Historical milestones and future prospects of cluster ion beam technology

Abstract

Development of technology for processing of surfaces by means of gas cluster ion beams began only about a quarter century ago even though fundamental research related to generation of gas clusters began much earlier. Industrial applications of cluster ion beams did not start to be explored until commercial equipment was first introduced to the ion beam community in around 2000. The technology is now evolving rapidly with industrial equipment being engineered for many diverse surface processing applications which are made possible by the unique characteristics of cluster-ion/solid-surface interactions. In this paper, important historical milestones in cluster ion beam development are described. Present activities related to a wide range of industrial applications in semiconductors, magnetic and optical devices, and bio-medical devices are reviewed. Several emerging new advances in cluster beam applications for the future are also discussed.

Ultrafast physical sputtering of GaN by electrosprayed nanodroplet beams

“…Conversely nanodroplets transfer their kinetic energy within a few monoatomic layers, and the resulting high energy densities deposited near the surface enhance the sputtering by non-linear collision cascades and thermal evaporation [9]. Nanodroplet impact proceeds similarly to that of gas cluster ions [10], although the much higher charge to mass ratio of electrosprayed drops enables higher impact velocities for given projectile diameter and acceleration voltage.…”

Features of formation of gas cluster ion beams

“…Accelerated gas-phase cluster ion beams are one of the promising methods of treatment and modification of surface on nanoscale [1,2]. The interaction of high-energy cluster (a complex comprised of hundreds or thousands of particles) with the solid surface cardinally differs from the traditional case of collisions of monomer ions with the solid.…”

“…It has been ascertained that modification of materials can only be enabled using intensive flows with cluster sizes from dozens up to thousands of particles per cluster, with an energy of up to 30 keV, which can ensure the radiation dose of 10 15 e10 17 particles/ cm 2 of the surface being treated [1]. Gas-jet method potentially allows one to produce cluster beams of practically any size and various compositions [7e9].…”

The Effect of the Molecular Mass on the Sputtering of Si, SiC, Ge, and GaAs by Electrosprayed Nanodroplets at Impact Velocities up to 17 km/s

“…In addition, electrosprayed drops are naturally charged near the Rayleigh limit (Fernandez de la Mora 1996), or maximum charge that a stable drop can hold, and therefore can be accelerated by an electrostatic field to the highest possible kinetic energy for a given diameter (solid particles can hold a higher net charge, but a suitable charging method has not been developed yet). These two properties make electrospray a unique particle source for beam research and applications, one that enables the investigation of a projectile size range inaccessible until now: the problem of energetic impact has traditionally been separated in two fields, the hypervelocity impact of macroprojectiles (Davison 2008) and the energetic impact of atomic (Sigmund 1969), molecular, and gas cluster ions (Yamada 2014). The intervening projectile diameter range, between the 3 or 4 nm of the larger gas cluster ions and the micron-sized projectiles accelerable by guns (Walsh et al 1993), has remained experimentally unexplored due to the lack of a suitable projectile source.…”