Surface growth processes induced by AFM debris production. A continuum picture

Recent ultra-high vacuum (UHV) scratching atomic force microscopy (AFM) experiments showed the formation of small clusters, larger aggregates or regular patterns on the surface being scanned. In this paper, we suggest a theory that should capture the basic mechanisms that produce the formation of such structures. Such cluster structures, generally self-organized in regular structures, are mainly produced by the flux of adatoms generated by the AFM tip stripping off adatoms during the continuous passage of the probe tip on the surface being analysed. We assume that surface diffusion is the dominant transport mechanism of mass and a nonequilibrium thermodynamics framework for the self-organized growth process is developed. The accurate knowledge of such growth structures is important for two main reasons: it is possible to have an indirect measurement of the incidence of the wear basic mechanisms involved during the AFM scratching test while analysing the structures generated and the patterned structures produced could be used as a base (precursor factor) for mature surface growth processes. Despite granular structure of atom-by-atom nature of the debris, our theory uses a continuum approach for the description of the surface growth induced during the wearing passage of the probe tip.