Out-of-plane STM displacement measurements and evaluation of elastic fields in iron silicide islands on silicon

Elastic deformations have been discerned with β-FeSi₂ islands grown on Si(111)7×7 by STM. Anisotropic mismatch between the β-FeSi₂ and the surface is -5.3% and +1.4% along FeSi₂[101]∥Si[112] and FeSi₂[010]∥Si[110] respectively. STM images of these islands show threefold symmetry and significant deformations of the surface (the normal to the surface deviates by several degrees from the average substrate normal), both on the islands and around them. Larger islands exhibit smaller deformation, and when deposited on a surface step the island normal tilts towards the upper terrace. Using finite element method in the framework of linear elasticity, the deformations of small islands were simulated, taking into consideration the surface stress. Best agreement with the experimental deformation is obtained when the islands are made of three domains rotated by 120^∘{} with respect to each other. The calculations of the deformation agree qualitatively with the measured displacements, and reproduce the deviation of the surface normal. The quantitative difference between the elastic theory and the experimental results may be utilized to gain additional information about the mechanical properties at the surface in the nm scale. The measured deformation of the island also enabled the calculation of the long-range stress fields it generates.