7×7 Reconstruction of Ge(111) Surfaces under Compressive Strain

Abstract

We have discovered a correlation between lateral compressive strain in an elemental material and the reconstructed state of its surface. We studied continuous films of pure Ge epitaxially grown on Si(111) substrates. The in-plane lattice parameter varies continuously with film thickness while the surface symmetry changes from $c2\ifmmode\times\else\texttimes\fi{}8 \mathrm{to} 7\ifmmode\times\else\texttimes\fi{}7$. The results indicate an important role of lateral compressive stress in the 7\ifmmode\times\else\texttimes\fi{}7 reconstruction.