Abstract
Structural properties of Ba-induced reconstructions on a Ge(001) surface, based on atomic-resolution ultra high-vacuum scanning tunneling microscopy measurements, are discussed. It is shown that while the Ba - Ge layer, which fully covers the surface, is dominated by a phase with an internal 2 × 3 periodicity, it also includes portions of higher order 2 × 6 and 4 × 3 surface reconstructions, always accompanied by 1D protrusions embedded into the dominating phase. Modelling the observed higher order structures, using the elementary cell of the 2 × 3 phase calculated within the density functional theory, is shown to reproduce the experimental data very well. As such the higher order reconstructions can be treated as local defects of the dominating 2 × 3 phase.
Highlights
The Si(001) and Ge(001) surfaces are known to be prone to the adsorption of residual gases in ultra-high vacuum (UHV) conditions
Ultra-high vacuum scanning tunneling microscopy (UHV STM) investigations demonstrated that the deposition of 1/3 ML Ba on
We provide a qualitative explanation of the reported observations, based on the structural models for the 2 × 3, c(2 × 6) and 4 × 3 surface reconstructions constructed using the elementary unit cell calculated for the defect-free 2 × 3 Ba/Ge(001) system [23]
Summary
The Si(001) and Ge(001) surfaces are known to be prone to the adsorption of residual gases in ultra-high vacuum (UHV) conditions. The chemisorption of atomic hydrogen is a typical example [5,6,7], deposition of the alkali earth metals on Si(001) and Ge(001), that promotes the growth of a two-dimensional continuous passivating monolayer, is technologically more relevant [3,8,9,10,11,12,13,14,15,16,17]. Ultra-high vacuum scanning tunneling microscopy (UHV STM) investigations demonstrated that the deposition of 1/3 ML Ba on the Si(001) substrate, kept at 1170 K during and after processing, lead to the 2 × 3 surface reconstruction of the formed passivating adlayer [8]. Consists of single Ge dimer and one alkaline earth metal atom creating the surface unit cell, supported by the density functional theory (DFT) calculations, explains very well the observed 2 × 3 and 2 × 6 reconstructions for the Sr/Si(001) [11,18,19] and the Ba/Si(001) systems [20]
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