Size effects of gas cluster ions on beam transport, amorphous layer formation and sputtering

Size effects of gas cluster ions on beam transport or collisions with residual gases, for amorphous layer formation and for sputtering effects were studied using a size-selected GCIB system. A GCIB releases its constituent atoms by collisions with residual gases, and as a result, it loses its acceleration energy. The number of released atoms is determined by the energy per atom and the cohesive energy of gas. By controlling the cluster size and electron ionization energy to carry out low-energy irradiation, formation of amorphous layer or crater-like damages on surfaces can be reduced. The dependence of the sputtering yield of Au on cluster sizes shows that a linear relationship exists between the number of Au atoms sputtered by one Ar atom and the energy per atom. It is shown that the cluster size, which defines the energy per atom, is the most important parameter affecting beam transport, low-damage processing and sputtering with GCIB.