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Gas Dynamic Considerations for Performance of Nanocluster Deposition System

Numerical simulations of the gas flow and cluster velocities in a UHV compatible nanocluster deposition system were performed in order to understand the problems of optimization of the cluster deposition rate. Skimmer geometry was initially identified as the key factor in defining the cluster velocity: our modeling suggested that using skimmers of a greater internal angle should lead to higher cluster velocities. However, the experimental results revealed only a minor enhancement in the cluster velocity. The lack of an effect of the change in skimmer geometry was attributed to the decelerating effect of the background gas in the mass selection chamber. When this effect was taken into consideration, the simulation results described the observed cluster behavior to a much better degree. The experiments and simulations both show a general trend for the cluster velocity to decrease as the cluster size is increased, for all the skimmer geometries used.

cluster velocity, UHV sputtering, mass selection, skimmer, Navier-Stokes equations, DSMC, AgAu.

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