Metastable phase of symmetric dimers on Si(001)

Abstract

The reconstruction of the Si(001) surface is reexamined by using first-principles density-functional calculations. We find that a symmetric dimer structure in which symmetric dimers are alternately displaced up and down along the dimer rows is more favored by 21 meV/dimer than the conventional symmetric dimer structure where all the dimers have an identical height. In this metastable p(2x2) structure, the up and down symmetric dimers accompany the lateral movements of the second-layer atoms: i.e., on the two sides of the dimer the second-layer atoms bonding to the up (down) dimer move equally toward (outward) each other by 0.15 Angstrom. With this predicted symmetric dimer structure we discuss the symmetric dimer phase observed in a recent low-temperature scanning tunneling microscopy experiment.