Page 107 - Nanotechnology an introduction

ambient relative humidity. Although not atomically precise manufacturing, it allows features of the order of 100 nm to be written, and may be
considered as featuring an approximately eutactic environment.
DPN was presumably inspired by printed electronic devices. Circuits can be fabricated at extremely low cost by printing onto a suitable substrate.
Conventional processes such as screen printing and inkjet are suitable, with inks formulated using “pigments” that are conductive or
semiconductive nanoparticles. This technology is especially attractive for radio frequency identification tags (RFID), which are expected to become
widely used in packaging, and as security devices on products and even on documentsif they can be produced at sufficiently low cost.
8.4. Summary

Top–down methods (exemplified by ultraprecision engineering and semiconductor processing) constitute the bulk of current industrial
nanotechnology. Due to the enormous expense of the capital equipment required, however, it is impractical for use other than for very high volume
products (such as computer or cellular phone chips) or very unique products for which a high price is affordable (giant astronomical telescopes;
long-range spacecraft).
The “real” vision of nanotechnology (especially associated with Feynman and Drexler) is based on mechanosynthesis (chemistry with positional
control), possibly facilitated by using pre-constructed nanoblocks as the elementary units of fabrication. A productive nanosystem is based on
assemblers, devices that are themselves in the nanoscale, hence the method is also known as bottom-to-bottom. Because of their minute size, the
only practical way to fabricate large or large quantities of entities is for the assemblers to first assemble copies of themselves, which then all work
in parallel. The practical realization of this vision is focused on tip-based methods inspired by the scanning probe instruments used in
nanometrology; at present single objects comprising of the order of ten atoms can be made in this way.

Originally inspired by biology, a third approach is based on creating objects (which could be nanoblocks) capable of spontaneously assembling
into useful structures. This method is known as bottom–up or self-assembly and has been quite successful at creating regular structures (e.g.,
nanoporous membranes for separating vapors) but the creation of arbitrary geometries requires programmable self-assembly. In other words
bottom–up is good at creating materials but not for creating devices. Biological nano-objects have this ability, but it is extraordinarily difficult to
reverse-engineer them and use the knowledge to create synthetic analogs.

These three methods can sometimes be advantageously combined; for example, self-assembly could be used to make a mask for
photolithography more cheaply and quickly than electron beam writing, which is then used in top–down fabrication (e.g., to create superhydrophobic
surfaces).
8.5 Further Reading
Castleman Jr., A.W.; Khanna, S.N., Clusters, superatoms and building blocks of new materials, J. Phys. Chem. C 113 (2009) 2664–2675.
Frauenfelder, H., From atoms to biomolecules, Helv. Phys. Acta 57 (1984) 165–187.
Kellenberger, E., Assembly in biological systems, In: Polymerization in Biological SystemsCIBA Foundation Symposium 7 (new series). (1972)
Elsevier, Amsterdam, pp. 189–206.
Mamalis, A.G.; Markopoulos, A.; Manolakos, D.E., Micro and nanoprocessing techniques and applications, Nanotechnol. Percept. 1 (2005)
63–73.
Merkle, R.C., Molecular building blocks and development strategies for molecular nanotechnology, Nanotechnology 11 (2000) 89–99.
Schaaf, P.; Voegel, J.-C.; Senger, B., Irreversible deposition/adsorption processes on solid surfaces, Ann. Phys. 23 (1998) 3–89.
Hall, J. Storrs, Architectural considerations for self-replicating manufacturing systems, Nanotechnology 10 (1999) 323–330.