Tapping mode and elasticity imaging in liquids using an atomic force microscope actuated by acoustic radiation pressure

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Abstract
We report the use of the radiation pressure generated by a focused acoustic beam near 170 MHz to implement tapping mode and elasticity imaging using the atomic force microscope (AFM) in liquids. Since the acoustic radiation force can be localized on an area of a few microns in diameter, this method enables efficient excitation and spatial mapping of both higher-order flexural and torsional modes of AFM cantilevers in liquids. We exploit the sensitivity of the higher-order cantilever mode shapes to the tip–sample contact stiffness for elasticity imaging. We present higher-order flexural and torsional AFM cantilever mode shape measurements in the 1–250 kHz range, and initial results on elasticity imaging on a sample with 1.3 μm thick patterned photoresist layer on silicon obtained at 50 kHz.