The nanometre (International spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American spelling) is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- (from the Ancient Greek νάνος, nanos, "dwarf") with the parent unit name metre (from Greek μέτρον, metrοn, "unit of measurement"). It can be written in scientific notation as 1×10−9Lua error: Unmatched close-bracket at pattern character 67., in engineering notation as 1 E−9 m, and is simply 1/1,000,000,000 m. One nanometre equals ten ångströms.
The nanometre is often used to express dimensions on an atomic scale: the diameter of a helium atom, for example, is about 0.1 nm, and that of a ribosome is about 20 nm. The nanometre is also commonly used to specify the wavelength of electromagnetic radiation near the visible part of the spectrum: visible light ranges from around 400 to 800 nm. The angstrom, which is equal to 0.1 nm, was formerly used for these purposes.
The nanometre was formerly known as the millimicrometre – or, more commonly, the millimicron for short – since it is 1/1000 of a micron (micrometre), and was often denoted by the symbol mµ or (more rarely) µµ. In 1960, the U.S. National Bureau of Standards adopted the prefix "nano-" for "a billionth". The nanometre is often associated with the field of nanotechnology. Since the late 1980s, it has also been used to describe generations of the manufacturing technology in the semiconductor industry.
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