Karthik Ramasamy1 Jeffrey Pietryga2 Sergei Ivanov2

1, UbiQD, Inc, Los Alamos, New Mexico, United States
2, Los Alamos National Laboratory, Los Alamos, New Mexico, United States

Germanium (Ge) is one of the extensively studied semiconductors possessing higher absorption coefficient and carrier mobilities than silicon. Because of low-cost and its compatibility with existing CMOS processing methods, germanium has found applications in many electronic and in optoelectronic devices. Recently, it has also been realized that Ge is well suited as an anode for Li and Na ion batteries. However, material’s inherently inefficient light absorbtion or large volume change during lithiation/delithiation process impede its further use in optical and energy storage applications. Although alloying of Ge with Sn was concluded to be potentially beneficial for addressing both issues, the finite solubility (< 1% of Sn in Ge) and large lattice mismatch between Ge and Sn made it challenging to prepare SnGe alloys with any significant degree of element mixing. Exploiting the tolerance of nanosize crystals to withstand large amount of strain, we have developed a facile synthetic approach to SnxGe1-x nanoalloys with almost entire compositional range of alloying, with tin content up to 95 %, while still retaining the cubic phase of the material and the homogeneous distribution of both elements within particles. Some insights in the mechanism for the alloy formation have also been elucidated. The synthesized nanoalloys are moderately thermally stable, with phase segregation starting at temperatures above 200 °C via tin diffusion out of the particle interior. Deliberate and controlled sulfudization of the nanoalloy surface via the deposition of a thin layer of sulfur increases thermal stability of protected particles up to 500 °C. The presence of more cationic Sn and Ge atoms on the particle surface after sulfur treatment enables the ligand exchange from the non-polar long-chain alkyl ligands to shorter and more polar hydrazine or even iodide, thereby rendering particles processible for the preparation of thin films with close interparticle contacts. The details of the synthesis methods, mechanistic studies, structural and optical characterizations will be presented and discussed