We are investigating ballistic impact assembly of nanoparticles to form a new class of materials for superhard coatings and micromolded MEMS parts. Nanoparticles are generated by dissociating vapor-phase reactants injected downstream of a thermal plasma and expanding the resultant flow through a converging nozzle into a low-pressure chamber. The nanoparticle-laden gases achieve hypersonic velocities due to the pressure difference between the reaction region (450 torr) and the low-pressure chamber (～2 torr). Particles are deposited by one of two processes: (a) by placing a substrate 20 mm downstream of the flow, which results in a bow shock at the substrate and high impact velocities (calculated to be over 2000 m/s for a 20 nm SiC particle): termed as high-rate deposition, (b) by focusing the particles into a tight beam (width of ～35 μm) using aerodynamic lenses, and subsequent impaction on a translating substrate: termed as focused beam deposition. Thus far, nanoparticle deposits consisting of combinations of Si, Ti, C and N have been explored.
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