Cantilevers and Tips for SPM

The SEM images shown below illustrate the geometry of AFM cantilevers and tips.  Cantilevers are available with pyramidal tips or conical tips.

Cantilevers for AFM work are nanofabricated from silicon.  The cantilevers shown at right are still attached to the original chip.  These cantilevers are fabricated with pyramidal tips of silicon nitride. 

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Four new cantilevers
AFM tips may be either low aspect ratio(usually pyramidal) or high aspect ratio (conical or pyramidal).

Pyramidal tips made from silicon nitride are the most durable variety.  They have a low aspect ratio (sharpness) and are suitable for low-profile subjects.  They are most often used for friction force microscopy because of their durability.

The silicon nitride tip shown below has a chip near the vertex and is not perfectly curved.  Each tip must be regarded as an invdividual.  For the most critical work, the shape of the tip must be verified.

Pyramidal tip Tip imperfection visible
Credits:  The above SEM images are courtesy of Ms Belinda Barry, Molecular Imaging, Inc.  They were taken on an Amray SEM by Jim Peterson, E. Fjeld Co., Inc., North Billerica, MA.

High aspect-ratio tips are commonly made from silicon and carbon.  These tips are more useful in vibrating (tapping mode), which greatly reduces lateral forces that would otherwise damage the tip.  Bryan Todd and Stephen J. Eppell, Case Western Reserve University have compiled data on tip sharpness using tip deconvolutiontechniques.
Conical tip High-denisty carbon tip
SEM image of a conical etched silicon probe for TappingMode™ from Digital Instruments. SEM image of a NanoTOOLS high-density carbon modification (HDC) tip.


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Revised:  November 11, 2003
Copyright © John W. Cross