Relevance of surface roughness to tungsten sputtering and carbon implantation

Tungsten sputtering and carbon layer growth by carbon ion bombardment has been investigated by experiments with thin W layers. Preparation of tungsten layers by magnetron deposition allows one to control the surface roughness by choosing appropriate substrates. The fluence dependent elemental composition of the bombarded surface has been studied in situ with ion beam analysis allowing separate measurements of the areal densities of tungsten and carbon atoms. In contrast to weight-loss measurements, this approach is much less affected by nonuniformities of the incident flux and therefore allows one to determine the dependency of the principal physics processes on input parameters with much higher accuracy. After bombardment, ex situ scanning electron microscopy has been used for the qualitative understanding of the evolution of the surface topography with increasing fluence. The experiments clearly show the influence of surface roughness, leading to increased tungsten sputter yields and strongly reduced carbon implantation rates. Comparison of the experimental results with simulations by the Monte Carlo code TRIDYN has verified the validity of the kinematic description for the interaction of carbon ions with mixed carbon-tungsten surfaces. At the same time, chemical effects, such as carbide formation, can be neglected in comparison with the contribution of surface roughness to the dynamics of sputtering and implantation. (c) 2006 American Institute of Physics.