A nanowire is a wire of dimensions of the order of a nanometer (10−9 meters).
Alternatively, nanowires can be defined as structures that have a lateral size constrained to tens of nanometers or less and an unconstrained longitudinal size.
At these scales, quantum mechanical effects are important — hence such wires are also known as "quantum wires".
Many different types of nanowires exist, including metallic (e.g., Ni, Pt, Au), semiconducting (e.g., InP, Si, GaN, etc.), and insulating (e.g., SiO2,TiO2).
Molecular nanowires are composed of repeating molecular units either organic or inorganic.