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Perturbation detection of electric force gradients using the phase shift method

A perturbation detection technique is proposed to enhance the measurement resolution of electric force gradients in electrostatic force microscopy. The technique benefits from the perturbation in the probe tip position as it responds to interaction forces, thus eliminating the need to externally modulate the probe-circuit spacing and avoiding unwanted mechanical vibrations. Force gradients are detected by monitoring the resulting phase shifts in the probe vibration using a sensitive phase shift monitoring system. The constructed system enables the detection of electric force gradients at a probe-circuit spacing as high as 0.5 µm with a sensitivity of 20 µN m-1 in 1 Hz measurement bandwidth. Scan images of electric force gradients above integrated lines structure are presented against typical force measurements and demonstrate a significant enhancement in measurement resolution.