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Frequency-modulation Kelvin probe force microscopy under tapping mode operation for surfaces with large protrusions

Kelvin probe force microscopy (KPFM) is a useful technique for simultaneously visualizing topography and contact potential difference (CPD). Although frequency-modulation (FM) KPFM has high spatial resolution and sensitivity, it is not readily applicable to measuring large protrusions owing to the instability of the feedback condition. Here we investigate the combined use of amplitude-modulation and FM for tip-sample distance control and electrostatic force detection, respectively. The proposed method enabled simultaneous acquisition of topography and CPD images of gold nanoparticles on a Nb-doped TiO2(100) surface. The effect of the tip shape and tilt angle on the CPD images is also discussed.