Guifeng Chen

Electronic and magnetic structure of Fe3O4/BiFeO3 multiferroic superlattices: First principles calculations

Fe3O4/BiFeO3(001) superlattices comprising multiferroic BiFeO3 and ferrimagnetic half-metallic Fe3O4 have been investigated using first principles calculations. Two models were simulated: Model (a) contains the interfaces of Fe(A)−BiO and Fe2O4(B)−FeO2; Model (b) contains the interfaces of Fe(A)−FeO2 and Fe2O4(B)−BiO. The magnetization enhances 13% and 8% for models (a) and (b) due to the interfacial bonding between Fe(A)/Fe(B) and Bi atoms, respectively. The much larger enhancement in model (a) is ascribed to the facts that the Fe(A) atoms are surrounded by relatively less O atoms than Fe(B) in model (b), which increases the hybridization between Fe(A) and Bi atoms. The calculated results suggest that the number of oxygen atoms at the interfaces plays an important role on determining the interfacial coupling strength. Meanwhile, the interfacial bonding also affects the spin polarization of the Fe3O4 at the interface.

Interfacial engineering of MoS2/TiO2 hybrids for enhanced electrocatalytic hydrogen evolution reaction

Herein, we show that the synergistic effect between MoS2 and TiO2 enhances the hydrogen evolution reaction (HER) performance of their hybrids, which is tunable via interface engineering. Among several interfaces, MoS2/TiO2–H complexes exhibit the best HER activity. The observed Tafel slope of 66.9 mV/dec is well in range of previous literature reports, suggesting a Volmer–Heyrovsky mechanism. Enhanced activities were attributed to abundant active sites at the interfaces, as well as improved charge transfer efficiency. Our results emphasize the roles that interfaces play in enhancing the HER activities of MoS2-based heterogeneous catalysts.

Geometric distortion and spin-dependent electronic structure of C6H6-adsorbed Fe3O4(001): A first-principles study

The electronic structure of C6H6/Fe3O4(001) interfaces has been investigated by the density functional theory. It is found that a weaker interaction exists between C6H6 and Fe3O4(001) in the adsorption models by comparing with the previous studies. The electronic states of C6H6 show a slight spin-splitting, which has the potential applications as a molecular spin filter. Meanwhile, a valence transition from Fe3+ to Fe2+ occurs in one model, which reduces the magnetic moment. The transition can be ascribed to the geometric distortion induced by C6H6 adsorption, which depicts the re-interaction process among Fe3O4(001) atoms. Furthermore, the high spatial spin polarization of C6H6/Fe3O4(001) appears with the increased density of states at EF. The calculated results offer a new mechanism to manipulate the interfacial electronic structure through C6H6 adsorption, which has the potential applications in organic spintronic devices.

Simulation of self-developed vertical HVPE system for growth of aluminium nitride

Abstract To understand the mechanism of aluminium nitride (AlN) film growth is of great importance for its potential applications. In this paper, we investigate the growth behaviour of the AlN film by using the computational fluid dynamics program FLUENT. It is found that the gas flow has a great impact on the temperature field. By equipping the aluminium boat area with a graphite ring and adjusting the heating power appropriately, the desired temperature field can be achieved. The simulation also shows that the V/III can have a significant impact on the deposition behaviour. With a V/III of 10, the trend of the curve is abnormal which is significantly different from the other curves. The distance between the inlet and the substrate is changed. It is found that with the increasing distance, AlN deposition rate decreases and the uniformity becomes better. Besides, when the operating pressure is changed, it is found that the operating pressure can also greatly affect the temperature field.

Zinc oxide nano- and micro-crystals synthesised by co-precipitation and hydrothermal process

Abstract Micro-sized zinc oxide (ZnO) crystals with different shapes (spindle-like, flower-like and rod-like) were successfully synthesised by a simple co-precipitation and hydrothermal reaction using zinc chloride, Pluronic F127 (PF127) and NH3.H2O as raw materials. The results from X-ray diffraction and scanning electron microscopy show that the morphology and size of the ZnO were strongly dependent on the content of NH3.H2O, and the aspect ratio of ZnO crystals is also controlled by PF127. The presence of enough hydroxyl ions (OH−) can polish and modify the morphology of ZnO in the hydrothermal system, but the hexagonal cylinder rods disappear in a strong basic environment. As the content of PF127 increases, the aspect ratio of the ZnO rods also increases. If the amount of PF127 is excessive, the average aspect ratio is reduced. Systematic reactions in the presence of different environments were conducted to control the formation of various well shaped ZnO crystals.