grown line. In other words, a smaller bias and smaller time of interaction between
the field and the substrate will lead to higher resolution. However, a bias lower
than the critical bias will not lead to any oxidation.
Since the applied field is a key factor for the anodic oxidation process the radius
of curvature of the tip is also important. Most AFM tips available commercially
have a tip radius of curvature of b10 nm. This limits the minimum resolution that
one can obtain in an AFM-based lithography. Since well defined and controlled
micromachining lithography is used to make these tips on the AFM cantilevers,
they are of reproducible size, shape and aspect ratio. This is a big advantage when
it comes to doing reproducible lithography of a given resolution. A sharper tip can
be obtained in STM but it is difficult to produce a tip of reproducible radius of
curvature and aspect ratio.
Fig. 21.13. Schematic of SPM-based nanooxidation.
21 Nanolithography and Nanomanipulation
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