Weiwen Wang

Technical Challenges and Progress in Fluidized Bed Chemical Vapor Deposition of Polysilicon

Abstract Various methods for production of polysilicon have been proposed for lowering the production cost and energy consumption, and enhancing productivity, which are critical for industrial applications. The fluidized bed chemical vapor deposition (FBCVD) method is a most promising alternative to conventional ones, but the homogeneous reaction of silane in FBCVD results in unwanted formation of fines, which will affect the product quality and output. There are some other problems, such as heating degeneration due to undesired polysilicon deposition on the walls of the reactor and the heater. This article mainly reviews the technological development on FBCVD of polycrystalline silicon and the research status for solving the above problems. It also identifies a number of challenges to tackle and principles should be followed in the design of a FBCVD reactor.

Effect of Boundary Layers on Polycrystalline Silicon Chemical Vapor Deposition in a Trichlorosilane and Hydrogen System

This paper presents the numerical investigation of the effects of momentum, thermal and species boundary layers on the characteristics of polycrystalline silicon deposition by comparing the deposition rates in three chemical vapor deposition (CVD) reactors. A two-dimensional model for the gas flow, heat transfer, and mass transfer was coupled to the gas-phase reaction and surface reaction mechanism for the deposition of polycrystalline silicon from trichlorosilane (TCS)-hydrogen system. The model was verified by comparing the simulated growth rate with the experimental and numerical data in the open literature. Computed results in the reactors indicate that the deposition characteristics are closely related to the momentum, thermal and mass boundary layer thickness. To yield higher deposition rate, there should be higher concentration of TCS gas on the substrate, and there should also be thinner boundary layer of HCl gas so that HCl gas could be pushed away from the surface of the substrate immediately.

Novel modification method of yellow pigment and its potential application in e-ink

Abstract Yellow SiO2/Hansa pigment composite particles were fabricated in an aqueous solution by electrostatic self-assembly method, in which cetyltrimethylammonium bromide was used as a coupling agent to give the yellow pigment particles a positive charge. Then, a thin shell of SiO2 was coated during the process of hydrolysis of Na2SiO3 to enhance the optical and mechanical properties as well as the charge load of the pigment particles. The product was characterised by transmission electron microscopy and thermogravimetric analysis, which showed that the SiO2 walls of the composite particles were compact. Fourier transform infrared spectroscopy showed the component of the composite particles. Zeta potential measurement proved that the SiO2/pigment particles had a higher charge load, and ultraviolet–visible spectra showed that the SiO2/pigment particles had a better optical property. Therefore, this type of composite particle had the merits of low density and strong durability in environments. The response behaviour of the microencapsulated electronic ink of the composite particles has been measured. This novel method is expected to produce various inorganic/organic nanocomposite particles with potential application in the fields of electronic paper and other material sciences.

Novel approach for fabrication of hollow metal compound nanospheres

Abstract A novel process to fabricate rigid hollow spheres of less than 100 nm is described in the current paper. These hollow nanospheres were fabricated in an emulsion via an electrostatic deposition approach to synthesise a metal compound shell around wax particles. The wax cores were then removed via the calcination of composite spheres under a process of intermittent temperature raising to produce metal compound hollow spheres. The shell/core composite spheres were characterised by transmission electron microscopy, thermogravimetric analysis, X-ray powder diffraction and Fourier transform infrared spectroscopy, while the hollow spheres were characterised by transmission electron microscopy and atomic force microscopy. The hollow core size and the metal compound shell thickness can be easily varied over significant size ranges.

Computational fluid dynamics study on the anode feed solid polymer electrolyte water electrolysis

A steady-state two-dimensional model for the anode feed solid polymer electrolyte water electrolysis (SPEWE) is proposed in this paper. Finite element procedure was employed to calculate the multicomponent transfer model coupled with fluid flow in flow channels and gas diffusion layers and electrochemical kinetics in catalyst reactive surface. The performance of the anode feed SPEWE predicted by this model was compared with the published experimental results and reasonable agreement was reached. The results show that oxygen mass fraction increases because of the water oxidation when water flows from the import to the export on the anode side. On the cathode side, hydrogen mass fraction varies little since hydrogen and water mix well. The flux of water across the electrolyte increased almost linearly with the increase of the applied current density. Since the ohmic overpotential loss increasing as the solid polymer electrolytes’ thickness increasing, the performance of the anode feed SPEWE with Nafion 112, 115, 117 decreases at the same applied current density.