In 2005,
Mihail Roco, one of the architects of the USA's National Nanotechnology Initiative, proposed four states of nanotechnology that seem to parallel the technical progress of the Industrial Revolution, of which productive nanosystems is the most advanced. 1. Passive nanostructures - nanoparticles and nanotubes that provide added strength, electrical and thermal conductivity, toughness, hydrophilic/phobic and/or other properties that emerge from their nanoscale structure. 2. Active
nanodevices - nanostructures that change states in order to transform energy, information, and/or to perform useful functions. There is some debate about whether or not state-of-the art integrated circuits qualify here, since they operate despite emergent nanoscale properties, not because of them. Therefore, the argument goes, they don't qualify as "novel" nanoscale properties, even though the devices themselves are between one and a hundred nanometers. 3. Complex
nanomachines - the assembly of different nanodevices into a nanosystem to accomplish a complex function. Some would argue that
Zettl's machines fit in this category; others argue that modern microprocessors and
FPGAs also fit. 4. Systems of nanosystems/Productive nanosystems - these will be complex nanosystems that produce atomically precise parts for other nanosystems, not necessarily using novel nanoscale-emergent properties, but well-understood fundamentals of manufacturing. Because of the discrete (i.e. atomic) nature of matter and the possibility of exponential growth, this stage is seen as the basis of another industrial revolution. There are currently many different approaches to building productive nanosystems: including top-down approaches like Patterned
atomic layer epitaxy and
Diamondoid Mechanosynthesis. There are also bottom-up approaches like
DNA Origami and
Bis-peptide Synthesis. A fifth step, info/bio/nano convergence, was later introduced by Roco as the convergence of the three most revolutionary technologies according to Roco. == See also ==