<P> Molecular nanotechnology, sometimes called molecular manufacturing, describes engineered nanosystems (nanoscale machines) operating on the molecular scale . Molecular nanotechnology is especially associated with the molecular assembler, a machine that can produce a desired structure or device atom - by - atom using the principles of mechanosynthesis . Manufacturing in the context of productive nanosystems is not related to, and should be clearly distinguished from, the conventional technologies used to manufacture nanomaterials such as carbon nanotubes and nanoparticles . </P> <P> When the term "nanotechnology" was independently coined and popularized by Eric Drexler (who at the time was unaware of an earlier usage by Norio Taniguchi) it referred to a future manufacturing technology based on molecular machine systems . The premise was that molecular scale biological analogies of traditional machine components demonstrated molecular machines were possible: by the countless examples found in biology, it is known that sophisticated, stochastically optimised biological machines can be produced . </P> <P> It is hoped that developments in nanotechnology will make possible their construction by some other means, perhaps using biomimetic principles . However, Drexler and other researchers have proposed that advanced nanotechnology, although perhaps initially implemented by biomimetic means, ultimately could be based on mechanical engineering principles, namely, a manufacturing technology based on the mechanical functionality of these components (such as gears, bearings, motors, and structural members) that would enable programmable, positional assembly to atomic specification . The physics and engineering performance of exemplar designs were analyzed in Drexler's book Nanosystems . </P> <P> In general it is very difficult to assemble devices on the atomic scale, as one has to position atoms on other atoms of comparable size and stickiness . Another view, put forth by Carlo Montemagno, is that future nanosystems will be hybrids of silicon technology and biological molecular machines . Richard Smalley argued that mechanosynthesis are impossible due to the difficulties in mechanically manipulating individual molecules . </P>

Future potential of bottom up approach in nanotechnology