The foundations of nanotechnology
A nanometre is a billionth of a metre — the length of a few atoms in a row. Nanotechnology is the making and use of structures between roughly one and a hundred of them, a range in which a material’s properties start to depend on its size.
A particle small enough to behave differently may also behave differently in a lung or a river, so a nanomaterial cannot simply inherit the safety record of the bulk substance. Agreed definitions and measurement methods come first: the international standards committee for nanotechnologies was set up in 2005, and its vocabulary fixes the nanoscale at approximately 1 to 100 nanometres.
Top-down methods pattern a larger piece of material; lithography makes every chip this way, and since about 2019 the most advanced ones with extreme-ultraviolet light of 13.5 nm wavelength. Bottom-up methods let atoms and molecules assemble themselves, as in crystal growth — or DNA origami, in which Paul Rothemund folded DNA into chosen shapes in 2006.
Visible light cannot resolve anything much smaller than a few hundred nanometres. The scanning tunnelling microscope of Gerd Binnig and Heinrich Rohrer (1981) instead measures the tiny current between a surface and a sharp tip, and resolves single atoms. In 1989 Don Eigler and Erhard Schweizer used one to arrange thirty-five xenon atoms into the letters I‑B‑M.
Confine an electron in a particle a few nanometres across and its allowed energies shift with the size of the box. A quantum dot of one material glows blue when small and red when larger. The discovery and synthesis of quantum dots was recognised with the 2023 Nobel Prize in Chemistry.
Weight scales with volume and so becomes negligible; what remains is surface forces, which make small things cling, and the random impacts of surrounding molecules, which keep them in constant motion. A machine at this scale works in something closer to a sticky storm than to empty space.
Cut a one-centimetre cube into cubes one nanometre across and the total surface grows from six square centimetres to six thousand square metres. Chemistry happens at surfaces, so finely divided matter reacts faster, melts lower and catalyses better than the same substance in bulk.
A human hair is roughly 80,000 nanometres wide; a red blood cell about 7,000; the DNA double helix about 2; an atom a few tenths of one. The nanoscale is the span between single molecules and the smallest things an optical microscope can show.
Read from the bottom up. The first four ideas are physics — why small is different. The last three are engineering — what can be done about it.