|AFM - Raman - SNOM||Bio AFM||Modular AFM||Automated AFM||Practical AFM|
Intermittent contact implementation with high amplitude vibrating probe.
Heterodyne Force Microscopy
In HFM, ultrasound is excited both at the tip (from a transducer at the cantilever base) and at the sample surface(from a transducer at the back of the sample) at adjacent frequencies, and mixed at the tip-sample gap (see figure 1).As the sample surface vibrates at a frequency w1, and the tip at a frequency w2, the maximum tip-surface distanceis modulated at w1 - w2 (beat frequency). Provided that the total amplitude is large enough to cover the nonlinearrange of the tip-sample interaction force, an ultrasonic force (stronger for larger amplitudes) acts upon the cantilever, and displaces it from its initial position. Owing to the varying ultrasonic force, the cantilever vibrates at the differencemixed frequency. In HFM, this vibration is monitored in amplitude (amplitude-HFM, A-HFM) and phase (phase-HFM, ph-HFM) with a lock-in amplifier, using the (externally) electronically mixed signal as a reference.
J. Phys. D 33, 2447 (2000).
HOPG is widely used in scanning tunneling and force microscopies substrate material becouse of his atomic flatness and cleanness.
Nature 315, 253, (1985).