Abstract
In the keV-energy regime, the scattering of krypton ions off a copper sample has been studied. In addition to the broad energy spectrum arising from multiple-collision scattering, the energy distributions of the backscattered ions exhibit prominent peaks at energies where single-collision (SC) scattering peaks are expected. Such SC peaks were shown to be absent in Sn – Mo/Ru scattering, systems of similar mass ratio and thus similar kinetics. The present Kr on Cu results allow for a comparison to a simulation package as SRIM. An important difference found between the present experiment and the predictions of SRIM is that the SC contribution is observed to decrease with scattering angle, whereas SRIM predicts this contribution to be constant. The intensity of the experimental SC peaks, though much weaker than in the SRIM simulations, may be used as markers to improve SRIM in its description of low-energy heavy particle scattering off surfaces.
Highlights
In a recent systematic study [1] of the scattering of keV-energy tin ions from Mo and Ru, materials commonly used in extreme ultraviolet (EUV) optics [2,3], a remarkable observation made was the absence of a single-collision (SC) peak in the energy spectra of the scattered ions
Within a binary collision approximation the kinetics of single scattering is the same for Kr–Cu as it is for Sn–Mo
While for Sn ion scattering on Mo no single-collision (SC) peaks show up in the energy distribution of scattered ions, in the present study we find that they do for the lighter system of Kr ions on Cu
Summary
In a recent systematic study [1] of the scattering of keV-energy tin ions from Mo and Ru, materials commonly used in extreme ultraviolet (EUV) optics [2,3], a remarkable observation made was the absence of a single-collision (SC) peak in the energy spectra of the scattered ions. The results led to the conclusion that most likely the SC peak prominently showing up in the SRIM predictions in contrast to the experiments is due to SRIM-related causes such as ignoring any inter action above the surface and using a fixed distance between consecutive collisions. In any kind of binary collision approximation one expects a SC signature to show up in the energy spectra of scattered particles. A complicating factor in a direct comparison between experiment and SRIM is that SRIM treats all particles as neutral, while experimentally it is most convenient to use ionic beams and to detect scattered charged particles and their energies by means of electrostatic analysers. The ToF measurements at a fixed angle supported the finding in the ion spectra that no clear SC peak is detected in the energy spectra of the scattered Sn particles
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