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Synthesis, Growth Mechanisms and Properties of Different Morphological 1D SiC Nanomaterials

Author: GaoWeiDong
Tutor: LiZhenJiang
School: Qingdao University of Science and Technology
Course: Materials Processing Engineering
Keywords: With different morphologies SiC one-dimensional nanomaterials Chemical vapor reaction Microstructure Growth Mechanism Optical properties
CLC: TB383.1
Type: Master's thesis
Year: 2009
Downloads: 176
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Abstract

In recent years, the wide band gap semiconductor SiC one-dimensional nanomaterials have attracted great interest in the study, to become one of the important research focus in the field of low-dimensional materials science. SiC one-dimensional materials due to its unique morphology and excellent performance make it have a wide range of applications in the optical, electrical, magnetic, and mechanical. Detailed study using chemical vapor reaction synthesis of one-dimensional materials with different morphologies SiC process conditions and product morphology, microstructure, growth mechanism, initially explored one-dimensional structure of the chain SiC Raman spectroscopy and fluorescence spectral characteristics. The main conclusions are as follows: the selection of ball milling Si-SiO2 mixed powder and high purity CH4 reactant homemade graphite mold as the reaction chamber through a series of reactions in an upright vacuum controlled atmosphere furnace, iron nitrate and nitrate nickel catalyst, the highest quality β-SiC nanorods and nanowires prepared on a graphite substrate. The analysis shows that: the high purity of the resulting product and morphology uniform diameter dimension uniformity, smooth surface without amorphous oxide coating for the cubic structure of the β-SiC crystal growth axially to the [111] direction. Possible growth mechanism for the β-SiC nanorods and nanowires were: Fe under catalytic conditions, the Fe-C-Si ternary alloy system with the changes in the concentration of the components of phase transition of SiC nanorods by periodically gas - liquid - solid (PERIODIC-VLS) growth mechanism for the formation of Ni-C-Si alloy system without phase change process occurs; the Ni catalytic conditions, the the SiC nanowire by the continuity of gas - liquid - solid (CONTINUOUS-VLS ) growth mechanism of formation. No the template space limit domain, the catalyst-assisted growth conditions on a graphite substrate, prepared the periodic composite SiC/SiO2 nano chain. Using field emission scanning electron microscopy (FESEM), X-ray diffractometer (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM) system characterization of the product, the results show that: the product high purity, having a two-phase composite of chain morphology, the core portion is cubic crystal structure of β-SiC nanowire, a diameter of about 20-30 nm, and within the large amount of crystal defects exist, the growth direction of the [111] direction , the external cladding cycle amorphous SiO2 nano ball, ball diameter of about 100 nm. Two-stage gas - solid (VS) growth mechanism of the formation process of the product a more detailed discussion. Raman spectroscopy and fluorescence spectral characteristics of the cycle composite SiC/SiO2 nano-chain explored and found excellent optical properties different from the bulk material. Successfully prepared through the pressure conditions in the adjustment and control of the chemical vapor reaction process, no template limited domain and no catalyst auxiliary conditions, on a graphite substrate, the spiral and quasi-helical SiC/SiO2 coaxially nano cable analysis results showed that: The product has a typical core - shell double-layered structure, the core portion is a β-SiC nanowires, an external cladding layer of amorphous SiO2, nano cable diameter 30-50 nm, and appearance of a typical spiral morphology, screw diameter of approximately 100-150 nm , up to a dozen microns. Product growth process: nanowire growth process of the core portion, the SiC crystal structure primitives Si-C4 in the stacker growth process, since the reaction gas pressure continues to increase its horizontal dislocation of the displacement increases, The movement trajectory of the spiral, so as to generate the appearance of contour spiral SiC nanowires, the subsequent residual SiO gas during the cooling process evenly coated on the outside of the nanowires formed coaxial Nanocable. SiC nano-aluminum substrate by electrochemical oxidation process to obtain a uniform distribution of the nano-aperture array of high-quality porous Al2O3 flakes, and as auxiliary template successfully prepared by a simple chemical vapor reaction shape very regular chain, chain The diameter size of about 30 nm, and the nanowires in the chain between approximately 10-15 nm, product of up to several tens of micrometers, as the cubic crystal form β-SiC, the axial direction of the [111] direction. Ventilation during the reaction due to the presence of the porous templates formed array distribution of the carbon gas concentration gradient as a center of the hole, causing the SiC crystal gas - solid growth rate fluctuate, eventually leading to a diameter fluctuation of the SiC nanostrands. Preliminary exploration of Raman spectroscopy and fluorescence spectral characteristics of the nano-chain products, also found excellent optical properties different from the bulk material.

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