 The jet of clusters passes through differential pumping apertures into a region of high vacuum (1e-8 atmospheres) where the clusters are ionized by collisions with energetic electrons.The ionized clusters are accelerated electrostatically to very high velocities, and they are focused into a tight beam.The GCIB beam is then used to treat a surface — typically the treated substrate is mechanically scanned in the beam to allow uniform irradiation of the surface.