Strain-induced quasi-one-dimensional rare-earth silicide structures on Si(111)

Abstract

After deposition of rare-earth elements (Dy, Tb) on Si(111) at elevated temperatures, a formerly unknown (2 √ 3 × √ 3)R30 • reconstruction is observed by low-energy electron diffraction, while scanning tunneling microscopy measurements exhibit a (√ 3 × √ 3)R30 • reconstruction. On the basis of density-functional theory calculations, the structure of the larger unit cell is explained by periodically arranged subsurface Si vacancies. The vacancy network in the first subsurface layer has a (√ 3 × √ 3)R30 • periodicity, while strain is released by a (2 √ 3 × √ 3)R30 • Si vacancy network in the second subsurface layer. In addition, this vacancy network forms quasi-one-dimensional structures (striped domains) separated by periodically arranged antiphase domain boundaries. The diffraction spot profiles are explained in detail by kinematic diffraction theory calculations, and average domain widths are deduced.

Effects of Domain Boundaries on the Diffraction Patterns of One-Dimensional Structures

“…The models e and f make up the first type of domain where the vacancies in the Si 3 and Si 4 layer are located underneath Si atoms in the Si 2 layer, whereas the models q and r make up the second domain where the vacancies in the Si 3 and Si 4 layer are located underneath Si atoms in the Si 1 layer. Both models exhibit different structural motives in Scanning Tunneling Microscopy (STM) measurements [11], which are indicated here by green triangles and red hexagons. The binary sequences after the projection onto the relevant crystallographic axis of the different models for the layer Si 3 and Si 4 are given reflecting the fact that the Si 3 layer exhibits a ( However, experimentally, neither the width nor the exact orientation of the different types of domains to each other can be determined by STM.…”

“…The atomic structure of the reconstruction is rather complex (see Figure 2 as analyzed in [11] Figure 2). …”

“…• reconstruction of (Dy, Tb) on Si(111) [11] will be discussed as an example demanding a detailed analysis in the framework presented above since the effective unit cells are too large to perform standard diffraction analysis.…”

“…Here, we introduce the binary surface technique to treat also surfaces with larger periodicities than surface unit cells [11,12]. Within this approach, the crystallographic lattice with the lattice constant a is represented by a one-dimensional binary array with an array length m and with periodic boundary conditions.…”

“…We demonstrate that the splitting or non-splitting of various superstructure peaks has to be taken into account to determine the correct structure of the DBs involved. In addition, we apply our results to analyze the complex structure of 2 √ 3 × √ 3 R30 • reconstructed Si(111) surface due to rare earth silicide formation where several layers are involved in the formation of the superstructure [11].…”