Biomedical Engineering Reference
In-Depth Information
AFM
SNOM
Contact mode
Aperture (ASNOM)
Non-aperture SNOM (NA-SNOM)
Evanescent field SNOM (EF-SNOM)
Intermittent Contact mode (IC-AFM, AM-AFM, Transmission SNOM (T-SNOM)
Tapping)
Non-contact mode (NC-AFM, close contact
mode, FM-AFM)
Collection SNOM (C-SNOM)
Chemical Force Microscopy (CFM)
STM
Lateral Force (LFM, FFM))
Scanning Tunnelling Spectroscopy (STS)
Electric Force (EFM)
Topography (STM)
Force Spectroscopy
Alternating Current STM (AC-STM)
Nanoindentation
Ballistic electron emission microscopy (BEEM)
Magnetic Force (MFM)
Scanning Tunnelling Optical Microscopy (STOM)
Kelvin Probe (KPM, SKPM)
Scanning Thermal Microscopy (SThM)
Nano oxidation Lithography
Dip-pen Nanolithography (DPN)
Fig. 3.1. Summary of the names of some SPM-based techniques.
of the AFM cantilever, and those that measure the dynamic oscillation of the cantilever.
The differences between the modes lead not only to different experimental procedures, but
to differences in the information available, differing suitabilities for particular samples,
and even to differences in the interpretation of the data.
3.1.1 Contact mode
Contact mode AFM was the first mode developed for AFM. It is the simplest mode
conceptually, and was the basis for the development of the later modes. Therefore
understanding contact mode helps to understand how the other techniques work. Although
the limitations of contact mode prompted the development of modes that could examine
different samples in different environments and give different information, contact mode
is still an extremely powerful and useful technique. Contact mode is capable of obtaining
very high-resolution images. It is also the fastest of all the topographic modes, as the
deflection of the cantilever leads directly to the topography of the sample, so no summing
of oscillation measurements is required which can slow imaging.
In order to understand the way AFM modes work, it is necessary to use so-called
force-distance curves. A cartoon of a simple force-distance curve is shown in Figure 3.2.
As the name implies, these curves are a plot of force (on the
y
axis) versus distance (on the
x
axis). Such a curve is simple to acquire with the AFM. It is calculated from a
deflection-distance curve which is easily measured by monitoring the deflection of the
cantilever as the piezo is used to move the tip towards the sample. Typically, at a set
deflection level, the direction is reversed, and the tip withdraws from the sample. This
results in a deflection versus distance curve, which may be converted to a force-distance
curve. Measurement of force-distance curves is a very sensitive and quantifiable way to
