Structural insight into doped and alloyed germanium nanoparticles prepared via microwave synthesis

Complex nanomaterials are finding important applications in many different areas of technology. The colloidal method has been widely used to finely control the size, morphology, and composition of nanocrystals in the development of advanced optical, electronic, and catalytic materials. Colloidal chemistry enables access to both thermodynamic and kinetic phases in the nanoregime allowing for the synthesis of metastable and previously unknown phases. Germanium nanoparticles (Ge NPs) are successfully doped with bismuth (Bi) and antimony (Sb) up to 1.5 mol %, which is not achievable in the bulk Ge system. The structures of oleylamine and dodecanethiol capped Ge NPs doped with Bi or Sb are probed with EXAFS. Analysis of the Bi-doped Ge NPs suggests that Bi resides on or near the surface/interfaces of the crystallites. The structure of Sb-doped Ge NPs is more complex and the best model is consistent with Sb on highly distorted sites next to a Ge vacancy as well as near or on the crystallite surface/interfaces. Increasing the amount of dopant from 0.50 to 1.5 mol % results in increasing disorder. Oleylamine to dodecanethiol ligand exchange is shown to partially restore order in doped NPs. These structural models will be compared with the EXAFS analysis of GeSn alloy phases prepared in the same manner.