Fig. 7. Large-area images at a Au–Si edge with a dirt particle sticking to the edge (length of scale bar in (a): 2 μm). Au is on the left side, Si on the right. (a) Topography, (b–d) 1Ω to 3Ω s-SNOM maps taken with the 180 nm TeraFET detector. Noise levels of the s-SNOM maps are not directly comparable as the 1Ω and 2Ω signals were recorded with a 7265 Dual Phase DSP lock-in amplifier, the 3Ω signal in parallel with the MFLI lock-in amplifier which has a better SNR. Integration time constant: 20 ms, time needed for recording the full image: 1.5 h.
