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Cantilevers are fabricated on chips.
What you get when you order cantilevers is a small micro-precision-machined
rectangular or triangular piece of silicon or silicon nitride
with a shiny surface. The minute cuboid you can see is not the
cantilever itself, but the chip that holds the cantilever. Generally
you need a magnifying glass to see the cantilever at the narrow
side of the chip. Sometimes there are two or more cantilevers
attached to the narrow edges of the chip.
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What you are unable to see without a good optical microscope
is the tip at the end of the cantilever. The radius of the end
of the tip determines the imaging quality. Typically the tip
is a few microns long, some are shaped like a needle, and others
look like an Egyptian pyramid.
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Cantilevers
can be seen as springs.
Remembering your physics lessons in school, you may recall that
the extension of springs can be described by Hooke's Law
F = - k
* s.
This means: The force
F you need to extend the spring depends in linear
manner on the range s
by which you extend it. Derived from Hooke's law, you can allocate
a spring constant
k to any spring. The four damping springs of a
car's wheels have a higher spring constant than the spring in
your ball-point pen.
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The spring constants of
the commercially available cantilevers vary over four orders of
magnitude; cantilevers with spring constants between 0.005 N/m
and 40 N/m are commercially available. You can deduce the properties
of a cantilever from its outer shape. Thicker and shorter ones
tend to be stiffer and have higher resonant frequencies. |
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