Nanotechnology, or, as it is sometimes called, molecular manufacturing, is a branch of engineering that deals with the design and manufacture of extremely small electronic circuits and mechanical devices built at the molecular level of matter. The Institute of Nanotechnology in the U.K. expresses it as "science and technology where dimensions and tolerances in the range of 0.1 nanometer (nm) to 100 nm play a critical role." Nanotechnology is often discussed together with micro-electromechanical systems (MEMS), a subject that usually includes nanotechnology but may also include technologies higher than the molecular level.
There is a limit to the number of components that can be fabricated onto a semiconductor wafer or chip. Traditionally, circuits have been etched onto chips by removing material in small regions. However, it is also possible in theory to build chips up, one atom at a time, to obtain devices much smaller than those that can be manufactured by etching. With this approach, there would be no superfluous atoms; every particle would have a purpose. Electrical conductors, called nanowires, would be only one atom thick. A logic gate would require only a few atoms. A data bit could be represented by the presence or absence of a single electron.
Nanotechnology holds promise in the quest for ever-more-powerful computers and communications devices. But the most fascinating (and potentially dangerous) applications are in medical science. So-called nanorobots might serve as programmable antibodies. As disease-causing bacteria and viruses mutate in their endless attempts to get around medical treatments, nanorobots could be reprogrammed to selectively seek out and destroy them. Other nanorobots might be programmed to single out and kill cancer cells.
Two concepts associated with nanotechnology are positional assembly and self-replication. Positional assembly deals with the mechanics of moving molecular pieces into their proper relational places and keeping them there. Molecular robots are devices that do the positional assembly. Self-replication deals with the problem of multiplying the positional arrangements in some automatic way, both in building the manufacturing device and in building the manufactured product.