Practical Realization of Apertureless Scanning Near-field Optical Microscopy Using Hybrid Mode Atomic Force Microscopy

Abstract

ABSTRACTThe local detection of optical response at the sub-wavelength scale on a materials’ surface is an invaluable characterization capability of apertureless scanning near-field optical microscopy (ASNOM). The technique is traditionally realized in amplitude modulation (AM) AFM mode. We have expanded this method by employing an alternative scheme for the detection of the near-field and far-field responses with the use of Hybrid (HD) AFM mode. In HD mode the sample is brought to the intermittent contact with the tip in a periodic oscillation at a frequency (1-2 kHz) much smaller than the probe resonance. In every oscillation cycle the probe deflection to a set-point value is used for surface profiling. For optical measurements the metal coated AFM tip was top-illuminated by visible laser. Simultaneously with surface profiling the light scattered from tip-sample junction was collected by a sensitive photomultiplier (PMT). The homodyne optical signal detection scheme was applied to discriminate near- and far-field optical components. Our method was verified by the studies of various materials (semiconductors, metals, polymers, etc.). The presented results show that the contrast of ASNOM images can be used for compositional mapping of heterogeneous systems.