Fig. 2: Nanoscale optical and electrical imaging of the MoSe₂ QDs embedded in the WSe₂ matrix.

a Schematic representation of nanoscale scanning probe techniques (top) on the 5 min-MoSe₂ QDs@WSe₂ heterostructures buried in an Au template (bottom: cross-sectional view). The samples are prepared by Au-assisted transfer process^25,26. b, c AFM height image and surface potential map of the heterostructures consisting of the 50 nm-sized MoSe₂ QDs and the WSe₂ matrix. (Inset) The height profile marked with a white line in (b) shows no discernible height difference across the crystal, proving truly in-plane epitaxy (embedding) of the MoSe₂ QD in the WSe₂ matrix. The MoSe₂ QDs are marked with black dotted circles. d Surface potential profile following the green dotted line in (c). e–g TERS spatial maps of the quantum heterostructures following the red dotted squares in (b) and (c). The TERS images were created within the spectral ranges of 245–255 cm⁻¹ (e WSe₂ A₁ mode) and 235–245 cm⁻¹ (g MoSe₂ A_1g mode) with a step size of 25 nm. The MoSe₂ QDs are marked with yellow dotted circles. f Overlaid image of (e) and (g). h TERS spectra of the MoSe₂ QD regions (red) and the surrounding WSe₂ matrix (blue) as highlighted in the TERS map.