Monodispersed Cr cluster formation by plasma-gas-condensation

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Abstract
Nanometer-sized Cr clusters in the size range of 7.6–13 nm have been produced by a plasma-gas-condensation-type cluster deposition apparatus, which combines a grow-discharge sputtering technique with an inert gas condensation technique. We have studied influences of the Ar gas pressure, PAr, and the Ar gas flow rate, VAr, on the size distribution of Cr clusters by transmission electron microscopy. Monodispersed Cr clusters are formed at both low PAr and low VAr. At low PAr, Cr clusters nucleate and grow only in the liquid-nitrogen-cooled growth region, and the deposition rate is rather low. At high PAr, on the other hand, a large amount of Cr clusters are formed even near the sputtering source, and the nucleation and growth occur over a wide region between the sputtering source and the growth region. Under this condition, the deposition rate is relatively high. Consequently, the formation mechanism of the monodispersed clusters is similar to that of monodispersed colloidal particles: The nucleation and growth processes are definitely separated and the coagulation of growing particles is prohibited. In the present experiments, these conditions are effectively attained by using a carrier gas flow and liquid-nitrogen-cooling of the cluster growth region.

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