Sulfur Passivation of Highly Crystalline Germanium Nanoparticles via a Microwave-Assisted Strategy

Germanium nanocrystals (Ge NCs) exhibit size-dependent optical properties, making them promising for optoelectronic and near-infrared (NIR) applications. However, their performance is often limited by surface oxidation and dangling bonds. A microwave-assisted ligand-exchange method is presented that replaces a significant portion of surface-bound oleylamine (OAm) with sulfur dissolved in octylamine (OA) and toluene, facilitating efficient surface passivation without additional etching steps. SEM-EDS mapping, FTIR, ¹H NMR, and XPS analyses confirm sulfur passivation and partial displacement of OAm ligands. High-resolution XPS spectra show a characteristic S 2p doublet, indicative of Ge-S bond formation. Elemental mapping shows spatial colocalization of Ge and S, and TEM, HRTEM, and SAED analyses confirm that the NCs' crystalline structure remains intact after surface modification. This scalable approach provides an effective strategy for enhanced surface control of Ge NCs in optoelectronic applications.