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HFM
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
Highly Oriented Pirolytical Graphite HOPG
is widely used in scanning tunneling and force microscopies
substrate material becouse of his atomic flatness
and cleanness.
Nature 315, 253, (1985).
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