$M$Si$_{20}$H$_{20}$ Aggregates: From Simple Building Blocks to Highly Magnetic Functionalized Materials

TL;DR

This study uses density-functional theory to explore hydrogenated silicon clusters as building blocks for creating highly magnetic, cluster-assembled materials with controllable aggregation and preserved magnetic properties.

Contribution

It introduces a method to control reactive sites on silicon clusters via hydrogenation levels, enabling the design of magnetic materials with specific architectures.

Findings

Clusters prefer aggregation through Si-Si bridge bonds.

Reducing hydrogenation controls reactive sites for attachment.

Aggregates retain high magnetic moments of dopant atoms.

Abstract

Density-functional theory based global geometry optimization is used to scrutinize the possibility of using endohedrally-doped hydrogenated Si clusters as building blocks for constructing highly magnetic materials. In contrast to the known clathrate-type facet-sharing, the clusters exhibit a predisposition to aggregation through double Si-Si bridge bonds. For the prototypical CrSi$_{20}$H$_{20}$ cluster we show that reducing the degree of hydrogenation may be used to control the number of reactive sites to which other cages can be attached, while still preserving the structural integrity of the building block itself. This leads to a toolbox of CrSi$_{20}$H$_{20-2n}$ monomers with different number of double "docking sites", that allows building network architectures of any morphology. For (CrSi$_{20}$H$_{18}$)$_{2}$ dimer and [CrSi$_{20}$H$_{16}$](CrSi$_{20}$H$_{18}$)$_{2}$ trimer structures we illustrate that such aggregates conserve the high spin moments of the dopant atoms and are therefore most attractive candidates for cluster-assembled materials with unique magnetic properties. The study suggests that the structural completion of the individual endohedral cages within the doubly-bridge bonded structures and the high thermodynamic stability of the obtained aggregates are crucial for potential synthetic polymerization routes $via$ controlled dehydrogenation.