Ge-Induced Reversal of Surface Stress Anisotropy on Si(001)

Using scanning tunneling microscopy, we show that the intrinsic surface stress anisotropy on Si(001) can be tuned through zero and reversed in sign by controlling the coverage of Ge adatoms. Values of the stress anisotropy, obtained by measuring the step separation distributions, range from 1.0 eV $/(1\times 1$ cell) for the clean surface to $-0.9\mathrm{}$ eV $/(1\times 1$ cell) for two monolayers of Ge. Absolute values of stresses in directions along and perpendicular to the dimer rows are also extracted.