Subcritical damping of S-A step energy on Si(001) vicinals by lowering terrace stress
Résumé
Si(001) vicinals with monoatomic steps present an alternation of (1 x 2) and (2 x 1) terraces and S-A and S-B steps. Our calculations, by using MEAM potential, show a surface stress difference between neighbouring terraces. By both energy minimization and lowering terrace stress, we observe a deformation transfer between neighbouring terraces. The deformation lowers the stress of the higher stress terrace. But the deformation logarithmically varies with step-step distance L. In theory of energy minimization, the great difficulty is to accept, or not, the logarithmic divergence for large L. We show that the logarithmic variation with L is accompanied by the vanishing of the S-A step energy. The terrace-terrace deformation transfer disappears when the S-A step energy is reduced to zero. This explains the large roughness of the step S-B in experiment, because it is perpendicular to S-A. This paper clearly confirms that surface stress and surface energy are different quantities to be considered in equilibrium of surfaces. The minimization of the surface energy is accompanied by the lowering of the surface stress for the higher stress terrace. Consequently, this terrace is contracted, while the other terrace is expanded in order to render the sum of equilibrium deformations over the period including the two terraces nul. (C) 2015 Elsevier B.V. All rights reserved.