By precisely controlling the surface composition of thin oxide films, films can be switched from a metal to an insulator. Atomic-scale control of the surface is achieved using molecular beams of atoms (the molecular beam epitaxy growth method). To understand why the thin film changes from a metal to an insulator, the surface is imaged using x-rays scattered from the film (see 3D image of film on left). It turns out that the surface itself generates an electric field in the film. When the atoms on the surface are changed, the electric field changes direction, which changes the film from a metal to an insulator.