| 其他摘要 | As an important II-VI semiconductor with a band-gap energy of 3.7 eV at room temperature, ZnS is one of the first discovered semiconductors, probably one of the most important electroluminescent materials in the electronic/optoelectronic industry with prominent applications in flat-panel displays, sensors, lasers and photocatalysis. Compared with bulk ZnS, quasi-One-dimensional (1D) ZnS nanomaterials are predicted to have novel physical and optical properties and promising applications because of their high aspect ratio and size effect. However, there are still several problems in this field at present: (i) the growth mechanism of 1D ZnS nanostructures is not clear and their growth lacks controllability; (ii) it is difficult to rationally design ZnS nanomaterials to meet desired applications; (iii) the purity and yield need to be further improved; (iv) fundamental theoretical analysis and properties of the as-synthesized nanostructures have not been well-explored.
BN nanotubes (BNNTs), as typical wide gap semiconductor III-V nanomaterials with a band gap energy of ~5.5eV independent of their morphologies and/or geometries, have continuously attracted significant interest. Due to their excellent far-ultraviolet optical and mechanical properties, high thermal conductivity, oxidation resistivity, and chemical inertness, BN 1D nanostructures show great potential for applications as unique electromechanical and optoelectronic components for laser, light emitting diode, and medical diagnosis. However, fabrication and rational assembly of BN 1D nanostructure still remain a great challenge, with low yield, high impurity, and poor crystalline structure. It is also of great significance to dope BN nanomaterials for band engineering in practical applications.
In this dissertation, controllable synthesis, growth mechanism and physical properties of 1D ZnS and BN semoconducotor nanomaterials were systematically investigated. The main research results and originalities are listed as follows:
1) Based on the analysis of kinetic processes and crystallographic characteristics, various 1D ZnS nanostructures were controllably synthesized through adjusting kinetic parameters, such as growth temperature, vapor supersaturation, diffusion rate and catalyst. Through investigating the relationship between synthesis conditions and morphology of the products, the VS and Au-catalyzed VLS mechanisms were suggested to be responsible for the growth of ZnS nanowires and nanobelts, respectively. Si-induced well-aligned mechanism was proposed to fabricate well-aligned ZnS nanobelt array. It was found that the polarity of the ZnS (111)/(0001) surfaces plays important roles in determining the novel dual phase ZnS tetrapod tree-like tetrapod heterostructures (a ZB core and hexagonal WZ branch), which clearly demonstrates that Zn-terminated ZnS (111)/(0001) polar surface is chemically active, inducing the growth of the ZnS wurtzite branches, and the sulfur terminated (-1-1-1)/(000-1) polar surface is inert toward the growth of the branched structures. Furthermore, through polarity induced growth and bottom-up stacking model, hexagonal ZnS zinc blende pyramid was fabricated. Finally, doped and undoped ZnS superlong ropes were obtained and a lattice substituted doping mechanism was elucidated by XPS analysis.
2) Based on ZnS and BN crystallographic characteristics, ZnS/BN core/shell nanocable and nanobelt heterostructures were obtained by coating a layer of BN honeycomb sheets over the entire surface of asymmetrically-grown ZnS nanowire or nanobelt templates. Through thermal evaporation of ZnS/BN nanobelt heterostructures to remove ZnS template, novel BN hollow nanobelts were firstly fabricated. The success of extending this simple templating method to synthesize other hollow nanostructures, such as BCN hollow nanobelts, suggests that this method can be adopted to fabricate other hollow nanostructures. Novel microbelts self-assembled from Cu-doped multi-walled BNNTs were firstly synthesized by a Cu-catalyzed CVD method. Novel yard-glass shaped BN nanotubes with periodic iron nanoparticles were synthesized by a floating catalytic process of ammonia reacting with boron precursor using ferrocene as catalyst precusor. The catalytic layered epitaxial assembly and simultaneous axial connection model was proposed to explore the growth.
3) The field emission (FE) properties of the as-synthesized 1D ZnS nanostructures were investigated. FE measurements showed that these 1D ZnS nanostructures have much lower turn-on and threshold fields than those of reported ZnS nanomaterials. Moreover, their FE current stability is much stable than that of carbon nanotubes. The superior FE properties of the present ZnS nanomaterials indicate that they are comparable with or even better than those of many other 1D nanostructures. Among them, the Cu-doped ZnS superlong ropes show the lowest turn-on field and excellent FE properties, indicating that the manipulation of geometrical morphology and doping are two effective routes to optimize the FE properties of the 1D ZnS nanostructures.
4) The Cathodoluminescence (CL) properties of the as-synthesized 1D ZnS and BN nanostructures were also investigated. Through structural control, such as purity, crystallinity, dimensionality, morphology and crystal structures, and doping modification, it is effective to modulate the band-gap of 1D ZnS and BN nanostructures and consequently tune their CL properties from far-ultraviolet to visible. Strong light emissions from 232nm to 700nm were observed at different 1D ZnS and BN nanostructures, indicating their great potential applications in light emission devices. |
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