Rationale: Collisions of clusters with solids have become important, especially in the fields of thin film growth or surface processing such as etching or topography smoothing. However, it is not clear how much of the theory or model used in macroscopic collisions is appropriate for the consideration of microscopic collisions.
Methods: We considered a cluster ion consisting of thousands of argon atoms as a continuum and examined the possibility that classical mechanics could analyze its collision with metals. A mass spectrometric analysis of the dissociated ions of argon cluster ions (Ar(+)1500) in collision with five different metals was performed.
Results: In the mass spectra at an incident kinetic energy per atom of less than 10 eV, no monatomic argon ions (Ar(+)) were observed regardless of the prominence of Ar2(+) or Ar3(+). The branching ratio for the ion yield Ar2(+)/∑Arn(+) (n ≥ 2), representing the dissociation rate, was found to be significantly different for each metal. The relationship between the branching ratio and the impulsive stress caused by the collision of the cluster ion with metal was investigated. The impulsive stress was calculated based on the Young's modulus and density of the clusters and metal, under the assumption that the collision was initially elastic. As a result, the magnitude correlation in the branching ratio corresponded well with that in the impulsive stress.
Conclusions: This result is important in that it indicates that collision of nano-sized clusters with solids at low energies can be modeled using elastic theory. Furthermore, the result suggests a new method for evaluating a physical property of a material such as its Young's modulus.
Copyright © 2014 John Wiley & Sons, Ltd.