Adatom effective charge in morphology evolution on Si 111/ surface

To clarify the effective adatom charge, an ultra-high vacuum reflection electron microscopy has been applied to study the morphology evolution of stepped Si 111.surface under resistive heating of the studied crystal. The only temperature range from 830 to f10008C was under consideration, when the regular steps were stable during sample heating by the current in the step-up direction, while the step bunches were created by the step-down current. The current direction dependence of step bunching was changed to opposite one during sub-monolayer gold adsorption on the Si 111.surface. Namely, the adsorbed gold atoms were responsible for transformation of regular steps into bunches or step bunches into uniform spaced steps for the step-up or step-down direction of the heating current, respectively. Such step behavior suggests a negative polarity of the effective charge of silicon adatoms on the gold adsorbed surface instead of positive one on the clean surface. The metal induced ‘wind’ MIW.model for the inversion of the charge sign was proposed to explain qualitatively the observed experimental results. By measuring the minimal amount of adsorbed gold atoms needed to exhibit the bunching instability, the qualitative dependence of the effective silicon adatom charge on the temperature was evaluated. q1998 Elsevier Science B.V. All rights reserved.