The scanning electron microscope image shows four rows of nanowires and their corresponding nanowalls, nicknamed "nano LEDs" because they emit light when electrically charged. The distance across the micrograph is approximately the diameter of a human hair. A nanowire is a nanostructure, with the diameter of the order of a nanometer. It can also be defined as the ratio of the length to width being greater than 1000. Alternatively, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less and an unconstrained length.