R.P. Andres, "Inelastic Energy Transfer in Particle/Surface Collisions," Aerosol Sci. & Tech., 23, 40 (1995).

J. D. Bielefeld, R.G. Osifchin, and R. P. Andres, "Comparison of the Physical Properties of Cluster-Based and Vacuum-Evaporated Thin Films, " Mat. Res. Soc. Symp. Proc., 355, 359 (1995).

W. Mahoney and R. P. Andres, "Aerosol Synthesis of Nanoscale Clusters Using Atmospheric Arc Evaporation, " Materials Science & Eng. A260, 160 (1995).

We have been involved for a number of years in developing aerosol methods for producing ultrafine metal particles. The approach we have taken is to evaporate the metal from a liquid pool, entrain the metal atoms in a hot inert gas carrier, and then rapidly mix in cold inert gas to cause nucleation and growth of small metal particles. We are able to produce particles of nearly uniform size with controlled diameters in the nanometer range by this approach. We can collect these particles by two methods: (1) expand the gas stream and impinge the particles onto a surface (because they are so small they stick with high probability) and (2) scrub the particles out of the gas stream with a liquid spray containing a surfactant species and collect them as a stable colloid. Our major thrust with this research is to synthesize individual clusters and take advantage of their unique electrical and optical properties, but we also have some experience depositing films. A couple of years ago we participated in an applied research program at Oak Ridge that was part of their Centers for Manufacturing Technology. The idea was to produce ultrasmooth mirrors by depositing nanometer gold clusters onto polished substrates. Our technology proved unsuitable that flaked off of the walls of our aerosol reactor and were incorporated into the gold film and (2) the film was not well bonded to the substrate, probably due to the fact that the particles impinged onto the substrate with a relatively low velocity.

Although we have never tried to make Cr of Al particles, I am confident that we can produce them with no difficulty. We have recently developed a source using a atmospheric pressure DC arc. The particles are produced as a dense aerosol in an argon carrier gas and the small source we have built in our lab is capable of producing up to a hundred grams per hour of particles with diameters in the nanometer size range. I believe our technology could be used to produce a continuous film in two ways: (1) if the particles in the aerosol were charged using a corona discharge and the aerosol nozzle was electrically biased, relative to the substrate, I believe that we could collect essentially all the particles and they would produce a strongly bonded film, or (2) if the particles were scrubbed from the aerosol using the proper surfactant, I believe that we could produce a metal colloid, which depending on the surfactant, might be used either as a electroplating bath or a metal paint.

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