Interstitial atoms in tungsten:: Interaction with free surface and in situ determination of formation energy

The energy of formation of self-interstitial atoms has been experimentally determined using an energy analysis of low-temperature field evaporation of tungsten in a field-ion microscope. An experimental approach, based on the strong dependence of the threshold field for evaporation on the total energy of the surface atoms, is used. It was found that the excited atomic states can be produced by the release of the formation energy of self-interstitial atoms emerging at the surface. The experimental results are discussed in the framework of the image-hump model of field evaporation and compared with theoretical data on the energy of formation of interstitial atoms.