Microscope and Optical Characterization of Ag2GeS3 Nanowires

As a polar thermoelectric material, Ag2GeS3 is a potential candidate for transforming heat into electricity. However, the fundamental mechanisms that govern the thermoelectric properties are not fully comprehended yet. We use Transmission Electron Microscopy and photoluminescence measurements to characterize this sample. 6 mm pallets of Ag2GeS3 samples are prepared using the conventional solid-state method with binary sulfides (Ag2S and GeS2) as starting materials. The sample is then vacuum sealed and heated up to 1000C⁰ for 12 hours, and held at that temperature for 168 hours. Scanning electron micrographs show semi-conical shape nanowires (NW) with a base of ~200 nm in diameter and a tip of ~50 nm. NWs are about 2 um long and are randomly oriented. Selected area electron diffraction measurements reveal a combination of both mono-crystalline and a poly-crystalline structure. High-angle annular dark-field imaging helped to map element concentration on different parts of the NWs. Room temperature Photoluminescence (PL) measurements show multiple peaks near UV, yellow-green, red and near infra-red.