Two-, One-, and Zero-Dimensional Elemental Nanostructures Based on Ge-9-Clusters

We investigated the structural principles of novel germanium modifications derived by oxidative coupling of Zintl-type (Ge-9)(4-)clusters in various ways. The structures, stabilities, and electronic properties of the predicted {(2)(infinity)[Ge-9](n)} sheet, {(1)(infinity)[Ge-9](n)} nanotubes, and fullerene-like {Ge-9}(n) cages were studied by using quantum chemical methods. The polyhedral {Ge-9}(n) cages are energetically comparable with bulk-like nanostructures of the same size, in good agreement with previous experimental findings. Three-dimensional structures derived from the structures of lower dimensionality are expected to shed light on the structural characteristics of the existing mesoporous Ge materials that possess promising optoelectronic properties. Furthermore, 3D networks derived from the polyhedral {Ge-9}(n) cages lead to structures that are closely related to the well-known LTA zeolite framework, suggesting further possibilities for deriving novel mesoporous modifications of germanium. Raman and IR spectra and simulated X-ray diffraction patterns of the predicted materials are given to facilitate comparisons with experimental results. The studied novel germanium modifications are semiconducting, and several structure types possess noticeably larger band gaps than bulk alpha-Ge.