Biomedical Engineering Reference
In-Depth Information
Fig. 3.27. Schematic of dip-pen nanolithography, showing how the water meniscus is used to
transport molecules to the surface. Adapted from [260].
patterns have been created from organic molecules [260], proteins [262, 263], synthetic
peptides [264], DNA [246], polymers [263], inorganic nanoparticles [265] and more [246,
249]. A major application of this sort of technology is in creation of arrays of receptors for
parallel testing, e.g. proteomics, genomics, etc. For large scale parallel arrays of differing
features, specialized DPN instruments, rather than commercial AFMS are typically used.
A number of other, less commonly used methods exist to modify surfaces with AFM
[249, 266]. These include thermomechanical writing, which like SThM uses a resistance in
the probe to control the temperature at the tip [267]. However, the temperature is used to
modify the sample surface, rather than to probe it, and the high temperature is typically
used to make holes in polymer surfaces without risk of damaging the tip. This has been
investigated as a high-density data storage technique, and via the use of parallel probes
(the so-called 'millipede' device [268]), has been shown to be capable of extremely high
storage density [269]. Several authors have reported the use of the AFM to directly
manipulate individual particles [270], molecules [271] and even atoms [272, 273] on a
surface by for example, pushing, lifting and dropping or cutting [249]. These procedures
are interesting for fundamental studies but are too slow to be of value as manufacturing
techniques. Some examples of assembly using AFM are shown in Section 7.2.3. Finally, a
Fig. 3.28. Examples of AFM-based lithography. Left: polymeric patterns on silicon formed
by anodic oxidation, showing line widths of approximately 2 nm. Reproduced with permission
from [250]. Centre: a bit-map image used as the input for a dip-pen nanolithography (DPN) routine.
Right: AFM (lateral force) image of the resulting surface patterns.
