T. NANDI
56
processes give rise to a surface potential at the entry sur-
face through which ions loose energy as a function of the
charge state. This fact is another interesting point in the
energy loss of highly charged slow ions in addition to the
fact as reported very recently that the unitary-convolu-
tion-approximation energy-loss theory explain experi-
mental data well for high to intermediate energies, how-
ever, significant deviations occur at low energies [22].
4. Conclusions
We have established that the surface stopping power is
directly proportional to the charge state of the ion.
Recently, Grüner et al. [23] theoretically suggested that
the bulk energy loss depends on the charge state due to
the charge exchange processes. Interestingly, the charge
exchange takes a role in generating a potential as well at
the entry surface. The stopping power due to the surface
potential varies directly with the charge state. Further,
charge state dependent surface energy loss is more pro-
minent than the charge state dependent bulk energy loss
for highly charged slow ions. We strongly believe that
the energy loss mechanism of highly charged slow ions
in solids can be understood better by including a suitable
surface potential with the existing theories. The renewed
mechanism will help us to understand numerous appli-
cations such as, thin-film growth, sputtering, plasma wall
interaction in fusion devices, soft-landing, space shuttle
glow, detectors, etc.
5. Acknowledgements
The author thanks Dinesh Shukla for his technical help
during this work and T. Schenkel, S. A. Khan, P. Kumar
for their comments on the manuscript.
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