Properties And Controllable Synthesis Of Semiconductor Self-assembled Nanostructures In Amine-assisted Mixed Solvent System

In this dissertation,solution-based chemical method involving the mixed solvent medium in the presence of various kinds of amines was developed to prepare variousâ…¡-â…¥semiconductor functional nanomaterials.In the solution composed of ethylenediamine and water,1D[ZnSe:Cu²⁺](ethylenediamine)_0.5 hybird nanostructures have been prepared at 180℃for 20 h with the different amount of CuSO₄.After calcinations of these hybird materials as precursor,the corresponding ZnSe:Cu²⁺ 1D nanocrystals were obtained.Moreover,the phase transformation from wurtzite to zinc blende came true.In tetraethylenepentamine/water/hydrazine hydrate solution system, ZnSe crystals with distinctive morphologies have been fabricated by tailoring various reaction parameters,including nanobelts,nanowires,and hierarchically solid/hollow spheres.And the formation mechanism and optical properties of products are studied. Via varying reaction parameters,ZnS hierarchical nanostructures have been synthesized including monodisperse chrysanthemums by nanobelt bundle self-assembly,ultrathin and flexible nanobelt networks,and solid/hollow microspheres by nanorod self-assembly.In addition,the growth mechanism,optical and field-emission properties of products are investigated in the paper.The details are summarized as follows:1.High-quality beltlike organic-inorganic[ZnSe:Cu²⁺](ethylenediamine)_0.5 hybrids were synthesized at 180℃for 20 h in the mixed-solvent system with different concentration of Cu²⁺.In the sequent procedures,these hybrids served as precursors which were then calcined at 500-600℃in the tube furnace full of Ar and in turn,various single-crystal 1D ZnSe:Cu²⁺ nanostructures were obtained,from nanowire bundles to near-helical and bone-like nanowires different from the pure ZnSe 1D nanostructures.Wurtzite and sphalerite ZnSe coexisted in the as-prepared ZnSe:Cu²⁺ nanocrystals,whereas undoped ZnSe is hexagonal phase.The above results of research have been published in the Journal of Physical Chemistry C.2.A novel tetraethylenepentamine(TEPA)-directed method has been developed to selectively synthesize ZnSe crystals with distinctive morphologies, including nanobelts,nanowires,and hierarchically solid/hollow spheres,which realized the controlled synthesis of nanostructures from 1D to 3D.We investigate the influence of various reaction parameters such as volume ratio of mixed solvent, reaction temperature and time on the morphology and size of products.In addition, the time evolution process of ZnSe nanobelts was systematically studied.According to the observed results and rational discussion,an in-situ decomposition of ZnSe precursors into ZnSe through solid-solid reaction mechanism was proposed.An energy-minimizing driven self-assembly of ZnSe nanorods on the base of N₂ bubbles induced by TEPA is responsible for the formation of hierarchically hollow spheres. PL spctrum of nanobelts show three strong emission bands at aroundλ=438,449,and 457 nm.And ZnSe ierarchically hollow spheres displays a broad and strong emission peak in low energy level ofλ=500-700 nm.The above results of research have been published in the Chemistry-A European Journal.3.Various novel ZnS hierarchical nanostructureshave been successfully fabricated in high yields and purities by a tetraethylenepentamine(TEPA)-directed method.A detailed study of the effect of experimental parameters on the morphology is presented.Tuning the molar ratio of Zn(Ac)₂ and dithizone from 1:2,1:3,2:1 to 2:2, ZnS monodisperse urchin spheres,microspheres constructed with nanoflakes and nanorods,chrysanthemums by nanobelt bundle self-assembly,ultrathin and flexible nanobelt networks could be selectively synthesized at 180℃for 20 h with V_H2O/V_TEPA=20:20.Result analyses reveal that Zn(Ac)₂/dithizone(DTZ) molar ratio, volume ratio of H₂O to TEPA and reaction temperature play a crucial role in the final morphology of ZnS products.A possible growth process of ligand(TEPA)-assisted gradual crystallization and subsequent self-assembling is proposed as a plausible interpretation for the formation of those observed structures.The photoluminescence properties were investigated and the prepared nano/microstructures displayed a very strong luminescence around 550-600 nm at room temperature.Field-emission measurments of ZnS nanobelt networks demonstrate the high field-enhancement factor of ca.2750.No notable current degradations during this period of 9 h are observed at 25 V/μm,proving the good emission stability of our product.