RESUMO
The decay of mounds about a dozen layers high on the Si(111)-(7x7) surface has been measured quantitatively by scanning tunneling microscopy and compared with analytic predictions for the power-law dependence on time predicted for a step-mediated decay mechanism. Conformably, we find an exponent 1/4 associated with the (3D) decay of the mound height and exponent 1/3 associated with the (2D) decay of top-layer islands. Using parameters from a continuum step model, we capture the essence of the kinetics. Qualitative features distinguish these mounds from multilayer islands found on metals.
RESUMO
We study the behavior of steps in a vicinal face with drift of adsorbed atoms (adatoms) by an external field. When the drift is in the downhill direction and its velocity exceeds critical values, v(x)(c) and v(y)(c), the vicinal face is linearly unstable to long-wavelength fluctuations parallel and/or perpendicular to the steps. By taking the continuum limit of the step-flow model, we derive an anisotropic Kuramoto-Sivashinsky equation with propagative terms, which describes the motion of an unstable vicinal face. Its numerical solution shows ripples or a zigzag pattern expected from the linear analysis. Nonlinearity becomes important in the late stage and, depending on the condition, various patterns are formed: regular step bunches, a hill and valley structure tilted from the initial step direction, mounds, and a chaotic pattern.
