H. Li

Regular arrays of GaN nanorods

Regular arrays of GaN nanorods have been synthesized by reacting gallium and ammonia using Au as a catalyst on a MgO single crystal substrate treated by chemical etching. They were characterized by field emission scanning electron microscopy, energy dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED) and X-ray diffraction (XRD). EDX, XRD SAED indicated that the nanorods were wurtzite single crystal GaN. We suggest that regular tactic square shape with steps on the single crystal MgO and discontinuity of the Au film may play an important role during the formation of regular arrays of GaN nanorods.

β-Ga2O3 nanowires on unpatterned and patterned MgO single crystal substrates

Large-scale beta-Ga2O3 nanowires and individual beta-Ga2O3 nanowires bridging adjacent metal Ag catalyst islands were synthesized on the unpatterned and patterned MgO single crystal substrates by direct reaction of gallium and water vapor. The samples were characterized by field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction (XRD), transmission electron microscopy and selected area electron diffraction. The results show that the line-like nanostructures are monoclinic beta-Ga2O3 nanowires. The individual beta-Ga2O3 nanowires are rooted in the islands, and some of them bridge adjacent islands of the Ag catalyst. This work offered the prospect of developing ultrafine nanoscale devices

Microstructure and mechanical properties of SiC fibres after exposure at elevated temperature

To understand the service behaviour of SiC fibres, the effects of ambient environment and temperature on the microstructure, mechanical property and oxidation behaviour of these fibres were investigated. The result shows that, the surface of SiC fibres becomes rough after exposure in air from 973 to 1573 K due to the formation of small SiO2 particles, and a smooth SiO2 film will be formed on the SiC fibre at 1773 K. In Ar atmosphere, SiC fibres will change into clusters of large SiC crystals after heat treatment for 2 h at 2373 K. The tensile strength of SiC fibres decreased by 66 and 95% when the fibres were exposed at 1773 K for 5 min in air and 2373 K for 2 h in Ar, respectively. This degradation is associated with the evaporation of CO and SiO from the fibres as well as with SiC grain growth in the fibres.

Deposition and ablation resistance of HfC-based coatings prepared on SiC-coated C/C composites by supersonic atmospheric plasma spraying

In order to improve the ablation properties of C/C composites, HfC-based coatings with different mass ratios of SiC were deposited on the surface of SiC-coated carbon/carbon composites by supersonic atmospheric plasma spraying. The morphologies and microstructures of the HfC-based coatings were characterised. The ablation resistance test was carried out by oxyacetylene torch. The results show that the as-prepared coatings are multiphase coatings consisting of HfC, HfO2, SiC and SiO2. The structure of different coatings is dense. After ablation for 60 s, the ablation centre region of coating is smooth without obvious microcrack and pinhole, and no interlaminar crack can be observed at the cross-section. An Hf–Si–O compound oxide layer is generated on the surface of coating, which is beneficial for protecting the C/C composites from being ablated. Meanwhile, the further generated HfSiO4 can play a pinning effect, which can prevent crack extension.