Template-induced structural phase transition of GeS 2 and GeSe 2 in organic–inorganic hybrid mesostructures

Abstract

We have synthesised layered organic–inorganic hybrid mesostructures of GeX 2 (X=S, Se) and corresponding bulk inorganic reference samples using various precursors and different growth temperatures. X-ray as well as TEM studies confirm the high degree of order of the superstructure of the synthesised organic–inorganic hybrids. The samples were studied by Raman spectroscopy to obtain information on their microscopic structure. With increasing growth temperature, the bulk GeS 2 reference samples exhibit an abrupt structural phase transition from the amorphous to the α-crystalline phase. In contrast, the GeS 2 layers of the hybrid mesostructures transform rather continuously with increasing growth temperature from the amorphous network to a quasi-crystalline Ge 4X 6+4/2 network consisting of Ge 4X 10 4− adamantan units, i.e. the organic template induces constraints which lead to a structural phase diagram of the nanostructured GeS 2 other than for bulk GeS 2. By rescaling the Raman spectra of the new quasi-crystalline Ge 4S 6+4/2 and Ge 4Se 6+4/2 phases with the appropriate scaling factors for bond-bending and bond-stretching modes derived from the α- and β-crystalline GeX 2 phases, it can be shown that both Ge 4X 6+4/2 layers have the same microscopic structure.