Deuterium desorption from tungsten borides

The deuterium retention in boron and boron/tungsten mixed films sputtered by deuterium plasma is an important question to address to understand and predict the deuterium lifecycle, as a complex tungsten-boron (W-B) alloy is expected to form over time on the boronized tungsten first wall due to repeated exposure to burning plasma and heat. Thin film layers of tungsten/boron were deposited by magnetron sputtering using argon and argon/deuterium mixed atmosphere. Chemical analysis was performed by in vacuo X-ray photoelectron spectroscopy (XPS), and the surface morphology was examined by scanning electron microscopy (SEM). The amount of deuterium in the film was analyzed using nuclear reaction analysis (NRA) and thermal desorption spectroscopy (TDS). As the boron concentration increases from 16 at.% to 37 at.% in the mixed W-B layer, the D/B ratio more than doubles, from 0.13 to 0.28, as confirmed by the NRA analysis. TDS results show that the addition of B to the pure tungsten co-sputtered in Ar/D2 plasma shifts the deuterium desorption peak to lower temperatures and modifies the peak width and intensity, depending on the B concentration in the film.