Atomic Force Microscope

1
Atomic Force Microscope
Joseph J. Podrazik Souderton Area School
District NSF Grant EEC-0402045
The bench top atomic force microscope (BT-AFM) is
used to simulate the operation of an AFM used in
research labs for imaging samples on the nano
scale. Its main purpose is to be used by
secondary schools to introduce nanotechnology and
microscopy. 
What is an AFM?
The atomic force microscope (AFM) is a scanning
probe microscope. It is designed to measure local
properties, such as height, friction, magnetism,
with a probe. The AFM provides a 3D profile of
the surface on a nanoscale, by measuring forces
between a sharp probe (lt10 nm) and surface at
very short distance (0.2-10 nm probe-sample
separation).
Open source Handbook of Nanoscience and
Nanotechnology
The probe is supported on a flexible cantilever.
The AFM tip gently touches the surface and
records the small force between the probe and the
surface.
Spring depiction of cantilever
How are Forces Measured?
The probe is placed on the end of a cantilever
(which one can think of as a spring). The amount
of force between the probe and sis dependant on
the spring constant (stiffness of the cantilever
and the distance between the probe and the sample
surface. This force can be described using
Hookes Law F -k x F Force the spring
k spring constant x cantilever deflection
Spring
Tip
Sample
Laser Pen
How does the Bench Top - AFM work?
Photo Diodes
The BT- AFM operates similar to an expensive
AFM.  A laser beam shines down on the cantilever
probe, reflects off a mirror, and strikes two
diodes. As the cantilever probe moves, it changes
the deflection of the laser, which is captured by
the diodes.  Thus, the diodes are able to record
the changes in vertical height ( Z direction ). 
A pair of rotary encoders are utilized to record
lateral motion ( X Y direction ). The laser,
cantilever probe and diodes, are mounted on a
threaded rod with a rotary encoder at one end. 
As the laser is moved, the rod spins, and the
rotary encoders record how far the light
traveled.  The signals from the diodes and both
rotary encoders are fed into a computer running
LabVIEW software. LabVIEW produces a three
dimensional image representing the sample.   
The electronic components from National
Instruments and LabVIEW software captured this
image of a sample using the 3D Graph and the
BT-AFM.
Cantilever w/ mirror tip