The problem of operation reliability of thermoelectric modules remains topical. Owing to pronounced anisotropy of properties and growth of the rate of semiconductor atoms’ mobility, the diffusion of conductor atoms into semiconductor can occur in thermoelements. For prevention of diffusion of conductor atoms into semiconductor and for increasing of thermoelement useful life, diffusive barrier layers are applied for separating commuting plate and semiconductor material in their contact. Deposition of such barrier layers can be realized by different methods, but in all cases the layer is deposited on the semiconductor surface, thus the effectiveness of thermoelectric modules reduces. At present work, mass-transfer processes at diffusion welding in vacuum of copper and nickel through ion-modified layers are investigated. The expediency of prior modification of copper surface (commuting plate) by chromium for creation the barrier antidiffusive layer is determined. Using radioactive isotope method, it is defined the features of diffusive interaction of contact materials through surface layers of copper modified by chromium due to ion treatment. As shown, the presence of such layers results in retardation of diffusive processes twice comparatively with contact interaction without modified layer. Blocking effect of such modified layer is confirmed by Auger electron spectroscopy on the example of heterogeneous joints of pair copper–nickel. As shown, a diffusion zone width after modification copper by chrome became 20 times lesser than one in non-modified sample.