Stability and structure of rare-earth metal and Ba-induced reconstructions on a Si(100) surface

• We have studied, by means of ab initio calculations, the energetics and the atomic and electronic structures of various reconstructions induced by rare-earth metals (RE=Eu, Nd, Sm, and Yb) and Ba on Si(100) in the coverage range up to 0.5 monolayer. It is shown that Si dimer buckling is an important structural element for such systems, leading frequently to oblique surface lattice symmetries. The strong metal atom-silicon binding favors the increased amount of metal atoms per unit surface area, i.e., the (2x3) reconstruction with two metal atoms per unit cell is found to be energetically unstable with respect to the (2x1) reconstruction with three metal atoms per the same surface area [Eu/Si(100) and Yb/Si(100)]. The influence of the atomic size and the valence of the adsorbates is also investigated. In particular, it is found that an increase in atomic size stimulates the metal-metal repulsion, stabilizing the (2x3) configuration [Ba/Si(100)]. In the case of trivalent metals, the stabilization of the (2x3) is mediated by the loss of semiconducting state in the competing phases [Sm/Si(100) and Nd/Si(100)]. Our results demonstrate the importance of many factors, which account for the abundance of RE/Si(100) reconstructions. Finally, prominent atomic models are proposed for (2x3) and (2x6) reconstructions, and the character of the wavy "(1x2)" reconstruction is discussed. The simulated scanning tunneling microscopy images for the proposed (2x6) reconstruction are in a particularly good agreement with the complex experimental images.

Nyckelord

ab initio calculations

adsorbed layers

barium

buckling

electronic

structure

elemental semiconductors

europium

monolayers

neodymium

samarium

scanning tunnelling microscopy

semiconductor-metal

boundaries

silicon

surface reconstruction

ytterbium

initio molecular-dynamics

total-energy calculations

augmented-wave

method

basis-set

adsorption

si(001)

stm

2x3

transition

coverage

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