Atomic Force Microscopy (AFM) is an extremely high
resolution scanning probe microscopy technique, which works analogously to a
Scanning Tunnelling Microscope (STM). 1 Unlike the STM, the AFM perceives the
interatomic forces present between a probe tip and the solid being examined.
There are AFM techniques for most measurable force interactions, including: van
der Waals, thermal, electrical and magnetic. 1 Both 2D and 3D images of the
object under examination are generated. The scale of these images is in the
nanometre (nm) range. In this type of microscopy, the probe tip is integrated
into a cantilever. Cantilevers are fabricated from silicon or silicon nitride
and range from 100-450 µm in length, 10-50 µm in width and 0.3-2 µm in
thickness. Contact between the probe tip and the sample is established. The
height of the tip is kept constant. During the scan the cantilever deflects up
and down due to variations in sample height and forces between the sample and
probe tip. The sample is scanned in a raster fashion, meaning the image is
captured in a rectangular pattern. The image is generated by the detection of
the cantilever deflection. AFM is a very useful technique as it can be used to
study almost any sample and scans only take several minutes.
AFM can be carried out in two modes: contact and
non-contact. The contact method involves the cantilever being held less than a
few angstroms away from the sample surface and there being a repulsive
inter-atomic force between the cantilever and the sample. The non-contact
method involves the cantilever being held between tens and hundreds of
angstroms from the sample surface and there being an attractive inter-atomic
force between the cantilever and sample. For samples susceptible to deformation
by the dragging of the tip across its surface there is a third mode available:
intermittent-contact mode (tapping mode). In this method, the vibrating
cantilever tip is brought closer to the sample so that at its lowest point
during travel it just barely taps the sample surface. Non-contact and tapping
cantilevers have higher spring constants, are stiffer cantilevers and have
higher resonance frequencies. For both contact and non-contact imaging, a tip
that is sharper than the smallest features on the sample should be used. The
sharpest tips available commercially can have a radius as small as 50Å.
As per manual.
1a 0.5s/line 64points/line 2D
This imaging is low resolution and tilted.
1b 0.5s/line 64points/line 3D
This imaging is low resolution and tilted. From the
start of one anomaly to another was 11.33 µm. The expected value was 10 µm. The
depth was measured as 119.4 nm. The expected value was 100 nm.
1c 1s/line 28points/line
1c 1s/line 28points/line
The tilt has been removed and the resolution is
higher. The start of one anomaly to another was 16.02 µm. The depth was
measured as 116.7 nm.
The chip structure sample is a piece of a large wafer
containing many identical formations. 2 The depth was measured as 1.314 µm.
The expected value was 1.6 µm.
The CD stamper sample contains a piece of the master
copy of a CD. This is the original that creates the imprint in the pressed CD
that you listen to. A CD will have small indentations; the stampers will have
bumps in the same places. 2
The depth was measured as 161.2 nm.
The staphylococcus (staph) aureus bacteria sample is a
glass slide covered with millions of bacteria. The bacteria have been killed
and fixed to the slide, so the sample is safe to touch and scan. 2
The width was measured as 0.634 µm. The expected value
was 0.7 µm.