Experimental evaluation of probe-sample force in tapping mode scanning force microscopy

Abstract

The probe-sample force in tapping mode scanning force microscopy was evaluated using the phenomenon of sublimation of organic benzamide crystal and the assumption that the equal rate of sublimation in both tapping and contact modes is caused by the equal probe-sample force. Contact force was estimated using force curves. It was found out that a benzamide crystal exhibits spontaneous as well as probe-induced sublimation at correspondingly low and high forces applied by the probe. The rate of sublimation was measured as the lateral displacement of the step on the crystal surface during the scan time. The sublimation rate dependence on the setpoint was studied. Both tapping and contact setpoints were varied in a wide range. The tapping setpoint was the operating amplitude of the probe vibration and it followed the free vibrating amplitude. At low setpoint, the probe-sample force in the tapping mode is smaller than that in the contact mode. When the setpoint increases, both of them rise but the tapping force rises faster than the contact force and exceeds it at a setpoint of >6 volts. The shear origin of forces causing sublimation is discussed.