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SiC is the ideal material for RF devices and power devices. Resistance-heated physical vapor transport method is considered a promising way to grow large size (especially 6 and 8 inch) SiC crystals due to its temperature uniformity. In recent years, the introduction of new technique such as the use of porous graphite improved the SiC crystal quality and yield, while there are only a few relatively comprehensive studies on its mechanism. This paper made comprehensive research on the influence of porous graphite on SiC growth system by means of numerical simulation. The crystal growth experiments under numerical simulation conditions have been carried out accordingly. The numerical simulation results show that the porous graphite raises the temperature and temperature uniformity within the powder area, which can strengthen the sublimation of powder. The temperature difference between the powder and the seed inside the crucible is improved and a greater growth driving force is obtained. The effect of decrease of the re-crystallization at powder surface has also been proved. Besides, the porous graphite improves the flow stability across the whole growth process, and assures a stable crystal growth. The C/ Si ratio has been increased under the influence of porous graphite, and thus reduces the probability of phase transition. The crystal shape has also been improved. The subsequent growth experiments verified the conclusions of numerical simulations such as the improvement of flow uniformity, decrease of poly-type transition probability, improvement of crystal shape, etc. The results of this paper have practical significance on comprehending the effecting mechanism of porous graphite and improving the SiC crystal growth conditions for better crystal quality. [ABSTRACT FROM AUTHOR]

With non-toxic nature, wide bandgap, and thermal stability, Sn-based perovskite materials have become a hot topic in the field of perovskite solar cell research. In this paper, the SCAPS-1D software was used to construct the FTO/TiO2/CH3NH3SnI3/Spiro-OMeTAD/ Ag perovskite solar cells and the performances of the constructed cells were calculated. The effects of the thickness of absorption and hole buffer layer, the surface defects between hole buffer layer and absorption layer, and the operating temperature on the device performance were studied, then the device performance was optimized. The photoelectric conversion efficiency of the optimized perovskite solar cell is 30. 955%. The theoretical analysis suggests a new approach for enhancing the photoelectric conversion efficiency of perovskite solar cells. [ABSTRACT FROM AUTHOR]

In this paper, the evolution of thermocapillary convection in melt of half-floating zone liquid bridge under the condition of zero gravity was studied by means of numerical simulation. Under the condition that the height L of the liquid bridge and the temperature difference ΔT remain unchanged, the aspect ratio (Ar = L / R) of the liquid bridge can be changed by changing the radius R of the liquid bridge. The convection in the liquid bridge exhibits various flow characteristics with the change of the aspect ratio Ar. Thermocapillary convection is in a three-dimensional steady state when Ar = 0. 5. The flow field and temperature field change from the steady state mode to the unsteady periodic multi-frequency oscillation mode satisfying the frequency doubling relationship (f n = nf 1) when Ar = 1. When Ar = 1. 25, the velocity oscillation frequency of the monitoring point increases, showing a smaller amplitude oscillation mode, and the temperature oscillation disappears. [ABSTRACT FROM AUTHOR]