Yanfang Zhao

Thermal management performance of bent graphene nanoribbons

The models of graphene nanoribbons (GNRs) with angles 0°, 30°, 60°, 90° and 120° were constructed to investigate the thermal conduction by using the reverse non-equilibrium molecular dynamics method. A substantially negative correlation between the thermal conductivity and the bent angle shows a nonlinear decline from 0° to 90°. It also shows that there is a little increase from 90° to 120° due to the edge effect. To weaken the edge effect, the nitrogen doping method is adopted to recompose the bent GNRs. The results show that it is effective for the thermal management, and a strict monotonous relationship between the thermal conductivity and bent angle can be obtained. In the meantime, an interesting phenomenon is observed that the GNRs with edge modification by N-doping can get a much better thermal conduction than original GNRs without edge modification. We can understand the physical mechanism by phonon analysis for these GNRs. The investigation implies that we can change the thermal conductivity of GNRs by design by N-doping.

Approach on the Life-Prediction of Solder Joint for Electronic Packaging Under Combined Loading

A life-prediction approach of solder joints for electronic packaging under combined loading is presented in this paper. The deformations of solder joints are calculated under vibration and thermal cycling loading based on the finite element method. The calculated results are used as the boundary condition of the multi-axial loading to investigate the strain and stress of the solder joints. Then the life of solder joints can be evaluated by using a linear damage superposition approach. The result reveals that the life of solder joints can be divided into three regions according to the vibration amplitude at the same temperature: the life of solder joints in the first region is affected by creep damage; the life of solder joints in the second region is greatly influenced by the combined loading damage; the life of solder joints in the third region is impacted by the fatigue damage. The trend of the simulation results approximately agrees with the experimental results of other researchers.

Approach using the electrical structure and optical properties of aluminium-doped zinc oxide for solar cells

Aluminium-doped zinc oxide (AZO) is attracting a continuously increasing amount of attention because of its potential as a solar cell material. To analyze the effect of the concentration of doped Al (set as x) on AZO, we investigated properties such as band structure, electronic conductivity, absorption and reflectivity under different doping concentrations by using a first-principles method based on density functional theory (DFT). The results demonstrated AlxZn1−xO (for x = 0.0625, 0.125, or 0.1875) to be an n-type degenerate semiconductor. The band gaps as well as electric conductivities decreased as x was increased. Meanwhile, the real part e1(ω) and imaginary part e2(ω) of dielectric function were investigated. The e2(ω) and e1(ω) were only slightly different with those of pure ZnO and positioned at higher energy direction in the concentrations of 0.0625 and 0.125, while yielded lower energy directions as x increasing to 0.1875. The reflectivity was found to be lowest for x = 0.125. This result may provide a theoretical reference for solar cells based on Al-doped n-type ZnO.

INVESTIGATION FOR MOLECULAR ATTRACTION IMPACT BETWEEN CONTACTING SURFACES IN MICRO-GEARS

The aim of this research work is to provide a systematic method to perform molecular attraction impact between contacting surfaces in micro-gear train. This method is established by integrating involute profile analysis and molecular dynamics simulation. A mathematical computation of micro-gear involute is presented based on geometrical properties, Taylor expression and Hamaker assumption. In the meantime, Morse potential function and the cut-off radius are introduced with a molecular dynamics simulation. So a hybrid computational method for the Van Der Waals force between the contacting faces in micro-gear train is developed. An example is illustrated to show the performance of this method. The results show that the change of Van Der Waals force in micro-gear train has a nonlinear characteristic with parameters change such as the modulus of the gear and the tooth number of gear etc. The procedure implies a potential feasibility that we can control the Van Der Waals force by adjusting the manufacturing parameters for gear train design.