  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.
