 |
|
|
|
AFMs can be utilized to scan a sample in two different modes: contact mode or tapping mode, according to the interatomic force vs. distance (tip-to sample) curve.
In the contact zone, the cantilever is held few angstroms from
the sample surface and the interatomic force between the cantilever and
the sample is repulsive. AFM tip makes soft "physical contact" with the
sample. - Contact operative mode.
The tip is attached to the end of a cantilever with a low spring
constant, lower than the effective spring constant holding the atoms of
the sample together. The magnitude of the total force exerted on the
sample varies from 10-8 to the
more typical operating range of 10-7
to 10-6N.
The AFM cantilever is vibrated near the surface of the sample obtaining
little or no contact between the tip and the sample. The magnitute of
the total force is very low, generally about 10-12N:
this low force is advantageous for studying soft or elastic samples. The
system vibrates a stiff cantilever near its resonant frequency
(typically from 100 to 400 kHz) with an amplitude of a few tens to
hundreds of angstroms. |
AFM tecniques