STRESS RELIEF FROM ALTERNATELY BUCKLED DIMERS IN SI(100)

First-principles calculations of the surface stress for the c(4 x 2) b uckled-dimer reconstruction of the clean Si(100) surface reveal a sign ificant relief of a compressive contribution to the stress in the dire ction parallel to the dimer rows, and thus a decrease of the stress an isotropy, when compared to similar calculations for 2 x 1 reconstructi ons. We show that the mechanism involved is not just the buckling but its alternation along a dimer row. Calculations using the c(4 x 2) mod el for the clean surface are also in close quantitative agreement with the experimentally measured excess tensile stress of the As-covered s urface.