Browsing by Author "Jantke, Laura-Alice"

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Chemi-Inspired Silicon Allotropes—Experimentally Accessible Si9 Cages as Proposed Building Block for 1D Polymers, 2D Sheets, Single-Walled Nanotubes, and Nanoparticles
(2022-02-01) Jantke, Laura-Alice; Karttunen, Antti J.; Fässler, Thomas F.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Numerous studies on silicon allotropes with three-dimensional networks or as materials of lower dimensionality have been carried out in the past. Herein, allotropes of silicon, which are based on structures of experimentally accessible [Si9 ]4− clusters known as stable anionic molecular species in neat solids and in solution, are predicted. Hypothetical oxidative coupling under the formation of covalent Si–Si bonds between the clusters leads to uncharged two-, one-and zero-dimensional silicon nanomaterials not suffering from dangling bonds. A large variety of structures are derived and investigated by quantum chemical calculations. Their relative energies are in the same range as experimentally known silicene, and some structures are even energetically more favorable than silicene. Significantly smaller relative energies are reached by the insertion of linkers in form of tetrahedrally connected Si atoms. A chessboard pattern built of Si9 clusters bridged by tetrahedrally connected Si atoms represents a two-dimensional silicon species with remarkably lower relative energy in comparison with silicene. We discuss the structural and electronic properties of the predicted silicon materials and their building block nido-[Si9 ]4– based on density functional calculations. All considered structures are semiconductors. The band structures exclusively show bands of low dispersion, as is typical for covalent polymers.
Structural characteristics of mixed nido-[Si9−xGex]4− (x=1, 2) Zintl clusters in solution and within solvent crystals
(2023-02-01) Jantke, Laura-Alice; Karttunen, Antti J.; Fässler, Thomas F.
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Mixed Zintl-type anionic clusters of silicon and germanium comprise an important class of potential materials in electronic applications. Herein, we present quantum chemical investigations to describe the mixing behavior of Si and Ge within [Si9−xGex]4− (x=0, 1, 2) Zintl anions that can be considered as precursors for novel Si−Ge materials. To understand the mixing behavior of such clusters in solution, we analyze the molecular clusters at using Density Functional Theory (DFT) and Coupled Cluster methods. Systematic assessment of relative energies of various structural isomers indicates that there is a preference to substitute Si with Ge in the open square of the monocapped square antiprismatic [Si8Ge]4− and [Si7Ge2]4− clusters. Population analysis reveals that the highest negative partial charge is also located at these positions. Investigation of Rb4Si9−xGex(NH3)5 solvent crystals using DFT methods and periodic boundary conditions further elucidates the behavior during crystallization. It is shown that in addition to the favored [Si8Ge]4− open-square isomers arising in solution, the weak intermolecular interactions in the crystalline environment affect which structural isomers are observed in the crystal structure. The experimentally observed Ge site occupations could be explained by analysis of their energetics. This analysis contributes to the understanding of the mixing behavior of these important building blocks for material design.