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Gas dynamic optimization of the atomic 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. The 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. This assumption can be tested by using a pump with greater pumping speed or by reducing the size of the skimmer aperture (initial value was d = 3.25 mm). Indeed in experiments with skimmer diameter d = 1 mm, the scattering effect of background gas was decreased by an order of magnitude and the cluster velocity significantly increased, in accordance with model predictions.

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

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