Abstract
An improved nonoptical shear force detection system based on a rectangular bimorph cantilever incorporating the force feedback technique has been developed for tip–sample distance regulation in shear force microscopy. The force feedback amplifier consisting of a phase shifter and a linear amplifier is adjusted in such a way that the motion of the cantilever is mechanically amplified, resulting in a great enhancement of quality factor Q. Driving a fiber attached bimorph cantilever at its first harmonic resonance, with a phase shift φ=π/2 and an appropriate amplifier gain, allows one to obtain a Q factor greater than 103 in air, which corresponds to a Q enhancement of more than 1 order of magnitude. The effect of Q enhancement leads to an increase in the signal to noise ratio and thus the force detection sensitivity of the system. Typically, the minimum interaction force that can be sensed by the system is about 2 pN/√Hz. Topographic images of a human aorta tissue section in its natural state, taken with the described shear force detection system, show that it is very sensitive, reliable, and particularly suitable for biological applications.
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