MoS2 impurities: Chemical identification and spatial resolution of bismuth impurities in geological material

Molybdenum disulfide (MoS2) is the most widely studied transition metal dichalcogenide (TMDC) material, in part because it is a natural crystal present in the earth, thus making it abundant and easily accessible. Geological MoS2 has been used in various studies that look at incorporating MoS2 into devices for nanoelectronics and optoelectronics. However, variations in the electronic properties of a single MoS2 surface are known to exist due to defects that are intrinsic to natural MoS2. This work reports the presence of bismuth impurities in MoS2 with concentrations high enough to be detected by X-ray photoelectron spectroscopy (XPS). These concentrations are further corroborated with inductively coupled plasma optical emission spectroscopy (ICP-OES). Localization of these bismuth clusters is shown using XPS-mapping, and the cluster size is determined to be on the order of tens of microns. This work provides important insights into the nature of impurities that are known to exist in MoS2.