Symmetry and stability of solitary dimer rows on Si(100)

Metastable, monolayer-high structures as narrow as one dimer row and as long as the substrate's terrace width decorate antiphase boundaries on Si(100) following 225 eV Xe bombardment. On the basis of tunneling microscope STM observations and first-principles calculations, we propose that the bonding toplogy of a buckled dimer row on an antiphase boundary is responsible for the metastability of this ``zipper'' structure, and in turn for the preferential nucleation of dimer rows on antiphase boundaries during growth.