What Are Nanometers?

Nanometers are units of length in the International System of Units (SI) equal to one billionth of a meter, or 10 to the power of negative 9 meters. The symbol is nm. A single nanometer is approximately 10 times the diameter of a hydrogen atom and roughly 100,000 times smaller than the width of a human hair. The nanometer is the fundamental unit of measurement used across nanoscience, nanotechnology, semiconductor engineering, structural biology, and photonics, because the critical dimensions of atoms, molecules, crystal lattice spacings, and electronic device features all fall in the range of tenths of nanometers to hundreds of nanometers.

The prefix nano derives from the Greek word for dwarf and was formally adopted into the SI in 1960 as a standard multiplying factor of 10 to the negative 9th power. The National Nanotechnology Initiative defines the nanoscale as the range of 1 to 100 nm, the regime in which matter frequently exhibits properties different from those of the same material in bulk form, because quantum mechanical effects, surface forces, and molecular interactions become dominant over gravitational and classical inertial forces.

The Nanometer in Atomic and Molecular Structure

The nanometer scale is the natural unit for describing atomic and molecular architecture. The covalent bond length between two carbon atoms in a diamond lattice is approximately 0.154 nm. A DNA double helix has a diameter of about 2 nm and a helical repeat of approximately 3.4 nm per base pair. Protein molecules range from about 2 nm for small peptides to more than 50 nm for large multimeric complexes. Semiconductor crystal lattice parameters, which govern the band structure and epitaxial growth of III-V and group-IV materials, are measured in tenths of nanometers using X-ray diffraction. Understanding dimensions at this scale is essential in fields from structural biology to crystal engineering, where angstroms (0.1 nm) and nanometers describe the geometry of bonding, packing, and defect structures.

Nanometers in Semiconductor Technology

Semiconductor fabrication has used the nanometer as its primary process dimension descriptor since transistor gate lengths dropped below 1,000 nanometers in the early 1990s. Current logic technology nodes are described in single-digit nanometers, though the actual gate length and other printed dimensions in a modern process differ from the technology node number, which has become a marketing label rather than a literal measurement. Interconnect linewidths and dielectric layer thicknesses in the back end of a semiconductor process are measured in nanometers by transmission electron microscopy (TEM) and X-ray reflectometry. NIST's three-dimensional nanometer metrology program develops the calibration standards and measurement tools, including atomic force microscope reference artifacts, that keep nanometer-scale dimensional measurements traceable to the SI meter.

Metrology at the Nanoscale

Measuring dimensions at nanometer resolution requires instruments capable of probing individual atoms and molecules. Scanning tunneling microscopy (STM) resolves atomic positions on conductive surfaces with sub-angstrom precision. Atomic force microscopy (AFM) images surface topography in three dimensions with nanometer vertical resolution on both conductive and insulating materials. Small-angle X-ray scattering (SAXS) characterizes nanoparticle size distributions and colloidal structures in solution without requiring direct imaging. Transmission electron microscopy resolves lattice spacings and interface abruptness in thin-film stacks. These tools, supported by measurement programs at NIST and national metrology institutes, provide the dimensional data that underpins quality control in nanotechnology fabrication and manufacturing across industry and research.

Applications

The nanometer as a unit of measurement is central to a range of technical fields, including:

• Semiconductor device engineering, where feature dimensions are specified and verified in nanometers
• Structural biology and pharmaceutical development, where protein and nucleic acid dimensions govern drug-receptor binding geometry
• Nanomaterials characterization, where particle size and surface roughness are quantified in nanometers to correlate structure with optical and electronic properties
• Optical thin-film design, where layer thicknesses in antireflection coatings, mirrors, and filters are specified in nanometers
• Metrology and standards, where NIST and international standards bodies maintain length-traceability to the SI at nanometer precision