Information Technology Reference
In-Depth Information
and placing molecular parts one by one, moving them along controlled trajectories
much like the robot arms that manufacture cars on automobile assembly lines.
The procedure is then repeated over and over with all the different parts until the
final product, such as a medical nanorobot, is fully assembled.
The positional assembly of diamondoid structures, some almost atom by
atom, using molecular feedstock has been examined theoretically [12, 20] via
computational models of diamond mechanosynthesis (DMS). DMS is the con-
trolled addition of individual carbon atoms, carbon dimers (C 2 ), or single methyl
(CH 3 ) groups to the growth surface of a diamond crystal lattice in a vacuum
manufacturing environment. Covalent chemical bonds are formed one by one as
the result of positionally constrained mechanical forces applied at the tip of a
scanning probe microscope apparatus. Programmed sequences of carbon dimer
placement on growing diamond surfaces in vacuo appear feasible in theory [20-23].
Diamond mechanosynthesis is being sought [11, 21] but has not yet been achieved
experimentally; in 1999 Ho and Lee [24] demonstrated the first site-repeatable site-
specific covalent bonding operation of a two diatomic carbon-containing mole-
cules (CO), one after the other, to the same atom of iron on a crystal surface. In
2003, Oyabu et al. [25] vertically manipulated single silicon atoms from the
Si(111)-(7 7) surface, using a low-temperature near-contact atomic force micro-
scope to demonstrate removal of a selected silicon atom from its equilibrium
position without perturbing the (7 7) unit cell and also the deposition of a single
Si atom on a created vacancy, both via purely mechanical processes. Efforts are
currently underway to achieve DMS with carbon atoms experimentally [11].
To be practical, molecular manufacturing must also be able to assemble very
large numbers of medical nanorobots very quickly. Approaches under considera-
tion include using replicative manufacturing systems [13] or massively parallel
fabrication, employing large arrays of scanning probe tips all building similar
diamondoid product structures in unison [13]. For example, simple mechanical
ciliary arrays consisting of 10,000 independent microactuators on a 1 cm 2 chip
have been made at the Cornell National Nanofabrication Laboratory for micro-
scale parts transport applications and similarly at IBM for mechanical data
storage applications [26]. Active probe arrays of 10,000 independently actuated
microscope tips have been developed by Mirkin's group at Northwestern
University for dip-pen nanolithography [27] using DNA-based ink. Almost any
desired 2D shape can be drawn using 10 tips in concert. Another microcantilever
array manufactured by Protiveris Corp. has millions of interdigitated cantilevers
on a single chip [28]. Martel's group has investigated using fleets of independently
mobile wireless instrumented microrobot manipulators called NanoWalkers to
collectively form a nanofactory system that might be used for positional
manufacturing operations [29]. Zyvex Corp. (www.zyvex.com) of Richardson,
Texas received a $25 million, five-year, National Institute of Standards and
Technology (NIST) contract to develop prototype microscale assemblers using
microelectromechanical systems.
Ultimately, medical nanorobots will be manufactured in nanofactories
efficiently designed for this purpose. One possible rough outline for a combined
 
Search WWH ::




Custom Search