It could be defects due to missing atoms, thermal vibrations of the crystal lattice, or even the boundaries between small, imperfectly formed crystals that make up the material.

ECONOMIST: MONITOR

Russell and Xu's method starts with a sliced crystal, either sapphire or silicon, cut at an angle that exposes a ragged section of the crystal's lattice structure.

FORBES: Nanotech

If an electric charge is applied to the crystal, these holes and electrons will move in opposite directions, knocking into the lattice and creating more and more holes.

ECONOMIST: Quantum information technology