Monodispersed Cr cluster formation by plasma-gas-condensation

Nanometer-sized Cr clusters in the size range of 7.6-13 nm have been produc ed by a plasma-gas-condensation-type cluster deposition apparatus, which co mbines a grow-discharge sputtering technique with an inert gas condensation technique. We have studied influences of the Ar gas pressure, P-Ar, and th e Ar gas flow rate, V-Ar, on the size distribution of Cr clusters by transm ission electron microscopy. Monodispersed Cr clusters are formed at both lo w P-Ar and low V-Ar. At low P-Ar, Cr clusters nucleate and grow only in the liquid-nitrogen-cooled growth region, and the deposition rate is rather lo w. At high P-Ar, on the other hand, a large amount of Cr clusters are forme d even near the sputtering source, and the nucleation and growth occur over a wide region between the sputtering source and the growth region. Under t his condition, the deposition rate is relatively high. Consequently, the fo rmation mechanism of the monodispersed clusters is similar to that of monod ispersed colloidal particles: The nucleation and growth processes are defin itely 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 regio n. (C) 1999 American Institute of Physics. [S0021-8979(99)03701-9].