Abstract
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.
Highlights
Silicon is the material of choice for trying to fulfill the energy demands for our steadily growing society [1]
We introduced an alternative search strategy—a so-called chemi-inspired search—for the discovery of new silicon modifications with tailored properties based on the formation of well-defined materials with known and experimentally accessible building blocks, which we primarily applied for tetrahedral frameworks [52]
We found several new structures with relatively low energy: (a) three two-dimensional networks, in two of which Si9 units are connected by tetrahedrally bonded Si atoms; (b) four polymers with and without linker atoms between the Si9 units and (c) several tubes and spheres derived from slabs in which the Si9 clusters are directly linked
Summary
Silicon is the material of choice for trying to fulfill the energy demands for our steadily growing society [1]. The fabrication of a two-dimensional monolayer of the lighter homologue carbon, graphene [4], and the elucidation of its optical and electronic properties raised the interest for two-dimensional structures of various kinds of elements [5,6,7,8,9]. The unique electronic situation for graphene gives rise to a vast variety of fascinating physical properties [10,11,12]. It was a short way along the periodic table to computationally search for analogous silicenes and other graphene-like element modifications [13,14,15,16,17]
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