Ben Li

Photoluminescence Properties of β-SiC Nanoparticles by Electric-Pulses Discharge in Liquid-Phase Compound

β-SiC nanoparticles have been synthesized by electric pulses discharge (EPD) in Hexamethyl disilane. Dependence of photoluminescence (PL) from the samples with air-annealing are presented. Emission bands around 400 nm and 470 nm are observed at room temperature. The corresponding PL properties and possible mechanisms are discussed. The 400 nm peak may be result from the atom excess defect center at the surfaces of β-SiC nanocrystallites, while the 470 nm peak is believed to be related to the defects created in the interface boundary between β-SiC nanocrystallites and amorphous SiO2.

The Side Effect of Spin Precession and Quantum Interference in a Four-Terminal Nano Device with Rashba Spin-Orbit Coupling

We propose a four-terminal nano device made of quantum wires with Rashba spin-orbit (SO) coupling. In each terminal there are several independent channels formed with quantum wires. The coherent transmission of electrons in such a nano system is a combined effect of quantum interference and spin precession. When defining two opposite terminals as source and drain leads, the charge and spin currents in channels of other two terminals exhibit spatial distributions which reflect the competition between spin precession and quantum interference during the tunneling of electrons. Since the four-terminal nano device is geometrically simple for the moving paths of charge and spin, our investigation may shed some light on the basic physical picture on this issue.

The Coherent Transport Properties of Electrons in a 4-Terminal Nano Device with Rashba Spin-Orbit Coupling in the Presence of Magnetic Field

We investigate the coherent transport properties of electrons in a side terminal of a four-terminal nano device made of quantum wires with Rashba spin-orbit (SO) coupling in the presence of magnetic filed. We numerically calculate the charge and spin conductances dependent on SO coupling strength and reduced flux. The results imply that the coherent transport in this device is determined by the interplay of Rashba SO coupling and magnetic filed. For specific values of magnetic flux and SO coupling strength, a complete blocking can take place. It also shows that there is a de-blocking phenomenon induced by the interplay of magnetic flux and SO coupling. Such a 4-terminal and multi-channel structure may provide more options of controlling methods for the coherent charge and spin transport.

Synthesis of MoO3 Nanostructures by a Solution Method

Synthesis and characterization of microsheets, microrods, microflowers and microspheres of orthorhombic phase molybdenum oxide (MoO3) were reported. The reaction between ammonium molybdate and hydrochloric acid was used to prepare MoO3 microstructures and followed by annealing in air at 400oC for 2h. The combined techniques of X-ray powder diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM) and Raman spectroscopy were used to investigate the effect of pH and additives on the as-prepared samples. Results indicated that they were of microsize. With alcohol as an additive, the sample was plate-like MoO3 at pH=2.5, and it was a mixture of MoO3 and MoO3•0.55H2O of irradiative corolla at pH=1. The sample obtained by hydrothermal was MoO3 flowers. Meanwhile, when silane coupling agent was introduced as the additive, the sample was MoO3 spheres.

Study on Dielectric Relaxation in BiFeO3/Bi3.25La0.75Ti3O12 Film

BiFeO3 (BFO) film is considered as relaxor ferroelectric film with a leakage current, and Bi3.25La0.75Ti3O12 (BLT) film is regarded as ferroelectric film with a leakage current. Maxwell- Wagner (M-W) theory has been used to study the dielectric relaxation behavior of BiFeO3 (BFO)/Bi3.25La0.75Ti3O12 (BLT) films grown on Pt/Ti/SiO2/Si substrate. Results show that the characteristics of BFO film significantly affect the dielectric relaxation behavior of the BFO/BLT film. The theoretical results agree well with the experimental data when the temperature is above 400K. It is inferred that the polycrystalline orientation of BFO film leads to the presence of disorganized polar nanoregions (PNRs) in BFO film. And BFO film exhibits relaxation characteristics at high temperatures.

The Ferroeletricity of Pb(Zr,Ti)O3 Films Grown on Compressive Substrates

The modified Landau-Devonshire thermodynamic theory has been used to investigate the ferroelectricity of Pb(Zr0.7, Ti0.3)O3 film grown on MgO substrate. A set of gradient thermal stresses is imposed on the films. The stress-temperature diagram, the spontaneous polarization and the dielectric susceptibility at 25°C on the stress were computed. Structure transitions of first order can be driven by the stress. The mean of out-plane spontaneous polarization and dielectric susceptibility on the temperature were also predicted.

Synthesis of MoO3 Nanorods by a Solution Method

MoO3 nanorods were synthesized by a solution method with stirring and ultrasound. The formation temperature of MoO3 nanorods were studied by XRD. The particle-size and morphology were characterized by TEM. The diameter of nanorods was ca. 60nm.

Study on the Dielectric Properties of CaCu3Ti4O12 Ceramics by the Brickwork Layer Model

A brickwork layer model was used to investigate the dielectric properties of CaCu3Ti4O12 ceramics. It is equivalent to Debye model under the Maxwell- Wagner-type mechanism. Arrhenius relation could be obtained by the assumption that the grains in the CaCu3Ti4O12 ceramic are of semiconductivity. The dependence of the dielectric constant on the grain size and temperature were well fitted by the model.