ELASTIC INTERACTION BETWEEN MODULATED STEPS ON A VICINAL SURFACE

We study in this paper the elastic interaction between modulated steps , in both homoepitaxy and heteroepitaxy. The influence of this interac tion on the step fluctuation spectrum is discussed. There are two impo rtant consequences that emanate from our analysis, i) in the homoepita xy case the elastic interaction favors a modulated step profile. Howev er, the gain in the elastic interaction does not generally overcome th e line tension effect and ii) more importantly, for the heteroepitaxia l case the elastic contribution to the energy modulation is of the sam e order as that of the line tension part. Elasticity results in an eff ective line tension (but singular), which may be either positive or ne gative depending on the phase shift between two adjacent steps. This a nalysis shows that the elastic contribution for non-zero wavevectors s hould be incorporated in any statistical theory of fluctuating steps, if one wants to account properly for experimental observations. We poi nt out similarities between this problem, and others arising in quite different systems. We suggest that, in general, tensorial (dipolar and multipolar) interactions between lines, surfaces, etc, of electrostat ic, magnetic, hydrodynamic, etc. nature, should lead to the same gener ic behaviour.