Role of missing rows in the adsorption of Te on Si(001)

We have studied the atomic structure of up to one monolayer of Te on Si(001 ) using first-principles total-energy calculations. A low amount of Te atom s deposited on Si(001) is adsorbed on top of symmetric Si dimers. This conf iguration is preferred to adsorption on cave sites between Si dimers. For t he one-monolayer coverage the most favorable structure corresponds to adsor ption of Te atoms on near bridge sites. The (1x1) symmetry is broken by a s mall shift of Te atoms from perfect bridge positions, giving rise to a slig htly disordered surface. This is a way to relieve the strain due to the siz e difference between Te and Si atoms. Missing Te rows is another way, and i t is the one observed experimentally. We have calculated the atomic structu re of the surface when one out of every five Te rows is missing. Two possib ilities were examined. The most favorable corresponds to missing Te rows or thogonal to original Si rows. In all cases, our results are in good agreeme nt with experimental data. [S0163-1829(99)01031-0].