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K. Dobes, M. Hinterhofer, K. Tichmann, A. Golczewski, T. Schwarz-Selinger, W. Jacob, F. Aumayr:
"The evolution of a hydrogen-depleted surface layer on a-C:H during bombardment with N₂⁺ Ions";
Poster: 37th EPS Conference on Plasma Physics, Dublin/Ireland; 22.06.2010; in: "Book of Abstracts of the 37th EPS Conference on Plasma Physics", (2010), S. P2.125.

During the interaction of energetic ions with hydrocarbon surfaces a modified surface
layer builds up with different properties compared to the bulk film [1]. Bond breaking within
the ion penetration depth modifies the carbon network and leads to a hydrogen-depleted layer.
In steady state the top layer is dynamically reformed and its underlying bulk becomes thinner.
Up to now key parameters like the sputtering yield could only be detected for that steady state
erosion but were not accessible for the transient phase. Here we report on the first
experimental measurements of the sputtering yield during this transient phase. A highly
accurate quartz crystal microbalance (QCM) has been developed at the technical University of
Vienna [2], and has been utilized to monitor the mass change of a plasma deposited,
polymerlike amorphous hydrogenated carbon thin film (a-C:H) in-situ and in real-time during
the bombardment with N2
+ ions at 460 K for various energies. With the known mass density
the sputtering yield can be directly inferred.
When the ion beam is switched on a sputtering yield is measured that is 6 times higher
than the expected yield. Starting with a virgin plasma deposited a-C:H surface the sputtering
yield decreases exponentially with fluence. The steady-state value that is reached after a
fluence of several 1015 ions/cm2 corresponds very well with sputtering yields observed before
[3]. It was also found, that the evolution of the sputtering yield over fluence corresponds
nicely to an exponential decrease with a constant offset. Since the steady-state sputtering
yields do not show a significant variation over the kinetic energy of the projectile, chemical
sputtering is likely to be the major contribution to the total mass removal.
References
[1] A. von Keudell, W. Jacob and W. Fukarek, Appl. Phys. Lett. 66, 1322 (1995)
[2] A. Golczewski, K. Dobes, G. Wachter, M. Schmid and F. Aumayr, Nucl. Instr. and Meth. B 267, 695
(2009)
[3] M. Schlüter, C. Hopf and W. Jacob, New Journal of Physics 10, 17 (2008)