The scattering through close to 180° of an ion when it impinges on an atom, the energy E of the scattered ion being given by

where E₀ is the initial energy of the ion and M and m are the masses of the atom and incident ion respectively. If the incident ion travels through a material before back scattering takes place, additional energy losses occur both incoming and outgoing. Such losses can be determined for different materials and different depths. Detection of the back-scattered ion and measurement of its energy can therefore determine both the mass and the depth of the scattering atom.

Use of a monoenergetic beam of ions and a high energy resolution detector can thus yield a picture of not only the impurity elements in a semiconductor crystal but also the perfection of the crystal structure, since back scattering also occurs from lattice defects. A depth resolution of approximately 10 nanometres is possible.