Properties of fast carbon cluster microbeams produced with a tapered capillary

We study the transmission properties of fast cluster ions (Cn+ (n = 2–4) with velocities ranging from 0.89 to 1.79 a.u.) through a single tapered capillary with an outlet diameter of 13.7 μm. We investigate the projectile-velocity dependence of the transmission fraction from the measurements of transmitted particle energy spectra. It is found that the non-fragmentation fraction of C2+ projectiles increases with decreasing velocity, indicating that fragmentation occurs mainly via close collisions with the surfaces of the capillary wall. For Cn+ (n = 2–4) ions with the same incident velocity, the cluster-size dependence of the non-fragmentation fraction shows even–odd alternation, implying that the fraction includes contributions from stable clusters surviving the grazing scattering process at the capillary surface. We also find that the angular distribution of transmitted particles is narrower for cluster projectiles compared with atomic projectiles.