Vibrating the sample or the cantilever base excites these modes. The vibration of the cantilever is detected by means of optical lever used with a fast photodiode. The dc force of the cantilever is adjusted to achieve continuous contact between the tip and the sample. The tip-sample interaction modifies the resonance frequencies of the cantilever. By detecting the shift in the resonance frequencies, the tip-sample stiffness is measured.
Current research focuses the characterization of the tip-sample contact.
Noise analysis of mechanical systems Random vibrations of mechanical parts set the fundamental limit on the minimal detectable displacement in many precision displacement measuring devices like the AFM, laser interferometric gravitational wave detectors, etc. Similar to the series voltage noise of a resistor in an electrical circuit, the source of random vibrations is the thermal agitation. To determine the merit of a displacement sensing system, it is crucial to understand this noise source. The mechanical noise and the correlation of mechanical noise can be calculated by using the analogy between electrical circuits and mechanical systems.