One of the techniques for nanofabrication is the gas cluster ion beam processing. Due to the unique interactions between the
cluster ions and surface atoms, modification of the surface becomes possible for surface smoothing applications at micro-/nanolevels.
The recent technological developments enable control of energy and size of the clusters, which makes the gas cluster ion
beam processing a favorable tool in surface engineering. The reactive cluster ion beams can be effectively used in etching of photonic
crystals. The smoothing effect by the cluster is derived from the horizontal moment of many surface atoms via impacts. Although
significant progress has been made toward the development of this technology, research into the extension of its application to
various areas is still in progress.