Model system for controlling strain in silicon at the atomic scale

Strain induced by antiphase boundaries (APBs) in the Si(111) 2 x 1 surface is investigated using scanning tunneling microscopy (STM), laterally resolved scanning tunneling spectroscopy (STS), and density functional theory (DFT). We determine the structure of all identified APB reconstructions and show that a band shift of states close to the Fermi energy leads to the previously observed electronic contrast. The orientation of the band shift and the observed movement of APBs within the surface are explained by surface strain resulting from the excess free energy of the boundary. We demonstrate that the location of APBs and their associated strain can be precisely manipulated, making them an ideal model system to study and control strain at the atomic scale.