We have measured surface stresses on clean Si(111) 7×7 by comparing this surface to a reference surface on which gallium atoms are adsorbed under UHV conditions. Stresses are determined by optically measuring the macroscopic strain induced in thin samples. We find a surface stress of 2.37 eV/(1×1 cell) for Si(111) 7×7, and a stress in the range 0.90–1.09 eV/(1×1 cell) for the Si(Ga) (111) superlattice associated with one monolayer Ga coverage. Comparison with theory suggests that our technique will be a powerful tool to measure equilibrium stresses in atomically clean surfaces.

• Received 14 September 1989

DOI:https://doi.org/10.1103/PhysRevLett.64.1035