Tutorials - Atomic Force Microscopy (AFM)

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.

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.

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.

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.