Apertureless scanning near-field optical microscopy (A-SNOM) with a superlens is a novel nano-optical system for sub-wavelength imaging purposes. This study presents a quantitative model for analyzing the heterodyne signals obtained from an A-SNOM fitted with a superlens at various harmonics of the AFM tip vibration frequency. It is shown that the image resolution is determined not only by the tip radius, but also by the superlens transmission coefficient in the high evanescent wave vector Kx. Moreover, the analytical results show that the images acquired from the A-SNOM/superlens system are adversely affected by a signal contrast problem as a result of the noise generated by the tip-superlens interaction electric field. However, it is shown that this problem can be easily resolved using a background noise compensation method, thereby resulting in a significant improvement in the signal-to-background (S/B) ratio. The feasibility of utilizing the system for maskless nanolithography applications is discussed. It is shown that the A-SNOM/superlens system with the proposed noise compensation scheme yields a dramatic improvement in the signal intensity and S/B ratio compared to that of a conventional A-SNOM with a bare tip only.
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