Near-field 2nd harmonic amplitude images of (i) lightly doped (40 Ω), (ii) medium doped (125 kΩ), and (iii) heavily doped (430 kΩ) global resistance states of the device. All near-field images were obtained at laser illumination frequency of ω = 953 cm–1. The near-field amplitude images in parts i–iii were converted to resistivity maps, shown in parts iv–vi. For this conversion, the Im(ε) values were obtained based on the calculations discussed inFigure 5for H-NNO with different dopant levels. The plots vii–ix are resistivity profile schematics that correspond to the images in parts iv–vi. Scale bar in panel d(i) is 1 μm.
