nanometres

Nanometre, symbol nm, is a unit of length in the metric system equal to one billionth of a metre (10^-9 m). The name combines nano-, meaning one billionth, with metre. It is widely used to express dimensions on the nanoscale, where features typically range from about 1 to a few hundred nanometres.

One nanometre equals 1,000 picometres and 10 angstroms, since 1 Å = 0.1 nm. It is common in fields such as nanoscience, materials science, semiconductor manufacturing, and biology to describe particle sizes, pore widths, film thicknesses, and wavelengths of light at near-visible to near-infrared ranges.

For visible light, wavelengths are roughly 400 to 700 nm, which is the scale at which many nanoscale phenomena occur. In biology, molecular assemblies and proteins often have dimensions of a few nanometres.

Metrology and standards: The metre, and thus the nanometre, are part of the SI system. Since 1983, the metre is defined by the distance light travels in vacuum in 1/299,792,458 of a second, making the nanometre a derived unit equal to 10^-9 metres. The nanometre is a non-SI unit accepted for use with SI.

Measurement techniques for nanometres include electron microscopy (transmission and scanning) and scanning probe methods (atomic force microscopy, scanning tunneling microscopy), which resolve features at the nanometre scale.