SKM 2023 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 32: Semiconductor Substrates

O 32.3: Vortrag

Dienstag, 28. März 2023, 11:00–11:15, GER 39

The role of mechanical strain in rare-earth silicide monolayers on Si(111) — •Kris Holtgrewe and Simone Sanna — Justus-Liebig-Universität, Gießen, Deutschland

Rare-earth silicide (RESi₂) nanostructures on silicon surfaces provide a very heterogeneous class of lower-dimensional metallic systems supported by a semiconducting substrate. The RESi₂ monolayer is a two-dimensional semimetal, which grows on Si(111) by self-organisation. While it has intensively been studied by experimental and theoretical works, there are major misunderstandings about the mechanisms which determine the morphological details of the monolayer. In particular, many previous studies state that mechanical strain is responsible for the structural differences between the RESi₂ monolayer on Si(111) (buckled Si honeycomb, vacancy-free), the RESi_2−x bulk phase (flat Si honeycomb, vacancy-rich) and the AlB₂ structure (flat Si honeycomb, vacancy-free). This DFT work sheds light on the stability of the established structure model of the monolayer by a combined analysis of the structural details and the electronic band structure. It proves that the buckling of the covering Si honeycomb and the lack of Si vacancies are not due to mechanical strain, but due to charge balance. In this context, the monolayer is structurally more similar to the unstrained CaSi₂ structure than to the strained AlB₂ structure, which explains its stability. It is very likely that the misinterpreted role of mechanical strain is transferable to all RESi₂ nanostructures.