Mingang Zhang

Chemical bath deposition of Cu2O quantum dots onto ZnO nanorod arrays for application in photovoltaic devices

Cu2O quantum dots (QDs) decorated ZnO nanorod arrays (ZNAs) were fabricated using a facile hydrothermal method followed by a chemical bath deposition (CBD) process. The surface morphology, crystal structure and photovoltaic behaviors of the heterostructure films were investigated. The results indicate that the Cu2O QDs decorated ZNAs can be used as a good light absorber improving the visible spectral absorption. In addition, the photo-induced electrons can easily transfer to ZnO, leading to an increase in the photovoltaic performance. When the number of CBD cycles was 10, an optimal photovoltaic performance could be obtained under simulated sunlight illumination (AM 1.5G, 100 mW cm−2) with a photocurrent of 3.21 mA cm−2, an open circuit photovoltage of 0.65 V and a conversion efficiency of 1.17%. Moreover, for improving the photovoltaic stability, a protective layer was prepared on the Cu2O QDs by a simple process of heat treatment in ambient air at 100 °C for 2 h. The results demonstrate that the passive CuO layer could be an effective protective layer to increase the photovoltaic stability.

Solution combustion synthesis and enhanced gas sensing properties of porous In2O3/ZnO heterostructures

Self-assembled porous In2O3/ZnO heterostructures were prepared by a low temperature solution combustion synthesis method, and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The results indicate that the as-synthesized porous In2O3/ZnO heterostructures were constructed from a large number of In2O3 and ZnO nanoparticles and showed high gas sensing performance toward Cl2. Compared with pure ZnO and other heterostructure sensors, the porous In2O3/ZnO heterostructures with an appropriate molar ratio of In2O3 : ZnO exhibited highly enhanced gas sensing performances toward Cl2. An extremely high sensitivity of 6610 could be reached when exposed to 50 ppm Cl2 at 370 °C; also, In2O3/ZnO heterostructures showed high selectivity toward Cl2. Furthermore, the gas sensing mechanism was discussed.

Microstructure and Magnetic Properties of NdFeB Films through Nd Surface Diffusion Process

Ta/Nd/NdFeB/Nd/Ta films were deposited by magnetron sputtering on Si (100) substrates and subsequently annealed for 30 min at 923 K in vacuum. It was found that the microstructure and magnetic properties of Ta/Nd/NdFeB/Nd/Ta films strongly depend on the NdFeB layer thickness. With NdFeB layer thickness increasing, both the grain size and the strain firstly reduce and then increase. When NdFeB layer thickness is 750 nm, the strain reaches the minimum value. Meanwhile, both the in-plane and perpendicular coercivities firstly drastically increase and then slowly decrease with NdFeB layer thickness increasing. The highest in-plane and perpendicular coercivities can be obtained at NdFeB layer thickness of 750 nm, which are 21.2 kOe and 19.5 kOe, respectively. In addition, the high remanence ratio (remanent magnetization/saturation magnetization) of 0.87 can also be achieved in Ta/Nd/NdFeB (750 nm)/Nd/Ta film.

Large magnetoresistance in highly textured Mn44.7Ni43.5Sn11.8 melt spun ribbons

Highly textured Heusler alloy Mn44.7Ni43.5Sn11.8 ribbons were prepared by melt spinning. The magnetoresistance (MR) properties were evaluated by the magnetic field perpendicular to the ribbon surface with the field up to 30 kOe. A large MR (about 25%) with a lower magnetic field (10 kOe) was obtained at 276 K. Due to the rapid solidification. The ribbons with a specific texture can get a large MR twice than polycrystalline alloys at the same magnetic field. The highly textured Mn?Ni?Sn melt spun ribbons may be broadly applied in magnetic memory and as temperature and magnetic sensors as well.

Effects of thickness and annealing condition on magnetic properties and thermal stabilities of Ta/Nd/NdFeB/Nd/Ta sandwiched films*

Ta/Nd/NdFeB/Nd/Ta sandwiched films are deposited by magnetron sputtering on Si (100) substrates, and subsequently annealed in vacuum at different temperatures for different time. It is found that both the thickness of NdFeB and Nd layer and the annealing condition can affect the magnetic properties of Ta/Nd/NdFeB/Nd/Ta films. Interestingly, the thickness and annealing temperature show the relevant behaviors that can affect the magnetic properties of the film. The high coercivity of 24.1 kOe (1 Oe = 79.5775 A/m) and remanence ratio (remanent magnetization/saturation magnetization) of 0.94 can be obtained in a Ta/Nd(250 nm)/NdFeB(600 nm)/Nd(250 nm)/Ta film annealed for 3 min at 1023 K. In addition, the thermal stability of the film is also linked to the thickness of NdFeB and Nd layer and the annealing temperature as well. The excellent thermal stability can be achieved in a Ta/Nd(250 nm)/NdFeB(600 nm)/Nd(250 nm)/Ta film annealed at 1023 K.

Magnetoresistance and exchange bias in high Mn content melt-spun Mn46Ni42Sn11Sb1 alloy ribbon*

Highly textured Heusler alloy Mn46Ni42Sn11Sb1 ribbons were prepared by melt spinning. The annealed high Mn content Mn46Ni42Sn11Sb1 ribbon cross-section microstructure, crystal structure, martensitic transformation (MT), and magnetoresistance (MR) properties were investigated. The MR in the annealed ribbon was assessed by the magnetic field direction perpendicular to the ribbon surface with the magnetic field up to 30 kOe. The large negative value of 25% for MR was obtained at 244 K. The exchange bias (EB) effects of the as-spun and annealed ribbons were investigated. After annealing, the EB effects have been improved by about 25 Oe at the temperature of 50 K. The magnetizations have increased approximately by 10% more than the as-spun ribbon.

Effect of Sm-doping on the morphology and magnetic properties of radio frequency magnetron sputtered Ni-Mn-Ga films

Ni55.5Mn21Ga23.5 and Ni54Mn22Ga23Sm1 films were prepared by radio frequency (RF) magnetron sputtering. The effect of Sm dopant on the morphologic and magnetic properties of Ni55.5Mn21Ga23.5 films was investigated. Sm doping can refine the particle size of the films from 100 to 60 nm, and further grain growth is not occurs even after annealing at 1073 K for 3.6 ks. Compared to Ni55.5Mn21Ga23.5 films, Sm-doped Ni54Mn22Ga23Sm1 films are easier to be magnetized and have a lower martensitic transformation temperature. In addition, the Curie temperature can also be adjusted, decreasing from 350 to 325 K after Sm doping. Martensitic transformation is not observed in the Sm-free films, which is close to the Curie temperature in the Sm-doped films, giving rise to the overlap of the structural and magnetic transition temperatures.