H- and D distribution in metallic multilayers studied by 3-dimensional atom probe analysis and secondary ion mass spectrometry

Abstract Pd/Nb- and Fe/V multilayers were prepared by either ion sputtering or laser ablation. They were deposited on tungsten tips for field ion microscopy using the 3-dimensional atom probe. D was added by doping from the gas phase. In agreement with thermodynamic data D is accumulated in the metal with the more negative heat of solution, i.e. V or Nb. However, SIMS depth profiles of H concentration measured at room temperature show a pronounced enrichment in the top regions of both Nb- and V layers. This is also observed in a deuterium depth profile obtained by the 3d atom probe measured at 60 K despite the moderate removal of atoms by field evaporation which does not give rise to the formation of lattice defects when compared to sputtering. Thus we assume that surface segregation is the reason for H/D accumulation in surface near regions. The effect vanishes if measurements by the atom probe were made at 20 K where the D mobility is too low to allow D transport to the surface during the time of measurements. With the superior depth resolution of the 3d atom probe being less than 0.5 nm we were able to show that at both the V/Fe and the Nb/W interface depletion of deuterium occurs in a range of about 0.5 nm within the Nb- or V layer due to intermixing of adjacent metals.