Fabrication And Growth Mechanism Study Of Te Nanowires

Since carbon nanotube was discovered by Iijima in 1991, nanostructures , which refer to structures with at least one dimension in the range of 1-100 nm, are attracted more and more interests by its unique properties comparing to bulk materials and some potential application in apparatus. Compare with zero dimensional materials, one dimensional material such as nanorod, nanowire, nanotube, and nanoband is a better one in studying physical properties depending on material size and its dimension. In particular, nanowires play important roles on the interconnects and active components. The key to synthesizing one dimensional material is how to assemble rationally atoms and other building blocks into the structure with diameter in the nanometer range and no limit in length. Many methods have been studied for synthesizing one dimension materials, including vapor-phase transport, chemical vapor deposition, arc-discharge, laser ablation, template-based, and solution chemistry methods.In our work, we obtained two Types of Te single-crystal nanowires with different growth orientations (GO) by vacuum vapor deposition. One GO of Te nanowires is along c axis when source temperature is 523K, and the other GO of Te nanowire is perpendicular c axis when the source temperature is 573K. The Transition States between different crystal facets and different atoms of Te crystal have been studied. We obtained the reasons of Te nanowires with different GOs from the calculation results by the CASTEP module in Material Studio solfware: We found there would be a great sharp tip on every end of Te nanowire, which was called as"Growth Sharp Tip". Atoms around the GST would touch frequently with the tip and was trapped by the tip for the loss of the energy; finally, atoms will grow on the tip. In other words, the GST will instruct the growth of Te nanowire. When the source energy was low(high), the growth on (001) facet will faster(slower) than it on (100) facet, the long axis of GST will be along [001]([100]) orientation. These GST with different orientations will induce Te nanowires with different GO. The calculation results showed: original energy of free atom is 4.06 ev, which is higher than the energy barrier on the (001) and (100) facets, so free atom can move freely on the two facets. When it move on the (001)((100)) facet, it can lost its energy fast on the region of GST and grow on this tip, finally, Te nanowires with different GO were obtained. We also developed a method called"quasi static precipitation"for synthesis of Te one dimensional nanostructure. In this method, syringe (20ml) is as reactive container, into which the two reactants and 2 ml water were sucked slowly. When the syringe was placed for some days, different Te one-dimensional nanostructures were obtained. When the concentrations of Na2TeO4 and N2 H4·H2O were 0.01mol/L and 16mol/L, the Te nanostructure was unique Te nanowire with average diameter of 10 nm. These Te nanowires were indexed hexagonal phase by Selected Area Electronic Diffraction and its GO was along c axis of Te crystal. When we changed concentrations of two reactants, Te products changed apparently in figure, and we gave the growth mechanism about these peculiar Te nanostructure.When only two reactants were sucked into syringe without water, we obtained a new Te nanostructure called"nanofork". We explain the formation of Te nanofork as follows. Tellurium often grows into one- dimension nanostructures with the preferred [001] growth orientation. There is a strong interatomic force along c axis, resulting in (001) surface can be considered as a polar plane. At the same time, the (100) surface can be considered as a nonpolar plane. Because N2H4·H2O molecules can be dissolved in polar and nonpolar solvent, we think they will strongly adhere on both (001) and (100) surfaces of Te crystal. We believe just this adhering interaction results in the formation of Te nanoforks. Via an instantaneous contact between the two solutions, at the midst of the syringe described in fig2a, abundant Te nuclei (in fig2b) come out during the oxidation and reduction reaction. While the syringe was laid stilly, Te nuclei grow slowly with the supplement of two reactants by the diffusion process. For the high anisotropy of Te crystal, new Te atoms will preferentially grow on the (001) surface and form growth tips symmetrically on the edge of Te muclei, resulting in there is a"V"shape hollow between the tips. In generally, generated Te atoms would grow in the hollow of"V"shape. But for the polarity of N2H4·H2O, in the hollow of"V"shape, there is a stronger action between N2H4·H2O and surface of hollow than that between N2H4·H2O and the sharp tip of"V"shape. This dynamics induced that Te monomers can't break through this block to growth on the hollow of"V"shape. Thus, Te nanoforks were formed finally.