Abstract
Ternary two-dimensional dichalcogenide alloys exhibit compositionally modulated
electronic structure and hence, control of dopant concentration within each layer of
these layered compounds provides a powerful way to modify their properties. The
challenge then becomes quantifying and locating the dopant atoms within each layer
in order to better understand and fine-tune the desired properties. Here we report
the synthesis of selenium substitutionally doped molybdenum disulfide atomic layers,
with a broad range of selenium concentrations, resulting in band gap modulations of
over 0.2 eV. Atomic scale chemical analysis using Z-contrast imaging provides
direct maps of the dopant atom distribution in individual MoS2 layers and hence a
measure of the local band gaps. Furthermore, in a bilayer structure, the dopant
distribution of each layer is imaged independently. We demonstrate that each layer
in the bilayer contains similar doping levels, randomly distributed, providing new
insights into the growth mechanism and alloying behavior in two-dimensional
dichalcogenide atomic layers. The results show that growth of uniform, ternary,
two-dimensional dichalcogenide alloy films with tunable electronic properties is
feasible.
