Direct measurement of tapping force with a cantilever deflection force sensor.

An experimental set up dedicated to the measurement of atomic force microscope tapping force was developed. In the set-up, a standard TappingMode probe cantilever was used to tap another cantilever equipped with its own low noise and high sensitivity deflection detection system for force measurement. The amplitude and phase change of the tapping lever as well as the deflection of the sensing lever were simultaneously recorded as a function of tip/surface separation. Since the deflection of the sensing cantilever reflects the average force over one interaction cycle, we measured the total average force quantitatively after calibrating the spring constant and deflection sensitivity of the sensing lever. Considerable effort was made to achieve the same force curve in the tapping force measurement as occur during imaging of conventional samples such that the detected tapping force reflects the same interaction of the imaging process.