Jinhui Dai

Si and SiOx nanostructures formed via thermal evaporation

Abstract Various Si and SiO x (x=1 to 2 ) nanostructures were formed via a thermal evaporation method of heating pure silicon powder at 1373 K under Ar flow. An alkali-treated quartz glass plate coating with catalyst precursor of a Fe(NO 3 ) 3 aqueous solution was used as substrate. The product exhibited morphologies of fist-capped SiO x fibers (Si-core), tree-like SiO x nanofibers and tadpole-like SiO x nanofibers in different areas of the substrate. The different local temperature gradient, concentration of silicon vapor and silicon oxide vapor, and also the substrate surface condition were suggested to be responsible for the versatile morphologies of the products.

Reversibly Switching Silver Hierarchical Structures via Reaction Kinetics

Here we report a study on controllable synthesis of hierarchical silver structures via regulating reaction kinetics. Silver particles with various morphologies are synthesized by a solution-based reduction approach at the addition of amino acids. The amino acid is used to coordinate with silver ions to slow down the reduction of silver ions. With the increase of glycine concentration, the morphologies of silver particles switch from dendrites, to flowers and to compacted spheres, which is attributed to the decrease of reaction rate as a result of the coordination. Three more amino acids are examined and confirms the role of reaction kinetic in shaping silver particles. Furthermore, by increasing the concentration of the reductant, the silver morphologies change from compact spheres to loose flowers as a result of the increase of reaction rate. Therefore the silver hierarchical structure can be reversibly switched by reaction kinetics. The silver particles synthesized are tested for surface enhanced Raman scattering (SERS) property and the dendritic particles present a remarkable SERS activity. This study shows that reaction kinetics is a powerful tool to tune hierarchical structures of silver particles, which is expected to be transferable to other material systems.

Growth and characterization of dumbbell-shaped MgO nanowhiskers

Abstract By depositing Mg vapor generated by carbothermal reduction onto boron powder, dumbbell-shaped MgO nanowhiskers were obtained. The diameters of these whiskers and balls are 50–150 nm and 1.4–2 μm, respectively. EDS analysis results reveals that the compositions of whiskers are Mg, O and small amount of B and Si. While the compositions of balls are Si, O and small amount of Al, B, C, Mg, K, Ca. SEM and TEM observation indicates that interfaces between balls and whiskers are very smooth. Experimental result shows that whiskers should grow in advance, and then balls grew by depositing silicon oxide and other vapor species onto the surface of these whiskers. The presence of silicon oxide was considered to play a key role in the formation of this peculiar morphological product.

Fabrication of decorated MgO crystalline fibers

By depositing Mg vapor generated via carbothermal reduction on boron powder in the presence of different additives, dumbbell-like MgO nanofibers, NaCl particle-decorated MgO nanofibers and camphor tree stalk-like MgO fibers were produced. SEM, TEM and EDS analysis showed that the additives of Si and NaCl deposited in the sites of stacking faults in fiber, which resulted in the growth of different morphologies of decorated fibers.