3.3.2 Binding to defects

This chapter discusses the binding of helium atoms to defects. The experimental situation is better in the case of binding of helium atoms to vacancies and vacancy clusters obtained by thermal desorption spectroscopy (THDS). The energy values extracted from such experiments together with the corresponding values obtained by computer simulation are given. Energies (in eV) of helium atoms in copper, molybdenum, nickel, tungsten, silver, aluminum, gold, iron, palladium, platinum, tantalum, vanadium are tabulated. THDS has also been applied to investigate the binding of helium to other substitutional rare gas atoms in tungsten and molybdenum. The binding energy for the undersized copper atom and for the oversized indium atom is reported. Systematic THDS studies on deformed molybdenum single crystals did not show contributions of single helium atoms bound to dislocations. It was concluded that helium, trapped by dislocations, forms small clusters which desorb in the same temperature range as helium desorbing from small vacancy clusters. Besides this result, the experiments yielded valuable information about the number of monovacancies and vacancy clusters generated by plastic deformation. This is an example for employing THDS as a general tool for the study of defects in solids.