AFM (Atomic Force Microscope)
Atomic force Microscope (AFM) developed in the mid 90’s, uses
electronics to measure the force exerted on the probe tip as it moves
along the surface. (The image below is a schematic of the AFM.) [1]
Operation:
An atomically sharp tip is scanned over a surface with feedback mechanisms
that enable the piezo-electric scanners to maintain the tip at a constant
force (to obtain height information), or height (to obtain force information)
above the sample surface. Tips are typically made from Si3N4 or Si,
and extended down from the end of a cantilever. The nanoscope AFM
head employs an optical detection system in which the tip is attached
to the underside of a reflective cantilever. A diode laser is focused
onto the back of a reflective cantilever. As the tip scans the surface
of the sample, moving up and down with the contour of the surface,
the laser beam is deflected off the attached cantilever into a dual
element photodiode. The photo detector measures the difference in
light intensities between the upper and lower photo detectors, and
then converts to voltage. Feedback from the photodiode difference
signal, through software control from the computer, enables the tip
to maintain either a constant force or constant height above the sample.
In the constant force mode the piezo-electric transducer monitors
real time height deviation. In the constant height mode the deflection
force on the sample is recorded. The latter mode of operation requires
calibration parameters of the scanning tip to be inserted in the sensitivity
of the AFM head during force calibration of the microscope.
Applications for AFM:
Biological materials
Polymers
Wafer testing, semiconductor industry
MEMS (Micro Electro-Mechanical Systems)
Hard Disk Drive platters, hard drive industry
Polymer fabrication
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