HYPERSONIC PLASMA PARTICLE DEPOSITION OF NANOSTRUCTURED SILICON AND SILICON-CARBIDE

A new process for the production of nanostructured materials, hyperson ic plasma particle deposition (HPPD), is experimentally investigated. In HPPD, vapor phase precursors are injected into a flowing plasma gen erated by a DC arc. The plasma under goes a supersonic expansion into a deposition chamber, with the pressure dropping across the nozzle fro m similar to 5000 Torr to similar to 2 Torr; Ultrafine particles nucle ate in the nozzle, accelerate in the hypersonic free jet downstream of the nozzle, and deposit by inertial impaction onto a temperature-cont rolled substrate. The low particle residence time (similar to 50 mu s) minimizes particle agglomeration, while the high particle deposition velocity (similar to 1 km s(-1)) results in the formation of a partial ly consolidated coating. We have characterized silicon, carbon and sil icon carbide coatings produced by injecting vapor-phase SiCl4 and hydr ocarbon (CH4 and C2H2) precursors into an Ar-H-2 plasma. The silicon c oatings are polycrystalline, while the carbon and silicon carbide depo sits are amorphous and hydrogenated. Both Si and SiC coatings had nano structured regions with grain sizes on the order of 20-30 nm, reasonab ly close to the diameters of impacting particles measured using an ext ractive aerosol probe coupled to a scanning electrical mobility analyz er. (C) 1998 Elsevier Science Ltd. All rights reserved.