Abstract-Modulation methods such as homodyne and heterodyne detections are employed in A-SNOM in order to eliminate serious background effects from scattering fields. Usually, the frequencymodulated detection signal in apertureless scanning near-field optical microscopy (A-SNOM) is generally analyzed using a simple dipoleinteraction model based only on the near-field interaction. However, the simulated A-SNOM spectra obtained using such models are in poor agreement with the experimental results since the effects of background signals are ignored. Accordingly, this study proposes a new phenomenological model for analyzing the A-SNOM detection signal in which the effects of both the dipole-interaction and the background fields are taken into account. It is shown that the simulated A-SNOM spectra for 6H-SiC crystal and polymethylmethacrylate (PMMA) samples are in good agreement with the experimental results. The validated phenomenological model is used to identify the experimental A-SNOM parameter settings which minimize the effects of background signals and ensure that the detection signal approaches the pure nearfield interaction signal. Finally, the phenomenological model is used to evaluate the effects of the residual stress and strain in a SiC substrate on the corresponding A-SNOM spectrum.

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