Fig. 4: STEM characterization of HCl/H2O p-type defects in MoS2.
From: Spatial defects nanoengineering for bipolar conductivity in MoS2
a HAADF STEM lattice image of a CVD-grown monolayer MoS2 flake heated in HCl/H2O for p-character treatment, as described in the main text. As a result of the mass contrast behavior (~Z2, where Z = atomic number) of HAADF imaging, Mo atoms (Z = 42) appear as bright spots in a 2H (trigonal prismatic) coordination with S2 (Z = 32) lattice sites. We observe the presence of dopants (outlined in green and yellow) that are not seen in pristine, untreated samples. b High-magnification STEM image of an individual dopant from (a) (outlined in green), in which a noticeable increase in contrast is detected at a chalcogen lattice site. c Intensity profile across the dopant site reveals an intensity rise that is consistent with an additional protruding S atom, the S3 dopant. d–f Numerous dopants observed across different CVD MoS2 flakes demonstrate similar structural and contrast features. g, h HAADF STEM lattice image of an exfoliated monolayer MoS2 flake exposed to p-character treatment, showing S3 dopants. Scar bar: 1 nm in (a), (d), and (g); 500 pm in (b), (e), and (h).
