Xiaoshan Wu

Understanding the formation of ultrafine spinel CoFe2O4 nanoplatelets and their magnetic properties

Cobalt ferrite (CoFe2O4, CFO) nanoplatelets with a rhomboidal shape were synthesized through a facile hydrothermal route using a very low concentration precursor at low temperatures. The effects of reaction temperature and time on the morphologies as well as the sizes of the products were systemically investigated. The as-synthesized CFO nanocrystals showed a special rhomboidal shape with crystal growth along the (111) direction. The very low concentration precursor plays an important role in forming CFO nanocrystals with such special shape and ultrafine size. The single-phase CFO nanoplatelets synthesized at 180u2009°C with size of 17u2009nm present high saturation magnetization (79.7u2009emu/g) and high coercivity (3100u2009Oe). The preparation conditions have significant effects on the crystal size and shape, magnetization and relaxation activation of the CFO nanoplatelets.

Two reversible ferroelectric phase transitions in diisopropylammonium perchlorate

Two reversible first-order phase transitions were found in an improper ferroelectric, diisopropylammonium perchlorate (DIPAP), due to the crystal symmetry transforming from P21/c to P1 at 296 K, and subsequently to P21/c at 338 K in the heating process, similar to the structural transitions of the first discovered ferroelectric, Rochelle salt. The dielectric behavior shows two remarkable dielectric step-like increases at 296 K and 338 K, characteristic of improper ferroelectrics. The mechanism of the two improper ferroelectric phase transitions involves the transformation of diisopropylammonium cations and perchlorate anions, as confirmed by X-ray diffraction and Raman spectroscopy.

An active metallic nanomatryushka with two similar super-resonances

The optical properties of a simple metallic nanomatryushka (nanosphere-in-a-nanoshell) with gain have been investigated theoretically. The spaser (surface plasmon amplification by stimulated emission of radiation) phenomena can be observed at two critical wavelengths in the active metallic nanomatryushkas. With increasing the gain coefficient of the middle layer, a similar super surface plasmon (SP) resonance is first found at the ω−+|1 mode of the active nanoparticles and then breaks down. With further increasing the gain coefficient, another similar super-resonance occurs at the ω−−|1 mode. The near-field enhancements in the active nanomatryushkas also have been greatly amplified at the critical wavelengths for ω−+|1 and ω−−|1 modes. It is further found that the amplifications of SPs in the active Ag–SiO2–Au nanoshell are strongest in four kinds of nanoshells and hence the largest near fields. The giant near-field enhancement can greatly enhance the Raman excitation and emission.

Investigation of the mechanism of the Ag/SiNx firing-through process of screen-printed silicon solar cells

The mechanism of a Ag/SiNx firing-through process in the manufacture of multi-crystalline silicon solar cells has been studied. The effect of firing temperature on the electrical performance of screen printed multi-crystalline silicon solar cells, with a conversion efficiency of up to 17.2%, has been investigated. It is revealed that with an increase in firing temperature both the series resistance and shunting resistance of the solar cells decrease monotonically, while the reverse leakage current rises gradually. SEM and EDX are used to study cross-sections of the Ag/Si interface under the fingers. It is revealed that hexagonal like silver crystallites are formed due to the chemical reaction between SiNx and Ag2O in the Ag paste during the firing process, through which the direct interconnection between the emitter and silver particles contained in the paste is achieved. The physical process of the firing-through is discussed. Moreover, the diffusion coefficients at different temperatures are obtained by fitting the diffusion profiles.

Structure and magnetic properties of melt-spun (Nd0.625Ni0.375)85Al15 ribbons

A metallic glass (Nd0.625Ni0.375)85Al15 with ferromagnetism at low temperatures is presented in the following paper. The structure, thermal stability, and magnetic properties have been investigated. The result demonstrates that the amorphous alloy has a certain glass-forming ability and forms a kind of spin glass below its Curie temperature.

Tunneling resonances and Andreev reflection through an interaction quantum dot coupled with two half metals and a superconductor

We investigate the transport characteristics of electrons through a quantum dot with two semi-infinite half metal (HM) leads and a superconductor by the use of the equivalent single-particle multichannel network technique that takes into account the multilevel structure and the Coulomb interactions on the dot, pairing potential on the superconducting side and the exchange field on the HM side. The transport properties depend on the interplay between the Coulomb blockade effect and Andreev reflection (AR). It is found that at finite temperatures and small bias the current versus the gate voltage exhibits a series of peaks, due to the AR, depending on the resonances controlled by the charging energy and level spacing of the dot. In the case of single occupation for the quantum dot, the current of the system can be enhanced or suppressed by the exchange field.

Structural, magnetic, and electronic transport properties of (Sr0.9Ca0.1)3Ru2O7 single crystal

We have studied the structural, magnetic, and electronic transport properties of (Sr0.9Ca0.1)3Ru2O7 using single crystals grown by a floating-zone technique. The structure analysis by Rietveld refinements reveals that the Ca substitution for Sr intensifies the structure distortion; the rotation angle of the RuO6 octahedron increases. This structure change tunes magnetic and transport properties dramatically. The magnetic ground state switches from an itinerant metamagnetic state for Sr3Ru2O7 to a nearly ferromagnetic state for (Sr0.9Ca0.1)3Ru2O7. The Fermi liquid behavior occurs in Sr3Ru2O7, but is suppressed in (Sr0.9Ca0.1)3Ru2O7. These results strongly suggest that lattice, spin, and charge degrees of freedom are strongly coupled in this system. The band width narrowing caused by the structure distortion should be responsible for the enhancement of ferromagnetic correlations and the change of transport properties.

Spin oscillation of a quantum dot embedded in a ferromagnetic ring with two interacting electrons

The spin oscillation of a quantum dot embedded in a ferromagnetic ring is investigated. We suppose that there are two electrons with an opposite spin in the system, which is a sort of excited state of the system that includes ferromagnetism. By numerically solving the time-dependent Schrodinger equations for the many-body states, the spin oscillations of a quantum dot are derived and studied in detail. It is found that the amplitude and frequency of the oscillations depend sensitively on the exchange energy of ferromagnetic lead, the coupling strength between the dot and ferromagnetic lead, the gate voltage, and Coulomb repulsion energy of quantum dot. We show also that the magnetic moment on the dot can be controlled by tuning the exchange field of ferromagnetic lead.