Papers by Author: Rong Zhang

Abstract: The AlN nucleation layer (NL) has been deposited on Si (111) substrate by metal-organic chemical vapor deposition (MOCVD). The result indicates that the growth mode of the AlN NL is in the form of 2-dimensional plane and 3-dimensional island. The proportion of 3-dimensional region increases gradually and the 2-dimensional region reduces correspondingly with the increase of growth time. The decrease of the coverage ratio of AlN grains in the 2-dimensional growth region is due to the effect of etching. AlN film with the single crystal orientation has been deposited on the optimized AlN NL.

Abstract: The dislocation density of GaN thick films has been measured by high-resolution X-ray diffraction. The results show that both the edge dislocations and the screw dislocation reduce with increasing the GaN thickness. And the edge dislocations have a larger fraction of the total dislocation densities, and the densities for the edge dislocation with increasing thickness reduce less in contrast with those for the screw dislocation.

Abstract: In this paper, the oxidation process of the VFD array material in wet hydrogen at high temperature was studied. By the aid of SEM, EDAX, and XRD, the effect of temperature, duration, volume and dew point of hydrogen flow during oxidation on weight gain, percentage of the oxide phase, constitution and morphology of oxide scale were investigated, and a suitable oxide technology was obtained, it was as follows: 950°C, 40 ~ 60 min, D.P. 35°C, 8 l/min.

Abstract: GaN films are grown on Si(111) with low-temperature GaN (LT-GaN) layers as buffer layers by hydride vapor phase epitaxy (HVPE). The LT-GaN layers are deposited at different temperatures ranging from 400 to 900 °C. The surface property, the structure and optical properties of the GaN films with different LT-GaN layers are studied. When deposition temperature of LT-GaN layer is 600 °C, the GaN film shows the best properties.

Abstract: Fe films have been grown on different oriented Si substrates by metal organic chemical vapor deposition (MOCVD), and then samples are put in the air without any protection for nearly fifteen years. In this paper, using methods such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM), we make a detailed research on the samples. We identify the composition and structure of the epitaxial films on different oriented substrates and compare the difference both in composition and magnetic properties. Different orientation of the substrates results in different epitaxial film with different characteristic. We also confirm the existence of single crystal iron in the heteroepitaxial film grown on Si (001), and discuss the possible reason why the single crystal iron film still exists without complete oxidation in air for such a long time.

Abstract: The MOCVD-growth and annealing of InN films have been studied in this work. The XRD spectra of InN films grown at 350 °C~500 °C indicate that the diffraction of In increases with increasing the growth temperature to 425 °C and the temperature higher than 425 °C causes the decrease of In diffraction. The corresponding SEM images show that In grains disappear from the surface as the growth temperature is higher than 425 °C. These are attributed to the increase of the desorption of In with the growth temperature. In addition, the SEM images of the annealed InN films also show that the In grains decrease gradually as the annealing temperature is higher than 425 °C. Thus, it is concluded that the desorption of In is the main process as the temperature is higher than 425 °C.

Abstract: The pulsed electric current produced by discharging of capacitors pass through the double solenoids with ferrosilicon core, the instant strong pulsed magnetic field with the oscillating and declining characters was made between two ferrosilicon cores. The effect of high-pulsed magnetic field on the unidirectionally solidified Al-Cu eutectic microstructure with 10µm/s withdrawn velocity was investigated. Under the high intensive pulsed magnetic field, the Al-Cu eutectic solidified morphology experience three evolution stages that are regular columnar structure to breaking off fine grain, coarsening dendrite to newly regularization columnar structure with increasing of 0～15.5J charge energy. It is found that rich copper phase evidently come out inter eutectic cells and the eutectic spacing decrease in newly regularization specimen. The induced electric field caused by high pulsed magnetic field in metallic melt brought into oscillating solute electro-migration in front of solidification interface, which has the effect of promoting solute diffusion and reducing the constitutionally supercooling region.

Abstract: The relationships between the morphologies of primary silicon and undissolved silicon particles in melt of Al-Si hypereutectic alloys are studied by holding the melt from 600 to 1100°C and then quench interrupting. The variation of growth process and mechanism of primary silicon is also investigated. The results show that undissolved silicon particles in the melt would become the nuclei of primary silicon precipitated in solidification and there is a close relationship between the shape of primary silicon and undissolved silicon particles. The growth of silicon would follow not only twin plane re-entrant edge (TPRE), but also layer mechanism as well. Meanwhile, the shape of primary silicon also relied on kinetic surroundings, such as solute transportation. At higher overheating temperatures of the melt, the primary silicon takes star-like and tree-like shapes.