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artículo con referato
"Catalytic effect of carbon in shaping Si(1 1 1) surfaces"
C.-C. Fu, J.-J. Métois, J.P. Astier, A. Saúl and M. Weissmann
Surf. Sci. 563(1-3) (2004) 48-56
This paper presents an experimental and theoretical study of the effect of carbon in the formation of pits on silicon surfaces. Experimentally we have searched for the best conditions to produce a homogeneous density of single shape pits in Si(1 1 1) using a C2H4 source. The result is that two steps are required: a rapid “precursor” process at relatively low temperature and high gas pressure and a longer “etching” step at higher temperature and lower gas pressure. Pits obtained with the two step process have a triangular shape that is not only due to the surface symmetry but also to the presence of carbon. In fact, we have found that the holes still remain after complete carbon removal by further annealing, but their shape becomes circular.
Motivated by these experimental results we investigated theoretically the beginning of the pit formation mechanism using a tight binding method. We have performed two types of calculations: structural optimization of Si slabs containing carbon at 0 K and high temperature molecular dynamics simulations. We have found that carbon atoms prefer to occupy substitutional sites near the surface rather than adsorbed or interstitial sites. Their presence weakens some Si-Si bonds near the surface and therefore induces surface silicon atoms to move away from their equilibrium position and to diffuse on the surface. This may start the pit formation. We have also found that there is an attractive interaction between substituted carbon atoms and surface vacancy clusters, which must certainly influence the pit growth.
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