Papers by Author: Min Hua Jiang

Abstract: Graphene, as strict two-dimensional material, exhibits exceptionally good electronic properties. In this paper, graphene was prepared on SiC substrates at different temperature based on two types of pre-treated surface. The surface morphology was characterized by atomic force microscopy (AFM) and scanning electronic microscopy (SEM). The results on SiC surface pre-treatment showed that chemical mechanical polishing (CMP) was an effective surface treatment method for reproducible and controlled growth of graphene. Images of the Si-surface revealed that the thickness of graphitic layers increased with annealing temperature. Meanwhile, a mesh-like network of wrinkles tended to tent-like features with the increase of temperature. The residual stresses, average crystallite size and number of graphene layers were analyzed by Raman spectroscopy. Little shift of 2D-band indicated the presence of certain stresses. Results among four samples showed that graphene layers grown on MP C-surface substrates had the thickest layers，contained the smallest average crystallite size L_a and exhibited no stresses. While graphene layers grown on Si-surface under 1600°C built upon compressive stresses, exhibited largest L_a and least number of graphene layers, indicating perfect quality.

Abstract: Periodic and non-periodic 1-3 type cement based piezoelectric composites were fabricated by cut and filling technique, using P(MN)ZT ceramic as functional material and cement as matrix. The influences of periodicity of piezoelectric ceramic rods in the composites on electrical properties of all the composites were discussed. The results show that the non-periodic composites have larger dielectric factor and piezoelectric strain constant than those of the periodic composite. The impedance-frequency spectra analysis indicates that the non-periodic arrangement of ceramic rods can effectively restrict the lateral structural mode of the composite, accordingly reduces the coupling resonant between the thickness resonant mode and lateral resonant mode. The thickness electromechanical coupling coefficient of non-periodic composites is larger than that of the periodic composite. With increasing the non-periodic level of P(MN)ZT ceramic in the composites, the mechanical quality factor of the composites increases gradually. Therefore, 1-3 type cement based piezoelectric composites with different special abilities can be obtained by varying the periodic arrangement of P(MN)ZT ceramic rods in the composites.

Abstract: The structural damage of mortar caused by simulated crack was evaluated using embedded PZT sensor combining with dynamic electromechanical impedance technique. The influence of embedded PZT sensors layout on detecting structural damage induced by the simulated cracks was also investigated. The results indicate that with increasing the simulated crack depth, the impedance real part of PZT sensors shift leftwards accompanying with the appearance of new peaks in the spectra. When more simulated cracks occur, the shift of the impedance curve becomes more obvious, and the amounts of new peaks in the impedance spectra also increase. RMSD indices of the structures with PZT sensors embedded in them with different layout can show the structural incipient damage clearly. With increasing more simulated cracks in the mortar structures, RMSD values of the structures with different PZT sensors layout become larger, under the same depth, RMSD indices of the structures with PZT sensor embedded transversely and horizontally in them show the increasing trend.

Abstract: 4H-SiC single crystal with a diameter of 1.5’’ has been grown by the seed sublimation method. Regions of mixed polytypes are assessed by high resolution X-ray diffractometry with the asymmetrical diffraction geometry. Multiple reflections are observed from the rocking curve measurements of a longitudinal cut 4H-SiC slice. Those reflections are indexed to be 2131 and 2131 of 4H-SiC, 2130 , 2131 , 2131 , 2132 and 2132 of 6H-SiC, 2131 , 2132 , 2134 , 2135 and 2137 of 15R-SiC respectively based on the lattice constants of different polytypes in SiC crystal. It is believed that the polytypes can be identified by high resolution X-ray diffractometry.

Abstract: 6H-SiC ingots were grown with different growth interfaces at different rates via the sublimation method. A model for the step flow growth mechanism is proposed to interpret the occurrence of 15R-SiC inclusions in the 6H-SiC single crystal. The results show that the 15R-SiC occurs more easily on the convex and the concave interface than on the slight convex interface and 15R-SiC inclusion also occurs when the growth rate of 6H-SiC exceeds the critical rate of 300 %m/h with the slight convex interface at the seed temperature 2250°C.