Fig. 2: Elemental analysis of a plasma-treated PtSe₂ film using atomic-resolution STEM.

a A cross-sectional HAADF-STEM image of plasma-treated PtSe₂ layers. The PtSe₂ layers near a surface exhibit a significant change by plasma treatment. Overlaid circles represent probe positions for STEM spectroscopy analysis. Two dotted lines are guides to the eye indicating the depth from the surface. The inset represents a magnified image of the white dotted box in (a) superimposed on a PtSe₂ atomic model. Scale bars for (a) and inset are 3 nm and 0.5 nm, respectively. b A depth profile of a Se/Pt ratio obtained by EDS measurements. The profile shows a clear gradient of the ratio down to 7 nm from a surface. The error bars indicate the standard deviations of the Se/Pt ratio. Insets are a HAADF-STEM image of a plasma-treated PtSe₂ and its EDS mapping images, showing spatial distribution of Pt and Se near the surface. A scale bars is 5 nm. c EELS spectra of Se M_4,5 and Pt N_6,7 and d magnified Pt N_6,7 spectra according to the layer depth. EELS data is normalized to the Pt N_6,7 peak and the scale bar represents a relative intensity. The Pt spectra show a gradual red-shift as approaching to the surface (red arrow). e A depth-dependent energy loss profile of Pt N_6,7. Color contrast of each plot corresponds to the depth location indicated in (a).