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The effects of gas flow on particle growth in silane RF discharges in a plasma chemical vapor deposition (PCVD) reactor with a shower-type powered electrode are studied using an in situ two-dimensional polarization-sensitive laser-light-scattering method. Particle growth depends on both the production of short-lifetime radicals and the loss of neutral clusters in the radical production region around the plasma/sheath boundary near the powered electrode. Gas flow of a velocity above about 6 cm/s is effective in suppressing particle growth because of increase in loss of neutral clusters. Moreover, particles larger than 120 nm in size that flow to the plasma/sheath boundary near the grounded electrode are found to pass through the sheath. This implies that such particles may deposit on film surfaces for PCVD reactors with the shower-type powered electrode.

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We coated the glass beads with TiO 2 thin films by a rotating cylindrical plasma chemical vapor deposition (PCVD) reactor and applied the TiO 2 −coated glass beads to remove NO and SO 2 in a dielectric barrier discharge-photocatalyst hybrid (DBD-PH) process. The thickness of TiO 2 thin films on glass beads was controlled precisely by changing the deposition time. The UV light generated from the plasma discharge in DBD-PH process activates the TiO 2 photocatalyst on glass beads and the NO and SO 2 removal efficiency are removed more easily by the reactive radicals generated from plasma reactions and TiO 2 photocatalyst. We found the optimum thickness of TiO 2 thin film on glass beads was about 600 nm to remove NO and SO 2 by the DBD-PH process. The NO and SO 2 removal efficiencies increase as applied peak voltage, residence time or pulsed frequency increases or as initial NO and SO 2 concentration decreases. ■ INTRODUCTIONIn 1972, Fujishima and Honda discovered the photocatalytic splitting of water on TiO 2 e1ectrodes, 1 which became the beginning of a new era in heterogeneous photocatalysis. Since then, many research efforts in understanding the fundamental processes of photocatalysis and also in enhancing the photocatalytic efficiency of TiO 2 have been made extensively by chemists, physicists, material scientists, and chemical engineers. Some related studies are also important for energy renewal and energy storage in energy crisis. 2−4 Recently, heterogeneous photocatalysis has been most actively applied to environmental cleanup. Especially, the application of TiO 2 -based photocatalysts is quite potential for the total destruction of organic compounds in polluted air. The size and shape of TiO 2 thin film affect the photocatalytic properties which are important for the industrial application of photocatalyst.There are several methods to prepare TiO 2 thin films with high surface area such as the sol−gel method, 5 sputtering, 6 spray pyrolysis, 7 atomic layer deposition, 8 and pulsed laser deposition. 9 The plasma chemical vapor deposition (PCVD) process can be used to prepare TiO 2 thin films uniformly onto particles with high surface area. 10,11 The removal of pollutants such as SO 2 and NO x (including NO and NO 2 ) from industrial processes and vehicle exhausts is important and urgent for environmental pollution control. Many researchers suggested that the nonthermal plasma technology can be one of the most effective methods for simultaneous removal of SO 2 and NO x from flue gas at relatively low energy cost. 12−18 The nonthermal plasmas have a low gas temperature, but a high electron temperature and can be produced by several electrical discharge methods (pulsed corona discharge, barrier discharge, and dc discharge) 19−24 or electron beam irradiation. 6,25 The majority of electrical energy goes into the production of energetic electrons rather than into gas heating. The energy supplied to the discharge is directed preferentially to electron impact ionization and dissociation of the background gas to pro...