4. Atomic force microscope (AFM) was developed to overcome a basic
drawback with STM – it can only image conducting or semiconducting
surfaces
5. Atomic force microscopy or
scanning force microscopy is a
very-high-resolution type of
scanning probe microscopy, with
demonstrated resolution on the
order of fractions of a
nanometer, more than 1000
times better than the optical
diffraction limit.
8. SEM's advantage is that it
can measure the chemical
composition of surface
features, while an AFM can
measure surface physical
properties, such as magnetic
fields (MFM), surface
potential (SKPM), surface
temperature (SThM), friction
(SFM), and many other
surface physical properties.
9. AFM microscopes operate on the principle of surface
sensing using an extremely sharp tip on a micromachined
silicon probe. This tip is used to image a sample by raster
scanning across the surface line by line, although the method
varies dramatically between distinct operating modes.
How does an AFM microscope work?
10. The underlying principle of AFM is that this nanoscale tip is attached
to a small cantilever which forms a spring. As the tip contacts the
surface, the cantilever bends, and the bending is detected using a
laser diode and a split photodetector. This bending is indicative of
the tip-sample interaction force. In contact mode, the tip is pressed
into the surface and an electronic feedback loop monitors the tip-
sample interaction force to keep the deflection constant throughout
raster scanning.
Principle of AFM
11.
12. Tapping mode limits the contact between the sample surface and the
tip to protect both from damage. In this mode, the cantilever is
caused to vibrate near its resonance frequency. The tip subsequently
moves up and down in what is described as a sinusoidal motion.
This motion is reduced by attractive or repulsive interactions as it
comes near the sample. A feedback loop is used in a similar fashion
to contact mode, except it keeps the amplitude of this tapping motion
constant rather than the quasistatic deflection. By doing so, the
topography of the sample is traced line by line
