76 Nanosensors: Physical, Chemical, and Biological
uid layer; and (iii) usually only applicable in extremely hydrophobic (repel-
ling, tending not to combine with, or incapable of dissolving in water) sam-
ples with a minimal uid layer.
1.20.6.3 Tapping Mode (Intermittent-Contact Mode)
In tapping-mode AFM the cantilever is oscillating close to its resonance fre-
quency. An electronic feedback loop ensures that the oscillation amplitude
remains constant, such that a constant tip–sample interaction is maintained
during scanning. Forces that act between the sample and the tip will not
only cause a change in the oscillation amplitude, but also a change in the
resonant frequency (natural frequency of vibration determined by the phys-
ical parameters ...