Nanometer cale surface charge mapping in liquids

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A surface charge mapping technique based on frequency modulation atomic force microscopy (FM-AFM) working in liquid environments has been developed. We implemented a phototheimal excitation setup for cantilever oscillation in liquids to perform quantitative force measurements. We analyzed the cantilever oscillation caused by an external modulation voltage between the tip and sample surface, and found that the conventional voltage modulation schemes for surface potential measurement cannot be applied in polar liquids. We also developed a method to estimate surface charge density by comparing measured electrostatic force with theoretically calculated force.