Ångström

Ångström (variant angström; symbol Å) is a unit of length equal to 10^-10 meters. It is named after the Swedish physicist Anders Jonas Ångström, renowned for his work in spectroscopy. The ångström is widely used in physics, chemistry, and materials science to express wavelengths of light, atomic-scale distances, and thicknesses of thin films and film interfaces.

Historically, the ångström was common in spectroscopy and crystallography before the wider adoption of the nanometer. By definition, 1 Å = 10^-10 m = 0.1 nanometers = 100 picometers. It is not an SI unit, but it is accepted for use with the International System of Units; the symbol Å is a distinct character and the unit is often written as Å or angström.

In practice, wavelengths of electromagnetic radiation are frequently given in ångströms in some subfields, particularly crystallography and solid-state physics, where lattice constants and interatomic spacings are typically a few ångströms. Visible light falls around 4000–7000 Å, while atomic-scale spacings are on the order of 1–5 Å. In recent decades, many journals prefer nanometers or picometers to align with SI, but the ångström remains common in historical literature and in certain disciplines.