activation energy of surface atoms. The structure and morphologies of the metal oxides were characterized by the advanced techniques including XRD, SEM, TEM, UV-Vis spectroscopy and EDS. It has been found from the XRD analysis that the zigzag nanowires exhibit the monoclinic single crystalline nature in agreement with the monoclinic crystal system P2n/c (no.13). The lattice fringe spacing "d" in HRTEM image identified the plane (-222) and (-322) which matched with the planes in XRD peak pattern.In the second portion of the dissertation, the synthesis and evolution process of carbon coated nanowires have been discussed. Solvothermal reduction-carbonization approach for the formation of one dimensional (1D) silver telluride nanocables and tellurium nanorods with a sheath of amorphous carbon have been proposed. Glucose assisted in the formation of carbon shell and acted as the carbonizing agent. In this case the ethylene glycol has been utilized as the reducing agent. Finally the average layer of100nm carbon with the core of silver telluride nanowire of about50nm was achieved. The simplified view for the undergoing reactions in the sealed autoclave started from the Solvothermal conditions and extended to the aromatization and carbonization process has been discussed along with the structural and morphological investigations.The last part of the thesis demonstrated the innovative applications of tellurium based nanostructures. Firstly the effect of zigzag structure on the absorption behavior and its comparison with the previous literature has been carried out. Due to the increase in aspect ratio the transverse surface plasmon ratio has shifted slightly towards the blue side as compared to the straight silver telluride nanowires. Z-scan experimental measurement has revealed the possibility of these materials to be used in the field of nonlinear optical limiting applications. The refractive non linearity of the wiggly nanostructures at800nm excitation wavelength was attributed to be greater than that of straight morphology. Similarly, NLO parameters for the core-shell nanostructures have been determined in the near infrared region in a very systematic way for both tellurium and silver telluride carbon sheathed nanostructures. The third-order nonlinearity parameters of Ag2Te/C and Te/C have been compared to those of known NLO materials, such as C60, ferrocenyl complexes, organic complexes and polymeric complexes. From this analysis, it has found that the values of both carbon coated structures are comparable to each other and both the materials constitute a rather low imaginary component, which implies minimal nonlinear optical losses.