Increasing the probe sensitivity of tapping mode atomic force microscopes using a positive feedback mechanism

A positive feedback mechanism is used in this research to enhance the resonant factor of the oscillating tip of tapping mode atomic force microscopes (AFM). In general, the higher the resonant factor, the higher the sensitivity of the tip. In other respect, increasing the resonant factor also improves the imaging resolution of the sample surface, in order to significantly enhance the resonant factor, the vertical amplitude signal of the tip is exploited as a feedback signal and is phase shifted, amplified, and then summed up with the original driving signal of the oscillating tip. Based on this, the resonant factor can be effectively increased and the image quality of the sample can be significantly improved. To validate the effectiveness of this method, the frequency response analyses are carried out to verify that it is possible to increase the resonant factor of the tip according to this proposed positive feedback mechanism. Further, for experimental verifications and comparisons, the AFM is operated with and without tuning the resonant factor.