Atomic arrangement and electron band structure of Si(1 1 1)-ß-√3 x √3-Bi reconstruction modified by alkali-metal adsorption: ab initio study.

Using ab initio calculations, atomic structure and electronic properties of Si(1 1 1)[Formula: see text]-Bi surface modified by adsorption of 1/3 monolayer of alkali metals, Li, Na, K, Rb and Cs, have been explored. Upon adsorption of all metals, a similar atomic structure develops at the surface where twisted chained Bi trimers are arranged into a honeycomb network and alkali metal atoms occupy the [Formula: see text] sites in the center of each honeycomb unit. Among other structural characteristics, the greatest variation concerns the relative heights at which alkali metals reside with respect to Bi-trimer layer. Except for Li, the other metals reside higher than Bi layer and their heights increase with atomic number. All adsorbed surface structures display similar electron band structures of which the most essential feature is metallic surface-state band with a giant spin splitting. This electronic property allows one to consider the Si(1 1 1)[Formula: see text]-Bi surfaces modified by alkali metal adsorption as a set of material systems showing promise for spintronic applications.

Effect of Na adsorption on the structural and electronic properties of Si(111)√3 × âˆš3-Au surface.

Adsorption of ∼0.1 ML of Na onto the Si(111)√3 × âˆš3-Au surface held at 300 °C has been found to induce pronounced changes in its structural and electronic properties. Domain wall networks, characteristic of the pristine surface, are removed completely, leading to the formation of a highly ordered homogeneous surface. The original atomic arrangement of the Si(111)√3 × âˆš3-Au is preserved and Na atoms occupy T4 adsorption sites at the centers of surface Si trimers. Upon Na adsorption, a pronounced metallic S1 surface-state band develops. It is characterized by a large spin splitting (momentum splitting at the Fermi level Δk∥ = 0.027 Å(-1) and consequent energy splitting ΔEF = 110 meV), large electron filling (on the order of 0.5 electrons per √3 × âˆš3 unit cell) and small effective electron mass of (0.028 ± 0.006)me. The natural consequence of the latter properties is a high surface conductivity of the Si(111)√3 × âˆš3-(Au, Na) surface.

Doping of magic nanoclusters in the submonolayer In/Si(100) system.

Si(100)4 x 3-In reconstruction is essentially a superlattice of magic (identical-size) Si7In6 nanoclusters. Using scanning tunneling microscopy (STM) observations, we have found that under appropriate growth conditions up to 35% of these clusters can be modified; namely, two Si atoms in the cluster can be replaced by two In atoms, thus forming a Si5In8 cluster. This modification can be considered as a doping of the magic cluster, as it changes the electronic properties of the cluster from semiconducting towards metallic. The doped cluster is less rigid than the ordinary one and swings in the electrical field of the STM tip. The atomic structure and stability of the doped magic cluster have been examined using first-principles total-energy calculations.