Wang Jian-Yuan

Leakage Current and Photovoltaic Properties in a Bi2Fe4O9/Si Heterostructure

A heterostructure composed of a Bi2Fe4O9 film and an n-type Si substrate is fabricated. The characteristics of leakage current density versus electric field are investigated and the leakage current density is about 6×10−6 A/cm2 at an electric field of 200 kV/cm at 300 K. A strong photovoltaic effect is observed when the heterostructure is exposed to a laser pulse with a wavelength of 532 nm and a power of 6 mW/mm2. It is found that the peak photovoltages initially increase with decreasing temperature, followed by a decrease at T < 210 K. These results reveal that the heterostructure is a promising candidate for photovoltaic devices that are compatible with Si integrated circuits.

Effect of rotating magnetic field on the solidification microstructures of Pb-Sn alloys

The influence of the rotating magnetic field (RMF) on the solidification process of Pb-Sn binary alloys is studied by comparing the solidification microstructures under the common condition and RMF condition. It is found that the RMF can completely eliminate the gravity induced macrosegregation, and result in dendrite fragmentation and promote solute diffusion velocity. These differences are regarded as the effect of complicated melt flow caused by RMF. Moreover, when the content of the primary phase is small, many spherical microstructures form under the RMF condition. The analyses indicate that these special microstructures are likely the conjunction action of melt flow and concentration and temperature field uniformity caused by RMF.

Dendrite to symmetry-broken dendrite transition in directional solidification of non-axially oriented crystals

In this paper, the morphological transition from dendrite to symmetry-broken dendrite is investigated in the directional solidification of non-axially-oriented crystals using a quantitative phase-field model. The effects of pulling velocity and crystal orientation on the morphological transition are investigated. The results indicate the orientation dependence of the symmetry-broken double dendrites. A dendrite to symmetry-broken dendrite transition is found by varying the pulling velocity at different crystal orientations and the symmetry-broken multiple dendrites emerge as a transition state for the symmetry-broken double dendrites. The state region during the transition can be well characterized through the variations of the characteristic angle and the average primary dendritic spacing.

The Rectifying Property and Photovoltaic Effect in the La0.8Ag0.2MnO3/SrTiO3-Nb Heterojunction

A p—n junction composed of Ag+-doped manganite La0.8Ag0.2MnO3(LAMO) and Nb-0.5wt%-doped SrTiO3(STON) was fabricated using the pulsed laser deposition method. The heterojunction exhibits a good rectifying property over a wide temperature range from 20 to 390 K. The minimum diffusion potential and the lowest leakage currents under different negative voltages both occur at 320 K, which is around the metallic-insulator transition temperature of the LAMO film. The photovoltage rises with the decreasing temperature and wavelength of the laser beam. Under the illumination of a 473 nm laser beam, the photovoltage grows as the light power increases and seems to be saturated at about 300 mW. The maximum Voc is 0.76 V, which is close to the diffusion voltage.