Pushing the Composition Limit of Anisotropic Ge1−xSnx Nanostructures and Determination of Their Thermal Stability

Ge1−xSnx nanorods (NRs) with a nominal Sn content of 28% have been prepared by a modified microwavebased approach at very low temperature (140 °C) with Sn as growth promoter. The observation of a Sn-enriched region at the nucleation site of NRs and the presence of the lowtemperature α-Sn phase even at elevated temperatures support a template-assisted formation mechanism. The behavior of two distinct Ge1−xSnx compositions with a high Sn content of 17% and 28% upon thermal treatment has been studied and reveals segregation events occurring at elevated temperatures, but also demonstrates the temperature window of thermal stability. In situ transmission electron microscopy investigations revealed a diffusion of metallic Sn clusters through the Ge1−xSnx NRs at temperatures where the material composition changes drastically. These results are important for the explanation of distinct composition changes in Ge1−xSnx and the observation of solid diffusion combined with dissolution and redeposition of Ge1−ySny (x > y) exhibiting a reduced Sn content. Absence of metallic Sn results in increased temperature stability by ∼70 °C for Ge0.72Sn0.28 NRs and ∼60 °C for Ge0.83Sn0.17 nanowires (NWs). In addition, a composition-dependent direct bandgap of the Ge1−xSnx NRs and NWs with different composition is illustrated using Tauc plots.