Abstract
The alkaline-earth metal adsorption on Si(001) has attracted much interest for finding a proper template in the growth of high-κ and crystalline films. Up to now on the flat Si(001) surface with double domains and single-layer steps, the adsorbed Ba atoms are known to induce the 2×3 structure through removing two Si dimers and adding a Ba atom per unit cell in each domain. In the present investigation, the Si(001)-4° off surface with DB steps and single domains has been employed as a substrate and the reconstruction at the initial stage of Ba adsorption has been investigated by scanning tunneling microscopy and synchrotron photoemission spectroscopy. On this vicinal and single domain terrace, a novel 3×2 structure rotated by 90° from the 2×3 structure has been found. Such a 3×2 structure turns out to be formed by adding a Ba atom and a Si dimer per unit cell. This results from the fact that the adsorbed Ba2+ ions with a larger ionic radius relieve tensile stress on the original Si dimers exerted by the rebonded atoms at the DB step.
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